What are the advantages and disadvantages to 101+ octane "race" fuel. Is this harmful at all to our G's, or would it be OK to use at the track when getting time slips? Does it really help you squeeze out some extra HP? Don't know much about this stuff, so any help is appreciated.
'03 AT Sedan | Brilliant Silver | Willow Leather | Sport | Premium | Aerokit w/Spoiler | Nav
The thing with 101+ is how it burns. Higher compression engines usually require higher octane for more controlled burning conditions, otherwise detonation occurs. The reason people run race gas at the track is for cleaner combustion, and if their engine has modifications that would require such fuel. For example, if you set up your engine timing to be optimal, so that the spark ignights only a couple of degrees from TDC you may need high octane fuel to allow for no premature combustion (one form of detonation).
I hope that does explain it... it always makes sense in my head, but when I type it it sometimes gets confusing.
To be a little more helpful, this is what happens.
When the piston compresses the gas in the cylinder the temperature of the gas increases (simple chemistry - volume decreases, pressure increases, therefore temp increses.) As it increses it is possible for it to ignite prior to the spark. This is pre-detonation, it is an uncontrolled reaction and causes shockwaves within the cylinder which leads to the destruction of pistons and valves and such forth. The high octane gas ignites at a higher temperature, allowing you to increse compression, which increses the pressure put on the gas. So there you go. Welcome a small portion of combustion 101.
On a stock engine you would just be wasting money. A good quality 92-94 octane is all we need in our cars.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Cool Gard. You learn something new every day! Thanks!
'03 AT Sedan | Brilliant Silver | Willow Leather | Sport | Premium | Aerokit w/Spoiler | Nav
Gard, especially with our ECU's it would take several days to realize any gain that may come with higher octane.
If we could prove that our knock sensor was actuating during driving with 91 octane, then a higher octane would help. But ift he knock sensor is not retarding timing during normal driving, you are wasting your money.
Even so we are talking about < 10 hp here (NA, turbo/SC is another story)
With the Technosquare ECU, 91 octane gas is not good enough. I was detonating with Chevron 91 octane gas (CA sucks for good gas). Tossed in some 100 octane to pull the octane level up and the sucker made 4 more HP, but more importantly stopped detonating.
How do you know you had detonation? Was your car pulling timing out? As far a 4hp, that is not much, I can put my car on the dyno and in three pulls have three different readings that vary as much a 10 hp.
We could hear the pinging that the engine was making.
4hp could be a fluke, yes. I want to keep higher octane gas in there to keep my engine safe though. Not being able to push much higher than 5000-5500rpm is pretty lousy.
About the consistency, my first run was 4hp lower than my 2nd run. So I take the performance numbers with a grain of salt. The other G35s that ran were pretty consistent though (+/- 1-2hp) (about 13 of us were there).
The only time higher octane is of any benefit is if the car pings on the recommended grade, the timing is advanced, compression is higher than stock, or the car has forced induction. Pinging occurs when the spark occurs too early in the cycle. If the fuel/air charge is not compressed enough (i.e. harder to light) the charge explodes rather than burning at a controlled rate. The two means of eliminating this condition are to a) use higher octane fuel which is more resistant to ignition and burns slower and cooler (roughly 1 degree per point of octane) or b) retarding the ignition timing. This is exactly what happens when the knock sensor detects pinging. In response, the computer pulls out timing to prevent the pinging.
High octane fuel is a waste of money except for the following situations: Very old motor designed to run on higher octane fuel stock, Modified compression on your stock engine, seriously advanced timing on stock engine, turbo or supercharger on engine and you want to run higher levels of boost, or engine with lot's of miles that has carbon deposits built up in the cylinders which creates hot spots or raised compression which leads to detonation.
"You don't say, 177 in a 70, are you sure officer?"
Interesting comments from Chenga, as I have not heard a collective howl about detonation from everyone using a TS re-flashed ECU and 91. Is that the exception rather than the rule, or have I been missing similar comments?
2004 | 6MTs | Diamond Graphite/Graphite
Upstate NY
AutoForums.com is the premier network of enthusiast-owned
enthusiast-operated automotive communities.
We operate more than 100 automotive forums where our users consult peers for shopping information and advice, and share
experiences and opinions as a community.
What's the deal with race fuel?
"You don't say, 177 in a 70, are you sure officer?"
