Rod/stroke ratio? really? are people still talking about the oil ring too? Here is a list of rod stroke ratios. If your 347 breaks down it wont be because of rod/stroke ratio.

302 SB Ford (1.70:1), or a 289 SB Ford (1.78:1)?

For the Chevy fans, how about a 350 SB (1.63:1) or a 454 BB (1.53:1)?

For the Chevy SB Stroker Motor racers, would you favor a 350 (1.63:1) or the ever popular 383 (1.52:1)?

For the Ford Stroker Motor racers, how about a 302 SB (1.70:1) or a 347 SB (1.58:1)?

or the chevy 400 (1.48:1)?

or the 408w (1.56:1)


newer motors are as low as 1.50:1

a ratio of 1.58 is plenty good
Smokey Yunick...I aint buying it

 

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Rod/stroke ratio? really? are people still talking about the oil ring too? Here is a list of rod stroke ratios. If your 347 breaks down it wont be because of rod/stroke ratio.

You really ought to be making all of your comparisons across engines of essentially the same displacement. On the SBC side, you'd match the 307 (1.75) against the 305 (1.64). I'd take the 307, but the extra 2 cubes would be about the smallest reason among several. For higher rpm competition duty where displacement might be limited to 310 CID, I'd start with a 302 (1.90) instead of either of the others.

About the 350 vs 383 SBC - I'd really rather have either a 347 (4.125 x 3.25, 5.7" rods) vs the 350, or a 377 (4.155 x 3.48, 5.7" rods) vs the 383.

FWIW, the 4.6L is at 1.675 and even the truck-motor 5.4 is at 1.60. There has to be a good reason for Ford keeping the rod ratio above 1.6, because otherwise these engines are both needlessly large physically relative to their displacement. A 3.55" bore is more consistent with a 4.2L V8, so the 4.6 is already a mild stroker when viewed from that perspective.

I really don't think you can get away from the geometry issue entirely. Like it or not, things like side forces against the cylinder walls, and the relationship between stroke and valve size that is implied by a long stroke engine are things you can't get away from. Crutch them, yes. And this is where I think the difference between squeezing the maximum possible displacement out of a given block size over a somewhat shorter life vs not pushing the geometry so hard and getting longer life comes in.


Norm

 

I agree with what your saying. Its not something we can dismiss. But if a 1.6 is a good rod ratio what makes 1.58 bad? I dont think anybody would see less engine life compared to a 331. But this is something that we could argue about till Obama saves the economy, and there have been thousands of 331 vs 347 threads on the internet. So Ill run my 347 and you run your 331.

Id rather talk about the proper way to super/turbo charge our 331/347. Id like to do a dart block kenne bell 347.

 

347 is fine for the street. There are plenty that have turned the odometer out there, it comes down to parts quality and how well built it is.

There are advantages and disadvantages to higher and lower rod ratios though. Lower rod ratios will result in higher piston speed at the top of the bore and create a stronger initial induction pulse during the intake cycle(boosts torque output, especially at lower rpms), but they also put more stress on internal components. Longer rod ratios help with piston dwell/combustion(and reduce peak piston velocity) which works to boost power in the upper rpm range where combustion time is limited, and they place less stress on internal components.

That's why you TYPICALLY see shorter rod ratios in lower rpm engines and longer rod ratios in higher rpm engines. Formula 1 engines that are turning 18,000rpm(previously were turning a little over 20,000 before rules changes) run rod ratios of 2.1-2.2 or higher. But keep in mind that they're also required to effectively combust pump gasoline at 18,000rpm and stay together at that same rpm for at least 2 full race weekends.

GM's new LS7 7.0L production engine has a rod ratio of just under 1.52, with a factory 7,000rpm rev limit....but also uses a Titanium alloy rod(though it's not a high end Ti rod) so internal weight is less than most other 4.00" stroke engines.

And the 347 makes noticeably more power than a 331, and it has nothing to do with the cubes. The mean piston speed is higher, which boosts the induction pulse strength and fills the cylinder better. Longer stroke helps to boost volumetric efficiency.

 

Yeah, have been since August. New rear main, oil pan gasket, water pump/timing cover seals, and everything seems to be working mostly ok. Next problems to fix are cooling (in 100F heat), traction, and possible oil burning via the pcv system.