COMPRESSION TEST
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From: ROCKVILLE, CT.
COMPRESSION TEST
I did a compression test on my 428. all cylinders were in a range of 150 to 160.
I'm not sure how good this is? The ratio is supposed to be 10.5-1
Can anyone tell me if this is good, bad, normal?
I'm not sure how good this is? The ratio is supposed to be 10.5-1
Can anyone tell me if this is good, bad, normal?
Fleet Mechanic
Joined: Aug 2009
Posts: 1,771
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From: Western Washington
If my engine had that good of compression I would be jumping for joy! The best cylinder on my motor has about 118, the worst has 40! I would consider anything above 100 to be good, above 120 to be excellent compression. It looks like you have a very nice motor!
Sam
Sam
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Senior User
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From: ROCKVILLE, CT.
If my engine had that good of compression I would be jumping for joy! The best cylinder on my motor has about 118, the worst has 40! I would consider anything above 100 to be good, above 120 to be excellent compression. It looks like you have a very nice motor!
Sam
Sam
She runs well. I need to get a new carb and I think the timing needs to be adjusted. She pings during rapid acceleration / load. I know it's not the fuel because all I put in her is 93 and a bottle of octane booster on each fill up.
I'm not sure if I should retard or advance it. I will do some research on it. If you or anyone else has advice I am all ears. Thanks again, Todd.
Laughing Gas
Joined: Aug 2008
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Thanks Rusty. I got the same response pretty much, from a mechanic I met at NAPA last night.
She runs well. I need to get a new carb and I think the timing needs to be adjusted. She pings during rapid acceleration / load. I know it's not the fuel because all I put in her is 93 and a bottle of octane booster on each fill up.
I'm not sure if I should retard or advance it. I will do some research on it. If you or anyone else has advice I am all ears. Thanks again, Todd.
She runs well. I need to get a new carb and I think the timing needs to be adjusted. She pings during rapid acceleration / load. I know it's not the fuel because all I put in her is 93 and a bottle of octane booster on each fill up.
I'm not sure if I should retard or advance it. I will do some research on it. If you or anyone else has advice I am all ears. Thanks again, Todd.
Back the timing off a little bit to avoid the pinging. I'd start with 2 degrees retarded from where it is now.
Your compression is healthy, but possibly low for your CR. When I had 9.5:1 I was getting about 195 psi per cylinder, and after some block and head re-surfacing,, which likely put it up to 10:1 CR, I was getting 210 psi.
However, I suspect different cams provide different results due to valve timing. If it's not smoking, I'd leave it alone.
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Senior User
Joined: May 2010
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From: ROCKVILLE, CT.
Back the timing off a little bit to avoid the pinging. I'd start with 2 degrees retarded from where it is now.
Your compression is healthy, but possibly low for your CR. When I had 9.5:1 I was getting about 195 psi per cylinder, and after some block and head re-surfacing,, which likely put it up to 10:1 CR, I was getting 210 psi.
However, I suspect different cams provide different results due to valve timing. If it's not smoking, I'd leave it alone.
Your compression is healthy, but possibly low for your CR. When I had 9.5:1 I was getting about 195 psi per cylinder, and after some block and head re-surfacing,, which likely put it up to 10:1 CR, I was getting 210 psi.
However, I suspect different cams provide different results due to valve timing. If it's not smoking, I'd leave it alone.
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FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
As long as they are all about the same, that's GREAT!
What cam is in it, and what was it set to, straight, retarded or advanced?
The bigger the cam, and depending on the cam timing (and overlap, etc), the lower the static (cranking) compression during a test. Was that with all the plugs removed, a healthy battery, and the throttle plates wide open?
What cam is in it, and what was it set to, straight, retarded or advanced?
The bigger the cam, and depending on the cam timing (and overlap, etc), the lower the static (cranking) compression during a test. Was that with all the plugs removed, a healthy battery, and the throttle plates wide open?
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Thread Starter
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Senior User
Joined: May 2010
Posts: 280
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From: ROCKVILLE, CT.
As long as they are all about the same, that's GREAT!
What cam is in it, and what was it set to, straight, retarded or advanced?
The bigger the cam, and depending on the cam timing (and overlap, etc), the lower the static (cranking) compression during a test. Was that with all the plugs removed, a healthy battery, and the throttle plates wide open?
What cam is in it, and what was it set to, straight, retarded or advanced?
The bigger the cam, and depending on the cam timing (and overlap, etc), the lower the static (cranking) compression during a test. Was that with all the plugs removed, a healthy battery, and the throttle plates wide open?
Yes, all plugs removed, good battery and throttle plates wide open.
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