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can i find out my actual compression ratio w/o taking the heads off my motor or anything like that? I have a 396 with 11:1 TRW forged closed chamber pistons and cast iron open chamber square port heads....i can get the casting numbers tommorow if that matters...any help here?

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The pike.net Pics of my 68
 

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maybe... the casting numbers might help
if the motor is original and allways owned by you .a good chevrolet book might help like
chev by the numbers.

that bloc used more than one crank anyway.
whats needed is to measure how far down the piston travels from the top to the bottom
in inchs,that is measure the top of the piston at the bottom of the stroke.
also measure the valve combustion area with a straight edge ,that is from the lowest point in the chamber to the flat bottom edge of the
straight edge.
example 12 to i means that the piston
travals down the cly 12 inchs and is
copmpressed in an area of 1 incn.
hpoe this helps.................
 
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Actual compression ratio requires all combustion chamber parts be CC'd. Engine must be taken out. You can usually get within .1 knowing your exact parts and get info from tech reps, C/R a matter of swept volume vs. cyl. head volume at TDC. DJD will probably check in with exact formula, if not I can post it later.

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67 Nemesix
 

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stephen you want me to get technical with
the guy for you .i just gave him the basics
with not to much details.you expect him to
figure it out mathematically.you have to ask
some one else to figuire it out huh .

here goes /example;


bore 3.00 inchs
stroke:5.00 inchs
clearence volume 5 cubic inchs

sv = cv
cp = --------------
cv
2
pie r square = 3.14
= 3.14 x ( 2 ) x 5 = 3.14 x ( 1.5 x 1.5 ) x 5
= 3.14 x 2.25 x 5
= 35.32

35.32 + 5 40.32
cp = ------------ = ------- = 8.06 to 1
5 5

8.06 to 1 compression ratio
 

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stephen you want me to get technical with
the guy for you .i just gave him the basics
with not to much details.you expect him to
figure it out mathematically.you have to ask
some one else to figuire it out huh .

here goes /example;


bore 3.00 inchs
stroke:5.00 inchs
clearence volume 5 cubic inchs

sv + cv
cp = -------------
cv
2
pie r square = 3.14
= 3.14 x ( 2 ) x 5 = 3.14 x ( 1.5 x 1.5 ) x 5
= 3.14 x 2.25 x 5
= 35.32

35.32 + 5 40.32
cp = ------------ = ------- = 8.06 to 1
5 5

8.06 to 1 compression ratio


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renny calisti

[This message has been edited by rennycal (edited 11-13-2001).]
 

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the formulas will not type
and tranfer properly so i `ll
tell you them .

compression ratio equals swept volume plus
clearence volume over divided by
clearence volume.............
 
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rennycal, I didn't ask you to do anything for me. Please re-read my reply. However, please enlighten us all by citing an example of an engine with 3 inch bore and 5 inch stroke.

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67 Nemesix
 

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I don't know if anyone else is following this thread but it is cracking me up. I liked the lawnmower comeback. Now, how about that motor with the 12" stroke? I gotta have one of those! Imagine the torque;}

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67 454 RS, M22 (Soon to be 427 with 700R4)
 

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That would make something like a 185 cc engine. What lawnmower sports this beast? I know a briggs classic is 149 cc, and the Tecumseh TVS and TNT engines are about 164 cc, but what has the 5 inch stroke? A B&S Quantum maybe? Just curious.
 
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