Does Octane Matter???? - Team Camaro Tech
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post #1 of 38 (permalink) Old Apr 10th, 08, 06:35 PM Thread Starter
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DeAngelo
 
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Question Does Octane Matter????

My 9:1 383 runs fine on 93 octane. What would happen if I put 100 octane in it and made no changes? Would it run poorly or hurt anything? Would I have to adjust the fuel mixture screws or alter the timing? Thanks! DeAngelo
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post #2 of 38 (permalink) Old Apr 10th, 08, 06:51 PM
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Re: Does Octane Matter????

Hi, should not be a problem to use a higher Octane in your car and should not have to do any adjustments. I use VP Racing in my cars and mix it up, I think VP is 110 octane but it is expensive though (7.00 per gallon)... Well unless regular gas keeps on going up of course....

I've had 350 small blocks with high and low horse power and Big Block cars with an assortment of configuartions, no problems...




Jeff
69 Verts Big Blocks.
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post #3 of 38 (permalink) Old Apr 10th, 08, 06:54 PM
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Re: Does Octane Matter????

With a compression as low as 9:1 it wouldn't make any difference in how it runs. You wouldn't need to adjust anything as far as I know. Is there any reason to run it on 100?
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post #4 of 38 (permalink) Old Apr 10th, 08, 06:55 PM
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Steps
 
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Re: Does Octane Matter????

I double if you would get any advantage
Power, its unlikely u have the dynamic compreesion ratio to take advantage of the higher octane
Economy, higher the octane, the lower power per volume...and higher the cost for the higher octane
So u althu may get better the $/miles will still be higher

Increase octane and u need to advance due to slower flame front to then get the main 'explosion' about 15 deg atdc

My Spelling is not incorrect...it is creative

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post #5 of 38 (permalink) Old Apr 10th, 08, 06:58 PM Thread Starter
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DeAngelo
 
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Re: Does Octane Matter????

Thanks, Jeff, Steptoe and 69Camaro1! I appreciate the quick responses. Just wanted to be sure because it still isn't running right and I want to adjust the carb but have 100 octane in it right now. Wanted to wait until I put 93 back in it just in case. Was also curious if the higher octane was causing an issue as it is harder to burn I would imagine. I have the timing back at 12 degrees inital and all in at 3000 with a total of 34. It was detonating for some unknown reason after I got it back from a tranny shop. They said they never touched the motor. It was running like a top when I dropped it off to them. It was detonating even at 8 degrees initial timing after I got it back.Then I put 100 octane it and it stopped detonating but then it started to bog down likle the carb was having problems. I changed my rotor and cap and it was still bogging and sputtering and cutting off occasionally. Someone adjusted the fuel mixture screws and it stopped bogging but it still had a detonation-type or "breakdown" issue at rpm's higher than 4 grand or so. It ran A LOT better. I was hoping the new plugs would stop the "breaking up". Well, I just finished adding new plugs. It still bogs and hesitates I figured that I would run the 100 octane down to empty and refill with 93 octane and adjust the fuel mixture again. I am at a loss and no one can solve my problem. VA Beach is not know for great hot rod shops in my opinion. Too bad I don't live in southern California where they are abundant. Thanks! D

Last edited by Deangelo66; Apr 10th, 08 at 07:10 PM.
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post #6 of 38 (permalink) Old Apr 10th, 08, 07:14 PM
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Re: Does Octane Matter????

What was done at the tranny shop and what gears do you have in rear? Regardless, make sure you take the vacuum line from your distributer off and
then set it to 12 or higher... You can leave the vacuum advance off for testing.... and take the car out for a ride.

What carb do you have, 750 double pump, make sure that darn choke is not in the way....
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post #7 of 38 (permalink) Old Apr 10th, 08, 07:40 PM Thread Starter
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DeAngelo
 
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Re: Does Octane Matter????

I don't have a vacuum as it is an MSD distributor (model 8360 ready to run). And I have a 700r4 so I dont have a vacuum for that either as it has a TV cable. I have a Holley 770 Avneger (vacuum secondaries). The tranny shop just replaced the 700r4 with another 700r4. The rear is a 3.73 posi. I don't know why it started running like crap. And I took it back and the ycouldn't stop the detonating so I put 100 octane in it and it stopped detonating but started to bog and sputter after 3 grand.
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post #8 of 38 (permalink) Old Apr 10th, 08, 07:56 PM
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Hank
 
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Re: Does Octane Matter????

You can have too much octane that can slow down your car.
Not likely in your situation though.
My 65 SS Malibu SBC 350 had 8.5-1 compression & I filled it up w/100 low lead avaiation fuel,it ran much slower than it did w/87 pump gas.

MBHD

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post #9 of 38 (permalink) Old Apr 10th, 08, 07:58 PM Thread Starter
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DeAngelo
 
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Re: Does Octane Matter????

Hmmm. I still am at a loss as to why it is running like crap. Only thing left is the carb.
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post #10 of 38 (permalink) Old Apr 11th, 08, 12:13 AM
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Hank
 
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Re: Does Octane Matter????

Sometimes you can get some bad gas.
Sump your tank & start w/a fresh couple of gallons.
Some vacuum carbs just do not seem to run that great compared to a nice double pumper.
Do you have any other carbs to try out?

MBHD

Chevy 250 turbo EFI
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post #11 of 38 (permalink) Old Apr 11th, 08, 05:20 AM
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Camarodude67
 
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Re: Does Octane Matter????

Yes, good sugestions, fresh gas would help and 383 stroker recommendations is for a 750 Double Pump, I bought a Professionally rebuilt one for racing applications and the my 350 450HP motor ran awesome, like day and night... I had 11.5 to compression so had to run high octane but should not matter in your case...

Jeff G.
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post #12 of 38 (permalink) Old Apr 11th, 08, 05:28 AM Thread Starter
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DeAngelo
 
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Re: Does Octane Matter????

Thx for the ideas. And this is the 3rd tank of gas. And it ran like a top when I took it in for the tranny swap. That's why I am doubtful it is the gas. And the current tank was filled with 100 octane. And I wish I had another carb to swap it out. Thanks again, D
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post #13 of 38 (permalink) Old Apr 11th, 08, 06:00 AM
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Gary
 
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Re: Does Octane Matter????

Back to the octane issue.
Octane rating is basically a fuel's degree of refinement. The more refined, the higher the octane and the higher compression you can run without detonation. Assuming a combo is optimized with timing and carburetion, you can run pi$$ gas with low compression but if you try to run that same stuff in a 15:1 race engine, it'll detonate itself to death. One side effect of the refinement process is that the higher the octane, the slower the burn. So, if you have a 9:1 engine that's happy on 87 octane, it'll actually make less power on 110 since it takes longer for the flame front to burn across the piston top.

Later model cars can make more power with higher octane, though. The computer controls timing and it'll push timing as far as it can without detonation. You will make a bit more power on higher octane with these engines, but not past about 93. It's not instant, either, it takes time for the computer to relearn the new fuel and timing scheme.

Gary Adrian
FCS Harmony Racing

Momma always told me not to look into the eyes of the sun.
"But momma, that's where the fun is!"
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post #14 of 38 (permalink) Old Apr 11th, 08, 06:38 AM
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Camarodude67
 
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Re: Does Octane Matter????

So in this case, sounds like it Ocatane does matter?... Looks like per this thread should put back 93... Keep in mind my config was 350, 450HP, 11.5 to 1 compression, Solid Cam, Holley Double Pump Racing Carb, 18 degress advance, 3500 stall and 4:56 rear and this car ran like a raped ape.... When I dropped the timing my car would not run at all....
or total loss of power....

That is why Busted Knuckles is "Senior Tech"...





Jeff G.
69 Verts...
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post #15 of 38 (permalink) Old Apr 11th, 08, 09:45 AM
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Gary
 
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Re: Does Octane Matter????

"Senior Tech" means I'm an old fart .
I'd probably start with mixing, don't get too much fuel at a time. With that compression, I don't think I'd drop it below premium.
Timing has as much or more to do with performance than anything else. When I thought I wanted a badass street/strip ride, my machinist suggested I build it as big as I could, then take timing out and slowly put it back in as I worked out the suspension issues. Those issues are easier to work on at the point where they start to appear, power-wise, than trying to get it all sorted out at once under full power.

Gary Adrian
FCS Harmony Racing

Momma always told me not to look into the eyes of the sun.
"But momma, that's where the fun is!"
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