427W / Holley carb jet recommendations?

[ProfessorB]

Getting ready to pull the trigger on a 750 Holley double pumper for my 427W (Victor Jr intake). I do know that every engine is different, but I'm looking for recommendations for a STARTING point for primary and secondary jets. Thanks.

[Railroad]

Just start with what Holley puts in the carb. Unless your engine/cam is really radical, the stock jetting will not be too far from right.
good luck,

[ProfessorB]

Just start with what Holley puts in the carb. Unless your engine/cam is really radical, the stock jetting will not be too far from right.
good luck,

.
Depending on the specific model (electric choke, manual choke, "race carb" no choke), even among 750 cfm double pumpers. jetting is different.

[cv2065]

I have a QF Brawler 750 with mechanical secondaries on my 427. After some simple adjustments it was right on the money, no rejetting needed.

[BUDFIVE]

Professor B, I agree with others saying to start with what the carb came with.
Before addressing the main circuits (primary and secondary jetting) make sure the float levels are correct and the idle mixture is correct (set to max vacuum or rpm at idle). Many folks just stop there if it runs and drives pretty well. Reading spark plugs after steady, part-throttle cruising for determining rich or lean (primary circuit)is difficult and few still do it. Same for after wide open throttle runs to check secondary. Most people who want to optimize jetting now use an air:fuel ratio (AFR) gauge with wideband O2 sensor (WBO2 such as Bosch LSU 4.9). I added a system from Performance Electronics with a controller that is Bluetooth connected to my phone for this exact exercise. I know my jetting is close because we used an AFR gauge when we ran and tuned my engine on a Dyno before I installed in the car, but I want to optimize (AKA fiddle with it) :)

There’s a few YouTube videos out there if you search (tuning carburetor with AFR gauge).

BTW many EFI systems (Sniper) utilize a WBO2 sensor to learn and adjust fuel trims.

Edit-after CV2### post-my Brawler 650 mech secondary jetting on my 347 was close too with more changes required for idle (big overlap cam).

[F500guy]

So I just did my first run with a Holley street avenger 670, vacuum secondaries and the stock jets. AFR was about average of 13, although my data is a little rough. There sure can be some trim at cruise to get it up to 15. According to my Vizard book, 13 is sweet spot for most power. This is out of the box, nothing but bowl/idle/idle mixture adjustments. Very driveable off the shelf at see level-500 ft.

[MB750]

Same thing BudFive said, get yourself a wideband o2 sensor and tune from there.

I've had an AEM Wideband for years and I tune everything with it. I have the luxury of welding an M18 sensor bung into any exhaust though. Then it's just a matter of knowing which carb passages are impacting the AFR and how to tweak them. That's what I did for my AVS2 and now it's smoother than EFI.

FWIW, I think most people who crap on carbs just never took the time to understand how they work, and how to make them work for you. EFI tuning has the exact same learning curve. If you're the type to "Install it and forget it", get a Sniper.

[Mike.Bray]

FWIW, I think most people who crap on carbs just never took the time to understand how they work, and how to make them work for you. EFI tuning has the exact same learning curve.

Hey! I take exception to that! Name a carb and I've probably owned and tuned it (successfully). The basic principle of a carb hasn't changed in 150 years and today they're little more than a Rube Goldberg contraption. There's a reason FI has been used in racing since the 30's and there hasn't been an OEM car sold with a carb for over 30 years. But I get the nostalgic thing and perception of simplicity. But why not do it right and run a generator, points distributor, drum brakes, and bias ply tires?

I kid you. The real reason I don't like carbs is I don't like getting gas on my hands working on them;)

[ProfessorB]

All good input. Regarding EFI, there's no such thing as "set and forget" and trouble free. All you have to do is look at the forum.....plenty of "sniper..." threads. I'm just an F.O.G and prefer a carb. Ironically, it's not "simpler" or even cheaper, considering I'm now planning on installing a wideband O2 gauge, plus "engine porn" fuel line and fittings, new air cleaner, adjustable fuel pressure gauge, etc Carbs are just my thang, I guess. Holley is running a sale, i got a 750 double pumper (no choke) on the way. Free shipping, and they didn't charge me SC sales tax, either. That wipes out my budget for a month, I'll get more of the parts I need next month. I hadn't originally planned to get a wideband O2 gauge...but yeah, it removes all of the voodoo of carb tuning.

[BUDFIVE]

This is a fun thread! I was wondering when you’s weigh-in, Mike.
Professor B, as MB750 mentioned AEM makes a good wideband. I have the 30-4110 temporarily on my Jeep Stroker (with MPFI). It has a gauge with digital and analog displays and comes with swappable white and black gauge faces and a Bosch LSU 4.9 sensor.

https://www.summitracing.com/parts/avm-30-4110?rrec=true

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[cv2065]

This is a fun thread! I was wondering when you’s weigh-in, Mike.
Professor B, as MB750 mentioned AEM makes a good wideband. I have the 30-4110 temporarily on my Jeep Stroker (with MPFI). It has a gauge with digital and analog displays and comes with swappable white and black gauge faces and a Bosch LSU 4.9 sensor.

https://www.summitracing.com/parts/avm-30-4110?rrec=true

218221

Love that. Best of both worlds. FAST also makes a wireless version to your smartphone. Gas N pipes have built in bungs, so it's plug and play.

[boat737]

Sounds like my setup is very similar. Here's what I'm running currently. The cam is on the mild'er side. Mechanical secondaries, elec choke. Starts easy, idles fine.

[ProfessorB]

Same thing BudFive said, get yourself a wideband o2 sensor and tune from there.

I've had an AEM Wideband for years and I tune everything with it. I have the luxury of welding an M18 sensor bung into any exhaust though. Then it's just a matter of knowing which carb passages are impacting the AFR and how to tweak them. That's what I did for my AVS2 and now it's smoother than EFI.

FWIW, I think most people who crap on carbs just never took the time to understand how they work, and how to make them work for you. EFI tuning has the exact same learning curve. If you're the type to "Install it and forget it", get a Sniper.

Regarding the bung, I will have to add one and am wondering WHERE to put it. I know very little about O2 gauges...just that I now want one. From what little I've read, it recommends placement "at the collector". Technically, on side pipes that's outside the car. So I'm looking for input on position of the bung.
.
Also, I haven't decided which gauge I want. Yeah, I'm on a budget. FAST products are reasonably priced but I have read some terrible reviews about the less expensive FAST gauges.
.
Ironically, I'm laughing at myself about my choice for carb instead of a Sniper. When I'm done getting all the peripherals (fuel line, adjustable pressure regulator, fittings, air/fuel gauge, etc) I'm realizing "Gee, I coulda had a Sniper". Guess I'm just a carb guy....

[johnnybgoode]

Make sure you set the primary T slot (with the curb idle adjustment screw) so that it is "square" measured at .020 with a wire feeler gage and set the secondary so you can just barely see the T slot. You can also flip the secondary idle speed screw around so it can be adjusted from the top or buy the kit to add secondary idle adjustment. If the car idles too low use the secondary idle screw to increase the idle speed vs changing the primary. The more you uncover the primary T slot the richer the motor will run and the less effective the idle mixture screws will become. You need to keep the primary T slot square or very close to it. Carbs are great fun, mine run better that EFI. Good Luck and enjoy! Scott

[cv2065]

Carbs are great fun, mine run better that EFI. Good Luck and enjoy! Scott

Agree. They are great. Keeping it simple is key. No ECU, sensor or firmware issues to worry about.

[MB750]

Regarding the bung, I will have to add one and am wondering WHERE to put it. I know very little about O2 gauges...just that I now want one. From what little I've read, it recommends placement "at the collector". Technically, on side pipes that's outside the car. So I'm looking for input on position of the bung.
.
Also, I haven't decided which gauge I want. Yeah, I'm on a budget. FAST products are reasonably priced but I have read some terrible reviews about the less expensive FAST gauges.
.
Ironically, I'm laughing at myself about my choice for carb instead of a Sniper. When I'm done getting all the peripherals (fuel line, adjustable pressure regulator, fittings, air/fuel gauge, etc) I'm realizing "Gee, I coulda had a Sniper". Guess I'm just a carb guy....

You definitely want the bung at the collector, but I didn't split hairs between the left bank and the right bank. My sensor is technically only giving me the average of cylinders 1-4, but if you follow the runners down I'm getting two cylinders from the upper runner, and two from the lower. (Yea, dual plane manifold)

You also do NOT want to put the bung within a foot of the outlet. Reversion will actually draw a little fresh air into the exhaust and give you false lean readings. As close to the exhaust ports as possible (but also in the collector). If you're running zoomies, well..... pick a cylinder I guess. ;)

[herb427sc]

What do you do if you do not have an bung in your headers?? Can you just stick a probe in the tailpipe??

[BUDFIVE]

Herb you either need to drill a hole and weld a bung in place or install one of these
https://www.summitracing.com/parts/avm-30-2355-250?seid=srese1&gclid=EAIaIQobChMI6-zK1bDvjwMVraZaBR1kLCVjEAQYASABEgLQbPD_BwE

I’ve always welded mine in but I’ve seen a few videos with the band mount
.219258

[cv2065]

What do you do if you do not have an bung in your headers?? Can you just stick a probe in the tailpipe??

Or a banana. :p

Buy yourself some O2 bungs and then take the headers somewhere and have them welded in. Shouldn't cost much.

https://www.amazon.com/Stainless-M18-1-5-Stepped-Suppied-Hohnnyreet/dp/B0DG8ZK8J7/ref=asc_df_B0DG8ZK8J7?tag=bingshoppinga-20&linkCode=df0&hvadid=80745583084800&hvnetw=o&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=72527&hvtargid=pla-4584345049682747&msclkid=5188017ab58b1001f86a69a843e4ae8c&th=1

[BornWestUSA]

From my Ford Racing 427W instructions:


efficiency and Brake Specific Fuel Consumption (BSFC) also have an effect. Here are some examples of a Holley
750 CFM 4V.
Jetting:
Octane Temp. Elevation Front Rear
94 80 F Sea level 81 86
Aviation 100LL 80 F Sea level 81 84
110 Race 80 F Sea level 78 83
94 80 F 3000 ft. 76 81
94 80 F 6000 ft. 73 77
94 40 F Sea level 84 89
94 120 F Sea level 78 83

As you can see by these examples, jet requirements can vary a lot depending on fuel, altitude, and temperature.
Oxygenated fuels are available in some states and can dramatically affect your jetting requirements.

[rich grsc]

Yep, don't need to know or do any of that with my 8 Stack EFI setup. Outside air temp, the computer adjusts fuel & timing for that, altitude change, sea level to 14,000 ft, computer does that too. Wasn't happy with my cruise economy 15-16 mpg, so hooked up the laptop, 5 minutes of change to the fuel map and now it's 18-20 with the same performance. It would take 3x that to just drain the fuel for a jet swap

[Mike.Bray]

^^^^this^^^^

[ProfessorB]

.
Regarding the bung position, I'd like to install it WITHOUT removing header from car. Does anybody have pics of an instaled (on vehicle) bung? Seems to me if it's on the "collector" it is outside of the body...

[MB750]

.
Regarding the bung position, I'd like to install it WITHOUT removing header from car. Does anybody have pics of an instaled (on vehicle) bung? Seems to me if it's on the "collector" it is outside of the body...

some people in the motorcycle community have fabricated a contraption that links a small chamber (with the o2 sensor) connected to a long piece of copper tubing that's shoved wayyyyyyyy up the pipe to get a whiff of the exhaust very close to the exhaust port.

That's one option. It's ghetto though, just have a bung welded in. Taking the exhaust off is much easier than tuning an 8-Stack. ;)

[cadtdi]

"Yep, don't need to know or do any of that with my 8 Stack EFI setup. Outside air temp, the computer adjusts fuel & timing for that, altitude change, sea level to 14,000 ft, computer does that too. Wasn't happy with my cruise economy 15-16 mpg, so hooked up the laptop, 5 minutes of change to the fuel map and now it's 18-20 with the same performance. It would take 3x that to just drain the fuel for a jet swap"

Wow, that is pretty impressive, Rich...I would be happy with 15-16, my 351W with a Holley 750 is around 12.5...

.c
.

[Mike.Bray]

"Yep, don't need to know or do any of that with my 8 Stack EFI setup. Outside air temp, the computer adjusts fuel & timing for that, altitude change, sea level to 14,000 ft, computer does that too. Wasn't happy with my cruise economy 15-16 mpg, so hooked up the laptop, 5 minutes of change to the fuel map and now it's 18-20 with the same performance. It would take 3x that to just drain the fuel for a jet swap"

Wow, that is pretty impressive, Rich...I would be happy with 15-16, my 351W with a Holley 750 is around 12.5....

I have a 68 Camaro that came with a very mild 350 that's been fitted with headers/dual exhaust and an Edelbrock aluminum intake with a #1906 carburetor. Other than the inconsistent starting, sometimes it kicks right off like an EFI car and other times it takes a bit, it doesn't run bad. But the gas milage is abysmal. I haven't actually checked it (afraid to) but I sure do fill it up a lot for the limited miles I'm driving.

Good thing I've already got a ProFlo4 for it.

[rich grsc]

Oh come on Mike, it'll look good with stacks.;)

[Mike.Bray]

Oh come on Mike, it'll look good with stacks.;)

Very true and believe me I've thought about it. Just a cost deal sadly.

[cv2065]

$2500 or $5 bung. The bung takes it in for the win! ;)