306 vs 331

Joes95GT said:

I was just about to not say anything because I knew that was coming. In some cases, and this being one of them, your rebuttals are ridiculous.

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I don't see how they are ridiculous. You put a blanket statement about how a 347 will beat a 331. Any other specs on those two engines in question?

Joes95GT said:

Ok, here goes. Use the 331 because of extreme b-splitting, side loading power of the 347. The 331 utilizes a better rod ratio and is much better than a 347 because it will burn less oil over a prolonged period of time in a controlled environment, since, as we all know, we all operate our engines in controlled environments.

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Exaggerated and that isn't how I portray it. You know that. It appears your taking it out of context.

Joes95GT said:

The 331 is for you.

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Nope, I would go with a 347.

Joes95GT said:

All hail 5spd GT, for he is the one who knows it all, yet is the one who can't convey it all clearly so he tells everyone that they take his words out of context to make himself feel better.

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I do not know it all. I don't take out of context if I can help it. I correct bias post if at all possible.

Michael - Cool, didn't know that...

4.030" bore X 3.250" stroke = 331.65 cubes = 332

I'm on a mission to change what we call it -- 332 from now on. By the way, the old FE 427 is actually a 426 -- but some other company already had a fairly famous engine with that displacement - so they went up one.

first off here, saying rod ratio doesn't matter is moronic.

second, engines with poor rod ratios can run well and have good life to them.

third, the 347 may have a good life expectancy for drag racing or daily driving, but put that engine on a road course or any type of endurance racing and you will find out why those guys prefer a shorter stroke.

the 347 did burn oil when they were introduced as a stroker, that is a fact. one way they circumvented this is using a shorter rod-5.315 in the chp version.

at the level of 100hp/liter the diff in a 331vs347 is roughly 40hp. so yes the 331 does give up some power.

i see sir you have chosen a 306, that is a very good decision as would be a 331, or a 347. the argument here is splitting hairs.

bimmertech said:

first off here, saying rod ratio doesn't matter is moronic.

second, engines with poor rod ratios can run well and have good life to them.

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So what are you saying here?

nmcgrawj said:

So what are you saying here?

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what i am saying is that the rod ratio has a great deal of impact as to how an internal combustion engine operates and to ignore that fact is foolish.

however there seems to be a number of engines, OE and aftermarket, that operate well despite there defficiencies in this area.

bimmertech said:

what i am saying is that the rod ratio has a great deal of impact as to how an internal combustion engine operates and to ignore that fact is foolish.

however there seems to be a number of engines, OE and aftermarket, that operate well despite there defficiencies in this area.

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Those engines that operate despite this rule are what make guys not care about it i believe.

The guys that i have talked to, brian at ADperformance comes to mind, have said that rod ratio shouldnt be the deciding factor. Sure it probably comes into play somewhere along the line, but i think that there are probably other things that are much more important and play a bigger role than just the rod ratio.

Oh and i read some things on hardcore that i found to be pretty interesting.....

Erik Koenig "racer7088" on hardcore said:

I've never really seen many oiling problems with the 347s that do have the pin in the oil ring either when done right but I agree with George Klass that if you really want to decrease cylinder wall side loading you should take all the power, or anotherwords cylinder pressure, out of the engine to even less than stock levels. You could run a destroked low power 2 bbl 289 at like 220 inches with 5.7 inch Chevy rods! This way your engine will last forever! The rod ratio and angle is where the cylinder pressure puts leverage on the crank and the cylinder wall, which is how the piston is located in space. The piston is side loaded in a line of action through the pin and is influenced by the rod angle AND more importantly the cylinder pressure at that point.

Cylinder pressure is WAY more detrimental to cylinder wall loading and wear than any difference in rod angle or ratio that you can ever achieve given the constraints of the stock deck height and the fact that the pins must clear the counterweights! So if you really want to reduce cylinder wall side loading you need to reduce power and torque because a 5 per cent increase on power has already increased side loading more on a stock engine than a 347 has with the same power. So I guess the moral of my story is that if you want 250,000 mile longevity your probably on the wrong forum and if you want easier, more reliable and more streetable power go for the most cubes that you can get within the limits of mechanical reliability of course.

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the post from hardcore is pretty much straight forward and i agree. however i am of the school of thought that bigger is not always better. i will give you the example of 2 347's.

the first is a top of the line 347 from CHP. it is a good motor and should last a while problem free and depending on the induction used can make 450hp.

the second is a 351w block bored .030, a used sonny bryant nascar 3.35" crank, used nascar carillo 6.2" rods, and some custome weisco pistons. this is a good combo and depending on the induction used can make 450hp.

now take those engines one after the other in a mustang and road race it for 1000 consecutive miles. which will last the longest? my moeny is on the shorter stroke/longer rod engine.

my point is that engines with poor rod ratio are ok, but they do have thier limitations due to the poor rod ratio.

i do agree that the rod ratio should not be the deciding factor. the deciding factor should be your intended usage and budget.

to make this clear, I AM NOT BASHING 347's. i don't drag race and so my opinions on engines is very different than most on here.

bimmertech - if you talk to the VERY reputable guys on this board that design and build VERY competitive motors for others, they're the first to tell you that in these engines at the relatively modest rpm they're used at -- they don't look at rod length and rod/stroke ratio as a significant variable. In the case of a 347 they'll tell you - 5.4" or 5.315" -- toss a coin. It changes the valve events on the cam a bit - but that's about it.

If you're designing an engine from scratch for a tightly contested series with limiting rules (say F1) - then, yes; rod length and rod/stroke ratio is something that's looked at closely along with everything else -- but I'd suggest to you that even in series like that, it's impact has more to do with packaging the engine in the chassis/body/aero setup than it does with rotational and combustion dynamics. They know that to create the HP they need to be competitive, it's gonna take "X" rpm -- and they know the displacement limits. That and average piston speeds dictate the bore and stroke once the # of cylinders have been determined. It's not as big a significant variable as you're making it out to be.

Lastly - there are LOTS of guys out there racing 347's in road racing series - both sprint and endurance racing. My brother crews for an outfit that runs a Shelby GT350 in vintage races -- running a 600hp, 7800 rpm carbed 347 that hits in the high 180's on the straights at Sebring. They've been running it in sprint races and endurance races for many seasons. I've even got a buddy up in the Boston area with a 347 in his 242 Volvo that he uses for track days on a regular basis.

As we've said before in this thread and others -- built and machined competently with quality parts, the 347 is no different than the 289, 302, 332 or any other (rather arbitrary) displacement of small block Ford you'd like to come up with. It works just fine.

And by the way - comparing a stock Windsor block 302 with a 347 stroker kit to a 351-based block with a Sonny Bryant billet crank is like comparing apples and artichokes. Nonetheless, not to beat a dead horse, built competently to the 450HP level, either one will cover 1000 miles of endurance racing with no problems as long as they're not rev-abused.

Michael Yount said:

It's not as big a significant variable as you're making it out to be.

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look, i am not saying it is the end all be all of engine dymanics, but to not even consider it a factor is not right. i'm sorry, piston speed is a variable.

here is another example.

take a ford 302, stock. then compare it to a chevy 302, stock. elimanate all variables in induction and exhaust and then compare hp/tq.

teh chevy will be very fortuante to break 250rwtq. mine made 225 and my instructors made 218. the ford will make 300rwtq. the chevy will make more peak hp than the ford. i know deck heights are different and you will prolly say this is not a fair comparo.

i really don't like beating a dead horse either and i am not bashing anyones ideas, but everything i've ever learned in schools about piston speed vs pumping/friction losses says that stroke and rod length are items that affect engine performance characteristics.

we all have our own opinions on this matter and this is what makes :SNSign: a great learning tool.

No one is saying it shouldn't even be considered -- what's being said is that for the easily available options -- pick one - it doesn't matter much which one you pick.

Your 302 Chevy/Ford example TOTALLY misses the mark. The reason that there were differences in the Chevy and Ford 302's is BECAUSE of induction and exhaust differences. The long runner efi intakes were developed with torque in mind -- the Chevy 302 never had those available. If you build comparable 302's both with 4" bores and 3" strokes, similar heads, similar exhaust, similar intake -- guess what? You're gonna get similar output. It ain't rocket surgery. If you want an example of a REASONABLE comparison between Ford and Chevy 302's --- all you have to do is look at the 67-68-69-70 TransAm seasons. The 302 Z28-based Camaros and the Boss 302-based Mustangs were very comparable. In fact, Ford had to pull out all the stops to finally unseat Donahue and the Camaro from the championship in 70. The cars ran very close. In the end what separated them wasn't internal engine dimensions - it was simply how much money the factory was willing to throw at the championship. And the simple fact is that ($$$$) is the single most critical variable in just about any racing series. It's not engine architecture or design (OK - occasionally there is technical breakthrough -- but those usually only last for a few races, then everyone else catches up) -- it's HOW MUCH BUDGET DO YOU HAVE?

Of course stroke and rod length affect things -- but what works and what doesn't in these engines has already been sorted out. The stuff that's available works. That's what folks are trying to tell you.

Actually I see many post about how the rod ratio doesn't matter. Then it is later twisted on how they will "run fine" or "last for what you want it too", etc...if I only had time to quote all of them

I simply just stick with it: Rod ratio does matter whether big or small it is a factor on wear.