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Could someone help me find my compression ratio?


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http://mywebpages.comcast.net/khartnett232402/home.htm

 

This guys got deeper dished pistons 19cc and stock LT1 heads 67cc and hes getting 10.95:1

 

My friend who I trust has been doing 99% of the work on this car and is also an automotive engineer is calculating mine to be even higher then that motor.

 

 

 

 

 

Heres a article from Streetrodderweb.com

 

"Prior to our arrival, Hye-Tech had assembled the Eagle SIR 5.7-inch I-beam rods to the Keith Black hypereutectic 197 pistons. With their 12cc dish, they yield a 9:1 compression ratio with our 76cc head chambers--perfect for current low-quality pump gas."

 

So larger chambers and same dish = 9:1

 

http://www.streetrodderweb.com/tech/0205sr_puller/

 

 

 

 

http://www.flatlanderracing.com/kbpistons_383.html

 

This says @ 63cc head with 12cc dish you'd get 10.3 and with 76cc you'd get 9.1

 

 

 

http://www.cnc-motorsports.com/product.asp?ProdID=8072

 

And this says with 64cc 9.5 with 76cc 8.6

 

 

 

 

No ones numbers match!! GAQhh

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Just because HE said he's getting 10.95-1 doesn't mean he"s getting it. You just can't bend physics. I pluged his numbers in KB pistons website , and I get 8.4. The Lt1 cylinder heads have 58cc. So I pluged that in the calculator and I get 9.8. So I just can't see how He could get almost 11 to 1 compression with the numbers he has on his webpage. Obviuosly there is some misinformation or wrong numbers. NOw if you plug in a -19 cc in the calculator you get 12.7 to 1. But you see by adding the minus sign to piston volume you are actually INCREASING the volume the the piston takes up in the bore. In essence you are putting in a 19 cc DOMED piston NOT a DISHED piston. I think that's where the confussion is coming from. NOw of courese we are taking some measurements from the air,like gasket thickness, gasket bore size, deck clearence. So simply substituting the gasket from a 40 thou to a 15 thou, you can raise compression by almost half a point. Don't worry about someone else's claims, just do your own calcs and match everything together as far as head flow , cam specs and compression ratio. They all got to complement each other.

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I'll give it a try and show my work.

 

383 is about 47.875 cid/cylinder or 784.5cc's/cylinder

 

cylinder volume= 784.5cc

gasket volume = 8.6cc

piston in the hole=4cc

cylinder head=70cc

piston dish=12cc

 

total volume with piston at bdc= 879.1 cc

total volume with piston at tdc = 94.6 cc

 

Compression ratio is 879.1/94.6 = 9.29:1 cr.

Assuming the piston is below the deck 0.020".

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Thanks for all your help guys, to save money I've decided to just put in new forged pistons and raise the compressoin up to 10-10.5. The current ones are Hyperutectic so I dont want to risk boost and shatter something.

 

http://www.performanceauto.us/store/product_info.php?cPath=2_18&products_id=475&osCsid=abab7385ac71e83f823b64960d652869

 

shooting for 500 hp.

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I'll give it a try and show my work.

 

383 is about 47.875 cid/cylinder or 784.5cc's/cylinder

 

cylinder volume= 784.5cc

gasket volume = 8.6cc

piston in the hole=4cc

cylinder head=70cc

piston dish=12cc

 

total volume with piston at bdc= 879.1 cc

total volume with piston at tdc = 94.6 cc

 

Compression ratio is 879.1/94.6 = 9.29:1 cr.

Assuming the piston is below the deck 0.020".

 

you win

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