Ok here is what i figured out tonight.

These weights are for a full set of rods of a leading brand

steel= 3320 grams = 7.31934662045 pounds
aluminum= 1820 grams = 4.01241241290639 pounds
witch is a difference of 3.30693371406 pounds

In the book Chassis engineering by Herb Adams they had a figure that showed that taking out 15 pounds of rotational weight is good for 32.1 horse

witch is 2.14 horse per pound

witch would mean that a set of aluminum rods should make 7.0768381480884 horse more then a set of steel rods.

Besides this fact and the fact that the aluminum rods are better for the life of the bearings why would I want to run them in a motor that is expecting 650 horse and up to 40 pounds of boost?

Price seems to be a little cheaper for the aluminum rods if you only look at the higher quality steel rods.

 

Well Al. rod absorb a lot of shock that would otherwise be transfered to the bearing, however Al. + a lot of heat and then start to get weak. I would like to Al. rod in my car but id like to see how long they are lasting for people using them.

 

It all depends on where the rotating/reciprocating mass is.

I would still prefer steel rods, because they hold up under extreme tension better than aluminum rods.

 

its the heat cycles that kill aluminum rods. not the shock. Personally I would feel comfortable building an all motor vehicle with aluminum rods. but not for a turbo application thats not a drag car. additionaly if you do decite to go this route. make sure when you build it that aluminum expands to heat differently than iron/steel. So take that into consideration because This usually ends up with a "noisy" motor untill its warmed up. and make sure your clearances will be correct.

 

significant figures.... use them

 

I think that price, weight, and increased bearing life should be enough of a reason to go with a set of aluminum rods over a set of steel. If you only plan on using the motor for 30k i don't see the rods giving up before the 30k are up.

 

While the tensile differences make steel more favorable, the harmonics induced because of the steel pounds bearings above 600whp far faster than aluminum.

I agree with you but practicality dictates something else at that power level I would think. Ti is an option but cost prohibitive for most.

 

Ti would be the way to go, but very very expensive if you have to change them out before their expected life span.