So I did a compression test on my engine. Has about 150-200 mi on this build (no signs of detonation on plugs). 350 roller block 4.030 64cc aluminum heads .45 quench, +6cc flat top pistons. My compression is right around 10.2. cam is a 218/224 .485/.500 lift. 112 lobe separation. Im getting 210 psi on all cylinders. I checked psi with all plugs removed and cranked engine till gauge needle stopped. I also hooked up the gauge to my air compressor (gave it 90 psi) and it reads accurately. Early on I was running super rich and built up alot of carbon in my cylinders. Im wondering if that carbon has clogged my piston rings?? Or is this normal?

 

Sounds about normal to me. I have a 11:1 383 with a 218/228 @ 0.050, 108 LSA and 106 ICL. It has rhoads vmax lifters that make that cam about 198/208 @ 0.050 at cranking speed. I see ~230 psi.

 

Yiu may not have the cam grind yiu ghink you bought.
The cam may be right but its installed wrong.
May be too far advanced. These effect the cranking psi.

 

I double checked the cam it should be correct. I checked lift and duration when degreeing it.

 

What are the advertised specs for that cam? Seat to seat.

Better still, do you know the intake valve closing point?

 

Here are the full cam specs..

Advertised Intake Duration:269
Advertised Exhaust Duration:276
Intake Duration at .050 Inch Lift:218
Exhaust Duration at .050 Inch Lift:224
Intake Valve Lift:0.495
Exhaust Valve Lift:0.503
Lobe Lift Intake:0.33
Lobe Lift Exhaust:0.335
Lobe Separation:112
Intake Centerline:108
Exhaust Close ATDC:22
Intake Open BTDC:26
Exhaust Open BBDC:74
Intake Close ABDC:62

 

Always do compression test with engine warm.

 

In the theoretical world you're pretty close.



This particular calculator works off of the IVC + 210 degrees. Which is slightly different than the seat timing of your 276 cam.

For the record, one of my earlier Vortec builds was centred around COMPs old 268H.
350: 4.00” x 3.48”
Speed Pro hypereutectic 5 cc piston H345NCP
.030” deck
Vortec heads (stock)
Comp 268H flat tappet w/ 1.5 rockers. 268 adv, 218 @ 050”, 60 ABDC IVC.
Corteco 55063 head gasket .028” x 4.130”
9.8 SCR / 8.12 DCR
Cranking pressure 200-205

The calculator used for your build predicted a 201 PSI cranking compression for that 268H assembly.

As suggested, there are a lot of variables that go into a compression test. Engine warm. Throttles wide open. Fully charged battery. I like your approach with cranking until there's no further movement on the gauge. In addition to that I like to record the first stroke compression as well as 3-4 strokes in. I can't say how all of that shakes out other than to say it's useful to me when comparing engines I've assembled.

 

I alao like to watch the first snap. Really helps gauge the overall health. Should be a substantial portion of the final reading and fairly even across the board.

 

I found that with a fresh engine, that the first crank was a substantial portion of the overall. This last 355 (I've documented the destruction here I think) was obviously hurt just by the results of the compression test and that the first crank was very wheezy on a couple of cylinders. Leak down was worse.

 

this is great info! I appreciate all the help. So it sounds like there isn't anything to be worried about here.

 

Yep. I'd say from a compression test standpoint, you're OK.
I still like to target about a 200 PSI cranking compression. This is great for a street engine where that low speed torque makes a difference.
I'm hoping it'll help my 60' time at the drag strip too. And if you can carry that torque up through the rev range, it's HP coming out at the top end. I'm hoping for that too.