Hi just a quick question. Im going for a re-tune soon on my b18c 13:1 pro2 set-up.
I resently put a 68mm TB and kidd-racing narrow tube header on to try improve my graph. So i decided to check everything in preperaton for the tune. I found all of my tappet clearence on the intake and very little on the exhaust needed to be made tighter.I also inspected for lobe wear or rocker arm pad wear and all was good.
My compression results before the tappet adjustment with a cold engine came up at 290psi+-5psi. After i adjusted them i performed another compression test and it came up at 275psi+-5psi.
on a good note the valve train is much quieter now.
Is this normal for compression to drop?

Car drives well but Vtec x-over is a bit agressive since the TB and header.
thanks

 

By reducing the valve clearance the intake valve will close later which is why your compression test results are lightly lower. Don't really worry about it though because the absolute value of the test is relatively meaningless, you're just looking for all cylinders to be even. 275 psi is really high. Are you running race gas?

 

yea sunoco 114.
thanks

 

Post your before and after grapsh when you get it tuned with the header and tb. I Just bought the header and thinking about getting a 68mm tb to match my s2 manifold too

 

If you think about it, having too much clearance effectively changes your cam timing right?
The valve will open later and close sooner. This is the duration. Different duration cams yield different compression numbers(as does cam timing).
This is perfectly normal...
got some vids?

 

sorry no vids, just some pics if you click on my username. have not had the car out much lately. I need a new clutch. I was expecting a difference in the compression after the valve clearence adjustment, just needed reassurance that a 15psi drop was normal.
My previous dyno tune was on a dyno dynamics. My new tune will most likely be on dyna-pack. So i will not be able to compare my graphs properly.

Thanks

 

Correct.

To the OP, did you do a compression test when the engine was first put together with a fresh valve adjustment with the cam install?

 

yes i did. it came up 285+-5psi on the first test. The valve lash was set to .30 intake and .25mm exhaust by the builder it also turned out he never degreed the cams. So after i got my belben kit and degreed the cams i returned the clearence back to his spec. The motor was tuned with this clearence. So in preperation for the next tune i checked the pro2 valve clearence spec. And adjusted the intake to .17mm (.007'')and exhaust .20mm(.008''). Like i said the vavetrain sounds a lot better now.

 

I see. That was really loose on the intake side though (~.012)", effectively making the cam smaller than it really is. The .007" and .008" Skunk2 recommends should have helped out tremendously in nearly all aspects.

 

cool hopefully it will show on the dyno.