Quote:
Originally Posted by Lynn A McCarty
With all due respect, this simply isnt true. One of the "natural" advantages of a 455 Pontiac is that it has a 6 5/8 rod 10.200 deck. This allows a 455 Pontiac to have a piston with a 1.500 compression height. With a single ring motor we have short piston skirts allowing a piston to be 380 grams without the pin. I now have a pin that goes about 53 gms. This makes a complete piston with two rings pretty freaking light. (one of our only true advantages) Our stroke is 4.223.
What if you have on the contrary a 3.75 stroke motor like a 440 or a Hemi with a 10.750 deck? This is a terrible disadvantage. It makes your piston like an air compressor. I measured Rick Allison's SS/AA piston about 20 years ago and it weighed over 1000 gms. Of course he didnt have a killer light set, but if you add 1/2 the additional stroke (4.223 - 3.75 = 0.473 then 1/2 = 0.2365 inches), then you add the difference between the Pontiac's 10.200 and the Mopars 10.750......that is another 0.550.
So you get a piston that is at least 0.550 plus 0.2365 or 0.7865 shorter. Not only does this take weight out of the piston it takes weight out of the crank to balance. We always used 0.300 compression height as worth a tenth. Maybe with piston technology it isnt that much, but it isnt zero. If you want to read some good info go to Wiseco's website about piston technology and power. It is a good read.
http://www.wiseco.com/TechTips.aspx click on "forged piston technology 101"
We have been talking to Wiseco about their strutted piston. We can get a compression height of 1 inch with this new strutted piston design with a single ring motor no problem. Pontiac has a block 9.200 deck. With our shorter stroke 9.200's we can get a 3.75 stroked 400 motor pretty killer. Like I said, if NHRA wants to go there we are going to have some weird looking motors out there. Like I said, I have no problem with the BBMopar guys getting it, but we should get it too. 400 Chevy guys would have a killer short block.
Rocket block's posts I agree have been excellent! Rocket, you dont know the 1/2 of it, the truth would shock you to the core!
Lynn |
It's just that the first half is reason enough. Speaking of ring count on a SS engine, an inherent advantage to a short deck, long rod engine (which is what this 440/400 is all about) is the wrist pin is moved up an extreme amount. That allows a very short piston design as I mentioned earlier. Maybe everybody doesn't know what is good about a short piston with a high pin besides weight. This design allows the piston more stability as the piston is at top dead center and maybe more importantly rock over towards bottom. An engine built to the rules may require two compression rings, an engine built against the rules may only need one compression ring which offers even less weight and less frictional loss. True, many in SS only use one ring but there may be compromises. Those compromises may be negated with a long rod motor. A short deck / long rod engine also has a piston that shows more dwell time at TDC, enhancing the burn rate for more complete combustion. And I agree with you, the crank can get a lot lighter because of the piston weight reduction.
Could you just mill a RB family block to obtain the same advantages? Probably. But I don't think there is enough material there and you would probably have a problem with head gaskets and warping the decks.