avaccani

I was just wondering if the stock LT1 crank could handle 6.0 rods.
Also what is the advantage of 6.0 over 5.7?

Thanks,
Anthony

Free Bird

iTrader: (1)

Not all that much. There's a lot of debates over this topic. The longer rod doesn't have as much side to side movement to it. Which 6" rods? Yes they can work. But almost anything will work.

Vader

Chevy used 5.97" (close enough) cast/forged and PM rods on the LT1 crank, along with smaller pistons to make the 265" L99 V-8s from '94-97. As long as you use pistons with the correct pin position, it's not a problem.

For a street engine, there is a slight power advantage to longer rods, not because of the slightly longer dwell at the ends of the stroke (the RPM is not high enouogh in a street engine for that to be much of an advantage) but because of the improved leverage the rod imparts on the crank throw and reduced side thrust on the pistons. With a longer con rod, a smaller percentage (mass) of the rod moves from side-to-side at a given stroke length, reducing that side loading.

snakeskinner

the rods and crank really don't have anything to interfere as long as the journals are the same size. You can put 6 foot rods on the LT1 crank if you want, The problem lies in the pistons and heads, and the bottom edge of the cylinders. If you use the correct pistons to work with the rod/stroke and heads and you aren't hitting the bottom of the cylinders, you'll be fine.

snakeskinner

the rods and crank really don't have anything to interfere as long as the journals are the same size. You can put 6 foot rods on the LT1 crank if you want, The problem lies in the pistons and heads, and the bottom edge of the cylinders. If you use the correct pistons to work with the rod/stroke and heads and you aren't hitting the bottom of the cylinders, you'll be fine.

snakeskinner

the rods and crank really don't have anything to interfere as long as the journals are the same size. You can put 6 foot rods on the LT1 crank if you want, The problem lies in the pistons and heads, and the bottom edge of the cylinders. If you use the correct pistons to work with the rod/stroke and heads and you aren't hitting the bottom of the cylinders, you'll be fine.

rx7speed

here is a question for you though vader

what about piston speed?, after the dwell point piston speed picks up a lot faster with the short rod then the long correct?
wouldn't that help a little bit, or would that mainly be better for carbs toget a strong signal at the carb or no difference either way?

Vader

RX,

At TDC, the piston speed is zero with any crank/rod/piston combination. At 90° rotation, teh piston speed is exactly the same with any crank/rod/piston combination. Given that the piston dwells just a bit longer while in the vicinity of BDC and TDC with a longer rod, the acceleration rater of the piston on a longer rod must be greater, since there are fewer degrees of crank rotation to accelerate from the TDC and BDC region to maximum piston speed at 90°.

Got CAD? Build a model.

rx7speed

ok what about this then.

just trying to figure out some things with short vs long rods
from what I am remember (kinda) up short rods are better for low rpm filling of the cyl due to piston speed. something along the lines of piston speed is greater at dwell point , while the long rod will might have a great peak speed avg speed through the first few degrees before the valve opens is slower which will creat less vac which will hamper low rpms filling of the cyl

also at low rpms wouldn't the short rods give the better signal to

now the long rods will help promote filling at high rpms because of that dwell point. where the short rod piston speeds through the dwell will be quick enough to cause an out of breath affect.


also with long rod vs short rod
the long rod because of it's dwell time will allow cyl pressure to go up being piston is dwelling at one point and pressure is still going up due to flame front. now with the short rod woudn't that cause it go right past TDC swing around for the first few degrees and almost start to reduce pressure?


again though a lot of this is based off the short rod havinga faster piston speed at the point right after TDC while the long rod is still "dwelling"


thanx vader...