Am am in the planning stages of building my new engine.


It will be based on a 350 1 piece rear main seal block, with splayed caps. The engine will be EFI with a Stealth Ram, and a big hit of nitrous, 200 -250 fogger.

I am going to run an Eagle forged crank, Eagle H beam rods, Forged pistons, Dart Pro 1 heads, etc....

I am unsure if I should, / need, to go with a 5.7" rod or a 6" rod.

I see a lot of engine being built with the long rod, but nort much reason why. I know whne I built my 406 I went with the 5.7" over the stock 5.565" because they say that short 400 rod puts to much side load on the bores.

I read something interesting it the Engine Masters Challange though, that makes me think 5.7" may be better.

It said that the shorter rod keeps the piston from spending to much time at TDC, which decreases the chance for detonation.

So, what rod do I need?

 

Besides cost, the differences are negligible in a street engine.

 

AS should be noted, this is not just a 'street engine'.

I will be running 215cc heads, 2.05" intake valves, fully ported steath ram, big roller cam, with about .550" lift, all forged intrenals, and a 200-250 fogger Nitrous oxcide system. Behind the engine will be a 3200 stall converter in a race preped tranny, 3.73 geared 9", etc...


So, what then is the pros & cons of long rods, in any application?

 

Longer rod gives a better rod to stroke ratio.

https://www.thirdgen.org/techbb2/sho...+or+6+inch+rod

12 posts down.

 

Thanks!

 

Longer rods give a longer rod to stroke ratio but not "better" Better is subjective.

Actually Nitrous motors tend to favour a shorter rod ratio.

Build it with 5.7" rods.

There is so much more to consider to build a "better" nitrous street motor then mulling over rod length.

There is much more to be gained by working on the optimizing the cylinder head port , induction and exhaust flow bias to augment nitrous power production.
You'll end up with a "better" result if you concentrate your efforts there, then on minor rod length differences.
Don't waste your time or your budget on this any further.

(Nitrous motors have a lot more exhaust volume to deal with) {think - "big exhaust valve"}

 

Heads are being taken care of by my port man, who build nitrous motors and holds a few NMRA records.

Cam is going to be ground for n2o use.

Crank and rods will be 4340. Heads and mains will have studs, etc...

The rod's were the only thing I was really unsure about.


Thanks agian for the help.

 

Your cylinder had man should consider smaller 2.00/2.02" intake valves over 2.05's as this will allow a much bigger exhaust valve to be fitted. (1.70" range) Then your camshaft will not need near as much blowdown bias (early exhaust opening) "nitrous grind" to make good power on Nitrous.

 

1.70" exhaust valve? Man, I didn't know you could put that big of a valve in a sbc head.

Might have to do a little talking with him about that.

He gets great deals on Dart and AFR heads, so I may do some looking at what they can do.

 

Would 5140 rods hold up, or is the 4340 the only way to go?