sound 8

I know I keep banging on about it, BUT I was at some local tuners to day, they were re mapping an MB diesel, I got talking to one of the technicians and he said 560 was possible if I used very high octane fuel. He said my cars ECU would know what type of fuel I had put in and would alter ignition and other parameters to stop engine damage. However it would also recognize high octane fuel and alter parameters to improve BHP. He said from bad to good octane could be 15-20 bhp. Now with all that snow I have only just started to open up my car, and it feels good, very good.
Please don't reply with a criticism, but I'm open to logical answers against this.
And No, I am not going to Atlanta to be yanked.

Benz-O-Rama

**SIGH**

Adding octane will not improve performance on a car not specifically tuned for it. Search on here, it has been discussed ad nauseum.

Here's a little test that 5th gear did too.

http://video.google.com/videoplay?do...2408751432237#

sound 8

So what you are saying is that high octane fuel is a waste of time, and if I put 91 octane in my car there would be no difference.
Answer please!

Benz-O-Rama

Not sure about the UK cars, but the US cars are tuned for maximum performance at a minimum of 91 octane. If you run less than that, your car's knock sensor will adjust timing accordingly and your HP will go down. But running 103 octane will gain you zero increase over 91 octane, unless specifically tuned for higher octane fuel.

TMC M5

I believe you have 99 RON available in the UK which would be about 93-94 AKI octane here in the US. It depends on how the tune was coded. Did they advance the timing to take advantage of the higher octane gas.... did the person who tuned the car tell you to put higher octane gas in the car?

In talking to tuners who tune cars for both US and world-wide applications, they generally feel that there isn't much room between 91 and 93 octane to "tune". They felt that the car's knock sensors may boost the timing by a very marginal increment. The major increases will be seen by creating a tune that is dialed in for race gas. Race gas such as Sunoco 260GT unleaded is 100 AKI octane (105 RON) and has a denser specific gravity compared to its 93 Ultra. You can see significant advances in timing, especially on forced induction applications without worrying about engine knocking/detontation.

Tom

Thericker

I gotta differ w/ya on this, I've seen definite seat of the pants increase EVERY time I use 93+ mix vs straight CA 91 ****. I took it further & have documented a valid 15-20 rwhp gain on a DynoJet (2) times on (2) different occasions as it adapted during the dyno runs (need minimum of 15-20 miles to adapt to higher octane in my exp)

Now, I will agree our CA cars are force fed 91 crap gas, when given 93+ it indeed adapts & gains power, after 93-94 octane the car will NOT gain anymore HP/timing/etc UNLESS specifically tuned for it. In Sound8's case they already run 93+ gas, & ZERO gains are to be had UNLESS he-she gets it tuned w/dedicated High oct tune.

(Turbo/Supercharged cars benefit much more from High Octane vs N/A variants)

Benz-O-Rama

Yep, we're saying the same thing. 91 California moon shine to 93, the car will see a slight increase. Being in Maryland, I can get 93 at 7-11, no lie. I should have stated above on 93 octane.

Sound8 is thinking he can just put in race fuel, or octane boost and see is phantom 560hp finally come to light. Not happening.

sound 8

I am confused

It seems some members say it does, some it doesn't.
Nobody has answered my question about the ECU detecting high octane fuel
and adjusting things like ignition, surely this must give a little extra.

A few years ago I had a Subaru, it ran on 99 Ron, when visiting a remote part of the UK I could only get 95 Ron. The car drove awfully, flat as a pancake until I used up a tankfull, when I changed back to 99Ron it was like having a stage one tune.
One of the reasons I ran 99 in the Subaru was to stop detonation, I never expected it to make so much difference to performance.
Maybe high octane matters less on a nat *** engine, I'm sue Tom can answer that one.

TMC M5

If your tune is designed to take advantage of higher octane gas (which I am pretty sure it does), then yes, you will see some gains. With a naturally aspirated car, all the ECU tuning is doing is advancing the timing and opening up the throttle faster. The advancing of the timing ties into using a better quality of gas, otherwise the knock sensors will retard timing if you are putting p!$$ water in your car. This is why I asked you if your tuner told you to use higher octane gas. But that is where all your gains (along with throttle openning quicker) are coming from...so it really isn't in addition to your ECU tune..it is complimenting the ECU tune.

Now on a stock car from the factory will higher octane gas help performance? It depends on the type of car and the knock sensors. Think of it as more like how much power do you lose from using lower quality gas. The car may incrementally increase hp output up to the maximum timing allowed. If you use lower quality gas, it is likely that the ECU will pull the timing if it senses any knocks. So if you use the better quality gas, it is maximizing the hp available. Now on turbo cars, the maximum timing may be set higher...and also the knock sensors may be set at the highest sensitivity. So you kind of get a huge deviation when using different qualities of gas (the lower the octane, the more you lose in comparison to a N/A engine).

Tom

sound 8

Thanks very much
Basically then there is an argument for high octane giving more power albeit a very small increase. I have always put as high as I can get octane in my Turbo cars, I did think though this was allowing me to run more boost without detonation, I couldn't see the benefit it a nat *** engine, although in my petrol cap it states minimum 98 ron.

Carl Lassiter

There is certainly a benefit on NA, but like FI, there is a point where increasing the grade will do nothing but make your wallet lighter.

As Ricker says, for some bizarre reason we only get a max of 91 here in cali (race fuel excluded). The Sl63, 65, 600, M5 etc can run on a minimum of 91AKI (which is the same as the UKs 95RON) but maximum power is not produced as the aforementioned vehicles are optimized to run on 93 AKI (97/98/99RON). That's why it says "minimum 91" and "recommended 93" or words to that effect by the gas cap and/or in the manual. AKI stands for anti-knocking index and is described well by Tom. The difference in power between 91 and 93 is subject to opinion, but is likely somewhere around 10-20whp as stated previously.

Anything above this will only return benefit if the car is tuned to run on it. So, in short, always put the best available street gas (up to 99RON) in your SL in order to retain every last bit of power and keep things running well.

Sunir

In the US from what I have observed the east coast has 93 -94 octane...the middle of the country (Oklahoma, West Arkansas, Amerillo TX, New Mexico) all have 90 octane at off hwy stations...and then AZ and Cali have 91 ...

the middle states would make me cringe Cali and AZ have the nicer weather...east coast has the better fuel lol