More Vacuum Issues

[Chezedik]

Here is the deal. When I put my motor together the ring end gaps are in spec, the compression is 160 even on all four cyls. My vacuum according to the autometer gauge (and confirmed by my vac tool) is 12"Hg, up from 10"Hg with timing correctly set at 20BTDC. I have a Cometic .120" gasket which lowers compression to 8.63:1 according to my calculations. The needle used to fluctuate until I reground the shims to spec. Cams are stock, and I cannot find any leaks (but I will keep looking). I do blow smoke at high RPMs and have not yet determined if it is in the engine or the turbo.

When I compare this to other cars (mostly V8's as it is all I can truly draw comparision to) I find that vacuum is a little low, but not too bad (ie:351 Ford Mach1 8.6:1 = 16"Hg spec). Idle is generally good, with the occasional misfire (which I know can cause this too). I have codes 21, 35, and whatever MAF is, I attribute this to emanage and will resolve them soon.

Is anyone else running 8.x:1 compression showing lower than anticipated vacuum numbers? Can a thicker than stock head gasket cause lower vacuum numbers?

Any ideas?

[Florida240sx]

i've always been at 20 on my car with stock and 8.8 pistons. My friend stock ka-t at 20, and a 300zx tt at 20. When mine was off down around 12-10 it was because my cams were off. Exhaust and intake were both off one, had perfect vaccum, rotated exhaust and vaccum was at like 11, fixed intake and it was perfect again.... When both cams were off car got choked up in high rpms. When I fixed exhaust car had little power down low and then would haul a55 to redline...

[wild_maxx]

I had 8.5:1 pistons with a Colt cam turbo reground camshaft in my KA24E-T and my vac. reading at idle was around 14-15. I know that I had NO vac leaks because I hooked up a smoke machine and tested for about an hour.

[gaehrings13]

Damn you make me want to check the timing on my engine now. Because my vac is around 16 sometimes . I was thinking it was a vac leak. Lol I still haven't checked for that. But I noticed that this motor I have has had the whole timing cover taken off and it leaks oil. Maybe someone did some work to the timing chain. I should take a look.

[HKSdrift3r]

^^ wouldnt the fact that you have your IAC source from the intake side create a boost leak, not necessarily a vacuum issue, but Im just trying to figure this out??

George

[Chezedik]

I have my IAC plumbed into the intercooler piping, and so no leak there. I did a test with the boost leak detector and no leaks. I drove it for the first time yesterday (WOOT!) and after it got some boost it is at 14-16Vac. Maybe this is just break in?

Timing looks right as per the 'pointing the cam lobe opposite' method. Wouldn't that effect compression and idle though? It smokes real bad but the plugs are good, so I am going to pull the turbo off and change that cup in the turbine housing. I think it ruined the EGO already. I also have a ton of other codes that I think (when resolved) will help vacuum. Also, I have a misfire which is hurting vacuum too, I am sure.

Worst of all, I blew off the coolant hose and now it won't start (no ignition, not seized) and the city is on my *** to get it mobile.

[Chezedik]

Well turns out I have bad rings, so I am selling the car. If you are interested, click my sig. Also, I will consider a part out after I move, if I do not get a reasonable response on the listing to sell it whole.

[S13FX]

Hey the link for your car is broken.

[DammitBobby]

I don`t get it how could the rings be bad if you are getting 160 across all cylinders?

Sorry you have to sell it:(

[Chezedik]

IDK, but I have changed turbos and it smokes and smokes. I'm just done with it. Maybe they are good and someone is going to steal it from me, I don't really care anymore.