compression

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Rolling Stone
Posts: 90
Joined: January 13th, 2011, 7:54 pm

compression

Post by Rolling Stone »

What is a good compression reading per cylinder on our engines?on average,I dont mean a freshly built top engine.
SR Racing
Posts: 1209
Joined: June 24th, 2006, 1:58 pm

Re: compression

Post by SR Racing »

A compression reading means almost nothing. It is fine for use to compare all your cyliners. You want them all within 10 or 15% of each other. However the actual number mean little. Suffice it to say, it will be somewhere between 90 and 150. Important. Your throttle MUST be all the way open, you valves adjusted properly and a charger on your battery. About 2 to 3 compression strokes (4 to 5 revolutions) should bring it to it's max. Do the same on all 4 cylinders. All 4 should be close. If one isn't, you have a ring/cylinder, valve etc. bad.

The only proper way to check the condition of the engine is with a leak down tester. With this you can determine cylinder wear, valve condition (exh and intake) A compression checker is primarilly to determine the gross condition of a single cylinder.
smsazzy
Posts: 703
Joined: June 24th, 2006, 5:56 pm

Re: compression

Post by smsazzy »

Even a leak down test may not tell you when the engine is soft. If you have dykes rings, those will seal up pretty good and mask any issues with the 2nd and 3rd rings.
Stephen Saslow
FV 09 NWR
hardingfv32-1
Posts: 1014
Joined: December 1st, 2006, 8:01 pm

Re: compression

Post by hardingfv32-1 »

The condition of the 2nd and oil ring show be of no consequence. You will be black flagged for smoke before the situation causes any loss of power. A leak check is the gold standard to tell if you have an engine or not.

Brian
billinstuart
Posts: 201
Joined: July 17th, 2006, 8:53 pm

Re: compression

Post by billinstuart »

The strongest engine we ever built had NO second ring. Unfortunately, since the major contribution of the second ring is as an oil scraper, it sure smoked when you closed the throttle.

The 3rd (oil) ring provides NO compression.
SR Racing
Posts: 1209
Joined: June 24th, 2006, 1:58 pm

Re: compression

Post by SR Racing »

Yes and Yes. (Brian and Bill)

Jim
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