Compression Test Results

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Jun 5, 2009 | 12:06 PM

LNF150

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Compression Test Results

Not having anything better to do, I pulled all my spark plugs, cleaned/checked gap and did a compression check when they were out. The tester I have is the fancy smancy screwing in the hole, hose attached to a big gauge, not unlike the ones you all have.
The following are the results: (#1, 120psi), (#2,130psi), (#3, 125psi), (#4,120psi), (#5,130psi), (#6,120psi), (#7,130psi) (#8, 125psi). The engine is a factory stock '85 351w with 193K on it.
What is the normal 'new' compression susposed to be? My Haynes manual on page 2D-5 says and I quote: 'Compression pressure....Lowest cylinder must be at least 75 percent of highest cylinder.' Great, how about a poke in the eye with a sharp stick, as well. What is normal? I've got the 75% and I know 0 psi is Bad.
Just wondering.
Eric

Jun 5, 2009 | 12:44 PM

uncle.stosh

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From: Out of here

There is no "normal". What you have is fine for that old of a motor.

Most new or rebuilt motors don't put out much more. It has a lot to do with style of rings, pistons (compression ratio), heads, cam overlap, etc.....

Jun 5, 2009 | 03:19 PM

LNF150

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True enough, Stosh. There is alot more going on then meets the compression gauge's 'eye' (so to speak). Like I said, the engine is just an origonal factory gig. I just was wondering if it's par for the course, being 24 years old and x amount of miles. Probably nothing to get wondered about.
Thanks,
Eric

Jun 5, 2009 | 03:21 PM

andym

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From: Bonita Springs FL

I'd say that's pretty darn good for a 24-year old motor.

Jun 5, 2009 | 07:04 PM

Franklin2

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You can't give "good" and "bad" numbers because you will get differences in the readings depending on were you live(sea level or the mountains are extremes), condition of the battery and the starter(if it spins faster you will get higher peak numbers) and other variables that need to be accounted for.

Jun 5, 2009 | 07:47 PM

LNF150

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Dave, thanks. Of course, I motarted that question, because I'm at 5,800'. I guess at sea level it would be higher because of more atmosphere weighting down or on mount Everest it would be about zilch. Thanks for not throwing in the towel on my dumas inquiries.
LNF150

Jun 5, 2009 | 07:49 PM

andym

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From: Bonita Springs FL

Dumas I get, but what is "motarted"?

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Jun 5, 2009 | 11:48 PM

LNF150

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Quote:

Originally Posted by andym

Dumas I get, but what is "motarted"?

Andym, I have no clue what 'motard' means. I picked the term up from a young forest firefighter who preformed a **** hissy one time on the Montana/Idaho line near Lolo pass. He over heard some communications on my radio about command wanting to make a stand against a fire we were involved in, and essentially he said George Carlin's seven dirty words and ended it with an 8th...motards! Insubordination? Nope just stating an opinion. But, I had to laugh. We knew were were out gunned at the time, but two days later we put the shank in that fire and it was a done deal. But at that motarted moment it was too big of a mess in steeeeeeppppp country with very few folks. So I guess Dumas equated to motard...at least when I ponder questions about my ford.
Lnf150