Tuning cams by using a compression tester!

[Rampage16V]

http://www.srtforums.com/forums/f169...tester-629499/


Interesting thread,


Ok Do I was goofing around and ran into a old thread about tuning cams with a compression tester seemed easy enough right....

This was performed on my car
New pistons rings ect.. Crower s3 cams

Before compression was at 120 my map EF4 hit 14lbs at 3800~ rpm
There was some mid range but nothing crazy. Vacuum at 8"~

Step 1. Do a normal compression test
Step 2. Loosen can gear and advance 2 degrees.
Step 3. Redo the compression test if it goes up you keep advancing if it goes down its time to go the other direction. Repeat till the compression does not increase.
Step 4. Do the same to the exhaust

Results.....

I ended at +4/+2 started the car and now in reading 12" of vacuum on crower stage 3s.... And 145psi of compression

The test drive.....

The turbo felt much more alive and at 2k rpm in 5th if I punch it I get 5psi instantly.... All from a MAP stage 3 and a TD06 exhaust wheel... The mid range is crazy while I was on the highway and I would go to pass I found my self not dropping gears and kept making sure I was in 5th lol.... The car is a lot smoother on take offs... Doesn't randomly stall like it used to... All by decreasing the valve overlap....

If you haven't done this I would do it... It only takes a 30 min and it worth every penny

[turbovanman²]

I used to do that with my old 8 valve, gave me the best bottom end and spool but did hurt the top end.

The best test would be track testing, test the baseline, then do this and see how much faster/slower you are.

[zin]

They sure like them some drama over there at the SRT forums, don't they?

Mike

[turbovanman²]

They sure like them some drama over there at the SRT forums, don't they?

Mike

Like my post over there?

[ShadowFromHell]

Very cool idea. A buddy of mine is putting some 272s in his EVO soon. I'm gonna send him this link.

[8valves]

Dean,

Keep in mind you're greatly increasing your peak dynamic cylinder pressures by doing this as well, so be weary with your timing advance around peak torque.

AM

[RoadWarrior222]

Interesting but... why would you want to adjust for best torque just off idle? ... I'd wanna find something to kick the motor over at 2000RPM or so...


I dunno if you are increasing your peak dynamic pressures or just moving them to a different part of the rev range. Also your torque peak has moved, so unless you wanna dyno it, you're working by guess on the advance.

[tryingbe]

I don't buy that test, his cam timing were just way off!!

These compression number are recorded when I had the bike schrader valve in my compression gauge hose, and it gave a much lower psi reading than it should (75psi rather than 132psi).

Car ran HORRIBLE with 10 degree advanced. http://www.turbo-mopar.com/forums/sh...ht=compression

I just tested # 4 cylinder. This is with the 88 TBI 2.2L roller camshaft.

70psi 2 degree retard
75psi Straight up on the cam.
80psi 2 degree advance
85psi 4 degree advance
90psi 6 degree advance
95psi 8 degree advance
95psi 10 degree advance
100psi 12 degree advance

[8valves]

It works on a DOHC car. It won't work the same way on a single camshaft car because you're changing your compression readings only from the relation of the cam to the crank. The gains in compression on the dual cam car is to be had via intake to exhaust valve timing events, primarily.

Changing your cam-crank relation is what shifts the powerband drastically, not just increasing or decreasing overlap.

AM

[BadAssPerformance]

I did this years ago on the 2.2L 8V with the offset cam keys... went from -1 tooth to +1 tooth on the belt and compression changed from ~100 to ~160. Driving at the higher compression I realized quickly that it just moved the powerband downward and hurt top end... this was of course before I knew how to centerline a cam correctly.

With a 2.0L/2.4L DOHC it is so easy to centerline the cams why wouldn't you just start there then make a few passes to see what +1, +2, -1, -2, etc does for each cam.

[turbovanman²]

I did this years ago on the 2.2L 8V with the offset cam keys... went from -1 tooth to +1 tooth on the belt and compression changed from ~100 to ~160. Driving at the higher compression I realized quickly that it just moved the powerband downward and hurt top end... this was of course before I knew how to centerline a cam correctly.

With a 2.0L/2.4L DOHC it is so easy to centerline the cams why wouldn't you just start there then make a few passes to see what +1, +2, -1, -2, etc does for each cam.

Yes, you can do that but if its mostly a street car or your short on track testing, you can run it then go back with your new setup and compare. I'll try it when I get my trans back together for shitts and giggles. I'll set them straight up-degreeing them, I'll then do the compression test method and mark the gears, go to the track and see what happens, should be fun.