Light weight parts vs heavy parts

Greg Reimer 7376 · 01-15-2010, 11:18 AM

One of the main advantages to light pistons,pins,etc. are found in the area of parts reliability.A heavy piston is harder to accelerate from either TDC or BDC. The rod likes to stretch more with a heavy piston and pin,(actually the rod DOESN'T like to stretch,but has to anyway).At the conclusion of the exhaust stroke, ther is no plug of compressed gas pro-viding resistance to the piston's headlong plunge up the cylinder toward the open valves in the head. The two rod bolts have the unenviable job of stopping the rod,piston,pin and rings from continuing out the top of the cylinder bore.When rod failure occurs, it usually happens on the exhaust stroke,hence two bent valves you usually find in the aftermath.NHRA has a minimum weight spec for the combined piston,pin,locks,rings and rod, and I found it to be rather generous. The minimum for a 327 is around 1200 grams, an OEM cast piston,stock pin, rings and rod (no bearing) is around 1402 grams. The legal weight allowance would also allow you to rebalance the crank by removing a lot of weight from the counterweights, making for a much lighter rotating mass.Any combination that would benefit more by a light flywheel as in a stick class, would like a light assembly as well.As to the drive train, in my earlier days with my Chevelle, I set the rear end up with a Moroso Brute Strength posi and OEM axles. No parts failures, but later I got a spool,billet axles, and a C clip eliminator kit. That whole assembly was several pounds lighter. I translated that into less inertia loads on everything else, and the car was consistantly .08-.10 quicker in 60 foot and subsequent ET's.Talk to Dave Smith at Pro Trans for an opinion of what aluminum drums and light trans parts will do for your combination. I'd rather put the weight back in the weight box rather than everyplace else. A further note, I used to race a 409 Chevy, and the stock forged piston,made by TRW, weighed 1040 grams with no pin, no rings or locks. That thing was like a forged aluminum flower pot!!!

01-15-2010, 11:18 AM	#9
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,132 Likes: 172 Liked 698 Times in 216 Posts	Re: Light weight parts vs heavy parts One of the main advantages to light pistons,pins,etc. are found in the area of parts reliability.A heavy piston is harder to accelerate from either TDC or BDC. The rod likes to stretch more with a heavy piston and pin,(actually the rod DOESN'T like to stretch,but has to anyway).At the conclusion of the exhaust stroke, ther is no plug of compressed gas pro-viding resistance to the piston's headlong plunge up the cylinder toward the open valves in the head. The two rod bolts have the unenviable job of stopping the rod,piston,pin and rings from continuing out the top of the cylinder bore.When rod failure occurs, it usually happens on the exhaust stroke,hence two bent valves you usually find in the aftermath.NHRA has a minimum weight spec for the combined piston,pin,locks,rings and rod, and I found it to be rather generous. The minimum for a 327 is around 1200 grams, an OEM cast piston,stock pin, rings and rod (no bearing) is around 1402 grams. The legal weight allowance would also allow you to rebalance the crank by removing a lot of weight from the counterweights, making for a much lighter rotating mass.Any combination that would benefit more by a light flywheel as in a stick class, would like a light assembly as well.As to the drive train, in my earlier days with my Chevelle, I set the rear end up with a Moroso Brute Strength posi and OEM axles. No parts failures, but later I got a spool,billet axles, and a C clip eliminator kit. That whole assembly was several pounds lighter. I translated that into less inertia loads on everything else, and the car was consistantly .08-.10 quicker in 60 foot and subsequent ET's.Talk to Dave Smith at Pro Trans for an opinion of what aluminum drums and light trans parts will do for your combination. I'd rather put the weight back in the weight box rather than everyplace else. A further note, I used to race a 409 Chevy, and the stock forged piston,made by TRW, weighed 1040 grams with no pin, no rings or locks. That thing was like a forged aluminum flower pot!!!