Compression and leak down tests

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gumper

gumper

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Had big plans to refresh my 408 along with a new trans, and spring move/mini tub. Decided to buy a TIG welder over Christmas, which really cut into the budget. In order to do the other two projects I decided to see if the engine was still healthy. Ran a compression test, and had 160 psi on all cylinders. Going to do a leak down Tuesday, but how does that number look? It's got a mopar 252 duration cam, so the pressure seems pretty good considering. Think the seal is still alright? It's getting a bigger cam and methanol either way.
 
Yeah 050, 296 adv.

What's good leak down numbers? The rings were gapped for nitrous, but I cannot remember the exact amount since it was so long ago.
 
There's compression (cylinder pressure) and there's leak down (ability to retain that pressure). Your pressures are ok. You need to do a leakdown and determine if everything is sealing up nice.
 
Worst hole was 9%. Most were 6%. Pretty damn good for so many passes. I think the Amsoil has a lot to do with it...

Had a panic attack when I tried to start it up to get it warm for the test. It would knock every time it turned over which I though may have been the starter. Pulled the valve covers to check to make sure the rockets didn't come loose (I had them off last week), but they were OK. Got back in to try again, and it kept knocking bad after it fired up with the starter disengaged. Now I was worried, but decided to check the converter bolts just in case. Sure enough one bolt was a few turns out. Just enough to hit the block on the way by. Tightened it up and all was good. The last time then were taken out was 5 years ago to change the converter. Lucky it didn't happen on a race day.
 
Depending on the rings and gapping you got it's either ok, or fine...lol. Good catch on the convertor bolts... Keep an eye on them. If they loosen you may have a balance issue
 
gumper said:
Worst hole was 9%. Most were 6%. Pretty damn good for so many passes. I think the Amsoil has a lot to do with it...

Had a panic attack when I tried to start it up to get it warm for the test. It would knock every time it turned over which I though may have been the starter. Pulled the valve covers to check to make sure the rockets didn't come loose (I had them off last week), but they were OK. Got back in to try again, and it kept knocking bad after it fired up with the starter disengaged. Now I was worried, but decided to check the converter bolts just in case. Sure enough one bolt was a few turns out. Just enough to hit the block on the way by. Tightened it up and all was good. The last time then were taken out was 5 years ago to change the converter. Lucky it didn't happen on a race day.
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So those numbers are warm?
 
Yeah warm. Wide ring gaps and forged pistons. Was originally put together to handle 250 horse nitrous jets.
 
Last edited:
gumper said:
Yeah warm. Wide ring gaps and forged pistons. Was originally put together to handle 250 horse nutrius jets.
Click to expand...


You're good then, as that's not bad with wide gaps.


Don't forget red lock tite on those converter bolts. Had a friend lose a great motor because he didn't use lock tite on his stuff. Cost him big.
 
Well the trans is coming out next, but when it goes back in you can bet there will be loctite. That'd be bad at 6000 rpm and 120 mph.
 
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