Data request, what is your cranking PSI?

What is your cranking PSI? Please specify hot or cold.

&...

What octane can you run?
How much advance are you running?
What combustion chamber?
Alum or Iron heads?

The more info the better, thanks!

I plan on doing a cranking pressure test to see if I'm high or low. The problem is, I have no frame of reference for this & would like to hear what others have. I'd bet there are plenty of others on this forum that would find this information interesting or useful too.

Smog 440, big old iron open chamber heads, atleast 36⁰+ of timing, any octane:

Average of all 8 hot is 142 psi

The cranking pressure won't tell you much. I have an aluminum head 11:1 hemi that cranks 185 psi and runs on pump gas w/ 34°. Also have an aluminum head 14.5:1 wedge that cranks 185 psi and needs 112 fuel. The same motor w/ a different camshaft cranked 275 psi and also ran 112 fuel. Both run at 38°.
Had an iron head 12:1 440 years ago that cranked 220 psi and needed 110 fuel at 38°.

How is you car acting now?

What is your setup?

My Predatoer is fairly low, but being an aluminum block they usually are. It is 210ish per hole, Q16 fuel 39 degrees in first gear and 33 in high gear, This is a 1200HP 15.8-1 engine. When it gets freshened later this year we will be going closer to 17-1 in an effort to up the cylinder pressure. FWIW the heads up car, aluminum block again only pumps about 175, its 16.4-1 runs on C45 and we have timing curves for each gear

Like said, this will not tell too much.

1984 Shelby 2.2, 0.039" over flat pistons with ported Aluminum G head, 252 deg cam (0.460 lift) installed 4 deg advanced , 0.030 cut on block, true measured 11.2:1 compression ratio. 20 degrees base timing, with factory Shelby computer and knock sensor. It would show 215 PSI warm. It ran on pump SUPER.

Shifted at 7200 RPM. Top speed on 85 MPH speedo was 15 MPH

UPDATAED^^^

10.2 to 1 in both my 493" RB & 408" Magnum. Both have aluminum heads, pistons 0 decked with high quench heart shaped chambers. The RB has reverse dome that matches the Indy EZ chambers. The Magnum has flat top pistons with Eddie heads.

Both motors crank 200 psi warm. I run 35* total advance locked in on the RB and reflashed factory JTEK computer controlled on the 408. They both run on California 91 ethanol pump swill. No detonation even on hot days.

(Installed on 105* centerline)

No one says where the cam is installed.. advancing or retarding it will change your cyl pressure

I think the real question is when does the intake valve close.

It is the question I think

I have a H ones inverse ground roller cam and he uses VERY long lash ramps. If you are a few degrees off when setting lash it can make a noticeable difference in opening point. Add to that aluminum block and heads and things must change a bunch from running cold to hot.

Not enough data: missing IVC closing ABDC, rod ratio, intake vacuum during test.
CCP is useful to compare the same (or almost identical) engine(s) with different tunes, not to compare different engines.

Hughes Engines HE3844AL hydraulic flat tappet cam, specs are: see attachment.

This is in a semi-blueprinted 360 block at 10.5:1 CR, cranking some 185 PSI @hot.

Engine runs on 91 pump gas, 21 initial and 38 total mechanical advance.

The two examples I listed might scare to many in here if they knew the cam specs

mines 210-215psi , 499ci
cam specs.

Installed at 106

The same CCP can be arrived at by many different combinations of CR & IVC, like late IC + high CR or early IC + low CR may produce the same CCP at cranking speed.
The cylinder combustion pressure of the low CR will rise immediately but not that much, the high CR will take longer (delayed VE and torque curve) but get much higher.
Two engines with the same CCP, produced the same way, may not have the same knock sensitivity.

Things to avoid: using the wrong cam (not the optimum choice for best power characteristics) to change cranking pressure.

Overlap has nothing to do with CCP, but it definitely affects knock sensitivity by retaining exhaust gas in the chamber.

It seems to me that the OP is trying to judge what octane you can run by the cranking compression of the engine. That's not gonna work.

I didn't say that, nor imply it.

Thanks to all those that have contributed to the thread.

for what it's worth one of my 440's does 160psi cold. might do 170 hot. 9.8:1static compression ratio, alum heads. closes the intake valve at 76 degrees after BDC. very pump gas friendly with 93 octane.