Torn........ 331 or 347??

[MPTech]

My roadster has been on the road 7 years and about 33k miles. I DRIVE IT!!
When I built it, I was on a conservative budget and installed a rebuilt 302 roller w/ GT-40P ported heads, GT-40 intake, FMS F-cam. It has run very well, but I've been itching for an upgrade and I think it needs a rebuild / some work. (I get oil burping back through the dipstick. blowby(??))

Anyway I want to upgrade to another SBF, so I can reuse my headers and not have to adjust my footboxes (they are modded/expanded and very comfortably sized). (please don't post about a 351, 408, 427, Coyote, Kaase Boss-9, etc. That's the next project :p

I enjoy a lively cruise and occasional auto-x once or twice a year. Not tracking or drag racing it. Something fun, but streetable. I want to keep the budget around $7k w/Holley Sniper Stealth.

I spoke to Blueprint Engines last week and left a message with Craft Performance (they were on vacation last week).

Johnny at Blueprint was great, he recommended the 347 / Holley EFI setup if I'm going to drive it. I'm leaning towards this, but still open to the 331.

Just wanted to hear some thoughts. Thanks!

Been to: Tail of the Dragon (TN), French Lick (IN), London (OH) twice, Deadwood (SD), Denver (CO), San Marcos (TX), Harrison & Little Rock (AR) 4 times, Blue Springs (MO), Grafton (IL) couple times a year.
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[Derald Rice]

I went through the same dilemma a couple of years ago. My choice was also a 331 vs 347, for the same reasons you have stated.

Cost wise they are both the same if you build with equal quality parts. Weight is the same. Both will require the same support parts...
.....( cooling, clutch, trans, gearing)

The 331 should, in theory, build power at a higher RPM, The 347 will theoretically have more low end torque. Either one will give you a boost over what you have now.

I went with a 347, really like it. The torque potential was what pushed me to the 347.

[edwardb]

Loved the 347 I had in my #7750 build. Really no reason to not opt for the additional oomph from the 347 IMO. Yes more of a torquer than the 331 I guess. But mine loved to rev in addition to the good torque. Used to be concerns about rod angles and such. But with the right pistons and setup that shouldn't be an issue. Pretty confident reputable builders have that worked out. Now there's always the 363 option. :p

[GoDadGo]

I've had the opportunity to ride in a car that Mike Everson built a few years back that had a 331 in it.
It was nice, quite peppy, plus it could shred the tires in 1st and spin a good bit in 2nd.
Either I think are good options if you want to pump up your existing block.

Mike's Build That Landed In The Dell, Slidell That Is:
https://thefactoryfiveforum.com/showthread.php?27437-Mark-4-Roadster-for-sale&highlight=slidell

If you are buying a new block, consider a 363 if you are leaning towards the 347. (4.125 bore X 3.40 Stroke)
Another 347 option, which isn't as popular, would share the shorter stroke of the 331 so think about a combo with 4.125 bore with a 3.25 stroke
This would be a high revving combo with a little bit better rod angle plus the 4.125 bore unshrouds the valves.

What Ever Path You Take, I Know You Will Be Happy In The End!

[FF33rod]

FWIW, I went 347. Why stop part way with a 331. The question then becomes, how "wild" do you want to make it with cam choices and such. The Blueprint 347 is a very nice combo and built rather conservatively for reliability/streetability and yet is very fiesty at over 400hp... They are also a fairly reasonable price for what you get...

Steve

[mburger]

I had the same decision to make as you. I went with a 347 long block from Blueprint and Mike Forte will install my Edelbrock Pro Flo 4, put it on his Dyno etc.. Should make over 400/400.
I went with the 347 because I didn’t want the HP and torque up in the higher RPM range. I don’t drive the car like that.
Ditto what Derald said. The torque pushed me over to the 347.
Hopefully I’ll be able to post my Dyno results in the coming weeks.

[bobl]

Are you upgrading heads, cam and intake or staying with what you have and just doing a shortblock? Everything should be designed as a package. The gt40 intake will make a ton of torque but limit power up top for example. Of course who can argue with displacement. If buying cylinder heads get the best your budget will allow. That's where the power is.You will need an intake to match the combination if you plan to gain any real performance.

Bob

[TrevorP]

What block are you going with? I would put in a 363

[GoDadGo]

Check out this old video, if you haven't already seen it, because the Daytona had a 363 in it.
The attached video was done by Hot Rod Magazine way back in 2013.

https://youtu.be/V96-AQ1FghI

The car had crappy 3.27 gears and still ran 11.87 at 117 120 MPH.
If you do the math the 363 was only turning 5,000 RPM in 4th gear on the big end of the quarter-mile which isn't too shabby.

[Mike N]

With the same top end package (heads/intake) and cam the 347 will make a little more torque at a slightly lower RPM than the 331. The peak HP will likely be about the same just because the 347 HP peak will be at a lower RPM. The difference in displacement is roughly 5% so that's how much of a difference there is likely to be. Not a ton. Take a look at this Richard Holdener video. Pretty good review of stroke and engine capacity effects on torque and HP. https://www.youtube.com/watch?v=AjJSK5sLOeE

Things to watch out for; the 347 might put the piston pin in the oil ring groove, a 347 will very likely have less ring land above the top ring. If you are not running forced induction or doing track days then it shouldn't matter. However the 331, at least on paper, is a little more robust. I've been ripping on my 331 for close to 20 years and it's still not complaining.

[rich grsc]

With the same top end package (heads/intake) and cam the 347 will make a little more torque at a slightly lower RPM than the 331. The peak HP will likely be about the same just because the 347 HP peak will be at a lower RPM. The difference in displacement is roughly 5% so that's how much of a difference there is likely to be. Not a ton. Take a look at this Richard Holdener video. Pretty good review of stroke and engine capacity effects on torque and HP. https://www.youtube.com/watch?v=AjJSK5sLOeE

Things to watch out for; the 347 might put the piston pin in the oil ring groove, a 347 will very likely have less ring land above the top ring. If you are not running forced induction or doing track days then it shouldn't matter. However the 331, at least on paper, is a little more robust. I've been ripping on my 331 for close to 20 years and it's still not complaining.

That was always my concern, and why I built a 331. The whole more torque issue, isn't, I call BS. My buddy has a 347, it uses some oil, and I have a way better torque curve than he does. He can't drive below 2000 rpm's in 5th gear, I can drive all day long at 1500 rpm's in 5th, it will pull cleanly without bucking or hesitation all the way to 7000rpm's. He has said more than once my engine drives way better than his.
BUT Mark knows all this, we have had this talk several times. One day soon, the three of us are going to do a little test drive so he can see which one fits his style.:rolleyes:

[Bob Cowan]

That was always my concern, and why I built a 331. The whole more torque issue, isn't, I call BS. My buddy has a 347, it uses some oil, and I have a way better torque curve than he does. He can't drive below 2000 rpm's in 5th gear, I can drive all day long at 1500 rpm's in 5th, it will pull cleanly without bucking or hesitation all the way to 7000rpm's. He has said more than once my engine drives way better than his.
BUT Mark knows all this, we have had this talk several times. One day soon, the three of us are going to do a little test drive so he can see which one fits his style.:rolleyes:

But those attributes are not really a function of displacement. They are a function of cam, intake, tuning, etc. It's pretty easy to build a 427 with the same attributes.

If you're going to use a stock block, you're probably better off with a 331. But if you're going to use an aftermarket block, I would go with a 347.

[rich grsc]

But those attributes are not really a function of displacement. They are a function of cam, intake, tuning, etc. It's pretty easy to build a 427 with the same attributes.

If you're going to use a stock block, you're probably better off with a 331. But if you're going to use an aftermarket block, I would go with a 347.
Bob, I know, but we aren't supposed to use logic and common sense. :( It's always, mine is better than yours and we (me) are trying to convince Mark he wants a 331. :rolleyes: :p
Oh, I out ran Tims 460, he was not happy. I had a good and lucky day. Bet he never lets it happen again. :D

[Papa]

Just for reference ... my dyno numbers from BluePrint on my 347:

https://thefactoryfiveforum.com/attachment.php?attachmentid=84569&d=1524421786

[NiceGuyEddie]

Hello old friend!

I had almost the same upgrade. Go for the longer stroke. Stroker motors are loads of fun. I like to put mine in 3rd gear at maybe 1,000 rpm, mash the gas, and go waaaaaaaaaaaaaaaay up to almost 100mph. It's a hoot to feel how the powerband kicks in so early. Just under 3,000 rpm like in the above chart.

It's also swell how the car pulls effortlessly up long hills at low RPMs. The sensation is similar to being pulled up a ski slope on a tow rope.

I'm not a Auto-X expert, but some courses seemed better with a higher rpm, some seemed better with a stroker and more power at lower RPMs.

What is your flywheel choice?

[Bob Cowan]

Bob, I know, but we aren't supposed to use logic and common sense. :( It's always, mine is better than yours and we (me) are trying to convince Mark he wants a 331. :rolleyes: :p
Oh, I out ran Tims 460, he was not happy. I had a good and lucky day. Bet he never lets it happen again. :D

I outran Tim's 460, and I only have a 302. ;)

[Avalanche325]

I don't see any reason not to go to 347. The block clearancing is hardly anything and any engineering issues were overcome many years ago. 347 is the most common stroker size out there for a stock block SBF. People hammer on them on the track, strip, street, and autocross. Just put quality parts inside.

That being said there are 347s that have 330hp and 347s that have 600hp. Very different animals. I have 500+hp and it is not what you would want for a pure cruiser. It has snotty street manners and is extremely loud. But, I love it. Well, the temperamental snottieness, not so much the loud. I autocross regularly and do some track. 400hp would probably be a sweet spot for most people and be a strong dependable engine.

[TrevorP]

363ci baby, boom. 600hp/500ftlbs

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how do you make the pictures larger?

[Old Timer]

The 347 from Blueprint works great! 400HP is a great spot. It will scare the s#!^ out of you any time.
I love the torque. With a 3.55 and T5, I can break the tires loose anytime in 1st and second, 3rd if you jump on it hard.
I am running fuel injection with a MS3pro, so I can get decent mileage, on the highway, if I stay out of it.
Does not burn any oil, plugs still look great after 8k miles.

[KDubU]

347 for sure however I really like a 363. :cool:

[NAZ]

Giving up 16 CI for a better rod ratio (1.662 vs 1.588) makes sense to me for a pure street car. Less wear on the cylinders, rings and pistons usually equates to longer TBO. Most folks don't realize how much more friction a shorter rod ratio will create. Longer rod ratios provide more dwell at TDC and tend to add combustion efficiency which coupled with lower friction equates to more HP per CI. As for low speed torque and longer strokes, cam selection will influence torque way more than .150" longer stroke can.

[Bob Cowan]

There's no replacement for displacement.

You can't beat cubes. :)

[NAZ]

There's no replacement for displacement.

You can't beat cubes. :)

So they say.

But, there is more to the science of horsepower. OK, I admit I was bored so I ran a couple of simulations on a generic 302 based SBF keeping everything the same except stroke. These models were a garden variety 331 vs a 347 using GT40P heads (wow those are poor flowing heads!), 10.5:1 CR, 650 CFM on a dual plane manifold, small tube headers thru mufflers, and a generic street performance cam. Both engines provided peak HP at 5000 RPM and the 331 produced 1 HP more than the 347 because the less desirable rod ratio sucked 11.6% more HP at 5000 RPM due to friction. The 347 made 12 lb ft more torque than the 331 and did that at 500 RPM lower (3500 vs 4000).

I've seen this before so it's not an anomaly. When I built my latest engine I ran a bunch of simulation models expecting to see a 434 CI SBC come out on top in the power dept but it became clear that I couldn't put a long enough rod in a 434 to overcome the friction losses and my 406 CI actually made ~12 HP more than the 434 (they both have the same bore). And would be way easier on parts. My 406 makes 1.97 HP per CI without power adders a 434 would have made 1.81 HP per CI with the same cam and induction / exhaust.

Rod ratios affect friction (and therefore, HP) more than most realize and it is not linear.

[swwebb]

Just for reference ... my dyno numbers from BluePrint on my 347:

https://thefactoryfiveforum.com/attachment.php?attachmentid=84569&d=1524421786

Are these numbers at altitude? I assume not. I have a 347 with much lower hp numbers but the dyno was done at about 5500 ft.

[Papa]

Are these numbers at altitude? I assume not. I have a 347 with much lower hp numbers but the dyno was done at about 5500 ft.

No, these were done in Kearny, Nebraska (about 2,100') at the BPE facility, and are at the crank. I figure at altitude I'm at ~325 WHP at my 6,100' elevation.

[swwebb]

No, these were done in Kearny, Nebraska (about 2,100') at the BPE facility, and are at the crank. I figure at altitude I'm at ~325 WHP at my 6,100' elevation.

Consistent with my results at altitude. 280 WHP at 5000 rpm (max rpm they went to) at 5500 ft elevation. Can't wait to go to sea level to see how much better it performs!!

131851

[rich grsc]

For the life of me I can't find the one Dyno pull I have. Memory says 342 at the wheels, altitude here is around 500 ft.

[1932]

Go play at sea level then go home and look at the parts to get that power at home!

[GoDadGo]

Go play at sea level then go home and look at the parts to get that power at home!

I'd rather play Below Sea Level when ever possible so with that said: Hit It Harry!

Album Version:
https://youtu.be/5nPeN7zFTas

Live Version:
https://youtu.be/gHakdT1F8As

All kidding aside about sea levels, but rod angle is important.
Think about this, the 302 and 327 Chevys had insanely good rod angles by comparison.

1.9 for the 302 and 1.75 for the 327.

I'd take the 331 just for that reason even though the 347 is far more popular.

[MPTech]

Crap! Just when I was just about settled on a 347, I'm now questioning the 331 again.
NAZ made some REALLY convincing arguments. Damn you NAZ! lol
and Rich has been telling me that 331 is the way to go all along.

I'm not in a hurry, so I'll continue to do some research and also want to talk to Lance at Craft Performance.

Thanks for all of the feedback guys! I asked for recommendations and you delivered!

[mburger]

I’m enjoying this thread. I’m learning a lot from you pros and it’s appreciated.

[TrevorP]

hey NAZ
Just curious of the spec's on the 406. 1.97 per ci is insane amount of NA power.

I have 1.65 per ci, which is really high. It takes a solid roller, 7100rpm redline, AFR race 205s, 13.6 to 1 CR and 110 race fuel to get there NA.

[Briansshop]

ATM,I'm planning on a 363 in my Coupe, boosted of course. Guy over on the turboforums is making 1600 hp with his,no issues. I'd say build what you want without worries.

[GoDadGo]

Crap! Just when I was just about settled on a 347, I'm now questioning the 331 again.
NAZ made some REALLY convincing arguments. Damn you NAZ! lol
and Rich has been telling me that 331 is the way to go all along.


I still think either will work just fine and having a fresh mill in the car will make a big difference if you are burping oil out the dipstick.

We all get stuck in the mud on minuscule issues when we contemplate things we want to do to our cars.
As an example, I agonized on my camshaft choice when I replaced my block when I decided to shorten the duration by only 4 degrees while adding a bit of lift.
Man, I loved the lumpier old camshaft, but it wasn't very happy at 1,850 RPM much less 1,700 which is where I needed to cruise at 70 MPH when I'm in 6th gear.

My point is that every decision we make about these cars is a compromise and we often find ourselves suffering from Analysis Paralysis.

Good Luck From The Dark Dart Side!

[NAZ]

Crap! Just when I was just about settled on a 347, I'm now questioning the 331 again.
NAZ made some REALLY convincing arguments. Damn you NAZ! lol
and Rich has been telling me that 331 is the way to go all along.

I'm not in a hurry, so I'll continue to do some research and also want to talk to Lance at Craft Performance.


Thanks for all of the feedback guys! I asked for recommendations and you delivered!

Not much risk in your choices that you're considering -- both will work well for the application. Not trying to increase your anxiety level, just adding some info you may not have considered. Between the 331 & 347 I'd choose the 331. The 331 will add some extra displacement and a bit more low end vacuum over a 302 equipped the same and that will result in better low end response. The 347 will increase that low end vacuum a bit more but at the cost of exponentially higher horsepower robbing friction and more waste heat energy the cooling system has to deal with.

Like Steve said, every choice you make when building an engine is a trade-off. But these two engines, assuming comparably equipped, are so close you really can't go wrong with eather.

Have fun and enjoy your car. Remember, we're always here if you need help spending your $$.

[NAZ]

hey NAZ
Just curious of the spec's on the 406. 1.97 per ci is insane amount of NA power.

I have 1.65 per ci, which is really high. It takes a solid roller, 7100rpm redline, AFR race 205s, 13.6 to 1 CR and 110 race fuel to get there NA.

131870
Trevor, as you expected this is a high compression engine at 12.97:1 static and 10.71 dynamic. I would have built it with even higher CR but this is a nitrous engine and pushing past 13:1 SCR on nitrous is asking for trouble. I need an engine that will last past two race seasons so went a bit milder than I could have.

The power curve above is adjusted for a standard day at sea level without power adders. Up here where the DA is 9,000' in the summer the engine acts more like a typical 70's era muscle car near the beach in SoCal. Since this car has a 6000 RPM stall converter you can look at the HP & TQ curves starting from 6000 RPM and note that the peak power is at 7500 RPM. The engine was built to drag race so has a very narrow operating window in that context so all the parts I selected were picked to work together in that power band. I spent maybe 40-50 hours computer modeling hundreds of off the shelf parts to achieve nearly 2 HP per cubic inch. And the car starts right up, idles, and runs good on the street. It does have a hint of a lope to it until about 1800 RPM but nothing that takes away from the driving experience. Since the engine was built for nitrous I could get away with running higher intake runner velocity than a supercharged car and that is the key to good street manners along with the LSA on the cam.

I spent many hours designing the cam for this combination and it has a 4-7 swap. I had Comp Cams grind it to my specs. The cam is key to power and like most racers, is a closely held secret. Everything else was off the shelf except the AFR heads are a spread port design but I selected all the parts from their menu so it's semi off the shelf.

[FFRSpec72]

why not a 363, nothing better than more CI

[CobraboyDR]

Unless it's money, all things being equal, the 347 will be stronger than the 331, especially down low where a car is driven most. Certainly you can build a 331 to be equal to a 347, but cubes are cubes and longer stroke generally = more torque.

[rich grsc]

Well that certainly isn't the case with mine, none of the 347's in our club are stronger. Torque, I can easily drive in 5th gear all the way down to 1200rpm's, and pull right back up to road speed. My buddies 347, can't manage under 2100rpm's in 5th, we both have the same tranny and rear gear ratio. I had Mark out for a ride a bit ago, he know's how my car runs. Don't underestimate a 331, it can be a mistake.

[NAZ]

Unless it's money, all things being equal, the 347 will be stronger than the 331, especially down low where a car is driven most. Certainly you can build a 331 to be equal to a 347, but cubes are cubes and longer stroke generally = more torque.

If we're talking "all things being equal" the 347 will have only slightly more torque "down low" as the poor rod ratio sucks a bunch of power on a 347 (see post 23 above). And it will be much harder on rings, pistons, and cylinder walls plus that extra friction is turned to heat the cooling system has to deal with. Offset pins will help to mitigate that but I didn't model that to quantify the result. The OEMs have been playing with offset bores and picked up a significant amount of power with engines constrained to short rods, but that won't help the poor short deck SBF.

[nucjd19]

Hey folks. Newbie here. Thanks for the excellent info. I have purchased the blueprint 347 (Carb) and TKO 600 combo for my build about 2 weeks ago. I spoke at length with the guys there about the 306 vs the 347. They really thought the 347 would be the right fit for my driving plan and overall gameplay for my build. I plan on using mine like MPTech. The price difference was about 800 dollars between the 347 and the 306. Also my wife loves here some torques when she is scooting around the back roads where I live ( she can autocross something fierce :) ). Anyway cool info and appreciated.

[CobraboyDR]

If we're talking "all things being equal" the 347 will have only slightly more torque "down low" as the poor rod ratio sucks a bunch of power on a 347 (see post 23 above). And it will be much harder on rings, pistons, and cylinder walls plus that extra friction is turned to heat the cooling system has to deal with. Offset pins will help to mitigate that but I didn't model that to quantify the result. The OEMs have been playing with offset bores and picked up a significant amount of power with engines constrained to short rods, but that won't help the poor short deck SBF.I am told those bugs have been eliminated in 347 stroker kits.

[NAZ]

It's not a bug, it's geometry -- has to do with the extreme rod angle. Short rod & long stroke equals extreme rod angle which during combustion forces the piston hard into the cylinder wall.

Not the end of the world, but it is something to consider when building an engine as there are drawbacks to short rod ratios. The 302 based strokers all have the same low 8.206" deck constraints and require low compression height pistons which will limit power capability due to piston durability.

The takeaway is: there's more to power output than just adding cubic inches. Building an engine is an exercise in balancing compromises.

[GoDadGo]

My Dark Side Chevy Examples:
1. A stock 400 SBC from the 1970's had a 3.75" stroke crankshaft with crazy short 5.565" rods, that loved to break, which yielded a Rod Angle Ratio of 1.48.
2. My 383 SBC (All Dart Engine) which can be easily punched to 400 cubes shares that same 3.75" stroke; however, my rods are 6.0" long so my RAR is 1.60.
3. I went with the longest rod possible in an attempt to get close to the RAR of the 350 Chevy which has a 3.48 stroke with a 5.7" rods which has a RAR of 1.64.

How It Equates To A SBF Mini Stroker Motors:
1. A 5.4" Rod wiht a 3.00 stroke yeilds a RAR of 1.80.
2. A 5.4" Rod with a 3.25 stroke yeilds a RAR of 1.66.
3. A 5.4" Rod with a 3.40 stroke yeilds a RAR of 1.59.

Just make sure that if you go with the 347 stroker that the sucker doesn't have the stock 5.09" stock rods because that would equate to a RAR of 1.50.
By the way, a 302 Ford with the stock shorty rods has a RAR of 1.7 in case this is something you'd like to know.

NOTE:..Please be advised that I am NOT an engine builder, just a Dark Side Banker who is obsessed with numbers and engines.
............My interest is specifically limited to our domestic American V8's and some inline 6 cylinder engines of various countries of origins.
............In addition, my extreme knowledge of engines was granted to me by sleeping at more than a few Holiday Inn Express Hotels over the years.

Good Luck From The Dark Dart Side!

[Hoooper]

Keeping the wrist pin out of the oil ring is obviously one thing to watch out for. After that, I would focus more on mean piston speed than rod angle ratio. The actual angle difference between at rod with RAR at 1.54 vs 1.8 really is not all that significant, but for reliability keeping the mean piston speed within reason for the quality of parts you are using is very important.

That said, if it were me with $7k to spend on a motor and want something around 400 HP, streetable, with good reliability and fuel injection, I would pick up a 376 from a 2008+ escalade with wiring harness, computer, and stick the other $3k back in my pocket.

[rich grsc]

Ya, like that'd just drop right in for a straight up swap.:rolleyes::confused: Sorta 100% opposite of what Mark is looking for.

[Hoooper]

He wouldnt need to modify the footboxes and should only need to weld a new flange on his headers + get a bellhousing adapter. I guess it depends on how much he likes that extra $3k ;)

[edwardb]

https://hosting.photobucket.com/images/ab234/edwardb123/200_(1).gif?width=1920&height=1080&fit=bounds (https://app.photobucket.com/u/edwardb123/a/186cc666-68d0-4881-b53c-af005ffe3552/p/1c38e2d6-782f-45ab-b64b-124a30f1b3f5)

[MPTech]

Hooper, Thanks, but ah................................................ ................................NO

I'm ok with spending the $3k to put a Ford in my Cobra. You are free to put whatever makes you happy in your Cobra.

Rich's ride and NAZ's comments have me re-thinking the 331, but I think Rich's 331 may be more performance than the Blueprint 331 I was looking at. Still undecided.

[bobl]

I think you guys are way over thinking the rod ratio deal. The difference between the 331 and 347 is minimal and would never be noticed in a street engine. Sure, as Naz stated a longer rod would be better (if it would fit in the block). But the benefit of increased stroke far exceeds the losses due to increased rod ratio. Both engines can make nearly the same power all else being equal, but bringing that power down by several hundred rpm in the 347 will be noticeable. That increased torque holds true all the way down the rpm scale. For example: 2 identical builds except for the stroke, at 1500 rpm the 347 will have roughly the same torque as the 331 at 1700-1800 rpm. You could definitely feel that in normal driving. My thoughts on the longer stroke being harder on pistons… yes it would be to some extent. However it will turn less rpm during the life of the engine to generate the same power so I believe it is somewhat of a moot point. I’ve built a ton of stroker engines and never seen issues. The pin overlapping into the oil ring groove is also not a concern. In all modern pistons that I’ve seen there is a support ring that goes on before the oil ring if required.
Attached is a dyno simulation of my 347, which I tweaked parameters so it closely matches the actual dyno results. I then changed the stroke to 3.25 with no other changes.

Bob

[CobraboyDR]

I think you guys are way over thinking the rod ratio deal. The difference between the 331 and 347 is minimal and would never be noticed in a street engine. Sure, as Naz stated a longer rod would be better (if it would fit in the block). But the benefit of increased stroke far exceeds the losses due to increased rod ratio. Both engines can make nearly the same power all else being equal, but bringing that power down by several hundred rpm in the 347 will be noticeable. That increased torque holds true all the way down the rpm scale. For example: 2 identical builds except for the stroke, at 1500 rpm the 347 will have roughly the same torque as the 331 at 1700-1800 rpm. You could definitely feel that in normal driving. My thoughts on the longer stroke being harder on pistons… yes it would be to some extent. However it will turn less rpm during the life of the engine to generate the same power so I believe it is somewhat of a moot point. I’ve built a ton of stroker engines and never seen issues. The pin overlapping into the oil ring groove is also not a concern. In all modern pistons that I’ve seen there is a support ring that goes on before the oil ring if required.
Attached is a dyno simulation of my 347, which I tweaked parameters so it closely matches the actual dyno results. I then changed the stroke to 3.25 with no other changes.

BobAgreed.

I totally understand NAZ's perspective in a racing engine which run balls-to-the-wall constantly where squeezing out the last hp & RPM is critical to winning or (as Ricky Bobby says) "First Loser."

But a street engine is a different animal. It will rarely suffer the same physical forces for as long as a race engine. And the additional grunt down low makes the street experience enjoyable.

I'm unaware of the 347 engines so popular in street Cobra replicas having major mechanical issues because of RAR. Even the FFR preferred engine builder offers a substantial warranty on their 347.

That said, the RAR discussion is educational, and I appreciate NAZ's input. I learn a ton from specialist geeks. Thanks!

[Duster]

I went with the Blueprint 347 and the Holley Sniper with the TKO 600. Fired up instantly, has a ton of torque and plenty of grunt. Have a power curve similar to what Papa posted.

All this and a warenty!