Off the Scale Compression Pressure Values?
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
I can't speak for the OP though I'm curious. For me, don't know. I had a machine shop replace the cam many years ago. Don't know if they ever gave me a copy of the specs or even the number of the cam. My engine is actually running 9.6:1 CR, pistons installed to lower the compression, ease issues with pump gas available in the mid 80's.
Melting Slicks
Joined: Apr 2007
Posts: 3,189
Likes: 111
From: Tolland CT
I skimmed a few articles on this topic. It seems higher pressures may be seen when there is less overlap of intake and exhaust valve timing? Interesting...
Racer
Joined: Feb 2012
Posts: 261
Likes: 3
From: Clawson Michigan
I was hoping for 170-180 psi cranking compression on my new engine. After 100 miles I ran a compression check and the results are 205-210, with 150psi on the first bump.Readings on the stock low mile L48 were 170-180.
All test were done on a cold engine all spark plugs removed throttle WFO and about 5 bumps.
New engine specs
Gm Goodwrench 350
Dart SHP180 cut to 62 cc
Pistons .03 in the hole.
.028 gm head gasket
Comp cams xr276hr 59 degrees overlap
9.2 approx static compression.
Run 93 octane and haven't noticed any pinging . timing 10, 30 all in @3000. Additional 20 degrees of vacuum advance full manifold.
From my research my cranking compression is higher than it should be for the amount of static compression I have. I do not know why it is higher than I thought it should be, but it runs strong from 1500rpm up. My tuning knowledge is limited so not much of a safety margin. I've been contemplating a larger cam to lower these levels.
All test were done on a cold engine all spark plugs removed throttle WFO and about 5 bumps.
New engine specs
Gm Goodwrench 350
Dart SHP180 cut to 62 cc
Pistons .03 in the hole.
.028 gm head gasket
Comp cams xr276hr 59 degrees overlap
9.2 approx static compression.
Run 93 octane and haven't noticed any pinging . timing 10, 30 all in @3000. Additional 20 degrees of vacuum advance full manifold.
From my research my cranking compression is higher than it should be for the amount of static compression I have. I do not know why it is higher than I thought it should be, but it runs strong from 1500rpm up. My tuning knowledge is limited so not much of a safety margin. I've been contemplating a larger cam to lower these levels.
Last edited by Flyinace3; Jun 16, 2014 at 12:29 PM.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
I was hoping for 170-180 psi cranking compression on my new engine. After 100 miles I ran a compression check and the results are 205-210, with 150psi on the first bump.Readings on the stock low mile L48 were 170-180.
All test were done on a cold engine all spark plugs removed throttle WFO and about 5 bumps.
New engine specs
Gm Goodwrench 350
Dart SHP180 cut to 62 cc
Pistons .03 in the hole.
.028 gm head gasket
Comp cams xr276hr 59 degrees overlap
9.2 approx static compression.
Run 93 octane and haven't noticed any pinging . timing 10, 30 all in @3000. Additional 20 degrees of vacuum advance full manifold.
From my research my cranking compression is higher than it should be for the amount of static compression I have. I do not know why it is higher than I thought it should be, but it runs strong from 1500rpm up. My tuning knowledge is limited so not much of a safety margin. I've been contemplating a larger cam to lower these levels.
All test were done on a cold engine all spark plugs removed throttle WFO and about 5 bumps.
New engine specs
Gm Goodwrench 350
Dart SHP180 cut to 62 cc
Pistons .03 in the hole.
.028 gm head gasket
Comp cams xr276hr 59 degrees overlap
9.2 approx static compression.
Run 93 octane and haven't noticed any pinging . timing 10, 30 all in @3000. Additional 20 degrees of vacuum advance full manifold.
From my research my cranking compression is higher than it should be for the amount of static compression I have. I do not know why it is higher than I thought it should be, but it runs strong from 1500rpm up. My tuning knowledge is limited so not much of a safety margin. I've been contemplating a larger cam to lower these levels.
