I still have it in the back of my mind that I will eventually build me a nice fat stroker motor. There is a lot of debate on 5.7" rods vs 6.0" and then there is always 5.85"

The motor I would be looking to build would be setup for a moderate compression. I would like it to make good power without any boost but would like it to be able to handle 10-15 PSI and be reliable. The stock vortech kit pushes close to 10 pounds and that is OK on a completely stock motor so I figure I could get away with 9.5 - 10:1 compression.

I would probably build a 396, knowing this I know a 6 inch rod puts the rod angle very close to that of the stock 350 and should be very reliable. Going with a shorter rod should create a stronger rod in theory and will also lower the wrist pin location in the piston. This can get it under the ring lands and seems as if it would make a stronger piston, especially for a boosted application.

As such it seems like a catch 22 situation. If you go with the shorter rods you will increase your strength but you increase the side loading and can effectively reduce your reliability. So which is better? I'd be looking at daily driver, 200k mile reliability, something I don't know that I would get with the shorter rods.

For a moderate boost situation I believe I should really look into the 6 inch rods. I feel like top quality parts on the 6 inch rods would be the best bet for long life. Any thoughts?

 

Im running 6" rods in my 500hp 383 and for that engine those were the correct choice, but keep in mind a supercharged engine is a differant engine by design, while 6"rods have longer dwell time (GOOD FOR HP ABOVE 5000rpm)
lower ring drag angle and cylinder wall thrust (slightly less wear)
shorter/lighter pistons (good for higher RPMs)
6" rods also have the lower oil ring not completely supported in the piston pin area
5.7" rods work ok,they generally weigh less, but the main reason Id chose them is that youll want about 8:1 NOT 10:1 compression in a supercharged engine, and youll want the rings fully supported, in a supercharged engine reliablity is more important that makeing 5 extra hp at 6500rpm. finding a 8:1 compression pistion will be difficult with 6" rods, but not with 5.7" due to the lower pin location , because unline a N/A engine youll have a massive tq curve due to boost if the engines set up correctly

have a long talk with both your supercharger manufacturer and cam suppliers, IM sure both will suggest a lower compression and a cam with a wide LSA for 10-15 lbs of boost in that engine


[Modified by grumpyvette, 6:24 PM 5/2/2003]

 

Althought there are benfits from a longer rod, 6", there is a serious downside that will definately effect you and its been touched on here. That is the wrist pin will be up in the rings. This causes WAY more potential for problems, oil leaking, burning etc etc, than side loading will cause. I properly built engine with good specs/clearance should last years through tons of abuse, if built properly.

Moving the pins into the rings, you are just asking to have problems, and most likely will especially on higher compression engines, and you will have that compression with boost. You not supporting the rings as well and therefore your builing your engine with a weak link, probably the most important and first thing to fail in most engines.

MY advice would be to build it with 5.7 rods, forged with a good piston for a low compression ratio, slap the boost on it and blow by the oil leaking 6" rodders. :D

 

i went with 5.85. 383 is NA though. lingenfelter uses a 5.85 in his LT1/4 applications so.... :cheers:

 

5.7 rod will also keep it out of detonation better with it spending less time at tdc :cheers: