JMon

As much as I hate to say it, I wouldn’t mind a little less HP if I could use 93 octane. (I’m just using the car in DEs right now). 2001 996. It has a 3.8 (Upgraded from a 3.6) running Bosch 3.1

Is the reason for the 98 octane just due to timing, or other issues such as compression ratios etc? Someone mentioned that running 93 would tear the engine up.

Also someone mentioned something about wiring up a switch to one of the pins on the ecu that changes the fuel consumption. Is it possible to enter more than one program into the computer and switch (Maybe between a 98 octane map and a 93 octane map)

Leigh2

I have a friend with an ex-Farnbacher Loles 6 cup with programs for different octane levels so it can be done. Not sure how though but it's out there...
FYI my 3.6 L 2007 7GT3 race car had 386 RWHP on 91 octane pump gas, my 3.6 L 2009 cup had 381 RWHP with 98 octane.

wpgt3cup

you will probably have to change out our plugs for cooler ones to prevent pre detonation and toasting your valves.

we ran too low octane once (93 instead of 98 +) and the pre detonation exploded the spark plug tips which then the pieces of porcelain broke a valve and scored the cylinder walls.....

FYI what could happen

mobonic

exactly ^^

The cheaper gas maybe cost you in the end.

Only way to be sure is to have a custom map made and thats hard with these stock ecu's

J richard

In some locals you can't get 100 only 110, which is more than you need, you can blend 91/110 to hit your 100 octane needed...

JMon

I thought about the "blend" of the 110 and 91 or something like that but here, 98 is unleaded, 110 is leaded. I'm not sure what running leaded will do.

So if I can get ahold of the correct program and correct plugs I should be ok? Anything else to consider? Any possibility of issues due to compression ratios or anything like that?

Do these cars lack a knock sensor and subsequent feedback+adjustment loop, or do they run a fixed map?

Now normal street GT3s run 93 octane. What is the fundamental difference between the engines?

Leigh2, can you possibly put me in contact with the guy that has the programs? PM of info sent.

DrJupeman

I thought the cars were spec'd for 98 RON gas (Porsche's literature for a '03 Cup says "98 ROZ Super Plus bleifrei"), same as the street GT3s. 98 RON is roughly the same as 93 in the US (where we use the (RON+MON)/2 for octane ratings and MON is typically 10 points lower than RON). If you can find a place with 94 octane, even better. Blending 100 with 93/94 would give a fine margin for error.

I am no expert, but I think for DE time in less than hot weather, you should be fine on pump gas*. (Flame suit on!)

Disclaimer: I run 93 pump gas in my 964 Cup with a compression ratio just a few ticks lower than early 996 Cups (not sure what your 3.8 is set to). The Porsche spec for gas in my 964 Cup was also 98 RON.

I did run a 100/93 mix in my Turbo 3.6 for track/race use as the turbos, obviously, crank up effective compression and I wanted some margin of error, particularly on hot days.

I do not think you want to run leaded assuming your car has cats.

I welcome education myself if my perspective is patently wrong.


*ethanol blend gas may be a whole other reason to go to 100 race gas without ethanol, but I don't know. If I recall, the ethanol actually boosts the octane, but can cause havoc with other engine bits that weren't designed for it.

analogmike

I agree with Charlie, the 98 RON can easily be achieved with a little race gas mixed with 93 octane (RON+MON)/2 pump gas.

Even the unleaded race gas we have here in the USA has ethanol in it

DrJupeman

Veloce Raptor

I know several folks who run 93 pump gas RON + MON)/2 in 6 Cups designed for 98 RON...

fstockcarrera

I have mixed 50/50 with 93 and 100 but question the wisdom of this especially on race weekends. You are really only saving a $100 in gas a day over all 93. If that matters I would think that you have the wrong car.
imo

DrJupeman

It is cheap in the scheme of things...

analogmike

Very true, even though I think it's very safe I always run race gas.

J richard

Not a question of cost, more of availability. 93 is hard to find locally, 91/ethanol blend most prevelant. There is only one station that carries race gas unless you buy a drum. The option there is 100 for $7gal or 110 for $12. So for the upcoming weekend I have three days probably 60m/110m/125minutes of run time. So 295m/(.2 gal a minute) means roughly 60-70 gallons of fuel. Fill the tank and I still need a pile of jugs to carry the remainder, if I carry down only 100 or 110 and mix with local 91 then I'm not carrying all that gas. In the end the cost is about the same.

Petevb

Between 100 and 94 or 91 is more a matter of safety and longevity than power output. The knock sensor alone won't prevent engine damage if you run too little octane, though it's a trangulation of conditions (heat, octane, engine condition) that's most likely to get you.

Re-tuned, my '06 made 350 whp on 91 tuning on the safe side. 380 whp on 100. The 3.1 ECU can take three maps you can toggle between to allow for different grade fuels, but the only one program will be optimised, the other two will be make less power than they otherwise could. With a program optimised for 91, 94 made 365, it probably could have made close to 380 if it was optimized for that. So a big difference in my motor between 91 and 94, then it flattens out but you continue to get more safety margin as you run higher octane. I'd always use 100 if I could get my hands on it, and believe it's false economy not to.

PMNA doesn't condone the programing of cup cars to prevent the posibility of cheating. I believe I was granted an exemption as my motor isn't actually in a cup car.