Rod length? Piston speed?

[WDCreech]

Originally Posted by art leong

A question about rod length, piston speed.
I'm running a 6.160 rod. the stock length is 5.94. The stroke is 3.98.
Will the longer rod.
A= make more lower end torque?
B= make more power in the higher rpm ranges?
C= not make a hill of beans difference?
This is for a 4 cylinder car with an automatic (2600 pounds), I need all the torque I can get.

Art, to answer your question, all a long rod will do is broaden the power band. It has nothing to do with average piston speed.

[crazyponcho]

Its been a few years now but through some connections we got someone at nasa in houston to run a simulation on a cray supercomputer as to the effects of rod length the computer came up with results that said for any realistic changes in rod length the change in piston speed was marginal at best when the velocity graphs were overlayed to the naked eye you could not see a diference.

[thewrench3]

I run a four cylinder drag car myself. I have a 3.126 stroke and I changed from a 5.205 rod length to a 5.7 rod length. The 5.7 rod is 105 grams lighter and uses a small rod bearing diameter. The piston is 225 grams lighter and uses thinner rings. The longer rod engine makes more power up high- above 5000 rpm. the short rod motor makes more torque at 2700 rpm to about 3700rpm then the long rod engine makes more. The long rod engine is more particular about the cam timing. Overall I'm happy with the long rod engine. In the car the long rod engine runs a quicker et and more mph. My combination maybe different than yours the car is 2400 lbs. with me in it at race weight. Just talking from experience here.

[mattclow]

Look at all the used NASCAR stuff for sale on eBay...... Big bore, short stroke, long rod. Piston weight seems to be the priority. They spent a little money on research and development. So you know they've figured something out. Mind you, all of the secrets won't make it to ebay until it's common. So there could be a secret short rod combo... But I doubt it.
I could be comparing apples to oranges. But you can't ignore decades of homework.

[Adger Smith]

Well, you sure took the rod length at face value. There are "other" parameters in cup engines that have an affect on the "total" engine package. Just like in F-1. Yes, they are very well designed and tested for the purpose they are built for. If long rods are the answer then why did most of the 358 cu in PST engines (making well over 2.5 HP per cu in N/A) use very , very short rods and BB pins?

That's the question I'd like to know the answer to. What is the advantage to a short deck block and short rods in a modified or comp engine? It has to do with the 9,000 to 11,000 rpm range...

[Adger Smith]

Intake manifold design