legacycentral bbs

will an increase of 6 points over premium gas increase the hp in for our turboed engines.

No, at least not directly. Higher octane will lower your chance of knocking. If your car is pinging or knocking you aren't getting full power so going to a higher octane will help with that, but if there's no knock then there's no reason to go with higher octane.

THAWA wrote:No, at least not directly. Higher octane will lower your chance of knocking. If your car is pinging or knocking you aren't getting full power so going to a higher octane will help with that, but if there's no knock then there's no reason to go with higher octane.

Unless you can tweak your computer to advance timing. With race gas or similar really high octane fuel.....you can run it in the car, and the stock computer will adjust timing to utilize it. It may not be immediate, or you may not be getting the best performance out of it, but it'd be some.... Also, it would be best to reset the ECU before hand, so all the computer knows is what it's currently seeing, which is race gas.

I haven't tried high octane fuel in my car, but I've heard from several different people that their turboed cars were noticeably quicker with it. I think legacy92ej22t said something about once using aviation fuel in his car and how it made more power.

The standard answer with naturally aspirated cars is that octane levels higher than what the manufacturer specifies won't do anything. With turbos, though, it will. The best pump gas you can buy isn't really good enough for a turbo, which is why engines have to retard timing and increase fueling so much on boost.

There is some room for even the stock maps to advance timing beyond what it usually does even on pump gas, so like Josh said, it should be able to perform better with better fuel particularly if you reset the ECU first. A proper remap should make the difference much bigger.

learns omething new everyday

It seems to me that there would be a point where an increase in octane wouldn't do much performance wise.

Be that at 115 or 200, I have no idea. But it seems to me that fuel can only burn so completely and cleanly and evenly before the differences aren't noticeable and the ECU runs consistantly. The higher you go, the less you'd notice the differences, it would seem, but the differences would be there.

Might not make more power, but would DEFINATELY run "better".

Oh, and don't spill octane booster on your paint. KILLS the clearcoat apparently.

I doubt you'd net any noticeable benefits on a stock car, honestly.

Obviously there will be a limit....if you have too high an octane rating....your engine won't be able to ignite the fuel.....sorta like diesel fuel needs extremely high pressure to ignite.

The key to the octane thing is on a stock car with stock engine management....the gains from octane aren't going to be that great. On a n/a car.....there pretty much are no gains. (my car however does seem to run better on 89 vs 87) On a turbo car the gains are typically higher, especially if you have cranked up the boost. The reason being is the stock management isn't designed to run that high, and does adjust to compensate for the extra heat that is generated.....it backs off timing. When you use higher octane the car can adjust timing forward a little more.

Legacy777 wrote:my car however does seem to run better on 89 vs 87

As does mine, probably because our cars are older and there is some carbon buildup in the combustion chamber that won't come loose without tearing the engine down.

But as for the octane discussion, it's pretty easy to summarize. Anyone feel free to correct anything I'm about to say:

The higher octane you have, the more energy is required to combust it. In truth, most of the energy used to combust the gas in the cylinder actually comes from the heat of the engine and the compression stroke. We'll call this "ambient" energy for the sake of discussion. The spark plug only "puts the icing on the cake", in other words, the gas is very close to combustion before the plug even fires.

Depending on how your engine is tuned, more or less of that "ambient" energy is used to combust the fuel. Cars with high amounts of ambient energy are cars with high compression ratios, or forced induction, etc. If you use a gas that combusts too easily (i.e. low octane gas), the fuel will fire before it's supposed to, which is the #1 cause of engine damage and failure. This is why you see rods get thrown through blocks.

Engines designed for everyday street use, with lower compression ratios, natural induction, etc. don't have as much of this ambient energy. So if you were to put a gas that uses too much energy to combust into this engine (i.e. high octane gas), the fuel will not combust as quickly or as efficiently. It would only cause the engine to lose power and possibly increase pollution due to incomplete combustion.

This raises an interesting question, then. What if I put high octane race fuel or even aviation in a WWI or prewar car? They had very low compression ratios so I wonder if they could run on it. I won't be attending any shows with cars like that for a while, so I hope I remember to ask if nobody here knows.

And don't say they used leaded gas - that didn't come in until just after and is a whole other OT story that involves me ranting about evil big business...

Steve