Pump gas motor questions

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Pump gas motor questions

Post  wowens on September 26th 2013, 1:18 pm

4.5 bore-4.25 stroke, aluminum boss or P51 heads, hydraulic roller, well worked 4150 carb. How much compression is feasible on a actual street car at 3150lbs with a 5 speed & 3.90 gear. Boss heads with .041 gasket  and flat tops give 11.4,   will a custom cam grind make this workable or does it need to go down to 10.5 or 10.0 to run with no issues on 91 ?  The motor in the car now is a SCJ headed 565 at 12.3 with a big roller and is a very unnerving to drive in traffic, not a true street engine.
Will be driven to cruise ins, shows, work 1 day a week and maybe a 200 mile run on weekends.
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Re: Pump gas motor questions

Post  bigblok2000ranger on September 26th 2013, 4:11 pm

Run the optimum compression and don't comprise on the cam shaft. Will make more average horsepower that way and you will be much happier.
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Re: Pump gas motor questions

Post  supervel45 on October 2nd 2013, 12:29 pm

I think you will be OK if you keep the fuel fat and the timing down a little. Alot of the SBC guys do it all the time, and I did too with no problem, but use 93 octane.

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Re: Pump gas motor questions

Post  dfree383 on October 2nd 2013, 1:52 pm

I'd use 93 if you can get it. A lot will depend on the cam timing too. But yes it can be done.

We have one on the dyno right now getting flogged that's a similar combo, I'll post some info later on when the contest is over.

I have run my boss 9 at 11.5 with 91 just fine.
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