crhait

I have an opportunity to put 5 gallons or so of 104 in my tank this weekend.(stock E55) Any advise, should I or not? Is this a stupid idea or could it be fun? Any thoughts of possible damage?

Thanks.

stevebez

It will not cause any damage ... but your ECU may need time to adapt. Also the stock mapping only caters for RON of 98 max I believe so to get the full benefit you will need to have a remap done specifically for this fuel. Thats partly the reason some have been disappointed with going race gas on their E's - the mapping is just not wide enough.

All that basically happens is the ECU is able to advance timing more with higher RON gas giving higher complression and more power. But with stock mapping there is a limit to how much it can advance timing as a safe guard.

Give it a try though but dont expect it to be WOW at the get go the ecu will need some time to adapt anyway.

Rgds Steve.

Grumpy666

Mix it with 8-10 gallons of 91 octane and then drive the car aggressively for a while. This will give you about 95-97 octane. Once the ECU adapts, the engine will make the most available power for your current configuration. If you increase the octane rating from this point, you will start to lose power.

stevebez

Grumpy666 - can you explain why power will drop and not plateua?

Rgds Steve.

Grumpy666

For a given octane rating, there is an optimum timing setting that will cause the maximum cylinder pressure to occur at the proper point of the combustion process. This point is between 0 and 15 degrees ATDC of the power stroke. If the timing is advanced too far, the maximum pressure occurs before the piston reaches TDC and the engine has to work against that force, which causes it to lose power. If the timing is not advanced far enough, the piston is already traveling down the cylinder when peak pressure occurs, which also results in reduced power.

Octane rating is another way of saying resistance to burning. The higher the octane rating, the slower the burn. If your engine is timed correctly for the octane rating of the fuel you're using, it is making maximum power. If you now increase the octane rating of the fuel, the combustion process will burn slower, and the maximum cyclinder pressure will occur later in the cycle. This is the same as the retarded timing scenario above.

stevebez

OK thanks - makes sense. I always thought higher octane meant resistance to igniting - but once ignited burnt quickly.

Rgds Steve.

crhait

Thanks. I'll give it a try.

Marcus Frost

Have done this already, Mercedes simply does not leave any room in their programming to take advantage of much higher than 93 octane. I've had trouble starting the car on multiple occasions with 104 in the tank too, seems like the ignition system has some trouble lighting up the 104 on cold starts.

It's a waste of money, saw absolutely no improvements with my stock car. Kleemann/etc cars would possibly see a benefit.

-m

crhait

thanks much for that info. I may not try then in the E55. what do you guys think if I put it in my M3? same story? Iam getting it (the 104) for FREE!

SoxFan

This thing about Octane...?

I have to admit to the following:

1) My wife puts 100% regular gas in her Acura MDX, even though they spec for premium gas. We have NEVER noticed a difference.

2) I have, on occaision, put regular gas, in my CLK55, and I have never noticed a difference, although I this was more an oddity than a standard practice...because I am not very mechanical and just don't know...but again, I never noticed and pings or performance issues.

MoMocedes230

If you have a lead foot you would notice a slight difference, but if you are very light then yea you won't notice anything.

SleeperX

Grumpy666,
How much horsespower do you think one could lose by using 100 octane? Interestingly enough, the last time I ran my car at the track, I drove there until the tank was almost empty. Less than an 1/8, maybe 1/16 of a tank. At the track, I put in a little over 1/4 of a tank of 100 octane fuel. My runs were ok, but I thought my trap speeds should have been better. Weather, bad launches, etc were some of the excuses that I have come up with, but after reading this old thread, I am starting to think that my use of 100 octane fuel could have hurt my performance. Amazing! You pay all this money for higher octane fuel, and it actually hurts your performance.

L8Apex

FYI! Make sure the 104 is not leaded, it will destroy your cats!

Mad TKD

Grumpy is right on

In order to really get a benefit from higher octane you will need to have a specific tune done on the ECU for it. MB has not allowed our cars to see this and make a change in the programing. Its all about the timing

But if you had someone make a specific map for this 104 or more octane you probably would see a difference. It will allow you to run more boost safely. Another plus with high octane

My supra was really amazing with race gas, 270rwhp difference. pump was 530s 16psi and 110 unleaded was over 800rwhp at 34psi.

On boosted cars it will make a difference but the fuel and timing maps have to be optimized for it.

Bipasha493

this guy knows his stuff

Grumpy666

OK - I'm not calibrated for your request, so this is basically going to be a rectal extraction. You ended up with about a 3:1 mix of 100/91 and you didn't allow the ECU a chance to adapt, so the effect would be a near-worst-case scenario.

I would say it would be similar to when the car starts to heat soak - somewhere in the neighborhood of 35-50 HP. For an E55, which normally traps at 115 mph, that would translate to about a 2-4 mph loss in trap speed. If you allowed adequate time between passes to cool down, this loss could be less for the last runs.

If the mix was actually closer to 2:1, the loss would probably be closer to 1-3 mph. I would also expect the 1/4 time to be off about a tenth or so, but the biggest impact would occur during the second 1/8 mile.

SleeperX

Grumpy666,
Thanks! As much as 2-4 mph loss? That seems like a lot. It was definitely at least 3:1. Does the ECU really need to adapt to higher octane fuel? And why do you think the biggest impact would be in the second 1/8 mile. Not questioning because I think I actually experienced this. Just curious as to why this occurs.

Grumpy666

A 1/4 mile race is a race of constant acceleration. Lower gears are used In the first half of the race, which make it easier to accelerate the car. Higher gears and increased wind resistance in the second half will make acceleration more difficult. Any loss of power will have the biggest impact when conditions are more difficult.

For your car, every 12-15 HP reduction will result in about a 1 mph loss of trap speed (this is based on a 3200 lb car requiring about 10 HP to change trap speed 1 mph at 110 mph). It's not too hard to envision a 35-50 HP loss of peak power in your car using near-98 octane gas. Especially if you weren't driving hard prior to racing. Your ECU might already have reduced timing due to casual driving. Couple that with the slower-burning fuel and power is down.

I don't have an E55, so the reduced timing comment is based on input from others on this forum stating that resetting the ECU and driving hard seemed to wake up the car. If this isn't valid, then your speed loss might be a little less than 2-4 mph. This may be an interesting experiment to try. Go to the track, add a controlled amount of high-octane gas, reset the ECU, and then race. Do this enough times and you could home in the the maximum octane number the ECU can support.

What were your times/speed compared to what you usually run?

SleeperX

Thanks for the insight!
My best time was a 12.0 at 115.8MPH
I think I should be running mid-high 11s in the 120s though wiht my upgrades. This explains ALOT!! Will try to run on 93 octane next time..