Alright, I will bite and play the devil's advocate.
Here are what two top-notch people have to say about a subject related to what is being discussed here:
Larry Meaux says:
From all the various Rod Ratio engines ive had on my Dyno so far, once you go under 1.50:1, blow-by CFM steadily increases, but you can resolve this with Vac-Pump or use some stages of DrySump Pump to scavenge/vacuum..and this will make more HP/TQ.
But if the particular Block you have is moving around and the Rod Ratio is small with a lot of stroke, + a lot of windage ..those small rod ratios have increasing BlowBy issues that have to taken care of.
Darin Morgan stated this below as well:
Most people tend to overgeneralize this issue. It would be more accurate to compare different rod-to-stroke ratios, and from a mathematical stand-point, a couple thousandths of an inch of rod length doesn't really change things a lot in an engine. We've conducted tests for GM on NASCAR engines where we varied rod ratio from 1.48- to 1.85:1. In the test, mean piston speeds were in the 4,500-4,800 feet-per-second range, and we took painstaking measures to minimize variables. The result was zero difference in average power and a zero difference in the shape of the horse-power curves. However, I'm not going to say there's absolutely nothing to rod ratio, and there are some pitfalls of going above and below a certain point. At anything below a 1.55:1 ratio, rod angularity is such that it will increase the side loading of the piston, increase piston rock, and increase skirt load. So while you can cave in skirts on a high-end engine and shorten its life, it won't change the actual power it makes. Above 1.80- or 1.85:1, you can run into an induction lag situation where there's so little piston movement at TDC that you have to advance the cam or decrease the cross-sectional area of your induction package to increase velocity. Where people get into trouble is when they get a magical rod ratio in their head and screw up the entire engine design trying to achieve it. The rod ratio is pretty simple. Take whatever stroke you have, then put the wrist pin as high as you can on the piston without getting into the oil ring. What-ever connects the two is your rod length.
So, does anyone think it is a coincidence that these R:S ratios exist?
NASCAR (9.00" deck height) - 1.93
Formula 1 - 2.0-2.5 (18-20K RPM)
Pro Stock - 1.71
What if you compare the rod to bore centerline angle between a few of the SBF engine combinations?
17.139* - 302 (5.090")
17.513* - 331 (5.400")
18.350* - 347 (5.400")
Rod is Divided by Stroke:
302 Blocks
289/293 (5.155"/2.87") - 1.79
302/306 (5.090"/3.00") - 1.70/1.80 (5.400")
327/331 (5.315"/3.25") - 1.64
327/331 (5.400"/3.25") - 1.66
342/347 (5.315"/3.40") - 1.56
342/347 (5.400"/3.40") - 1.59
352/355 (5.205"/3.50") - 1.49
351 Windsor
351/357 (5.956"/3.50") - 1.70
387/393 (5.956"/3.85") - 1.55
387/393 (6.200"/3.85") - 1.61
402/408 (6.200"/4.00") - 1.55
412/418 (6.200"/4.10") - 1.51
351 Cleveland
351 (5.778"/3.50") - 1.65
383 (5.850"/3.75") - 1.56
396 (6.000"/3.85") - 1.56
408 (6.000"/4.00") - 1.50
426 (6.000"/4.17") - 1.44
Big Bore
427 (6.200"/4.00" - 1.55
429 and 460 Strokers
429 (6.605"/3.550") - 1.86
460 (6.605"/3.850") - 1.72
501 (6.800"/4.150") - 1.64
532 (6.800"/4.300") - 1.58
557 (6.800"/4.440") - 1.53
Modular:
4.6L 2V (5.933"/3.543") - 1.674
4.6L 3V (5.933"/3.543") - 1.674
4.6L 4V (5.933"/3.543") - 1.674
5.4L 2V (6.657"/4.165") - 1.598
5.4L 3V (6.657"/4.165") - 1.598
5.4L 4V (6.657"/4.165") - 1.598
GM:
LT1-1.638
LT4-1.638
LT5-1.568
383-1.520
383-1.600
LS1-1.684
LS2-1.684
LS3-1.684
LS6-1.684
LS7-1.517
LS9-1.657
L92-1.684
Mopar:
5.7L HEMI-1.744
Either way, I would choose a 347 over a 331 in an N/A situation. Just have a good engine builder that knows what he is doing.
By the way, a 347 does not and never has used a stock rod length. Also, there is not "new technology" that fixed the 347 "oil problem." They just got rid of the oil ringland wrist pin gap, like 99.99% of vehicles on the road.
but if not why would i ask these questions
