This was my impression as well.

 

Race fuel will always make your car run better (safer?) in that, it may not ADD power, but you can be assured that you're ECU will not retard timing, thus making LESS power...

 

Your car will make different power levels based on what gas you test with.

Let look at a scenario 1... I own a 996 that will run 93 oct 95% of the time. On 93 octane, the car is tuned so that knock sensor voltages are ~20v and timing retard is ~1-2 degrees with stock knock control enabled in the ecu. (how I tune my ecus)

If you add race gas to the car above, you will see a very minor gain from the gas, less then 10 hps. This is because the ecu is tuned optimally for the octane it is run on. This allows the largest window for safety that the DME can provide. (See testing here https://www.6speedonline.com/forums/...les-knock.html )

Scenario 2 - Now run this same ecu on 91. This DME will now sense more knock activity, and will pull 5-6 dgrees of timing. Measured power will decrease, and head room in your knock control system will be much smaller.

Scenario 3 -Running a slightly de-tuned 91 octane file with slightly less ignition advance. This will result in the same over all timing (requested timing - ingnition retard) yet will increase the over head in your knock control system. Power will be identical because over all timing will be identical.

The factory DME can pull up to 12 degrees of timing (18 in an EPL ecu, due to an extensive code change), you better believe that if you get a bad tank of gas, you will be maxing out the knock control system on in your DME. A DME that cant pull anymore timing + bad gas + boost = large repair bills.


Correct, higher octane will always suppress detonation. In general, we usually recommend to out customers to run at least a mix of race gas at the track.

 

great info. I have read in the past that fuel loses about 1 octane point per month. Premium tends to sit longer than other fuels because most people are cheap, so I basically assume that 91 is really 90 and I add a few gallons of 100 or more to every tank now, to be safe. MY local race fuel supplier does not get a lot of business either so anyone tuning with his gas is likely to have a few points lower than stated.

who's got an octane tester?

 

If a car is tuned for pump gas (certain octane like 91) adding race fuel WILL NOT give you more power unless the car is tuned for what ever octane race gas ur using, in some cases it might even decrease power becaues the timing is off. It will make it "safer" .. but thats about it ur wasting ur money. And if you do add race gas make sure its unleaded.

Water/Methanol kits are a great alternative to raising octane on street cars. You can set it to come on at what ever PSI you want, and with 20% methanol for fuel up top you can reach numbers close to race gas.

 

So your saying that for every tune there is nothing to be gained by adding race fuel? What about a tune that is on the edge with timing at a certain octane and on hot days pulls timing, or when doing many runs and heat soak occurs, will higher octane keep the ecu from pulling timing, thus give you more power than you would have had otherwise?

 

I think you're close. The tune in your ECU is a maximized program for your car. Based on information given by sensors, (MAF, MAP, O2, temp sensors, etc...) the ECU will compensate "down" ( retard timing?)to save itself, but not make more power.
If you use race fuel or any kind of "octane booster" (Meth?), there will no reason for your ECU to retard timing, thus getting you ALL the power you were tuned for.

 

Exactly, that was my thinking. If this isn't defined as giving extra power, then neither is putting better IC's, after all they work on a similar principle, in that they keep things cooler allowing more power production in extreme conditions.

 

True, sort of...

Intercoolers WILL give you more power, as denser (cooler) air holds more fuel...more fuel, more power.

 

ideally, it would be nice to have a file for every octane level that would automatically load itself based on what the ecu reads for fuel.

 

In a perfect world...the guy who figures that out will be rich!!!

Until then, I plan to maximize my custom pump gas tune and have my spare ECU loaded up with a custom MC109 tune...

 

exactly what I plan on having, but will probably rarely use the race tune. ok well maybe once or twice

 

yeah, just a track thing for me...change ECU and tires the night before and go have a blast...

 

If the car has a bunch of modifications and it hasn't been re-tuned where it might be running on the lean side, than race gas will help in that case, and yes on a hot day if the ECU picks up knock than it will reduce timing, but I would think that Porsche has a decent knock sensor so the power loss were talking about is minimal 5-10hp. Its a good idea if your doing a track day because it will keep your power consistent, but other than that spend your money on mods that actually make a noticeable difference.

 

The E46 M3 DME automatically adjusts to the higher octane race fuel. It's been dyno proven. You add the high octane fuel you want, go drive it some, do pulls, then dyno it again and you gain another 20-50whp depending on the octane used... A lot of guys dyno'd 440-450whp pump and 500whp on race gas without ever having to 'switch' to a race file.

Have you guys heard of this?