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Discussion Starter · #1 ·
My 5m was running poorly as of the tail end of my last rip in my '85. I pulled the plugs and found that the gap on #4 had closed right down to just about nothing. This was the problem as she is running superbly again now. What might cause this? I currently have some cheap ass Delco plugs in it as my new NGK's are on the way.

While I had the plugs out I decided to do a compression test. I came up with:

1- 146
2- 150
3- 143
4- 134
5- 134
6- 142

I know this is low in all cylinders. I have a slightly shaved and ported head as well, so I expected the comp's to be higher. I had not checked the compression for about 18 months. I was in the 160's in some cylinders then (before I rebuilt the head). I do burn a good deal of oil so it would only stand to reason that I could use new rings (I did not drop some oil in the chamber and re-test compression, maybe I should have) I have been looking for a good reason to buy a 6m and rebuild it, but this 5M seems to run really strong especially after my recent acquisition of a DT header and Brullen exhaust system. Am I missing a lot of HP with these compression numbers? Sorry for the ridiculously long post. :p
 

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Discussion Starter · #4 ·
I turned it over 3-4 times for each reading, I did not have an assistant to crank it over while I watched the guage, so I don't know if it shot right up or not. I think the rings are pretty bad as I am burning a lot of oil and the head is fresh. I should have done the bottom end when I had the head off. Maybe I will get a 6M longblock and rebuild it outside of the car. Or maybe I will pull the 5M and rebuild it over the winter.
 
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