Humor me... Aluminum rods 'n' piston weight.

joefarmer

joefarmer

MR. Supreme Overlord
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Jul 31, 2006
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How light does the piston need to be for an aluminum rod to survive at 6000rpm? How light can you make the stock crank?
 
joefarmer said:
How light does the piston need to be for an aluminum rod to survive at 6000rpm? How light can you make the stock crank?
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I'll let you know, soon!:evil Dont lighten the stock crank too much....:badidea:

There is alot more to the rod design other than piston weight.
 
If your working on a Cummins drag racing engine, then the best way is to cut the crank down to a Dmax rod throw, and Dmax wrist pin. This reduction in rod throw diameter will take a lot of weight off the crank, and well at allowing you to destroke.

A good combination would be a 4.5 inch stroke with a 4.25 bore. With this kind of setup, the rod weight would be around 1400 grams down a 1000 from the stock Cummins rod. Even in a steel rod you would lose 800 grams. The piston weight would be about 1100 grams with wristpin and rings
I did a test piston, and rod about 5 years ago , it looked nice.
 
Yep. I should have specified a Cummins drag engine. By Duramax throw, do you mean stroke or position of the rod journal in relation to the main?
 
he means the rod journal dia because it is smaller on a dmax. a cummins has a 2.717 dia rod journal not sure on a dmax however the new stroker crank from destroked uses a 2.375 which is a hemi size journal. if you wanted to cut a cummins journal down to a hemi size to make aluminum rods more available you could also destroke to about a 4-3/8 stroke by offset grinding.
 
gotta12v said:
he means the rod journal dia because it is smaller on a dmax. a cummins has a 2.717 dia rod journal not sure on a dmax however the new stroker crank from destroked uses a 2.375 which is a hemi size journal. if you wanted to cut a cummins journal down to a hemi size to make aluminum rods more available you could also destroke to about a 4-3/8 stroke by offset grinding.
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exactly grind it down to a readily accesible size, like the hemi !
 
Are you not losing power by destroking What's Project X at like 5.0 liters now. Seem's people are still stroking and not De Stroking.
 
I destroked that crank to 4.00 inches. the dyno results showed no loss in power , which showed that the smaller engine was more efficient . if you can’t feed the engine air , then bigger is not going to make more power.
 
SPEAKSUP said:
Are you not losing power by destroking What's Project X at like 5.0 liters now. Seem's people are still stroking and not De Stroking.
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I'm not worried about losing power. I'm thinking a lighter rotating assembly would help the whole thing accelerate faster.
 
if you dont change the size of the turbo the peak power out put will not change. however the power curve will. the smaller engine will make peak horse at a higher rpm and in a drag engine this reduction in torque may make it easier to hook off the line.

the tractor world also shows this to be true a 470 3X4 will make similiar horsepower to a 640 superfarm however the superfarm makes much more torque and on the pull track that equals going farther by pulling a bigger final drive
 
Brandon, what weights you have for your crank, rod and piston?

I've been thinking the same thing, make more horsepower and less torque, with a lighter rotating mass.

Cummins stock stuff is pretty heavy.
 
Mike Holmen said:
Brandon, what weights you have for your crank, rod and piston?

I've been thinking the same thing, make more horsepower and less torque, with a lighter rotating mass.

Cummins stock stuff is pretty heavy.
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I'm trying to figure out how light I can get away with at 6k. I know if I had the resources of a F1 team, I would just keep building it lighter until it broke. Then go one step stronger. :hehe:
 
Can't even keep a stock crank alive at 6K Need counterweighted cranks so I think lightening it will not work well.
 
I've had pistons built, that are 1060 grams and thats a 4.125 bore, stock 4.020 would be less, according to my calculations they will turn 6k+

The wrist pins i had made are 500 grams, while stock is 638(5.9) they should also go to 6k with out issue.

you will have to grind the crank down(journal) to get a aluminum rod big enough not to break and it has to clear the cam and block , but the rod will have to be longer to compensate for the destroked config, or you change the compression hight on the piston.


knocking all this weight out of the assy, makes the crank much happy er and it will ahndle more power, been there, done it, i know it works!

Now with the destroked crank and above options you have every advantage possible.
 
joefarmer said:
I'm trying to figure out how light I can get away with at 6k. I know if I had the resources of a F1 team, I would just keep building it lighter until it broke. Then go one step stronger. :hehe:
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Just keep us in the loop buddy on what you find out. I'm just lighten-up the stock parts. My budget is small, like real small..:doh:

I pulled out one stock out a VE engine rod/piston/wrist pin/retainers/bearings, everything weighed abit over 8lbs. Imagen six of those, going 5000 rpm's.
 
Brandon, you going to add any mallory to the crank just so you can balance the crank.

I hope to get some stock weights on all the parts, just for kicks and giggles. I bet just running an aluminum rod would save 1 to 2 lbs, per rod by itself. I was planning on milling the bottom of the stock piston. I'm running a 370 marine piston, at $75 a hole, I can go thru a few.
 
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