compression test? - Team Camaro Tech
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post #1 of 9 (permalink) Old Feb 22nd, 07, 01:43 PM Thread Starter
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Russ
 
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compression test?

I ran the car a little today I was going to take it for a ride and it started to rain 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

Russ
1969 RS conv,hugger orange,396 4 speed,373 12 bolt posi.


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post #2 of 9 (permalink) Old Feb 22nd, 07, 02:15 PM
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Re: compression test?

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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post #3 of 9 (permalink) Old Feb 22nd, 07, 03:12 PM Thread Starter
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Re: compression test?

Yes that's right travis it's actually 8.5 comp. So you think tose are good numbers?

Russ
1969 RS conv,hugger orange,396 4 speed,373 12 bolt posi.


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post #4 of 9 (permalink) Old Feb 22nd, 07, 04:36 PM
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Re: compression test?

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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post #5 of 9 (permalink) Old Feb 23rd, 07, 07:53 AM
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Re: compression test?

Quote:
Originally Posted by travis View Post
Sounds right in the ballpark to me. I'm guessing it is one of the later 402's with under 9-1 compression?
I have a A71 built 402 in my Camaro. When did the lower compression engines start being built?

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post #6 of 9 (permalink) Old Feb 23rd, 07, 12:00 PM
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Re: compression test?

I have about 180-185 on my cylinders. What would you estimate that compression to be?
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post #7 of 9 (permalink) Old Feb 23rd, 07, 04:29 PM Thread Starter
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Russ
 
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Re: compression test?

Quote:
Originally Posted by StumpZ View Post
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.

Russ
1969 RS conv,hugger orange,396 4 speed,373 12 bolt posi.


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post #8 of 9 (permalink) Old Feb 24th, 07, 01:54 AM
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Re: compression test?

Quote:
Originally Posted by mkpatrick View Post
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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post #9 of 9 (permalink) Old Feb 24th, 07, 03:43 AM
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Re: compression test?

Quote:
Originally Posted by dnult View Post
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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