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Discussion Starter #1 (Edited)
Okay, let me first start by saying my compression tester reads low... used it on other healthy motors before and it just reads low.

My motor is built, Eagle/Vitara bottom end, delta 272/bisi springs top end.

On my last bottom end(built), I had similar compression readings to those ive just taken. So im fairly confident the problem is in the head, since the readings are just about the same on the new block. The readings are:

Cyl 1 115
Cyl 2 110
Cyl 3 105
Cyl 4 95

The thing thats odd to me, is that these numbers follow a trend from right to left, on this bottom end, as well as my last. I had this head machined when i built my first block, blew up that one, and then just slapped this head back on the new one.....

Couple questions:

1. Is it possible that the head was milled "flat" but not level ? Such that Compression Ratio is decreasing from left to right?

2. ..... Actually that is the only thing that would make sense to me? Unless the problem lies in the intake or exhaust manifold where the flow is distorted somehow. The only other thing that would affect compression numbers are going to be rings and valves, and im fairly certain the problem lies within the valves . If so, is there anything to do about that other than rebuiling.... again? =/

Oh, and before someone suggests that perhaps my battery was low and as i did the compression test the engine was cranking slower and slower, I got the readings from lowest to highest, so that wouldnt be it, and i double checked the numbers again... the same. The spark plugs also reflect the readings, cyl 3 and 4 deffinitely looking a little "sootier" than 1 and 2.

Anyways, gonna do a leak down shortly, that should help figure this out. I was never good at telling where the air was escaping by ear though

Oh let me add real quick, The whole reason for doing the compression check was just because i was getting ready to pull my manifold and fit a new turbo i just got which will require some cutting and welding and whatnot, and wanted to just check it before i got started to make sure it was gonna be worth my while lol. Car runs great otherwise, power is fine.
 

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The valve timing won't vary from cylinder to cylinder.

It sounds to me like your head or block is milled more off the #1 end.

Only way to know is to measure deck clearance on the pistons in the block and CC the chambers.
 

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Those numbers don't seem linear enough though, as cylinder 4 is 5% less than what it should be if one were to suggest the lack of "flatness" (as opposed to the levelness, as suggested by the OP) of the deck or head. If it were 100% "flat" it should (theoretically) read 115, 110, 105, 100. The fact that it dips down to 95 coupled with only the theory that it is due solely to the variances of the mill would suggest that the deck/head are, in fact, not "flat". This, in turn, could give rise to a great host of other issues.

Maybe that's just my overly analytical statistics training talking.
 

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Discussion Starter #7
^^ thanks haha, seems the problem mustve been at least somewhat valve lash related, did it again on the cold motor today and got 115-110-115-100. Im sure they would look a lot better if i warmed it up.

Also Im sending you a pm lol
 
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