What compression numbers do you get?
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Senior User
Joined: Nov 2009
Posts: 125
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From: TX
What compression numbers do you get?
I'm trying to decide if it's time to rebuild the whole motor, or if I can do with just the heads and 4bbl intake swap. The motor is a '72 model year (DIAE-A1C, manufactured in November of '71), and doesn't smoke, sounds good, but looks old - and maybe the fact that I found the nylon timing set teeth in the oil pan might give a clue as to the last time it's been cracked open.
Here's the results of a compression test I did a couple months ago:
#1: 118 - 127 - 133
#2: 130 - 134 - 134
#3: 122 - 118 - 118
#4: 130 - 135 - 130
#5: 120 - 115 - 110
#6: 112 - 110 - 110
#7: 110 - 109 - 107
#8: 122 - 116 - 119
How are these numbers compare to yours? What would you do with this motor?
Some gratuitous engine **** (click on 'em):
Thanks in advance.
Here's the results of a compression test I did a couple months ago:
#1: 118 - 127 - 133
#2: 130 - 134 - 134
#3: 122 - 118 - 118
#4: 130 - 135 - 130
#5: 120 - 115 - 110
#6: 112 - 110 - 110
#7: 110 - 109 - 107
#8: 122 - 116 - 119
How are these numbers compare to yours? What would you do with this motor?
Some gratuitous engine **** (click on 'em):
Thanks in advance.
Senior User
Joined: Dec 2008
Posts: 226
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I believe a fresh stock 351M/400 should be around 140 psi. An engine with some miles on it but still in good condition should have the cylinders within 10% of one another. You could squirt some oil in the low cylinders to maybe figure out why the low reading. If the reading doesn't improve then the rings might be ok and your new heads should help. How is the oil pressure? That usually goes 1st on these engines. My numbers were 120-125 psi but only 10 psi oil pressure at idle.
Thread Starter
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Senior User
Joined: Nov 2009
Posts: 125
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From: TX
The block may have to wait 'til I get back from deployment. The heads can be done before I leave.
I'll have to do another test. Since I did the one above, the valve seals have been changed out, along with the pushrods. Also the transmission shop tightened-up my headers after they put the trans back in.
I was just trying to get a feel on what kind of numbers you guys get on a stock 400.
I'll have to do another test. Since I did the one above, the valve seals have been changed out, along with the pushrods. Also the transmission shop tightened-up my headers after they put the trans back in.
I was just trying to get a feel on what kind of numbers you guys get on a stock 400.
Posting Guru
Joined: Nov 2008
Posts: 1,937
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From: wyoming
just did a compression test!
just did my buddies 400 compression test. he would pray for your numbers. he got it hot and some damage was done. 2 of his cylinders didn't make 100psi. its time for a rebuild for my friend larry. going in a 1978 ford 4wd f-150. catch you later but your engine is in need of some help here soon especially the ones near 100 psi. good luck and siemper Fi.
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Senior User
Joined: Dec 2008
Posts: 226
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I agree with you guys that it's getting worn out but it's not smoking, sounds good and still has some oil pressure left. I would keep driving it til it starts knocking unless it doesn't have enough power to get up to 60 mph. But then I'm not a performance junkie.
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