dhasselhoff

I have a 2006C4s. I drive the poop out of it. Has 23000 miles at least 20000 of them very hard. My friend and I were at a gas station with 100 octane gas. So, I figured, what the heck. The engine reves smoother, is way less apt to stall without the perfect launch, pulls harder, like a lot harder, has way less exhaust filth on the tail pipes and I went from 16.4mpg to 20.3mpg while driving harder because it was fun.

My question is, is this normal, or could my car be having problems on 92 octane. I'm in California by the way. My firends theory is that the gas also doesn't have the emissions crap in it.

Anyway, would love some feedback. I almost hope my car is broken, otherwise I'm spending 6 bucks a gallon on gas from now on.

Joe

Dr. No

Try a blend of 2/3 91 oct and 1/3 100 oct and see how you like that. I don't think the engine management system is designed to take advantage of anything north of 93 octane. The jump in MPG doesn't make any sense to me however.

Coochas

My understanding is that without altering air/fuel ratios and timing that higher octane will not do much if anything. Many ECU reprograms feature serial port switchers (e.g. Revo SPS or GIAC Flashloader) which you plug into your OBDII port that alter timing and fuel/air based on what level of octane you're running.

dhasselhoff

That is what I'm worried about. The difference is so signifigant that I'm afraid maybe I'm getting pre-detonation when on normal fuel and the o2 sensor is modifing the timing on it. And, perhaps that with 100 octane my car is running as advertised. The change was considered signifigant by 3 different people. Like, holy crap, better.

Rick in Colorado

I agree. Another (cheaper) option is to add toluene to standard premium fuel. You can get it a paint supply shops. And...you don't have to visit the 100 octane station every time you fill up.

zumaron

I've had good results mixing 91 & 100.

Here's some light reading on fuel: http://www.rennsportsystems.com/2a.html

PAULSPEED

Hi,
The racing gas should clean the top of the pistons. I
run a little now and then and can see the difference on
the exhaust tips. The racing gas can eat up rubber parts.
If you run racing gas, then do not let the car sit. Use regular
gas if you go on a vacation.
Paul

spiderv6

If you are stalling the car under normal conditions or without a "perfect launch" (whatever that is), then you are doing something wrong with your driving technique.

Dave07997S

That is the case unless you live in Ca. in which you can only get 91 octane, and it's crappy 91 at that. You can see definite improvement by blending a 3-4 gallons of racing unleaded. I know I did...

Dave

Edgy01

Many years ago I ran a turbo with ST104 octane additive. It helped to keep engine destroying knocking from trashing the engine. I happened to have a can of it leftover from that car and tried it in my California-fueled 997S. It fully eliminated the knocking that I was getting occasionally with the straight 91 oct. junk that they sell here. You can essentially blend your own fuel by following the earlier guidance of mixing some in. But as you have already read, putting in more than needed is just a waste of money. The engine won't be able to exploit it. You will get better mileage with the better octane. This has been an economic trade off for many years,--pay more for the fuel, but get better mileage. If you do a cost study on that you can determine whether the additional mileage justifies the additional expense of the higher priced fuel. For routine street driving the 91 octane will suffice. If you're heading to a track event or even something a bit more challenging you might want to slip in about 2 gallons of the higher stuff to round out the tank. You will immediately see the difference. I am certain that if you put these cars on a dyno will will find them performing considerably shy of 355ps. It's the octane that you're missing that is robbing you of that. I suspect it's really performing like a 325ps engine on the straight 91. My 1981 turbo was roughly around 270 ps and I swear it seemed faster than this 3.8 liter 355ps engine. Perhaps these are closer to 325 than 355 with the reduced octane available.

When picking up my car in Europe last summer for 3200 miles of Euro driving the factory suggested that I run it on the super found over there,--but not on the ultra high stuff as the engine would not even notice it, much less exploit it. It would be simply a waste of money. With the super over there already at $6.50 a gallon I didn't question them!

Dave07997S

What I notice with the 997S on dynojet's is that here in Ca. on 91 they rarely break 300rwhp, while back east where 93 octane is readily available I've seen stock dyno's in the 315rwhp range...so you can definitely be off 10-15hp because of the crap we sell here. I blend in 3 gallons of 104 sunoco unleaded...the car runs great.

Dave

Moogle

The car is not programmed in a manner that it can take advantage of fuel higher than 93 octane (MON/RON)/2 method.

100 octane will give no different performance than 93 except maybe a cleaner burn and less engine wear. The difference is likely because you were using lower than 93.

drmarkp

Or the placebo effect .....

Moogle

That's probably it.

Dave07997S

Actually running to much octane can slow the car down...100 straight octane is a total waste. Now if you get software that can use this, it will be a whole different story.

Dave