fast951

With the difference in Octane rating between the USA and other countries, I think it'll be a good idea to start a thread. We talk about pump gas and race gas. The way the octane is rated can be very misleading. At the same time, we are seeing some additives in the fuel, this WILL affect the way your car runs.

USA
- PUMP GAS as 91oct, 93oct or even 94oct, depending on your location.
- Race gas is 100oct or higher.


Europe or ROW:
- The PUMP GAS is 98oct, this is similar to USA 93oct. DO NOT ASSUME Euro 98oct is close to USA 100oct race gas.

Fuel Additives:
We are starting to see/ notice a trend in changes at the pump. In some areas the fuel is getting additives ( ??-ethanol or ???). The additives are affecting the octane rating. BE WARN, of your car starts to ping at the same boost level, it "might" be the fuel!! Don't ignore it, addrss this issue. Fuel and/or timing as well as boost must be addressed.


BOOST:
Yes, this is the ingredient that keeps us happy! The more boost you run, the higher the octane rating should be to keep detonation in check. To play you have to pay, there is NO WAY around it.

- Don't assume more boost is free, it is not!

- I recommend 15psi on pump gas. Not because you cannot run a bit more boost, but it's for safety. (A wider margin for error). Yes you can run a bit more, but you will be reducing your margin for error. Few people do run 17-18psi on 93oct without a problem. On the street or dyno you get away with it! Still, you are taking a risk.

- Of course you can retard the timing and richen the mixture to run more boost while using the same low octane. However, this is less than ideal. THERE IS NO FREE LUNCH!!! When you retard the timing to run higher boost, the EGTs will go up. Put the car on the track, hammer it a bit while checking the EGTs.. you will not be happy! High EGTs are NOT good for your engine. You are taking a HUGE risk!!! In addition, when you reduce timing, you will give up torque and crisp response...

- DO NOT compare the 951 to other cars. The 951 head design is not detonation firendly.


What are your options?
You want to play, you must pay! There is no way around it. So how do you pay?

- Make sure your car is in top condition
- Always use the highest octane possible. Set your boost accordingly. For more boost add race fuel, octane additive or run water injection. It's less expensive than buying a new engine.
- Run pump gas, turn up the boost and risk blowing up the engine.


There is a correct way and a wrong way! For some reason, at times, the wrong way is more bling-bling and sexier...

This is a bit longer than I intended...

lejams

Not too long at all. Well stated and something that those of us who have mods, in particular those with boost control, cannot have repeated enough. I wonder how much $$$$ cumulatively, people have spent on this board re-building due to lack of attention & discipline when it comes to fuels and tuning, or, not paying to play.

I think it's worth adding that a wideband is invaluable once you start playing, and the addition of EGT monitoring like ST's setup even better for saftey.

Jake951

Regarding ethanol, I've noticed that almost all the gas stations in the Boston area are now pumping gas with 10% ethanol content. I'm not sure exactly when this started but I have observed this recently with some concern. However, 10% ethanol content is "claimed" to be compatible with all vehicles.

My understanding of ethanol is that it actually increases the effective octane rating, i.e. greater knock resistance, but reduces the energy content of the fuel. Therefore you'll get less power from ethanol than from pure gas. The advertised octane ratings for the 10% ethanol fuels remain the same as in the old days (87 for "regular" and 93 for "premium" in my area).

E85 ethanol, which is 85% ethanol, is a different story. Only vehicles specifically designed to run on it (there aren't many and no Porsche models the last time I checked) can use E85. Also, I understand that fuel mileage takes a big hit (something like 20% or more) with E85. Furthermore, there aren't many E85 pumps around, so I think this one is not an issue for most of us.

If my understanding here is incorrect, please jump in and set the record straight.

lart951

John, I think you forgat to address Octane Boosters like Xylol or toluene for those who are running more than 15 psi of boost but do not have access to racing fuel.

fast951

Jake951, you are correct. However with the 10% ethanol, you might experience some knock. This is something that came to our attention not from a 951, but from a M3 race shop we will be tuning for.

Lart, I did not want to get into details on the octane additives/booster . Check second item, "What are your options?" paragraph. Maybe we should start a new thread or expand here about octane boosters.

Duke

In Europe pump gas is rated in RON and you usually have the choice between 95 and 98. In some cases also 96 and Shell have 99 or 100 (depending on country) instead of 98.

An upcoming fuel is E85 which is 85% ethanol and 15% 95 octane. It's classified as an enviromental fuel and more and more factory models are released with the capability to run this fuel.

It needs a totally different tune (fuel and ignition wise) compared to straight gasoline but the gains can be substantial. The drawback is reduced milage.
Many highly modified cars run this fuel (like 900+ bhp 2.2l 5 cyl Audi engines running 2.7 bar of boost etc)

renvagn

Shaken not stired gentleman. It's time to mix if your not already running 100.

944CS

U.S.A takes the Research Octane number and the Motor Octane number of a specific fuel and averages them to get what is displayed on the pumps, the Pump Octane Number.
So if you are in Europe and want to compare your boost levels at specific octane ratings to guys in the U.S.A, you must find out the fuels Research Octane Number, Motor Octane Number, add them together and then divide by two and that is the Octane rating that fuel would have in the U.S.A
(RON + MON)/2=PON

Rogue_Ant

Here is a good thread about E85:

http://forums.coloradoracing.net/ind...owtopic=100251

And a follow-up thread:

http://forums.coloradoracing.net/ind...owtopic=101465


The short answer is that E85 allows for significantly more boost/power but takes a 15-25% hit in fuel mileage because its stoichiometric ratio is approx. 10:1, compaired to gasoline 14.7:1


Rogue

Rogue_Ant

Yes you can run leaded but as you already said it will kill the O2 sensor (eventually).


Rogue

blodstrupmoen

The fuel companies wont give me the Ron numbers , I`ve tried several times .. I only know the lower limits..

Trucho-951

John, do you have any data on what range of intake charge temperatures one might consider safe on pump gas? Say to keep us out of trouble in case we decide to run higher than 15 psi of boost?

Mike1982

Well, not sure how many people measure the intake temp before the engine, but the EGT (exhaust gas temp) is one that I know at less a couple people here measure. I don't know the figures, but I know once you get the EGT up to high, things like to melt!

Rogue_Ant

I'm planning on getting some post-intercooler intake temp data here pretty soon....


Rogue

Jake951

More on ethanol ...

The June 2006 issue of Panorama ran an article about use of the ethanol blended fuel (see page 58). The article strikes a rather cautionary tone, mainly with respect to older Porsches (pre-1980's) which don't have the closed loop O2 sensor control of fuel programming.

The article also says a 10% ethanol fuel has a 94-95 octane rating when blended with 92 octane base gasoline. However, I don't see these higher octane numbers posted at any pumps so I'm not sure what the real octane numbers are. Also the article says that the "heating value" (BTU/gal) of the ethanol blend is about 3% lower than straight gasoline, which is an indicator of the expected loss of power. I suppose the higher octane might allow the use of higher boost on turbo cars, which may more than offset any BTU loss. However, I am definitely not advocating running more boost on ethanol fuels unless I see positive evidence of the benefit.

Anyway the article is worth a read if you have the Panorama issue.