993 Engine Top End Rebuild

[rbp]

I had the engine out, heads were rebuilt, cylinders cleaned and new rings were installed. When I started the engine it seems to be running very rich, is hunting and seems unstable. I did a compression test to see what I had and got 205 all around. Is this possible, anyone know what I should have. Maybe the 205 is correct considering the assy lube on the new rings and all. Anyone experience this?

I was thinking there is something wrong as people are telling me I should have say 170 PSI. If the specified compression ratio of 10.5:1 is true then say 15 x 10.5 is around 160. How can I have 205? Am I missing something here?

As far as the bad running I've double checked everything and all connections are correct. I ran my buddies Durametric OBDII scan tool to see what I can find out. It doesn't seem to want to save any running data so I have to write everything down by hand. I have no CEL or fault codes. It reported the injection time at 36.8 ms, throttle plate angle at 0. I have some other info but now have to try to determine what are good bench marks so I know what I should be read as opposed to what I am reading. I have something called a "load signal" at 4.0. Not sure what that is, maybe that's causing the injector time to be way to high.

[Flat6pac]

Your compression, at least C2, is 11.5 or better.
My build on 10.3 carrera compression came in at 200 #
Build on 8.5 SC comes in about 170#
Bruce

[rbp]

Engine is the stock engine in the car, 1996 C2. So if its 11:5 to 1 then it should be 170# or so, that assumes of course that atmosphere x the ratio gives you the max compression you can expect. Can't be the case though since others also have different outcomes, at 10:3 x 14.7 should have been 150 not 200. Must be other factors in the mix I'm not aware of.

[lightbulb8817]

I think if you're getting ~205 psi consistently across all 6 cylinders, that's a probably good sign and not too from where it should be (based on Flat6pac's 200 psi at 10.3 CR...). My CR is about 10.5 and measured ~165 psi on a cold motor, maybe 185 psi hot if i recall correctly. If you have 205 on 1 cyl and ~160-180 on others, than I'd interpret the 205 as a red flag.

Some things I'd check:
-make sure your injectors are clean or send them out for cleaning/flow testing if you're not sure
-Check cam timing. Mine was way off (bought rebuilt motor thinking it was timed) and the motor barely ran

[rbp]

The injectors were sent out and serviced before reinstall. Would cam timing have an affect on the injector time at idle? My injector time is 36.8 ms way too high for idle. Is there a simple way to verify if my cam timing is reasonable? I set the cams using a Z block, solid rocker/lifter and gauge as follows.

Setup valve clearance at 1mm

Set Cyl #1 to TDC

Cyl #1 Intake valve should be set a 1.26mm lift

That spec is the same as the 964 I believe.

Same process for other side on cylinder 4.

[K24madness]

I got 185psi on a 5k 993 engine with stock pistons. It does have mild aftermarket cams so I bet the compression is down from what stock should be. That 205psi number seems high to me. I am betting the cams are not set right. Pinging and early Power fall off would be something to look for if that’s the case.