I'll tell you what Falcon67, if it's OK by you I'd rather separate the rod topic from the 2V vs 4V thread so it doesn't get lost in the mix.

"mo' better would be "Use a longer lever (the rod) and you apply more force to the crank" i.e., there is less lossage due the the angles involved "

Definitely, although I think the gains are minimal compared to increasing the crank throw. The Modular 5.4L(329) and 6.8L(415) were designed to be an improvement over the 351 and 460. Not just for emissions and gas mileage but also for better drivability in the lower rpm range. I think the 4.17" stroke was a major contributor for increasing the torque range below 3K RPM.

 

i think any gains in a long rod engine are from the lighter piston than anything else?

 

That's similar to the point I was trying to make in the other thread when I said,

"A longer rod in itself does not contribute very much, however I believe the rod angle reduction and the reduced piston weight would allow a higher maximum RPM before a structural failure."

When Aussie 302C owners decide to upgrade to a 351C crank it makes sense to use the long 302C rods (6.03" vs 5.78") because there are inexpensive, short pistons available. They are fine for mild applications but a custom forged piston would be needed in an extreme application for any real advantage coming from the longer rod length.

I agree with this info as a general guideline however as always, there are exceptions with every application.
http%3A%2F%2Fwww.grapeaperacing.com%2FGrapeApeRaci ng%2Ftech%2Fconnectingrods.pdf

 

The other thread got too mixed up to figure out who was argueing what, but one thing I did notice, was that a bunch of you made a lot of mistakes when it came to 351W heads. The 69-70 heads had the smallest chambers. And up untill 1974 they all had the 1.84/1.54 valves. From 75--up they used the same castings and valves as the 302's, with the exception of the GT-40 headed Lightnings. And the 69-70 heads had slightly larger ports than the others, GT40 heads excepted.

 

It would be interesting to see exactly how much the cylinder wall side loading was actually changed as the rod/stroke ratio got better/worse by changing the connecting rod length for a given crank stroke.

I know that high cylinder pressure & RPM can make cylinder wall life short in a factory Cleveland block without grout/filler, but I bet side loading plays a part too.

 

I think side loading would be hard to measure because the rod isn't the only thing changed. Longer rods also mean a shorter pistons. A short piston usually means thinner rings spaced closer together and a shorter piston skirt. There is less surface area in contact with the bore so the load is concentrated in a smaller area. A taller piston is more stable. I like to see about a 1.4" minimum compression height for a C piston used in street applications.

 

Hey bad,

You are correct on the chambers and the larger ports (got the port specs around here somewhere). The early heads ran a 60.2cc if I remember correctly. I never mentioned specific volumes but the later heads went up to a 69cc...correct me if wrong as I'm going from memory. I don't mess with Weezers much and I have cleaned out all W parts.

 

Good idea to separate this out. IHMO, it's not cost effective if you shop the parts available. The Aussie rods are a tad too long for use with the Probe piston designed for a 6" rod. And you can figure $150~200 (I priced it) extra to have a set of 6" chebbie rods narrowed to fit a Ford crank pin width. Add in grinding the crap out of a crank and you've spent a lot of cash to add .28 inches to your rod length.

So if you're going to drop that kind of $$$, might as well get the levers going good and make it a stroker - you'll get more out of it (and your moeny) I'd think.

From what I read and the comments of noted builders, an engine with a large intake port is going to like the piston moving away from TDC faster anyway. Generates more depression faster to pull harder on the port. So the stock shorter rod is probably preferable to a longer rod with a 4V head, with a 2V - maybe either. I still think you'd have a time finding results on a dyno.

Don't think it's necessarily a BAD idea, just any gains -IF any- would be hard to justify against the cost of getting there. Money just might be better spent elsewhere.