2003 S600

I noticed my timing is being pulled big time at wot, it goes into +3 to +5. At cruising with no gas pedal movement it is -25 to -30 TDC. I also noticed a pinging sound for a second when I floor it. I have Kleemann tune so boost now goes to 22.3 psi max. I put in 10 galons of 100 octane 76 race gas with about 10 or more galons of 91 octane gas in tank, so total octane is around 95. Will timing advance with higher octane to get more power due to anti-knock octane level?

JAYCL600

depends on the tune....i personally have never seen any improvement in using race gas with my specific application

hooleyboy

I'm a fan of saying 100oct will had some power due to slight timing advance. Its my my understanding that MB's will learn up to about 95oct with out tuning for it.

This may not fit your problem, However we just had a s600 on the dyno Friday that was also pulling timing. The dyno results showed very inconsistent runs, along with random power spikes and spots of time being pulled. It lead us to point the finger at a bad Intercooler pump.

Adding Race fuel will help the car from knocking, Thats if its an octane of fuel style knock.

If your situation sounds like this. Then I would look into checking out the IC pump.

Quadcammer

this whole "learning" of fuel is bizarre for me.

The car has no idea what fuel is in the car with the exception of pulling timing if the knock sensor is active. How would it know?

Furthermore, race fuel had a different stoich a/f ratio, which I'm pretty sure the computer is not adjusting for.

hooleyboy

Adding fuel and subtracting fuel is also controlled by the o2 sensors. The o2 sensors will see that race fuel is not burning completely. So it will pull fuel and lean out the mixture.

It will also work exactly in the opposite way. If you have an exhaust leak before the o2. It will see there is not enough fuel (false reading) and then add fuel. You will end up with a code for Bank1 or 2 lean condition. On a dyno you will see this "false reading" because your AFR will not be lean it will be rich. From the ECU adding fuel. Typical stuff on a pre-o2 sensor exhaust leak.

Its my basic understanding that the knock sensor will now add the timing up to the point of detecting a very slight knock. Then pull out enough timing to what it thinks is the optimal setting.

I would suspect you could see the addition of race fuel(un-tuned) by checking the fuel trims. I would think they would show a negative percentage of fuel.

For example: If the car reads "0" for long term fuel trim on pump gas. The addition of a slower burning race gas should make that "0" reading go into the negative side... So like -3% or something.

The time it takes for the ECU to adjust to race fuel is not long. A few pulls on a dyno should be enough to mis the gas... then the learning starts.

Quadcammer

Cool, the only trouble is that the car doesn't read from the 02 sensors in open loop. Closed loop, absolutely, but once you put the pedal down, it reads from fuel/timing tables (hence commanded a/f and such) based upon ect, IAT, load, maf ad counts, etc.

Furthermore, in light of the different stoich a/f ratios of race fuel, I'm not sure I'd just want the ecu pulling fuel.

Finally, I highly doubt mb knock sensors would advance timing so far to the edge. From what I know about OEM tuning, its overly rich and the timing advance is quite conservative.

2003 S600

Bank 1 LTFT before adding race gas was +5%, bank 2 was +2%, when accelerating, bank 1 shoots up to +14% and bank 2 to +9%. Is this normal? After race gas added it is about the same, and timing still goes +3 when wot and boost is up to 22 psi. No effect on timing or noticable power increase yet. Intercooler pump is fine, IATs stay below 110F while driving.

Exotic-metal55

You can not compare part throttle timing to anything at WOT.. You can always run a lot higher timing at part throttle..

Are you saying you read +3 - +5 at WOT under the whole rpm range? What data log you using?

Did you test your boost at 22.3 or hear that from somewhere? If your tune has you in that boost range, they may have it pull timing to be safe.. Very common in a tune with high boost..

You should not need race gas.. I would work on making sure your IATS stay cool under a full boost run.. Cooling mods can do way more than race gas..

2003 S600

3000 rpm and above was at that +3-5 timing at wot. Dashdaq gave me all the numbers.

hooleyboy

what does it say for long term fuel trims at idle?

2003 S600

bank 1: 3%
bank 2: 1%

hooleyboy

I want to say it should be zero at both. This could be ok only being 1 and 3 %. It also means the ECU is adding 1% bank 1 and 3% to bank 2. It could be a plug one of 24 you got. Slightly having an incorrect gap?

I will look into this for ya so I can give you the best advise I can.

2003 S600

Thanks Hooleyboy

Quadcammer

eh, close to zero, but not being zero is ok. any number of environmental factors could cause LTFTs to change.

Could you provide some input on my previous post.

I stick by my argument that the car has no idea whether race gas is in the tank.

2003 S600

You are probably right about everything you said. Except, why would race fuel have diff a/f ratio? density? Most gas is between .7 and .75g/ml I think. What do you mean 0 is not ok but close to 0 is? I think the system is pretty smart though, if running lean, cel will tell you ie. running ethanol e85 without tune for it. I did get some detonation tonight when hitting gas at high iat 150*F and ect 93*C at around 3000rpm where boost spikes big time with Kleemann tune. And that is with 95+ octane still in tank. Who knows?

Vic55

OT but what would happen with my 997TT if swapped 91 oct for 100 oct- one tank.

Im running:

Exhaust
Headers
BRV's
Plenum
91 oct ECU Tune

Would I see benefits immediately or during the tank depletion or none at all since the tune is for 91 oct?

hooleyboy

I 100% know that you will pick up some HP from timing advance. Not nearly as much is you tuned for it. IF you were on a dyno with 91oct and then mixed in 109oct in equal parts you would gain HP. As soon at the gas was mixed into your fuel. You would see your dyno numbers creep up.

We do it all the time at the shop. We have Sanoco 109 on hand. for S&G's people like to toss in a mix of 109 in their 91 to see the gains. These modern cars a smart.

Quadcammer

http://www.highperformancestangs.com...ad.php?p=66934

that should help.

As to the LTFT, what i meant to say was that they do not have to be zero to be normal. Anything close to zero is ok. 1% is a bit high, 3% is quite high, but say 20bps is not a big deal.

Running lean is not hard to figure out. Running race gas though...

From what I know, ethanol has a different volumetric efficiency (i believe thats the correct term) than gasoline, so you will need a whole lot more of it to keep the engine happy, despite the octane rating being over 100 r+m/2

Probably nothing, in fact you may lose power as you will not be burning the fuel as completely.

Running race gas without tuning is a safety measure, not a power enhancing measure.

I stand by my argument that the car has zero clue what the octane is.

Vic55

Well thanks for the replies, two conflicting ones at that. I guess Im gonna try one tank and see what the placebo/butt dyno tells me.

Thericker

Vic, I'm w/Hooley on this 1.... As you know I ran race gas mixtures as well as pure 100 from few pumps in LA (Chesbro exit) in my 600tt before ECU tune...

The stk ECU will adapt in 20 mi or less, I even watched it adapt on previous dyno @ HK motorsport Dynojet started @ 487 rwhp then shot up to 501 rwhp. The demeanor of the car would also change IE burnout from dig w/91 would quickly = ESP nannies & thrtle cut off etc 1/3 way thru red light, after 95-100 oct it was Jeckyl n' Hyde

Burnout from dig after adapted to hi-oct NO esp cntrl nannies thru entire intersection friggin' John Force style baby! very noticeable aggressive power delivery even though net gain couldn't be more than 20-25 rwhp w/OUT being tuned for extra octane. I firmly believe TT's react stronger to hi-oct vs SC'd platforms all else being = IE stock tunes Turbo's love race gas...

I'll be running 105+ oct & Ice reservoir on same DJ I made 501 rwhp 3-4 mo ago while ECU was stk & report findings here I'd be shocked if you didn't notice a solid SOTP increase after 20 mi w/ 100 oct, DooooEEtttttt

Quadcammer

the only reason you'll gain power is if your knock sensors are pulling timing on pump.

MB cannot defy the laws of an ICE.

2003 S600

I still have not noticed any change in timing or power. My LTFT is 6 and 5% now bank 1 and 2.

MRAMG1

BINGO

I would run it in my race car for two reasons.

1. I had an adjustable timing box in my cabin, aka turn the boost retard to zero and run FULL advance.
2. SAFETY, when racing hard, you will NOT always hear the spark rattle, and then its too late

If you car does not need more octane, aka NO rattle, you will NEVER see any gains from running more octane. In fact you will LOOSE a little power do to slower combustion burning as octane is ONLY that, aka slower flame propagation.

However, IF you car is pulling timing because of low octane, NOT high IAT's, then you will see gains.