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Discussion Starter #1 (Edited)
I am going to help a neighbor (daughter - good kid) with a pump gas S-10 that should run mid 10's.
I am looking at building a flat top 10 to 1 355 or a 11 to 1 383.
Now I talked to an "expert " tonight, and was told that I can run pump gas with an aluminum head at 11 to 1 with no problems.
I am not sure that I am comfortable with that -- what do you think?
I'm used to 14 to 1 on alky. :cool:
 

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it all depends on the efficency of the chamber and the cam shaft. I run 10.8 on with a 150 of nitrous on 93 no problems. i have 160 psi cranking compression. if youre in the 150-175psi range i think you will be ok.
but... youre only talking 10-15 hp diff from 10:5 to 11:0 cr probably not worth pushing the fringe
 

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Discussion Starter #4
I'm looking at a 12-900-9 comp cam -- Intake 252 at .050 -- Exh 258 at .050 -- 106 centerline -- .630 lift.
RPM --3500 to 6900. That was chosen with their software Cam Quest - I am going to call them tomorrow.
I want to keep this thing reliable -- should be a torquer.
 

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i run pump gas with 11.2 comp no problem
 

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The Grouch
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About 4 years ago my Buddie bought a 11-1 383 pump gas motor. On the dyno it did not ping one bit. We put in the car and , same timing and fuel and it pinged like a pop corn maker. Mix the gas with some 100 ot and it runs good.
And it has a smaller cam than what you are looking at.
Now this is in California and we have crappy gas here.
Hope it helps.
 

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like smallblock nova said, the static is only a piece of the pie, overall components will weigh heavily into the equation...cam specs being one. Trying to run that compression on pump gas with a say 234 @ .050 it wont work since it's "keeping" more compression, whereas getting a cam int he 250/260 or 260/266 @ .050 will help bleed off a bit and keep you plenty safe. Mine was 11.8:1 since the 13.5:1 slugs were deeply nestled in the block, ran car and car with juice on 93 octane. 34* total timing and pulled back 6* when using the 150shot. Plugs always looked great, no pepper or "wear" on electrodes..even on tear down, the combustion stains looked perfect in the chambers and the slugs- nothing to ever say hey, you better up the fuel a bit.

but it's more than compression alone that factors into pump or race fuel additive.
 

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My LT1 is about 10.8...(it's a reversed cooling engine..cools the heads first)
I've driven allot on the Power Tour..
it hates the western states gas..mid to high 80's for Premium octane..
you can hear it ping on the hills..I was constantly changing timing in my ECU to correct for it..
I now carry octane boost every time I go out now..
 

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A lot of it is in the piston design and short block set up. Use a flat top instead of a dome piston. Coated pistons help, check the Mahle powerpack series for an excellent off the shelf coated piston. Reduce quench area in the cylinder as much as possible, pistons at zero deck or even a couple thousandths positive. Set deck clearance around 0.038-0.040" for steel rods. With a smallish chamber volume that can get you in the low 11:1 range static and it should be relatively detonation resistant. Cam accordingly.

Personally, have built and run several low to mid 11 ratio combos on the street w/ 89- 91 and no detonation issues. I am in Colorado though and this is one more area where DA does interesting things to an engine.

Good luck.
 

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Discussion Starter #11
Well -- apparently 11 to 1 is not going to be an issue.
It will probably be a flat top 383 with 64-68cc aluminum AFR's.
Don't stop yet -- Thanks for all the input.
 

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Just another data point - 350 ci with factory LT1 pistons (the OLD version of the LT1), small dome, stock newer 1.94 "double hump" iron heads, Comp Cams 280H Magnum hydraulic cam but with 1.6 rockers installed straight up. Cranking compression about 190 psi. Will run on the street with 93 octane pump gas, but if you get on it at all it will ping. I mix 50/50 93 octane with 110 race gas when on the track (which is 100% of the miles lately on this car). I am at sea level too.
 

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like smallblock nova said, the static is only a piece of the pie, overall components will weigh heavily into the equation...cam specs being one. Trying to run that compression on pump gas with a say 234 @ .050 it wont work since it's "keeping" more compression, whereas getting a cam int he 250/260 or 260/266 @ .050 will help bleed off a bit and keep you plenty safe. Mine was 11.8:1 since the 13.5:1 slugs were deeply nestled in the block, ran car and car with juice on 93 octane. 34* total timing and pulled back 6* when using the 150shot. Plugs always looked great, no pepper or "wear" on electrodes..even on tear down, the combustion stains looked perfect in the chambers and the slugs- nothing to ever say hey, you better up the fuel a bit.

but it's more than compression alone that factors into pump or race fuel additive.

Isn't it true you went through holly hell getting the last engine ironed out though? If I remember correctly you had a couple of major failures........
 

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Isn't it true you went through holly hell getting the last engine ironed out though? If I remember correctly you had a couple of major failures........
Between hack machine shops and faulty parts from praised maufacturers...yes, yes I did have a shit ton of problems...and it was'nt for lack of trying to be cheap either, not saying money was no object, but whatever it costs to get it done right, I have and always will pay for...just flat out got fucked, literally that simple.
 

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I'm looking at a 12-900-9 comp cam -- Intake 252 at .050 -- Exh 258 at .050 -- 106 centerline -- .630 lift.
RPM --3500 to 6900. That was chosen with their software Cam Quest - I am going to call them tomorrow.
I want to keep this thing reliable -- should be a torquer.
You still plan on using this cam or have one spec'd out for your combo?
 

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what rpm you plan to shift at? if the power range is to 6900 on a smaller motor i'd figure 65-66 would be all its good for on a 383 but i could be wrong
 
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