Rod Question ?

[d.friction]

I just found out I have a cracked 6 pack rod so I am planning on new rods as well as getting rid of my TRW pistons. My question is frist how much HP will I see by going to a lighter piston and rod combo and should I stay with steel rods ( h beam) or should I go to aluminum. I know that a stock 71 440 block are not as strong as mega blocks so would the aluminum rods help on stress with 13.5 to 14.0 to 1 comp. Do aluminum have good longevety or will i need to send the in once a year to get checked. I want to keep my stock stoke. It is a race car. Starting over and wan't to get it right this time.

[rumblefish360]

Alum. rods don't make HP. But the allow the engine to make it easier. Less rotating weight allows rpms to climb quicker and will add a few rpms up top. It will fatigue quicker so end year checks should be done. I don't see the rods a big help in stress.
Steel rods will last a long time.

[d.friction]

HP is not really what I met, I ment more in the way of ET, because it does spin up faster how much of a differance would it be? would a aluminum rod be night and day compaired to a steel rod, is it worth the trouble that comes with using a aluminum rod?

[Windsor377]

I don't see where an alloy rod will help your block. They are easier in bearings from what I can tell, but not by much. They do rev quicker do to less mass. I run GRPs. Take a look at grpconrods.com. Nobody makes a better alloy rod...they also have Ti.

If you run on the street, even for Sat night "drive ins" I really recommend a good steel rod. I prefer LA, but Oliver, Crower, Lunati, etc all offer excellent steel rods. I'd have a tendency to stay away from "ultra light" H beam rods in very long rodded BBs...especially if you spray.

[rumblefish360]

That makes good sense 377. A good steel rod for the street is fine. Just what the doctor ordered.
If your a racer, not a street strip driver but pure racer, the lighter aluminum rods are the way to go.

[Windsor377]

[DartGT66]

Aluminum rods do help the block survive, the hit to the crank and to the block is softer. Since mopars used to have only 2 bolt wedgie blocks, it was common stuff to use fuelie rods in very high hp streeters to help the block survive without cracking. The fuelie rods aeren't necessarily lighter than LY rods, but they soften the hit. Another solution to this is aluminum main caps, also used with good success. And the light pistons and rods do help hp. The upper ends of the rods, pins and pistons are not rotating mass, they are reciprocating mass. It makes a difference in the power needed to pull a piston back and forth 100 times a second if the piston weighs 600 or 900 grams. Someone familiar with physics could propably calculate the difference in power needed at different rpm knowing the stroke. It's propably not a lot, but still something. And it will stress the other parts less.

[d.friction]

I know the skirt on a 440 piston is bigger thus making a 440 piston heavier than a 400. And sence a 440 piston has a lower pin placement I was wandering if you can run a 400 piston in a 440 block with a longer rod. Or will the longer rod hit the walls or will the pison with a higher pin cause problems?
Plus I have looked at many rods by many makers and I cant find a sure winner should I go I beam or H beam and from who they range in price from about 450 to 1200, some are rated from 450HP to 1000HP But they all look the same and they all look to be made out of the same mat. I think I am going to stay with steel rods. Any ideas the motor I hope will be in the 750HP range

[Windsor377]

I know I don't have that much experience with the vintage Mopar stuff, but I'm really surprised that an alloy rod will lead to better block life. I see marginal improvement on rod bearings going from steel to alloy, but zero difference on the mains. I guess this goes to show how important it is to know the animal you are working on.

I'm about to start cranking out some numbers on the Cam Grinds thread that we can use to demonstrate the effects of mass on the piston/pin etc as the discussion opens up. I might be able to begin tonight?..if not tomorrow?

[Windsor377]

"Lugging motors" I like I beam (Oliver, Crower). "Reving motors" I like H beam (LA, std weight in a big block). Depend on the good stuff. Good, material, machining, finishing, QA are good things to have inside your engine.

[cuda66273]

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