would cam timing effect the results of a compression test? If not would there be any other reason for having a higher reading then expected other than milled head/block?
would cam timing effect the results of a compression test? If not would there be any other reason for having a higher reading then expected other than milled head/block?
Cam timing can affect readings. Also carbon buildup or higher compression pistons and as you said, milled head and block.
1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS!12.57@104 :O)
1984 Chev Getaway van, 6.2 Diesel with a remote mounted turbo setup burning WMO-For sale.
2003 GSW 2.0L TDI, auto, fully loaded, modified, 360K-wife's.
2004 GSW TDI, 5 speed, fully loaded, modified.
Aurora ignition wires for sale. Link to info
Super60 roller cams or custom/billet cams. Link to info
as i thought!. I did compression test today and the readings were insanly high. The timing belt is pretty loose so im thinkn the timing is pretty off.
when you say insanely high, what are you getting. My 1999 Chevy truck 9:1 compression shows 230psi, my 1988 TD 190psi 8:1 but my Stroker N/A 2.2 (actually 2700cc's) 14:1 compression only has 140psi w/total seal rings. Cam profile has a huge effect on compression. if cam timing is off by a tooth or more, you should see equal but lower compression.
im getting 180psi across the board on my iroc R/T.
that's PERFECT
Originally Posted by 22mopar
uhhhhhh, 22mopar
i know your a smart man and you have helped out alot of people but, i have read many times on these forums and even in manuals (shitty ones[all i can find]) that the perfect compression was 150-160 psi and thats when these cars rolled out of the factory.
i thought 180psi was detonation city!!
hell, even my fullly rebuilt 8v was reading 140!
there really is nothing wrong with high compression pressures, just shows you have awsome ring sealing and very low valve overlap. like I showed in my example my 9:1 compression 5.7 chevy truck has 230 psi while my 14:1 compression 2.2 has only 140. the 2.2 has the best rings money can by and shows less than 2% leak down (blow by) the chevy truck has more compression pressure but has less compression ratio. this is because of the cam profile.
My 2.5L with G-head have 150psi all four cylinders.
Folks, he has a TIII, different ball of wax. I seem to remember around 160-170 is normal.
1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS!
1984 Chev Getaway van, 6.2 Diesel with a remote mounted turbo setup burning WMO-For sale.
2003 GSW 2.0L TDI, auto, fully loaded, modified, 360K-wife's.
2004 GSW TDI, 5 speed, fully loaded, modified.
Aurora ignition wires for sale. Link to info
Super60 roller cams or custom/billet cams. Link to info
w/ a DOHC engine, cam timing will effect compression pressures. like I stated about valve overlap. if you have one cam off one tooth, you will effect overlap and pressures will be higher or lower depending on which way you are off on the cam. if you have an SOHC head and are off one tooth, you can expect the cylinders to be lower.
thanks for clearing everything up.
i didnt realize that the 16v would have different readings than the 8v
i also didnt realize that a 16 valve would be that much different..
cams make a huge difference, imho
i have found that a generalized rule of thumb for most engines(without wild cams ect.), approximate cranking compression is close to:
140psi=8.0
160psi=9.0
180psi=10.0
200psi=11.0
i have done a few hundred different tests on 8 valve 2.2/2.5's over the past couple years(cold/hot/wot/non-wot ect.ect)
usally a 1 tooth change on the cam sproket equaled out to be about 5-10 psi in cranking compression. even the difference between wot/non-wot was in the 5psi. range and about 5-10psi in hot/cold tests. and of the new motors i have built, 150 psi seems to be the magic number for me(cam straight up, stock deck surfaces), most pulled this number before even starting the engine for the first time.
Hey Adam, nice avatar! All of a sudden I'm thirsty......
I know, I have a craving for milk,
1989 FWD Turbo Caravan-2.5 TIII, GT35R, auto, a/c, cruise, pwr windows/locks, fully loaded with interior and ran with full exhaust. RETIRED FOR A FEW YEARS!
1984 Chev Getaway van, 6.2 Diesel with a remote mounted turbo setup burning WMO-For sale.
2003 GSW 2.0L TDI, auto, fully loaded, modified, 360K-wife's.
2004 GSW TDI, 5 speed, fully loaded, modified.
Aurora ignition wires for sale. Link to info
Super60 roller cams or custom/billet cams. Link to info
milk does the body GOOD
guys, the cam has a HUGE effect on compression pressure. like in my report a 9:1 engine pumping 230psi, while a 14:1 only at 140 psi. what is really funny in my years of racing, the ignorant tech inspectors had rules that the engine could not exceed 180 psi compression pressure. they figured that by having this rule, guys couldn't increase the compression ratio. so I'd install a cam with a ton of overlap and tight lobe center (104) stock street engines run a lobe center in the 114 range. this allowed me to have 14:1 compression and be within the rules.
22mopar thank you for sharing
i really didnt see this on the forum anywhere and its good to know this info for anyone who needs to know
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