Carburetor or EFI on your roadster?

[Fman]

Trying to get some perspective on Carb vs EFI on a SB 302/347/351/427.

I have been dead set on going aftermarket EFI, my engine build is currently spec'd with a Dart 427 build but after researching and talking with a few different people I am beginning to also consider old school carburetor setup. From what I have been reading the aftermarket EFI systems seem to be hit and miss (Fi-tech, Sniper), some even returning them and going back to a carb setup. If you are running a carb please reply back with what carb your running and your experience both good and bad. I would also like to hear from aftermarket EFI owners what your experience has been and what system you are running. I live at 600' elevation and figured EFI for this engine would be a nice step up for performance, reliability and fuel economy.

Thank you...

[seagull81]

I have the Sniper system. I love it. Once it was set up, it fired right up and hasn’t missed a beat since.

[wallace18]

I have done 2 -427 MK4's. One with Carb, Quick Fuel and one with FITECH. Both worked great here in FL.

https://thefactoryfiveforum.com/showthread.php?31169-PB-and-son-MK4-build-thread-by-wallace18

http://thefactoryfiveforum.com/showthread.php?21008-Bill-amp-Laura-s-MK4-build-thread

[boat737]

Plain and simple, if I have an old school hot rod, it's going to have an old school motor and carburetor. I went with a 427w (so I could put the 427 fender badge on) with a Holley 750 (auto choke and mechanical secondaries). The carb works just fine. I'm basically at sea level. It starts right up cold or hot (one throttle pump if it's been sitting a week, two throttle pumps if sitting two or more weeks, and don't touch the throttle if its warm or hot.). It's not fuel efficient, and it smells a little. It's basic and simple.

I know very little about EFI, TBI or any of the new fangled fueling systems. I know enough about carburetors where I can disassemble and assemble it, and do the basic adjustments. If I were racing and needed specific, precise settings, I probably couldn't do that. But Mine is street only, and so it's a carb for me.

I think when the big EMP explosion goes off, my car will be the only one running.

[GoDadGo]

Ditto Regarding Boat-737

Low Tech, No Tech, Carburetor & Like It!

AVS-800, 383 SBC (Dart), ZF 6-Speed Transmission & Dana-44 Rear.

Like Boat, I'm either a tad above Sea Level or 5-12 feet below Sea Level.

[Badfish]

Started with stock EFI, then explorer intake, vortec blower, ended up here with dual quad Holleys. Very happy.

126785

[jimmylukeii]

I have a 351w bored and stroked to 427. Dart block. It started life with fuel injection. Not sure the brand/model. Was switched before my time to a quickfuel 650 black diamond. I prefer the carb because even novices like me can work on them, especially with this forum and YouTube to help. Tuning it is a fun thing to learn.

I am told that today's fuel with ethanol is not a great match with carbs, especially if you let the car sit a lot. However I drive mine a lot (6k per year) and rebuilding a carb is also a fun thing to learn.

[Papa]

At my altitude, carburetors are a royal PITA. I had a 1970 El Camino with a ZZZ 350 crate and a Holley 750 carb that came from my dad's place at 12' above sea level in California. I took it to a guy to get it re-jetted to try to make it run better, but it never really ran good. I swapped it out for a Demon 650 and got some drivability, but still stunk to high heaven and wouldn't idle cold. When I decided to build the roadster, I decided it would have EFI or nothing. My engine shipped with a FAST XFI Street EFI that I never got dialed in and was dumping fuel to the point of concern for washing the bearings. I swapped over to the Holley Sniper and have had much better results, but still need to get it dialed in by a pro tuner. With the EFI, the car starts right up and idles cold without smelling like a fuel spill in the garage. The Sniper also looks a lot like a 4150 style carb sitting on the intake, which keeps the old school look. A little clever routing and wrapping of the wires and the casual passerby at a show wouldn't notice it was fuel injected. I haven't had a chance to get into the high country yet, but it's running well at 6,100'. We'll see what 12,000+ feels like later this summer. My first highway trip of about 100 miles was able to get ~14 miles/gallon at 70 miles/hour most of the trip.

[Norm B]

I had a carb and am switching to Sniper. Not up and running yet so no first hand experience with the Sniper. Like Papa, I live at fairly high altitude and large altitude changes are common on a summer drive. I would get the carb set up perfectly and running great at home level of 3600 ft but a 45 minute drive into the mountains and it was dog shirt. Hoping the Sniper is better.

[PaulProe]

If you are willing to learn, understand and fine tune an EFI system, it will give you better engine performance in the normal driving range. There is arguement about it's value at full throttle, But in reality, how often are our cars used at full throttle. Fuel mileage can be superior.

If you think you can just bolt it on and it will learn to tune itself. Save your money, time and aggrevation and go with a carb. Regardless of all the hype, they have to have a reasonable tune before they can learn, and they will never learn timing settings, cold start, de-acceleration, etc. Learning is there but it has been twisted and being misunderstood.

I went from Webers to fuel injected EightStack due to issues with altitude and air density changes experienced in the summer in the midwest. But it was a VERY STEEP learning curve.

Only you can answer the question. You willing to invest the time, effort and money to make it work or are you just a 'plug n play' guy

Paul

[Papa]

Paul makes some very valid points about the "self-learning" EFI. To help set expectations, the Holley Sniper only self-tunes the base fuel map; nothing else. The default map is usually good enough to get you up and running and will smooth out over time as you drive the car. The dozens of other parameters can be very confusing to understand and you MUST understand the way each interacts with the others or you will never get a decent tune. Now that my car is legal and on the road, I will take it to a tuner to dial it in. I want drivability; not looking to squeeze out every last bit of horse power. The good thing is that it's a lot easier to find a good EFI tuner these days than it is to find someone that can tune a carburetor.

[Bob Cowan]

^^^^ everything he said is correct. I will never mess with a carb again.

Fuel injection can be very very accurate. It will easily compensate for changes in air density, temperature, etc. That improves driveability and efficiency. IMO, if you want a car that's a drive anywhere anytime kind of car, EFI is the answer.

As Paul said, there can be a bit of a learning curve. Or, you can just take it to your local dyno shop and let them do it. But once it's tuned correctly, it's a real joy to drive.

[mike223]

I am not going to disagree with the last three pro-efi posts.

I will say I think the aftermarket EFI systems have more potential failure modes than a Holley DP.


And if you want either (carb or aftermarket EFI) to work "right" - you're probably going to end up knowing a lot more about it than you really intended in the first place.


Holley DP here (and I know a lot more about it than I ever intended to learn, lol).


Good luck,

Mike



P.S. - For me it came down to the knowledge base I had available - I had multiple people around with Holley DPs that worked right, all the time - worst come to worst, we could swap them around and figure out what was different.

It depends on who you have around to ask, and what they're familiar with.

Or what interests you enough to become "the expert" on.

[Jim1855]

427 SBF, manual. Big heads, single plane intake and custom exhaust. ProSystem (Holley 4150 HP) 780 cfm double pumper, no choke or horn. Started with a 670 Avenger w/ choke & vac secondaries – too small but well mannered, bumped up to a 770 Avenger – a good carb, ran really well. Have also run a ProSystem 950 DP, no choke - too big but rocked 6-7,000rpm. I am considering a new Holley Ultra XP 850 if I ever finish this build - lots of tuning options.

About 65k miles on the various combinations. I've had difficult days but generally pleased making great power, controllable and drivable. Starts with a single pump and idles well after a bit of warm up, maybe a minute or so, ambient temp dependent. It doesn't like to drive at less than 1,500 rpm, but it's seldom there. Cruises at 2,200 / 80mph in 5th, about 18mpg on the e-way. I've driven through Colorado multiple times; the fourteens cause a bit of trouble and I've dropped a few jet sizes which helps but there’s more to tuning than just jets. No issues on I-70 west of Denver and through the Eisenhower but you can feel the power drop off. Ran on a drag strip once (11.8/120) but lots of road track use. BTW, same motor for my two previous cars and it will go into the current build, I’m kinda partial to this one.

I have considered EFI but not the "carb" styles. Would be stacks or some form of tuned plenum with sequential control. Every time I add up the cost it would be close to $5k, hard to justify. I have a friend with a dyno and he's an excellent tuner so that part of EFI isn't a concern

Won't argue the benefits of EFI but I'm not looking for a new car, isn't part of the "charm" the old school? If I wanted civilized, I'd buy a Vette.

Jim

[chuckster]

Back in the day, 1974 I used to pick up spare change modifying Holley‘s with those good old Holley trick kits. On my Shelby when I was running one 4 barrel 715 dual feed double pumper mechanical secondaries. It was making huge power. I put my first sniper on in April 2017, ( purchased Dec. 2016) fired right up on the test stand,and ran great. We had our bumps in the road. The TPS went bad, Holley replaced it. Then had 02 sensor issues sent the unit back to Holley they ran diagnostics and send it back still the problem. Call them two years out of warranty set a new O2 sensor no problems Since. Throttle response is awesome and drivability is second to none. I won’t go back to the carburetor except for looks and Holley‘s newest sniper stealth is indistinguishable from the big Holley carburetor. I attribute the early issues to the fact that mine was an early unit.

[stack]

I used the fitech system on my last MK4 build. I really found it interesting and spent several hours learning how it worked and how to tune it. Going efi gives you the opportunity to learn a new skill. Be careful as you research and install you system. Any issues with the ignition system, vacuum leaks, or fuel delivery are compounded when you are efi and you will chase your tail blaming the efi system the whole time. I put a fitech on a 65 mustang and we had all sorts of issues but we replaced the coil and distributor and added a MSD igntion box and all the problems went away.

I am not trying to sell you on fitech in fact i have used projection efi, fast ez efi and fitech. If i had the opportunity i would go sniper next.

stack

[Gumball]

My FFR is old-school all the way, so only a carb would do. It's forced me to learn more about them so that I can tune it and keep it running right, but that's part of the experience.

That said, for a car with some modern touches and creature comforts, then fuel injection is a reasonable addition and one that makes the car more usable at varying altitudes with less fuss.

[KDubU]

Ah the age old question. EFI is definitely the modern way to go but if you want old school then carb or go better with Weber’s. :cool: I had a QT680 carb on mine and it worked very well, I prefer the cleaner look of carb when I have looked at some engine bays with EFI as they are cables and hoses all over. Note that I have also seen some really nice EFI engine compartments and it was obvious the owners had eye for detail.

[karlos]

So far all the EFI discussion has been limited to throttle body-style systems. Sequential port, load-based injection systems like the OEM's use are also available, albeit at a significantly higher cost (one example linked below). The primary advantage these systems offer is the ability to achieve daily-driver type reliability and driveability (including cold starts, idling, cruising, deceleration, etc.) with any combination of engine type, heads, intake, camshaft, exhaust system, and so on. This enables modern, OEM performance with legacy style (pushrod) engines.

Most of us (myself included) tend to get wrapped up in the numbers and the specs. Since installing a recent-model Pro-M system on my roadster, the aspect of the system that impresses the most is its ability to support driving the car like a minivan on the way to soccer practice. The top-end performance is there, of course, but the complete absence of any driveability issues is what makes these systems worth the asking price.

Anyway, maybe another option to consider.


https://www.promracing.com/why-the-pro-m-efi-system

[Big Blocker]

Being old school, I wanted a pushrod engine that looked like an original 289. When my car was built 18 years ago, fuel prices were reaching $3.00+ [again] and I wanted something somewhat economical for the long cruises I was planning in the future.
I settled for a SBF (5.0) with the factory EFI with its ugly crossover ram style upper manifold. Didn't take me very long to swap out the whole upper end of the engine to be of GT-40 specification. Different completely with the available tubular configuration.

I have to say that that was a good choice on my part - 18 years of early morning starts at freezing temps, no fuel smell from the morning "rich" mixture, starts after a long run in the desert high temps, runs great from 29°F to 121°F, drives the same from sea level to 12K feet at our local mountains, doesn't care that i'm driving at an accelerated rate on mountain "twisties" or care that I can floor it and then stomp on the binders with no fuel "slosh" or hesitation, I can go to almost any auto parts store and get parts (although haven't needed to since I fixed the TFI module overheating issue by relocating it) AND gets 22 mpg at a sustained 80mph on the open road.

Just my biased opinion . . .

Doc

[phileas_fogg]

... if you want either (carb or aftermarket EFI) to work "right" - you're probably going to end up knowing a lot more about it than you really intended in the first place...

Truer words are few & far between.

When I was a freshman in college, my grandfather gave me his 1966 Rambler station wagon. It had sat in his driveway for a couple of years, so he and I refurbished it. He had worked his way through the Great Depression as a mechanic for International Harvester. They gave him a truck full of tools & some parts, and he drove out to whatever farm & worked until whatever was broken was running - to the farmer's satisfaction. If he didn't have the part, he made the part. When it came time to refurbish the carb on that Rambler, my grandfather took it to a guy. That told me everything I needed to know about my chances of getting a carb to run correctly!

I chose the Holley Terminator system for my car. I fought a couple of intermittent fuel problems, and am currently working with a buddy to get the Terminator dialed in. I've definitely learned more about that system - and my car - than I ever thought I would.


John

[GoDadGo]

My FFR is old-school all the way, so only a carb would do. It's forced me to learn more about them so that I can tune it and keep it running right, but that's part of the experience.

That said, for a car with some modern touches and creature comforts, then fuel injection is a reasonable addition and one that makes the car more usable at varying altitudes with less fuss.

Sort of like this Little Blue Cobra?

https://youtu.be/E-qPkepYZjk

[Avalanche325]

I am running a QF750 Q-Series double pumper (no choke) on a highly strung 500hp 347. I actually wanted my car to be temperamental, snotty, and something that I have to really drive, including warm-ups, shifting (up and down) at the right PRM, working the throttle, etc. Not just get in and go and drive like my daily driver. I really wanted it low tech, and Cobra-like. It is certainly not everyone's cup of tea.

I am very happy to see, unlike many other threads, how many people are mentioning that you really do need to tune both carbs and EFI.

If I were going to go EFI, well of course stacks would be what I want. However, for something that wouldn't melt my credit cars, I would look at a Sniper system. They seem to have the most consistent happy customer base. Others are a little more hit and miss. One day, I might put a smaller cam in and EFI........but not today.

[NAZ]

If I was building a street car it would be EFI.

I grew up with carbs and have been tuning on them for more than a half-century so I have a lot of experience tuning carbs. As a Ford Service Tech, used to get paid to tune them. Most people don't know a lot about tuning carbs beyond the basics of adjusting the idle mixture and maybe changing main jets. And there are few professionals out there that have been around longe enough to have the experience with them to really dial them in. Most just settle on whatever they get out of the box and call it good.

Some folks base their decision on going with a carb because of first cost which is very short sided. A garden variety carb is less than half the cost of an EFI system. But to really fine tune one you need the tools and change parts necessary and you can easily spend more than the cost of an EFI system on tools & change parts -- not practical for a hobbyist that has but one carb to tune. I have a couple thousand $$ in tools and change parts for Holley carbs and their clones. And then once you have the tools and parts, you still need the knowledge. It takes a lot of time to tune a carb on a OEM vehicle where engineers have spec'd the combination and the parts all complement each other. It takes considerable more time to tune a carb on a modified engine where there is no service manual to refer to for setting up the carb, ignition curve, and cam timing.

Choose wisely.

[brewha]

This is said with no disrespect to the carb guys.

One of the reasons I went with a Fitech is covered by Naz. Finding someone that can really tune a carb are getting scarce.
EFI systems are making thousand of decisions a minute based on block temp, air temp, atmosphere pressure, altitude, timing, air fuel ratio and other factors. My motor starts when cold with no touch of the gas pedal and runs the same cold or hot. I get great gas mileage compared to a 71 challenger I use to own. My 331 has to run on premium fuel so having decent mileage in town helps me pass the gas station multiple times with having to stop.

I have been the carb route in the 70’s and 80’s and it wasn’t always fun. Choke, float, vapor lock, jet issues...
I have been broken down with carb issues at the track and had to guess my way out of trouble.
My mantra in the 70’s was “Death to Quadrajet”. I had to switch to Holley.

When I think I hear a twitch in the the motor, I turn on EFI logging and get to see issues moments after they happen.
There is a reason no new cars are running carbs.

[js65cobra]

I recently purchased my FFR Mk1 from my father who was in PA, and moved it out to me here in Colorado. So my first projects was to move to EFI because the car always ran rich on the Holley DP 650 it had even when at sea level.. and when I brought it out here, it was a pig stinking up the house.

It starts up perfect, drives great. I do need more warm weather and time to tune the idle control and fuel tables... something I also need to learn about more. I've only had it on a few months and driven maybe 6 or so times, but as the weather gets warmer I hope to find a tuner somewhere in CO that can help dial it in as a nice driver.

[2FAST4U]

48 IDA Webers (carbs)

https://thumbs2.imgbox.com/a6/ca/0O8XxZZk_t.jpeg (http://imgbox.com/0O8XxZZk)

https://thumbs2.imgbox.com/24/bb/lBpxGPDK_t.jpeg (http://imgbox.com/lBpxGPDK)

[Fman]

I really do appreciate all the feedback and recommendations from everyone.

I have been in contact with a couple engine builders, recently I was introduced to a local builder about 30 mins from my house that came highly recommended. I met with him today, he has a nice shop on his property and is a one man show building engines for about 25 years now. He mentioned Sniper/FiTech systems he has installed have had mixed results and require a little more tuning, he said on the Sniper he changes the linkage to progressive style to make it more driveable. He did mention he is just not a fan of the ECM being right off the EFI unit because of the heat generated. His carb recommendation was a Holley 3310 (with auto choke), he runs them on a couple of his cars and has had nothing but good results. He was definitely also open to doing EFI just wanted to give me both options.

I have some time to digest it all, just looking at all pros and cons and what would be the best setup for what I am planning on doing with the car. This car is going to be a weekend street driver no plans of racing or tracking.

I also got a nice call from Stewart shipping today, my car is being delivered tomorrow! Cant wait to get it in my garage!!!;)

[mike223]

His carb recommendation was a Holley 3310 (with auto choke), he runs them on a couple of his cars and has had nothing but good results. He was definitely also open to doing EFI just wanted to give me both options.

I have some time to digest it all, just looking at all pros and cons and what would be the best setup for what I am planning on doing with the car. This car is going to be a weekend street driver no plans of racing or tracking.



It's been generally accepted that vacuum secondaries don't often make people as happy in these cars as mechanical secondaries.

Because the cars are so light and instantly responsive to operator input - the vacuum signal is not as stable as it would be in a heavier car.

It introduces an extra variable you probably don't want - you're going to want to control throttle position with throttle position - not a vacuum signal.


Lots of people do the electric (auto) choke and seem to be satisfied with it.

I removed the choke plate from mine (mechanical secondary, manual choke, 4150) and only use the manual choke for high idle warmup (no actual choke - the plate isn't there).


Lots of stuff to consider and learn what might work for you.

[NAZ]

I agree with Mike, 4150 DP is a better carb choice on a light car. Also, agree that the choke is superfluous but the fast idle can be a benefit. Even in cold Northern AZ I don't need to run a choke, it's just one more thing to tune.

Here's another tip: get a low profile single plane manifold if you go with a carb as if you want to upgrade later to EFI you wont need to change manifolds. EFI likes single plane manifolds better than most dual plane.

[mike223]

I did some more research this morning to make sure I wasn't to far off track on vacuum secondaries.

Here are a couple of good reads in that regard:

https://help.summitracing.com/app/answers/detail/a_id/4730/~/carburetor-secondary-types

https://www.hotrod.com/articles/vacuum-or-mechanical-secondary-carburetor/


Critical takeaways:

Manufacturers and engineers liked vacuum secondaries because they are less "ticky" when placed on varying engines in varying applications - closer to a one size fits all answer, fewer headaches.

Mechanical secondaries are a lot more sensitive to sizing and tuning issues for specific engines and applications.


One of my observations is that most outfits seem to send them out (mechanical secondary carbs) where they're a lot more likely to run "pig rich" than cause a lean failure (lean detonation) - because they don't want to hear about the pistons you accidentally burned - Especially not for a $300-700 carb sale.

I found the same (pig rich) in every aftermarket metering plate I've fooled with - especially in the emulsion restriction orifices - especially in metering blocks that claim to be set up for "standard calibration".


The first thing you'll need to approach improving that situation is a good wide band AFR meter or logger - the only two I can recommend are AEM or Innovate LM2 (there may be others).

And a place in the exhaust for an O2 sensor (not a minor problem in this application).

And a considerable amount of somewhat obscure research.


But it's all "do-able" - and we're here to help.

[BradCraig]

Sniper is my choice, but as another member stated be aware the ECU is in the unit so use a non-metallic spacer to control the heat and use a single plane (or cut down divider like the Air-Gap intake). Mixed results on the progressive linkage, better results with extending the throttle arm to make it a bit friendlier. You'll also need spark plug wires that will reduce RFI.

[GoDadGo]

Hey Gang,

I know a lot of folks love the Holley and Holley Clone carburetors and those folks who truly understand them can make them run great, heck some can get phenomenal results but that isn't me.

If you have a larger sized engine (Over 375 Cubic Inches) and stink at tuning the beloved Holley then consider an Edelbrock AVS or AVS-2 800 CFM carburetor....The only things that I needed to do was to set it up with a dual feed line to equalize the pressure on the needle and seats....I also created a baffle between the fuel bowls which is placed in the rear trough to reduce side to side fuel sloshing....The newer AVS-2 uses annular boosters on the primary side compared to the original AVS that I currently have.

Please know that all AVS Carbs are mechanical secondary designs, but the rear boosters have an adjustable spring loaded flapper which is basically a choke similar to the old Rockchester Quadrajets. The big difference is these carbs don't use a metering rod set up for the secondary jets like the Q-Jet carburetors that were used on so many 1960's and 1970's General Motors vehicles.

While Not Popular With Most Hot Rodders, These Carbs Work & Work Well If You Properly Adjust The Rear Flapper!

Steve

NOTE:..The 800 Series Are A Square Bore Design..............(400 CFM + 400 CFM = 800 CFM)
...........The 650 Series Are A Mini-Spread Bore Design.......(250 CFM + 400 CFM = 650 CFM)
...........The 500 Series Are A Square Bore Deisgn..............(250 CFM + 250 CFM = 500 CFM)

AVS-2 Promo Video:
https://youtu.be/3npwfIOdKPc

[Fman]

Anyone running the stack fuel injection setup?

[KDubU]

Anyone running the stack fuel injection setup?

Now that is what you want. There are a couple, forgetting their forum names right now but this would be one of my top choices on my next build.

Edited to add Richard Oben and Mark Reid were two that had them.

[Papa]

Anyone running the stack fuel injection setup?


Now that is what you want. There are a couple, forgetting their forum names right now but this would be one of my top choices on my next build.

I would love to do the same on my car. Based on my very limited knowledge about these, I'd simply state that you want to go with a high-end unit, not a bargain version. I've looked at Borla some and like what they have to offer, except for the $$$ they want. FAST has one that's affordable, but based on my experience with FAST, I'd be skeptical about their offering without a lot more information.

[GoDadGo]

Being The Chevy Guy I'd Love Something Similar To What Was Used On The Five Corvette Grand Sport Light Weights From 1963!

https://www.hemmings.com/blog/2011/05/05/sidedrafts-for-your-small-block/

Here's the link for Jim Inglese should you want the ultimate Eye Candy Under Your Hood!

http://www.jiminglese.com/cobra-and-gt40

[PaulProe]

Anyone running the stack fuel injection setup?

I am running an EightStack system on an FE - Performance Electronics ECU. Car performs great. Easy start, good mileage. No issues. But it did take some work to get there - and it isn't inexpensive.

Paul Proefrock
https://proefrock.net/Images/HM1078-StackInjection.JPG

[stacked33]

Anyone running the stack fuel injection setup?

How about 10 stacks? I designed and built this system for my 33 Hot Rod. Uses Holley's Dominator for electronics.126908

[skidd]

Just adding my anecdotal 02c to this thread.

I'm one of the few happily sporting a 600cfm vacuum secondary with electric choke.
I got a sick deal on it used, so figured it would get me going easy enough for low $$.
It's one of those Summit Racing branded carbs.
It's worked so well for me so far, I don't if I ever will want to change it to a mech secondary.
I put in the lightest secondary spring I had, tweaked the size of the primary jets down 2 sizes, and fine tuned the elect choke timing.
The transition into the secondaries is nearly invisible. I did the old zip-tie trick on the 2ndary plunger arm to see how much they are even opening, and they are going all the way.
My innovate wideband shows good AFs in all situations.

Anyway.. the math and facts all point to a mechanical secondary carb being the best for these cars.. but I'm here to tell you that a vac secondary can work perfectly.

[rich grsc]

Like Paul, a Borla Eight Stack, only with a Fast XFI Sportsman ECU. I had plenty of issues to sort out, first and foremost, I was sold the wrong ECU sent up, a Fast EZ-2, pure junk. Once I got the correct ECU it was able to be tuned. As Pauls said; not inexpensive. :rolleyes:
126912

[mike223]

I put in the lightest secondary spring I had, tweaked the size of the primary jets down 2 sizes, and fine tuned the elect choke timing.
The transition into the secondaries is nearly invisible. I did the old zip-tie trick on the 2ndary plunger arm to see how much they are even opening, and they are going all the way.
My innovate wideband shows good AFs in all situations.

Anyway.. the math and facts all point to a mechanical secondary carb being the best for these cars.. but I'm here to tell you that a vac secondary can work perfectly.



That's good info to know - I was struck by what I read about the reasoning for vacuum secondaries.

Mainly the fact that using a vacuum signal generated by airflow on the primary side to open the secondary makes them less "ticky" about sizing and tuning.


And considering prudence suggests you should very rarely get into the secondary on a "street" application in these cars anyway...

It's definitely food for thought - and maybe a second look / further examination.


And the bottom line key quote - "My innovate wideband shows good AFs in all situations." - speaks volumes.

[Avalanche325]

That's good info to know - I was struck by what I read about the reasoning for vacuum secondaries.

Be careful venturing into the general race car vs street car rules when it comes to these cars. These are very light , so generally have a high power to weight ratio.
Here are a couple old school "rules" that don't really apply to our cars.

Vacuum secondaries for the street - mechanical is for race cars.
Dual plane for the street - single plane is for race cars.
Vacuum advance for the street - centrifugal only is for race cars.

Mechanical secondaries, single plane intakes, and centrifugal advance all work very well for an FFR. Nothing wrong with reading everything you can get you hands on. But I would put a lot more weight on what are on this and the other forum as it is specific to our cars. I am not saying that the other things won't work. But you might be leaving some performance on the table depending on your engine setup.

Frankly, with those more "race car" items, you will need to learn how to properly drive your car. It won't reward you for a full pedal stomp at 1600rpm in 3rd gear. Learning to really drive the car is one of the best things about owning one in my book. Autocross is always my recommendation for a Cobra owner.

I read the articles. Both of them have statements FOR mechanical in our cars. Mainly the light weight and not a daily driver points.



And considering prudence suggests you should very rarely get into the secondary on a "street" application in these cars anyway...
HaHa. That's funny!

[mike223]

No arguments with any of that here.

It just struck me that it might be worthy of further research for the 427w street cruiser / never going to track or autocross it crowd.

[edwardb]

Vacuum vs. mechanical secondaries used to be hot topic on both forums (maybe the other one mostly) but has really died down. I suspect because EFI is so much more common now. With roughly 50% of builds now being Coyotes (according to several recent Facebook daily videos from Dave Smith and the gang) and a bunch more using the now widely available add-on EFI systems, just not as many carb builds it seems. Count me as one who tried a vacuum secondary carb (Holley 570 Street Avenger) in my #5125 Mk3 build on a warmed up 302. 306 with AFR heads, COMP Cams camshaft, Edelbrock RPM Air Gap intake, etc. Never could get it to run right. Would bog and never seemed happy. Tried everything including all different size springs. Gave up and installed a Quick Fuel SS-650 double pumper which after some minor tuning woke the engine up and ran perfectly. Still is to this day. There were multiple similar stories on the forums with a before and after story like mine. Not saying that some don't get them running OK. But for the reasons already cited, a double pumper is the way to go for these cars. But to tag onto comments already made in this thread, both carb and EFI systems require tuning for optimal performance. Neither is likely plug and play.

[NAZ]

Vacuum vs. mechanical secondaries used to be hot topic on both forums (maybe the other one mostly) but has really died down. I suspect because EFI is so much more common now. With roughly 50% of builds now being Coyotes (according to several recent Facebook daily videos from Dave Smith and the gang) and a bunch more using the now widely available add-on EFI systems, just not as many carb builds it seems. Count me as one who tried a vacuum secondary carb (Holley 570 Street Avenger) in my #5125 Mk3 build on a warmed up 302. 306 with AFR heads, COMP Cams camshaft, Edelbrock RPM Air Gap intake, etc. Never could get it to run right. Would bog and never seemed happy. Tried everything including all different size springs. Gave up and installed a Quick Fuel SS-650 double pump which after some minor tuning woke the engine up and ran perfectly. Still is to this day. There were multiple similar stories on the forums with a before and after story like mine. Not saying that some don't get them running OK. But for the reasons already cited, a double pumper is the way to go for these cars. But to tag onto comments already made in this thread, both carb and EFI systems require tuning for optimal performance. Neither is likely plug and play.

Once you have an EFI dialed in that's likely the last you need to tweak on it. But if you want the ultimate performance out of a carb it will require constant tweaking as it is extremely sensitive to density altitude as well as even small changes to the engine. Most will just settle on the performance they get out of a carb but for a racer that is looking for the best performance it will require constant tuning. I can dial in the carb on my race car in the morning and will be adjusting it throughout the day as temp and humidity will affect the AFR and max power. If you live near sea level and never travel to higher elevations or hotter environments you may not notice the performance changes -- but change it does. EFI will automatically adjust to those changes.

[7tvette]

I have stacks on both my cars. Inglese on the Spyder and Borla on the Cobra. Really like the performance and looks of the Borla.
E-Z EFI on both. Choose to go EFI because I like to drive the cars all over North America. So I'm at sea level one day any 10,000 ft the next without issues.
I also live in a frigid climate. No carb for me.

Troy

[mike223]

Most will just settle on the performance they get out of a carb but for a racer that is looking for the best performance it will require constant tuning.




That reminds me of one of my original build goals:

I specifically wanted to build more engine than I needed so I wouldn't be needing to constantly dork with it to get the last 50 hp out of it.

EFI or Carb.


Mission accomplished - but I have also scared hell out of myself in third gear with it too (careful what you wish for)...

[johnnybgoode]

I am running a QF750 Q-Series double pumper (no choke) on a highly strung 500hp 347. I actually wanted my car to be temperamental, snotty, and something that I have to really drive, including warm-ups, shifting (up and down) at the right PRM, working the throttle, etc. Not just get in and go and drive like my daily driver. I really wanted it low tech, and Cobra-like. It is certainly not everyone's cup of tea.

I am very happy to see, unlike many other threads, how many people are mentioning that you really do need to tune both carbs and EFI.

If I were going to go EFI, well of course stacks would be what I want. However, for something that wouldn't melt my credit cars, I would look at a Sniper system. They seem to have the most consistent happy customer base. Others are a little more hit and miss. One day, I might put a smaller cam in and EFI........but not today.

2X I like the simplicity of a dist. and carb. To me its part of the experience/attraction of owning one of these cars. I've got a fairly healthy 414W (408 kit .060 over, that makes an easy 500hp and 520 ft/lbs) I'm running a smaller 650 QF DP that runs great, haven't touched it since the motor was built. There are also tuners that will custom build/calibrate you a carb for your motor for a few extra bucks that you can bolt on straight out of the box and go. Brent Lykins comes to mind. Just my 2 cents. Scott

[Fman]

I would love to do the same on my car. Based on my very limited knowledge about these, I'd simply state that you want to go with a high-end unit, not a bargain version. I've looked at Borla some and like what they have to offer, except for the $$$ they want. FAST has one that's affordable, but based on my experience with FAST, I'd be skeptical about their offering without a lot more information.

I know they are stupid expensive, way out of my budget. I was just wondering if anyone on the forum had one and if they performed as good as they look.

[Fman]

Like Paul, a Borla Eight Stack, only with a Fast XFI Sportsman ECU. I had plenty of issues to sort out, first and foremost, I was sold the wrong ECU sent up, a Fast EZ-2, pure junk. Once I got the correct ECU it was able to be tuned. As Pauls said; not inexpensive. :rolleyes:
126912

That looks so BA, you just cant beat that look!

[rich grsc]

That looks so BA, you just cant beat that look!

Thank you. Every time I open the hood, there is a new smile, and I've already forgot how much it cost. The sound it makes when it starts, everyone stops and looks and above 5000rpms you must have ear protection.

[Avalanche325]

The problem with stacks is that I would never drive my car. I would just stand in the garage staring at them........with a little puddle of drool at my feet.

Rich,
I like your extra large access panel on the drivers footbox. Mine is a little larger then the one FFR does. But rolling over the side would have come in handy when I had to change my pedal box.

[rich grsc]

Thanks, I have lots of little extra's I added, learned a few things from a couple builds, and helping my buddies.

[caesarmascetti]

my two cents, I have a 347 stroker with a 600cfm QuickFuel. I'm very happy with it. If I were do do FI, I'd invest in the headers that have a collector so I'd be able to place the O2 sensor in the collector sampling an entire bank of cylinders

[FFR 3099]

I have a street 347 in my roadster. Originally had a carb, switched to Mass-flo injection 16 years ago. It worked ok, dead reliable but not adjustable and I always felt it ran a bit too rich. Just removed it all and installed an Edelbrock Pro-Flow 4 system. Amazing difference!!!! Started right up, idled cleanly after about a minute and has gotten better and better as it learns. The wireless pad is easy to use and makes any needed adjustments simple. The only modification I've made is the on-off temp for the cooling fans. The cars runs cleaner and, I think, better than it ever has in the last 18 years. The price is great considering all the parts that are part of the package, including the intake and distributor. I'm very happy with my choice and would highly recommend you look at this system. I seems it is being overlooked by a lot of guys considering a change.

[rich grsc]

my two cents, I have a 347 stroker with a 600cfm QuickFuel. I'm very happy with it. If I were do do FI, I'd invest in the headers that have a collector so I'd be able to place the O2 sensor in the collector sampling an entire bank of cylinders

Everyone says this, but the makers of the systems all recommend and approve of using a single tube sample.
I stand corrected. My experience was with the FAST system, and a few of the older setups.

[nick7405]

Dont forget about edelbrock pro flo set up. The multi port injection has its advantages over the wet throttlebody set up, not to mention it comes with the intank manifold and distributor.

[phileas_fogg]

Everyone says this, but the makers of the systems all recommend and approve of using a single tube sample.

Not true for the Holley Terminator system. From their instructions: "The oxygen sensor should be mounted at a point where it can read a good average of all the cylinders on one bank." From https://documents.holley.com/199r10653rev10.pdf

Now, that said, many folks report no ill effects from placing the sensor in a single tube. But that was not a compromise with which I was comfortable.


John

[TMartinLVNV]

Everyone says this, but the makers of the systems all recommend and approve of using a single tube sample.

Page 8 of the Holley Sniper install manual:

"1. Locate a position for the oxygen sensor as close to the engine as possible. The oxygen sensor should be
mounted at a point where it can read a good average of all the cylinders on one bank. This would be slightly
after all the cylinders merge. If you have long tube headers, mount the sensor approximately 6-10” after the
collector. You must have at least 18” of exhaust pipe after the sensor. "

[caesarmascetti]

I called Holley and spoke to two different techs and neither one would "guarantee" me that the system would work properly in one tube. At the time FFR had not released their headers with the collector so I went to the Quickfuel 600VS carb. I must say it has electric choke and it has run great

[Sdonnel]

I'm using the Fitech system on my car. I sample from one tube with no issues. My engine builder and I pulled all the plugs last fall and they were all the exact same color. Great burn, no buildup, and car runs great. Do your homework on whatever system you buy and follow the directions to the letter. There are many people on the fuel infection forums that bash the products because, in their opinion, they don't work. It usually boils down to an underlying issue already in the motor, or not following the instructions. I can provide pics of my setup if needed. It's nothing spectacular, but runs like a pissed off gorilla if I lean on it.

Scott

[Avalanche325]

I've mentioned this before. Hopefully not in this thread....

In an episode of Engine Masters, they put a sensor in each tube just to see how even things are. There was a huge difference between cylinders. A dual plane, as you would expect, was worse than a single. So, getting an average is better. And of course it is more expensive. That is one of the few automotive TV shows that I bother with. They have done some good engine myth busting using a dyno.

If you are doing a middle of the road tune, which is what self tuning does, you will likely be fine. If you are really tuning to get the most out of your setup, it would be unlucky to be sensing your richest cylinder and risk leaning one or two out.

[NAZ]

I've mentioned this before. Hopefully not in this thread....

In an episode of Engine Masters, they put a sensor in each tube just to see how even things are. There was a huge difference between cylinders. A dual plane, as you would expect, was worse than a single. So, getting an average is better. And of course it is more expensive. That is one of the few automotive TV shows that I bother with. They have done some good engine myth busting using a dyno.

If you are doing a middle of the road tune, which is what self tuning does, you will likely be fine. If you are really tuning to get the most out of your setup, it would be unlucky to be sensing your richest cylinder and risk leaning one or two out.


Agree with this. We know that each cylinder sees a different mixture when introducing fuel & air through a common plenum and especially when using a dual plane manifold. Drag racers and some serious circle track racers running carbs will use stagger jetting to help eliminate large AFR variations between cylinders. Much of this phenomenon is caused by the firing order and the sequence of the intake cycle of cylinders next to each other. So using a combined sampling of O2 form a collector will dampen out the lean & rich mixture variations. But the absolute best configuration is sampling each cylinder independently and adjusting both AFR and ignition timing. But now we're talking some sophisticated systems.

[Blue Viking]

Like Paul, a Borla Eight Stack, only with a Fast XFI Sportsman ECU. I had plenty of issues to sort out, first and foremost, I was sold the wrong ECU sent up, a Fast EZ-2, pure junk. Once I got the correct ECU it was able to be tuned. As Pauls said; not inexpensive. :rolleyes:
126912

What was the problem with the FAST EZ-2?

[Boydster]

Just realized this thread is titled "... in your roadster."
I am also running an FiTech. 450/520 427W with 1-tube sampling. I did the 1-tube because my pipes were on order and I wanted to get it running. The F5 collector style headers didnt exist yet. Have done a few tweaks to it to fine tune, but not anything that has to be done. Very nice to drive easy and 'normal', Pulls like a pissed-off freight train when you cut it loose.

Once I'm settled in my new house (new garage!), I will probably move to the sidepipe just to get better sampling.

[caesarmascetti]

What was the problem with the FAST EZ-2?

funny enough Dave Smith had a video regarding engine choices on the FFR facebook page and he doesn't hold back on this thoughts about stack type FI systems, spoiler alert: He's not a fan

[Blue Viking]

funny enough Dave Smith had a video regarding engine choices on the FFR facebook page and he doesn't hold back on this thoughts about stack type FI systems, spoiler alert: He's not a fan

Gotta see that one then. I am already committed to stack injection, so it'll be interesting to see what my personal wxperience will be, given the relative high amount of negative comments.

[rich grsc]

Gotta see that one then. I am already committed to stack injection, so it'll be interesting to see what my personal wxperience will be, given the relative high amount of negative comments.

What setup do you have? If you have a Borla setup, you are going to have problems using a FAST EZ-2 system, it just won't work. The Borla stacks have the injectors above the throttle plates, and the EZ-2 system is not tunable so it's not possible to map the fuel tables and timing. It may work if the injector are in the runners under the throttle plates, have no experience with that type system.
I know that I spent a lot of time and money trying to use the EZ-2 computer. I got lucky and had a friend with direct contact with FAST, after talking with their head of development, I was told, "you will never be able to successfully use the EZ-2", they swapped me a XFI Sportsman ECU. My car now runs very well, and I bet even Dave would enjoy how it runs.
Stacks ARE NOT slap on and go systems. More than once I was pissed at myself for going down that road, but now all is forgiven. :D

[Blue Viking]

What setup do you have? If you have a Borla setup, you are going to have problems using a FAST EZ-2 system, it just won't work. The Borla stacks have the injectors above the throttle plates, and the EZ-2 system is not tunable so it's not possible to map the fuel tables and timing. It may work if the injector are in the runners under the throttle plates, have no experience with that type system.
I know that I spent a lot of time and money trying to use the EZ-2 computer. I got lucky and had a friend with direct contact with FAST, after talking with their head of development, I was told, "you will never be able to successfully use the EZ-2", they swapped me a XFI Sportsman ECU. My car now runs very well, and I bet even Dave would enjoy how it runs.
Stacks ARE NOT slap on and go systems. More than once I was pissed at myself for going down that road, but now all is forgiven. :D

I have a speedmaster stack. Injectors under the throttle blades. Common plenum, will use IAC valve for good idle. I am curious to see how the self tuning works, but I am willing to switch to the XFI ecu if I don't like the ez efi.

[rich grsc]

The Borla has a common plenum and a built in IAC as well.

[Blue Viking]

No experience with Borla. The speedmaster package was relatively cheap, so I thought why not? It'll be interesting to se how it performs.

[Bob-STL]

If you are willing to learn, understand and fine tune an EFI system, it will give you better engine performance in the normal driving range. There is arguement about it's value at full throttle, But in reality, how often are our cars used at full throttle. Fuel mileage can be superior.

If you think you can just bolt it on and it will learn to tune itself. Save your money, time and aggrevation and go with a carb. Regardless of all the hype, they have to have a reasonable tune before they can learn, and they will never learn timing settings, cold start, de-acceleration, etc. Learning is there but it has been twisted and being misunderstood.

I went from Webers to fuel injected EightStack due to issues with altitude and air density changes experienced in the summer in the midwest. But it was a VERY STEEP learning curve.

Only you can answer the question. You willing to invest the time, effort and money to make it work or are you just a 'plug n play' guy


I had a Holley Sniper installed last August. (It replaced an Edelbrock Pro Flo II that fried itself). The Holley Sniper ran but did not run correctly. There were multiple issues that included the installation as well.

At the point of flushing the car down the drain, I had PaulProe teach me how to program the Sniper. Understand the most I had previously done was tune a single barrel carbeurator.

I had found a tech guy on the Holley Tech Service line who was very good, and ONLY went back to him. Email or phone.

Paul taught me some basics on efi and we worked out a couple tunes that worked very well. As of now, I would say the system is 95% there. I have run 90+ datalogs. The car runs better than it has ever run before! Let me repeat that "The car runs better than it has ever run before!"

The key seemed to be that the system with a base tune will run(like PaulProe said). However, to get it optimum, you have to go in and adjust and fine tune it.

Bob