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Discussion Starter · #1 ·
We all know the tragedies of having too low of an octane on a higher compression motor. But can you ever have too high of octane?
 

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To high of a octane will decrease your power if a octane is higher than your engine really needs. Octane is used to slow the burn which if your car does not need anything over 87 octane you could be not only wasting money but costing horsepower.
 
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Discussion Starter · #3 ·
LOL, no no no, I'm talkin about big boy gas. I'm talkin, maybe my motor will run on 93, but what if I want to go to the track and run it on CAM2(110)?
 

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In your particular case I would think that, if it doesn't suffer from pinging or detonation on the 93, that the 110 wouldn't hurt anything but your wallet, but you wouldn't really gain anything either.

What's a gallon of 110-octane going for these days? I know that it was $3.50/gal about 4 years ago at the track I raced at.
 
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Discussion Starter · #5 ·
Well, you'll get more complete combustion and cleaner combustion from it. I just didn't know if it was possible to have too much octane.

A friend of mine went and got some for his car a couple weeks ago and I wanna say it was like around $8 a gallon. And that was at a local gas station(don't ask me why a public gas station has CAM2) so god knows what the track is charging.
 

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speedytang said:
To high of a octane will decrease your power if a octane is higher than your engine really needs. Octane is used to slow the burn which if your car does not need anything over 87 octane you could be not only wasting money but costing horsepower.
Thats right, however, if you advance your ignition timing accordingly, you should see some gains. Afterall, thats what efi engines with knock sensors do, they advance igintion untill they register a knock, then bring it back down slightly.
 

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I'd have to say that you'd only see some real gains if it had to be de-tuned, have some timing pulled, and the dizzy recurved and tweaked a bit to run on pump gas. If that's the case, then putting a performance curve in the dizzy, tuning it "UP" and adding high octane gas will help. OTOH, if you've got a 9:1 street motor with a mild cam, that'll run all day on pump gas without a ping, knock or fart, then IMHO, you'd have a better chance of loosing power than gaining it. I know I was advised NOT to run avgas in my 9.7:1 5.0 because it wouldn't do anything but cost me $$$. Avgas being a good thing or not is a different matter, but I live in BFE, with no race fuel within 65miles, and less than a mile from a small airport :D
 

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Yes. "Octane" rating is the ability of gasoline to RESIST being ignited before the spark plug fires. The higher the octane, the harder it is to light off. One of the reasons you see great big dual magnetos on top fuel dragsters. They need the most spark they can get to get the very high octane fuel they use lit off. (OK, there are other reason too)
On a street car, you can get more power with more compression, a camshaft change, more advanced timing, etc. All stuff that contributes to to detonation. Sustained detonation leads to engine destruction. Period. A simple way to combat the problem is to run a higher octane fuel. You will actually give up some power over using a lower octane fuel but it's way more than offset by the gains to be had with high performance tuning and parts.
For the best power, you should use the lowest octane rated fuel you can while keeping the engine out of detonation. The first sign of detonation is pinging, the last sign is generally big holes in the tops of your pistons.
I remember one magazine (Hot Rod maybe?) got bored enough to dyno a stock car that was happy with 87 octane. They changed its fuel over to 110 octane race gas with no other changes and dynoed it again. In stock form they lost something like 30 horsepower. A hefty hit on a car that didn't make a whole lot of horsepower to begin with. Some minor tuning of the car to make it run better cut the loss to around 25 horsepower on another run. Thus proving using too high an octane fuel can be a bad thing along with a big waste of money. The article's still out there somewhere if someone cares to find it.
Diesel is another animal. Diesel fuel is rated in "cetane". Cetane is a fuel that burns PDQ. Diesel fuel mixes are rated as to how well and quick they ignite compared to cetane. Thus the higher the cetane rating, the more power can be gotten out of the fuel. Diesel cetane ratings are pretty much what most people think is what's going on with octane ratings which are actually the opposite.
 
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