will it run on pump gas ?

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AdamR

AdamR

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I was reading a thread on Moparts that got me wondering if my motor will run on 93 oct. I know Im pushing it and I doubt it will but I figure I'll get some feed back from others.

My motor has an 11:1 static compression ratio., iron open chamber heads and flat top pistons that stick .020" above deck height.

My dynamic compression 8.384:1. I also ran a quick compression check and get 150 cold. Cant warm the motor up yet so I dont know how accurate that is.

Anyone think I'll blow it up on pump gas ?
 
Hey Adam, as long as your running harden sets and 108 octane booster i dont see a problem. Les
 
Try squirting a drop of oil in each of the cylinders. If you're below 175 psi, you should be fine.
 
That is a pretty reasonable cranking pressure, I would have to say it would run on pump premium.


Chuck
 
I have 10.8 to 1 and with 32* (the car wants 38) of timing and 93 pump gas I`m still spark knocking. How did the guys in the Mopar Muscle Magazine`s big block shoot out run 11-1 cr on 93 octane? I`d like to mix some 110 octane with my pump gas but 50/50 is getting too expensive. Is there a formula I can use to calculate octane when mixing the two? Another thing is if I let the car sit for several days, I have to pump the crap out of the pedal to get her going again. Where`s my fuel going, into the air? It`s a Holley 2300.
 
Longgone said:
I have 10.8 to 1 and with 32* of timing (the car wants 38*) and 93 pump gas I`m still spark knocking. How did the guys in the Mopar Muscle Magazine`s big block shoot out run 11-1 cr on 93 octane? I`d like to mix some 110 octane with my pump gas but 50/50 is getting too expensive. Is there a formula I can use to calculate octane when mixing the two? Another thing is if I let the car sit for several days, I have to pump the crap out of the pedal to get her going again. Where`s my fuel going, into the air? It`s a Holley 2300.
Click to expand...

Thought I`d tag this again and see if anybody`s got a reply.
 
Sorry I missed it Longgone. If shes a knockin, theres only two things to do as it sits. Feed it more octane or retard the timing.
Otherwise, a tighter centerline cam or a larger one to bleed of cylinder pressure or (And/or) a thicker cylinder head gasket to reduce pressure. Though this could be bad for quench and cause pining too.

The reduction in timing is more of a power loss than a reduction in compression.

OH, some tricks to run a high comp. engine on 93 octane would be under anti detionation soulutions type of header.
Things like coated / polished piston tops & cylinder chambers, cooler fuel and engine, highly atomized fuel, quenched cylinder head area, bigger cams with tighter centerline and other cam event changes.
 
My old 69 GTS 340 popped and banged like it was comming apart on 93 octaine. 10.8, .484 DC cam, headers, and an aluminum intake. With 108 race gas it would burn the tires at 20 mph. After retarding the timing to run on 93 it wouldn't do that anymore. What a pig in comparison.
 
The car loves 38* BTDC timing and on 50/50 Cam2 and 93 octane she`ll do fine, but $6.00 a gallon for 110 hurts my wallet. This is especially true in a car that gets about 7 miles to the gallon. I`ve haven`t yet been able to find a compromise with timing, performance, economy, and high octane fuel. To fill up just with 1/2 110 and 1/2 93 is about $80.00.....ouch!
 
I'm running E-85, it's 105 octane and cheap. The engine is a 440 at 12.5:1 compression and 32*. 582 Tq @ 4900, 584 HP @ 5500. I've got another easy 40 HP with a bigger carb and intake.
 
GaryKephart said:
I'm running E-85, it's 105 octane and cheap. The engine is a 440 at 12.5:1 compression and 32*. 582 Tq @ 4900, 584 HP @ 5500. I've got another easy 40 HP with a bigger carb and intake.
Click to expand...

Awesome Gary! Tell us more about your build as I was planning something similiar but with a stroker small block but the same compression ratio. Supposedly, the number of E-85 fueling stations are going to triple here in Colorado. Very nice numbers by the way, seems as if it would be quite streetable. :)
 
AdamR said:
I was reading a thread on Moparts that got me wondering if my motor will run on 93 oct. I know Im pushing it and I doubt it will but I figure I'll get some feed back from others.

My motor has an 11:1 static compression ratio., iron open chamber heads and flat top pistons that stick .020" above deck height.

My dynamic compression 8.384:1. I also ran a quick compression check and get 150 cold. Cant warm the motor up yet so I dont know how accurate that is.

Anyone think I'll blow it up on pump gas ?
Click to expand...

blow it up - no, ping it up yes.
I had a similiar combo 340 with 10.6 at 3200 ft elevation and it need a mix of ±96 to run without the rattle. you do have more cam to bleed off compression and if you rework the dizzy to delay total mech advance in the 3000rpm range you may get away with 93/94. :thumbup: JMHO
 
FWIW, my 360 has 10.6:1 static compression and cranking pressure between 175 and 185 psi, it also has closed chamber magnum heads. I have 15 degrees initial and 33 degrees total mechanic advance, all in at 2500 rpm.

This engine runs with no audible detonation on 89 octane. A testament to what a closed chamber head with an ideal 0.040" quench does for you.
 
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