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Discussion Starter #1
I ran the car a little today I was going to take it for a ride and it started to rain:sad: so I decided to do a comp. test after the motor cooled down a little, the lowest cyl. was 147 and the highest was 150 is that good or bad. I know all cyls. being that close is a good thing , but is the comp. high enough? Seems a little on the low side to me. The engine is a stock 1971 402 bbc with a mild cam. Thank's
 

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Sounds right in the ballpark to me. I'm guessing it is one of the later 402's with under 9-1 compression?
 

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Yep. Most of the low compression engines I have ever built or worked on with small cams in them come out around 150 pounds. I think your in good shape.
 

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Discussion Starter #7
I have a A71 built 402 in my Camaro. When did the lower compression engines start being built?
On the 396 , 1971 is when they lowered the comp. to 8.50 from 10.25 they had in 1970 except on the 375 h.p. motors they had 11.00. Also in 1971 all 396 motors were 030 over and were actually 402 ci which you may already know.
 

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I have about 180-185 on my cylinders. What would you estimate that compression to be?
Compression ratio and peak cranking pressure are two different things. The camshaft has a lot to do with it. You could have a 14:1 compression motor only give 140psi cranking pressure due to the valve overlap and such. You cannot take a cranking pressure measurement and derive a compression ratio from it.
 

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Compression ratio and peak cranking pressure are two different things. The camshaft has a lot to do with it. You could have a 14:1 compression motor only give 140psi cranking pressure due to the valve overlap and such. You cannot take a cranking pressure measurement and derive a compression ratio from it.
Exactly. For example, the 9.4-1 355 in one of my trucks with an XE268 cam cranks 180psi, while the 10.3-1 388 in my nova with a much larger 294s solid cam cranks 185psi.
 
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