Posted By: 65 Hemi
What cylinder pressure on pump gas? - 03/31/15 08:55 PM
Changing my Hemi over to pump gas. What cylinder pressure can I get away with on 92 pump gas? All aluminum 4.50 bore motor.
What cylinder pressure on pump gas?
Posted By: an8sec70cuda
Re: What cylinder pressure on pump gas? - 03/31/15 08:59 PM
Mine has 185 psi.
Posted By: 65 Hemi
Re: What cylinder pressure on pump gas? - 03/31/15 09:32 PM
Quote:
Mine has 185 psi.
Thanks.
Posted By: an8sec70cuda
Re: What cylinder pressure on pump gas? - 03/31/15 09:48 PM
You're welcome. My 14:1 wedge motor also has 185 psi...definitely not running pump 93 in that one though. 
My 14:1 wedge motor also has 185 psi...definitely not running pump 93 in that one though.
Posted By: 65 Hemi
Re: What cylinder pressure on pump gas? - 03/31/15 10:45 PM
Quote:
You're welcome.
Yes, it's a little tougher to run that high of cylinder pressure in a wedge.
Posted By: D-50
Re: What cylinder pressure on pump gas? - 04/01/15 12:15 AM
I run 93 octane in my small block and I have 195-201 lb cranking cylinder pressure. 10.9-1 comp, .255/.266 @.050 camshaft with aluminum heads. Distributor locked out at 35 degrees.
Posted By: 65 Hemi
Re: What cylinder pressure on pump gas? - 04/01/15 04:44 PM
Bump. Anybody else?
Posted By: an8sec70cuda
Re: What cylinder pressure on pump gas? - 04/01/15 05:08 PM
Quote:Quote:
You're welcome.
Yes, it's a little tougher to run that high of cylinder pressure in a wedge.
The wedge had 275 psi before I changed the cam.
Posted By: 68LAR
Re: What cylinder pressure on pump gas? - 04/01/15 05:22 PM
Not a Hemi, but mine is at 185 with RPM heads and iron block. Cr is 11.8. I run 93 octane pump gas. 
Posted By: moparniac
Re: What cylinder pressure on pump gas? - 04/01/15 08:18 PM
I crank at 170, I run 9s on local 93 gas.
Posted By: 1967dartgt
Re: What cylinder pressure on pump gas? - 04/01/15 10:26 PM
I have 190s on pump puke.
Posted By: astjp2
Re: What cylinder pressure on pump gas? - 04/02/15 12:28 AM
212 psi is a little too high.
Posted By: 1980volare
Re: What cylinder pressure on pump gas? - 04/02/15 12:33 AM
Cylinder pressure is not directly related to compression ratio. You need to know cam specs, bore, stroke, rod length, static compression, and valve closing angle. other wise you're just guessing.
Posted By: gregsdart
Re: What cylinder pressure on pump gas? - 04/02/15 12:43 AM
There was a point made in one of the posts on compression and pump gas that the true test is how well it will run when the motor hits the peak torque area where max volumetric efficiency is achieved. With a big cam and high compression the motor will still need the octane to handle the static (not cranking) compression due to ram intake and exhaust tuning.
Posted By: an8sec70cuda
Re: What cylinder pressure on pump gas? - 04/02/15 02:17 PM
Quote:
Cylinder pressure is not directly related to compression ratio. You need to know cam specs, bore, stroke, rod length, static compression, and valve closing angle. other wise you're just guessing.
Just b/c my wedge cranks 185 psi doesn't mean it'll run on 93. It still has the same 14+:1 compression it did before when it cranked 275 psi...the cam is the only difference.The compression ratio still needs to be on the low end (for the most part) to be pump gas friendly.
Posted By: Diplomat360
Re: What cylinder pressure on pump gas? - 04/03/15 05:50 PM
360 mopar, 9.8:1 CR, 175 PSI cranking with a Hughes hydraulic flat tappet cam: 238/244 @ 0.050, with nasty/crappy quench on stock heads. I run 93/94 pump gas...pretty aggresive advance curve: 21 idle@900, 35 @2000. No ping.
Posted By: Dragula
Re: What cylinder pressure on pump gas? - 04/03/15 09:22 PM
Quote:
360 mopar, 9.8:1 CR, 175 PSI cranking with a Hughes hydraulic flat tappet cam: 238/244 @ 0.050, with nasty/crappy quench on stock heads. I run 93/94 pump gas...pretty aggresive advance curve: 21 [Email]idle@900[/Email], 35 @2000. No ping.
I would advance final timning even more on that one. All my low compression 340's and 360's liked at least 38...
And for the nay sayers, you can run 14:1 on pump gas....Its called water injection and it works really well. If you can tune a carb, you can tune a water injection system. We have guys tired of paying for race fuel and went this route and will never look back.
Posted By: 572charger
Re: What cylinder pressure on pump gas? - 04/06/15 01:28 PM
my 606 cuin hemi is 180 psi it is at 12 to 1 comp i run it on pumpgas 93 octane with the total timming at 32 degrees and take out 8 degrees on the spray !!! 
Posted By: 72Swinger
Re: What cylinder pressure on pump gas? - 04/06/15 03:58 PM
With a loose verter you can get away with 185-195 all day long. Go to a manual trans with the same setup and plan on taking about 5-6 degrees out of total timing or it will be ping city.
Posted By: 65 Hemi
Re: What cylinder pressure on pump gas? - 04/06/15 04:34 PM
Quote:Quote:
360 mopar, 9.8:1 CR, 175 PSI cranking with a Hughes hydraulic flat tappet cam: 238/244 @ 0.050, with nasty/crappy quench on stock heads. I run 93/94 pump gas...pretty aggresive advance curve: 21 [Email]idle@900[/Email], 35 @2000. No ping.
I would advance final timning even more on that one. All my low compression 340's and 360's liked at least 38...
And for the nay sayers, you can run 14:1 on pump gas....Its called water injection and it works really well. If you can tune a carb, you can tune a water injection system. We have guys tired of paying for race fuel and went this route and will never look back.
Who is doing water injection? Can you please give more info on this?
Posted By: justinp61
Re: What cylinder pressure on pump gas? - 04/07/15 03:29 PM
My 408 had 180# cranking pressure with good quench. The cam was a Hughes 260/264 @.050 flat solid. Total timing was set at 34*, it didn't run any better set higher. I pulled the engine in February for refreshing and found some signs of cap walk.