I put 100 octane in Heidi last night and boy does she love it! I went out this morning to start her and this time no stumble! I usually wait about 3 minutes before driving to let her warm up and get past the stumble. I am guessing that the stumble is related to timing retard... I see now why people get addicted to racing fuel!

 

Interesting. I'd love for the stumble in my Cooper to go away. You'd think there would be a fix from MINI by now.

 

I cannot find anything better than 91 octane in Miami! Anyone seen higher than 91 in SE Florida?

I would LOVE to get rid of that stumble.

 

Woah weird. I thought CA was the only place that had nothing higher than 91 as premium. I'm in Orlando right now and premium is all 93 octane. I'm surprised Miami is any different

 

Just out of curiosity when is the "stumble" happening? At idle when cold and you first take off or in the rpm range somehwere? My 2006 MCS hasn't stumbled yet - still on the first tank of fuel!

If it's when your engine is cold and start to drive off and goes away after a few minutes it could basically be carbon build-up on the intake valves. I've seen a photo of a head off of a MCS (don't know the miles) but the pistons and head looked dirty compaired to other cars I've owned. The standard OE lack of an oil trap on these engines only leads to oil into the intake.

If you have carbon build up on the intake valves
When first started cold, the carbon is dry and absorbs the fuel mixture creating a lean condition, this *could* be the cause of the stumble - running lean and race fuel could mask this. When the carbon is saturated, all is well. This is a known condition on many Audi quattros and even happens on my '95 S6. I just need to run more fuel treatment through the tank and it usally clears up after several tank fulls.

MoF, I used to drive a '85 Porsche 944 and recently had to remove the intake runner to replace the heater valve at the back of the head. The intake valves were spot-on clean and this engine NEVER had a stumble problem when cold.

We have 93 octane at Shell, Mobil, Exxon and 94 octane at Sunoco here in Vermont.

 

I don't think people should get the idea that 100 octane will improve performance, because it hardly does, if at all. It's good to use while racing or aggressive tracking as it will help keep the motor cooler at very high revs. and the car will stay lean, but if you are not specifically tuned for it, it does nothing.

Maybe I should back step a bit. Yes, if 91 is the highest octane you use then you just 'might' possibly feel a slight difference in performance with 100. Otherwise those who use 93 will just be wasting their money.

 

my car seems to stumble a lot...it's usually during the change between giving the car light throttle to an increase in throttle. I feel a little (slight) jerking sensation. I was thinking this was normal..but have been questioning it as of late. ...I only use 91 or high gas and only Shell or Exxon fuel.

Is this normal?

 

I just read the entire sticky above in "Beneath the Bonnet" titled, "Is your car stalling upon starting the car". Seems like this could all be tied in together. I'd like to figure out how to *see* what software version on my 2006 week 6 build MCS. Is remember reading a way to do this on the dash to see voltage, etc.

Saakey, I feel the same sensation that you explained to a tee. Only seems to happen in third gear when feathering the throttle but not all the time. I'm only on my first tank of fuel still.

 

AZ has 91 as the highest commonly found. Only two stations in all of Phoenix (5th largest city in the USA) area sells anything higher than 91

 

Yeah it's normal I believe. You just have to be really delicate when applying the throttle or slip the clutch a bit to make acceleration a bit smoother.

 

I'm in daytona and was equally suprised, all 93 around here except for one station carrues 91 as well, I tried the 91 once (was .05 cheaper and within parameters) and the MINI was not happy.
OT: Barnabas are you on SSM at all?

 

Since this doesn't sound like the typical Yo-Yo effect that the Coopers usually see... You should check out this thread from one of our members. It seems to be the same thing that you're experiencing. According to the SA that this member has been to... it's the way she drives the car. I haven't driven or been in the car at all to experience this, but it sounds like she's got a lemon.

Read here

as for the race gas inproving performance... I'd say as mentioned above, unless the car is tuned out, it shouldn't really help that much. I've never experienced the higher octane fuel in my MINI. I'll let you know after AMVIV

 

What are you paying for 100 octane? Around Denver it's $5.51/gal.

 

well can you explain the yo-yo effect a bit more?...I have a tendency to exaggerate the situation...I did say my car seems to stumble a lot..but that's really not the case. It is like a slight hiccup sensation i experience every once in a while. I'm not so concerned about such as the girl with the link you posted. I don't have any other symptoms - car starts just fine, no bad idle, etc... it's certainly nothing i'm feeling is a problem.

 

$5.00/gal at Dayotna International for 98

 

The Yo-Yo chronicles can be found here: https://www.northamericanmotoring.co...ght=chronicles

The girl from our club, has issues with the a hiccup between 10-30 mph... Sounds like that's what you have...

 

I am just a Cooper (non-s) owner, but I am curious what software your ECU has that you are feeling a difference with 100. I'm currently running MTH tuner for 91, but am waiting for a 100 update from Herr Volker Kurch.

 

mine has nothing to do with just 10-30 mph..mine can happen as i'm going down the highway and i let off the gas to slow down (say like in 6th gear) and the rpms drop to around 2500 rpms, so rather than down shift, which sometimes when I'm feeling lazy I do put off, I start to give it some gas and you feel a slight hiccup (or yo-yo) effect - such as the description you just posted from that link.

 

running race gas WILL improve performance....how do I know...NOT FROM A BUTT DYNO....I have data logged test after test...and normal timing is 18-20 degrees with that horrible stuff called 91...but with 100 + octane...timing jusmps to 25-30 degrees and stays there....on car it was at 30 and never droped....ofcourse not...there was no reason to dial back the timing...

if you then tune your car for such fuel you will see even more gains...this is fact not bench racing

 

I agree with Tuls on this one, the improvement in performance from 91 to 100 is HUGE. From the simple fact that timing is no longer pulled, (or at least not pulled as much) power is no longer robbed from the ECU retarding the timing due to detonation. Unfortunately at $4.70 /gal, regular fill ups with 100 octane is not a reality for me.

 

Just pretend you're driving an SUV....LOL....the price is same...for fill up

 

Good point Tuls. I have never ran race gas. I guess you're right... I'm gonna get addicted. I'll see you at the pumps at AMVIV!

 

WOO HOO! at least this is way more fun than an SUV!

 

I already have an F150, I don't have to pretend. thats why I bought the mini!

 

100 octane race gas from union 76 in Honolulu is $7.50 gallon. I use half a tank mixed with our 92 octane premium (at $3.00 gallon) for my MCS with 19 pulley, Giac, JCW injectors, header/cat & Alta CAI but can't say i notice any difference in my lap times. Heard it cools better at high rpm as onasled says. Guess it can't hurt but always wonder if i'm wasting $.