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#1
07-21-2023, 11:58 AM
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Lowering compression?
Right now I have 12-1 with 72 cc E-heads. I have it detuned now to run 10.00. It has gone 6.04 in the 1/8 so I am thinking that is the 9.6 range. I want to lower it to pump gas compression and still go 10.00 in the summer. My cranking compression right now is 180 psi i am afraid to try pump gas it.
My plan it to get in in the 10.5-10.75 range and change the cam to match the new compression. Do you think I should get dished piston or new heads with bigger chambers? I was thinking new heads with more cfm (have 330 now at .700). Can you run 11-1 on pump gas? Thanks Mike |
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#2
07-21-2023, 12:40 PM
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You can get 93 where you are at. People run 11-1 all the time, even more.
But 10.5-10.75 is a good safe number. Have you tried taking off at a lower RPM, short shifting it or a smaller fat carb ? I have 74cc heads and going to run pump gas. 10.00 goal. I know plenty of guys run dished pistons but Cliff has dynoed a lot of pump gas 455s and says they run better with flat tops and the right head vs a dish for whatever you need. Ran 11-1 with iron heads too. |
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#3
07-21-2023, 12:42 PM
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Maybe if you tested each batch of fuel for the "corn" in the fuel.
Boost guys do that all the time. Dished Pistons or new heads with bigger chambers would work but try to keep the same compressed head gasket thickness on either combination. Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
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#4
07-21-2023, 01:27 PM
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Quote:
Stan
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Stan Weiss/World Wide Enterprises Offering Performance Software Since 1987 http://www.magneticlynx.com/carfor/carfor.htm David Vizard & Stan Weiss' IOP / Flow / Induction Optimization - Cam Selection Software http://www.magneticlynx.com/DV Download FREE 14 Trial IOP / Flow Software http://www.magneticlynx.com/DV/Flow_..._Day_Trial.php Pontiac Pump Gas List http://www.magneticlynx.com/carfor/pont_gas.htm Using PMD Block and Heads List http://www.magneticlynx.com/carfor/pont_pmd.htm |
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#5
07-21-2023, 01:44 PM
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My race motor is 11.2:1 static CR and I usually run 3 gal 110 octane and 7 gal 93 pump. I have run it with only 93 pump and there was no indication of any detonation with the water temps getting to 200 F by the end of the run.
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1967 Firechicken, 499", Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3550#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule. |
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#6
07-21-2023, 09:25 PM
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My 463 is 10.5 to 1 , maybe a bit more and my cranking compression is 178-182. No problem with 93 octane. KRE d-ports, 85cc. 262/270 solid roller.
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69 Bird w/1970 400 block(409 cubes), #64 heads, hyd. roller, Q-jet by Jeff E., original interior, ps, pdb, th350, and 3.73 gears. Pump gas, street driven muscle. 3800 lbs. race weight. Best, 11.39 @118, my son's car. 79 T/A w/463, Scat crank, Eagle rods, Icon pistons, Lunati solid roller, 262/270, KRE 325 heads, Northwind intake, QF950 carb, full interior, ps, pdb, th350, and 3.73 gears. Pump gas, 3650 lbs. race weight. 10.68 @ 126 so far... no tuning yet. |
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#7
07-21-2023, 09:33 PM
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Clean, effective, and cheap way to go is dished piston.
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#8
07-21-2023, 10:56 PM
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I ran my last 455 at 11.3 to 1 for 14 years on 93 octane pump gas. It had CNC ported KRE aluminum "D" ports on it with 74cc chambers and a 289/308 @ .006", 236/245 @ .050", 112LSA with the ICL at 109.5. It was a HR cam with .381" lobes and .639" lift with the rockers I was running on it. I ran 10 degrees initial timing and 30 total, all in around 3200-3300rpm's. My converter flashes to 3400rpm's so timing was all in at full load when the car launched. Never had any issues with detonation or anything else. I even ran 87 octaine in it a few times and it didn't ping but would "run-on" if the engine was well heat soaked on a hot day.
Cranking pressure was right at 198-200psi in all cylinders.......
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
| The Following 3 Users Say Thank You to Cliff R For This Useful Post: | ||
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#9
07-22-2023, 08:32 PM
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Lower the compression and increase the head flow.
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#10
07-23-2023, 04:00 PM
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You should be able to get down to 10.00 with the heads you have. Or close to it.
Cam change might help. This Wallace Racing calculator might help. All the inputs are pretty easy. But myself not sure about the right VE to use. Someone who has dynoed a lot of engines might know the best number to input there. http://www.wallaceracing.com/eff-cr.php |
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