Leaded race gas gas in a modern computer controled car with O2 sensors . 100 octane unleaded is out there, but a waste unless you are running something like FI that would allow you to run a few more pounds of boost without detonation.

 

 

Grumpy is a man of few words.

 

Racing fuel is very expensive ...maybe 5 or 6 times the cost of a 93 Octane...and if you do not have the set up the gas is a waste....... The cost to go faster in a vette is not a cheap fix, it takes money to buy the parts and a experienced vette mechanic to do the job.

 

I run 1/2 pump and 1/2 110 at the track plus a bit of methanol for good measure, but I write a tune to take advantage of it. the 110 is unleaded and expensive. 10.00/gallon. Cheap insurance IMO. I can tell you that the specific gravity of fuels is different from fuel to fuel. If you tune on pump and hit the track on race fuel, it is possible to run lean. Even changing from one race fuel to another should prompt a review of the tune. A car tuned on pump gas will slow down on the track.

 

Some time ago I read in a scientific journal that when you mix high octane gasoline with regular it doesn't average out the way you may think,you would think that for example 5 gals reg and 5 gals hi test 100 octane and 90 octane would yield 95 octane according to this you would need just about 1 gal hi test to 5 parts regular to get 95 octane and the more you mix you get diminishing returns so a 50 50 mis may only yield 96 octane

 

Hmmm, so non-premature detonation is a good thing???

 

Detonation does not occur in an internal combustion engine. Combustion does.

 

uncontrolled combustion can be one of two events ..pre ignition,. when some hot spot ignites the air fuel mixture before the spark plug does could be a red hot piece of carbon in combustion chamber or the spark plug itself the ground electrode getting red hot ...then theres what is usually referred to as detonation that occurs when the air fuel mixture is ignited by the spark p-lug and as the air fuel mixture ignites and the flame front travels across the top of the piston it compresses the remaining air fuel mixturewhich as a result of being compressed instead of burningacross the piston top the remaining mixture explodes....(or detonates) the air fuel mixture is given lead time at speed usually 30 to 40 degrees and it is designed to start as the piston is coming up and completed as the piston crosses top dead center so maximum cylinder pressure is generated to push the piston down with detonation this cycle is disrupted and the uncontrolled combustion occures when the piston is coming up and tries to push the piston basck down in the opposite direction which is bad .The worst part about detonationis it most timesoccurs at hi load and high engine speed and is unnoticed until damage occurs

 

Hopefully the OP with his expensive education has enough common sense to comprehend your explanation.

 

What happens when all the fuel isn't burned in the combustion chamber?

 

thats what the cat converter is for ....excessive fuel ruins cat conv, then cat clogs... your car runs hot.... no power, and you get 8 miles per gallon

 

yeah but before all of that happens, the engine will detonate is the point. I know the emissions system catches the "crap"

 

excessive fuel in itself alone will not cause detonation,as a matter of fact it may help deter detonation...the fuel is consumed when you experience detonation the problem is that the fuel is consumed at the wrong time and in a manner that is counter-productive to making horsepower,although I'm not sure this answers your question or exactly what your point is

 

Detonation or preignition can happen in several ways, the common 2 are:

1) Carbon buildup causes hot spots igniting the fuel before the cylinder is ready.
2) High compression causes "dieseling" where the fuel is ignited from the heat caused by compression (like a diesel engine)-this is the case for High Octane fuel. The higher the octane, the less likely you are to diesel.

 

Octane rating of gasoline is a measure of the antiknock properties of that particular gasoline blend.

Octane has no direct relation to power output. Let me say that again: increasing octane does not increase power.

Premature ignition (aka knock, detonation, etc.) occurs when conditions in the cylinder cause the fuel charge to ignite before the spark ( out of time ignition). This process is similar to dieseling, except that it is premature to the stroke of the engine (which is why it leads to engine failure -- 2 opposing explosive forces acting at the same time on the same parts).

Detonation can be caused by:
1) bad fuel (low octane, water, old age, etc.)
2) too much timing
3) temperature (both cylinder temps, and by extension, temp of the intake charge)
4) compression ratio (really, cylinder pressure is the culprit, but SCR and DCR always get the blame)

These 4 items, though, give you a picture of why and when to use higher octane:
1) the octane rating of your fuel is too low, which results in the combustion of the fuel producing heat instead of power (and therefore more knock by virtue of 3 above)
2) you want to run more timing than your current fuel allows without producing knock
3) something in your build produces too much heat -- too much timing, boost without good intercooling, etc.
4) your engine runs at the big end of the cylinder pressure range -- cam timing, boost, high CR, etc.

Octane helps you produce more power by allowing you to maximize cylinder pressure and timing, while also allowing you to run hotter cylinder temps safely (a by product of higher pressures and more timing). Adding more octane in the absence of more timing, heat, or cylinder pressure will HURT performance rather than boost it.

Excessive fuel (or unburnt fuel) will NOT produce detonation. Backfiring in the exhaust is not premature ignition, it is simply ignition of unspent fuel in the exhaust pipes and, while it may hurt the exhaust components, doesn't impact the engine. In fact, running rich is another method of lowering cylinder temps and combatting detonation-- there's a reason why boosted cars run a lower AFR than NA cars after all. It should also be said that higher octane fuel has nothing to do with running rich. Lead in racing blends will ruin the cats to be sure, but the octane doesn't.

 

Just wondering...what's better...torque or horsepower?

 

Funny, I was wondering if you get more torque or horsepower with premature detonation??

 

Neither, you get LESS. And as an added bonus, you could burn a whole in a piston or worse.

 

Definitely premature average torquepower under the curve is better unless you use a left handed socket on the torque wrench when you installed you rear wheels. In that case, the answer is average octane per pound.