Octane question

[goldminer]

Originally Posted by bmwpowerf1

in australia. 91 octane is not recommended and could damage your engine. it says 98 octane minimum should be used

There are 2 different methods for determining the octane rating of a fuel Research Octane (RON) and Motor Octane(MON). There is about an 8 to 10 point difference between the two. In Australia and Europe it is common practice to show the RON number on the pump whereas in North America the average of the 2 is usually shown. So the numbers are not directly comparable. See:

http://en.wikipedia.org/wiki/Octane_rating

[dcstep]

PencilGeek compares 91 to 100 in this Dyno Thread

Dave

[dcstep]

Originally Posted by r53s65e90

Thanks for the pointer.

In theory and based on the manual using 100 vs using 93 should not make a difference. If it does you could argue that BMW misrepresents their specs to their customers.
.

BMW's specifications are for whatever octane they specify (it's 93 or 94, but I'm not pulling out the book that's out in my car). PG's charts and the chart you posted are at the rear wheels, while BMW's are at the crank.

The M3's ECU adjusts to the octane and advances spark as the octane increase, up to a limit; therefore, the horsepower at 100 octane will exceed the published, claimed hp at 93 octane.

Stock, with 91 octane, my car dynoed at 333 rwhp, but unadjusted for the 5300 foot altitude at the dyno shop it was more like 270 rwhp. That loss is due to physics, not any misrepresentation by BMW.

Adding octane gives us a very inexpensive, temporary hp boost. That's a benefit, not anything misleading.

Dave

[r53s65e90]

Thanks for the insights below!

Originally Posted by dcstep

BMW's specifications are for whatever octane they specify (it's 93 or 94, but I'm not pulling out the book that's out in my car). PG's charts and the chart you posted are at the rear wheels, while BMW's are at the crank.

I understand drive train loss. I posted the graph just to add an extra data point.

The M3's ECU adjusts to the octane and advances spark as the octane increase, up to a limit; therefore, the horsepower at 100 octane will exceed the published, claimed hp at 93 octane.

Where is the limit? 100? 110? 95? Would be nice to find out

[dcstep]

Originally Posted by r53s65e90

Where is the limit? 100? 110? 95? Would be nice to find out

Earlier in this thread, PencilGeek estimated between 100 and 105. You can buy high octane gasoline in your area and there are plenty of dynos, so why don't you check it out? In my area, dyno runs are about $65 per set of three.

I was going to do a dyno run in the next week or two to see what my gain (hp and torque) was from adding the Dinan throttle bodies, Active Autowerke Signature exhaust. My baseline runs were with 91-octane and I was planning to use 100-octane for the followup, to see where I'm at in racing trim. 105-octane is available one pump down from the 100-octane no-lead, so I might just go ahead and spring for that. Given PG's estimate, there could be an advantage in going up one grade.

I'm not interested enough to mix grades and run out one tank and replace it with various octanes, but a tank of 100-octane followed by a tank of 105 would give us a clear indication. Each tank is $120 to $130 around here, so the dyno runs are cheap in comparison.

Dave

[M3Rolly]

Hi, I'm new to this forum as you can all see and this is my first post to the forum. So I hope you all feel honored that i chose this thread for my first post.

Is 100 octane bad for the engine? Doesn't BMW design the M3 engine specifically for 93 AKI. Otherwise, in the user manual it would say maximum 100 AKI allowable. Sorry, I'm not a compression ratio guy, so may be you guys could clarify/elaborate for me.

[dcstep]

Originally Posted by M3Rolly

Hi, I'm new to this forum as you can all see and this is my first post to the forum. So I hope you all feel honored that i chose this thread for my first post.

Is 100 octane bad for the engine? Doesn't BMW design the M3 engine specifically for 93 AKI. Otherwise, in the user manual it would say maximum 100 AKI allowable. Sorry, I'm not a compression ratio guy, so may be you guys could clarify/elaborate for me.

The 93 octane is used in order to facilitate a rating using real world fuel that owners can buy at the corner station, it's not a limit. It will do no harm. If you didn't gain power it would just simply be a waste of money ($8 to $10 per gallon) since the car wouldn't respond to it. The M3 adapts to the extra octane by advancing the timing to just under the point of detonation. The tranny and drivetrain are plenty strong to handle the extra 30 or so rwhp.

Dave

[FStop7]

Originally Posted by TRZ06

Given that the compression on our cars are 12:1, do California drivers get screwed out of a little HP & TQ since we max out at 91 octane?

Luckily, here in the Bay Area, there is a 76 station that offers 100 octane. Would I see any increase in performance from mixing half/half of 100 and 91?

Yes and yes.

[spyderco10]

Very interesting thread. I think there are a few 76s that sell race fuel here, I might have to try this.

[jdogg2000]

Anyone else here try running 100 octane gas or a 50:50 mix of 91 & 100? Just wondering how much of a difference you can actually feel. Now I wish I hadn't filled up my tank a couple days ago, going to try getting some 100 octane at the station nearby once I burn some of this 91 octane off. Will report back...

[pmeloche]

Originally Posted by bmwpowerf1

in australia. 91 octane is not recommended and could damage your engine. it says 98 octane minimum should be used

Australia uses the RON grading. North America uses the (R+M)/2 rating. Our 91 octane rating is equivalent to your 95 octane. Your 98 octane would be equivalent to our 93 octane. In Québec, only Pétro-Canada offers a gasoline with octane rating higher or equal to 93, 94 in this case.

You can easily find 93 octane gasoline in the U.S.

BMW specifies that the engine should run on 93 octane (your 98) but can run on 91 (your 95).

[M3Rolly]

Hey guys for those living in southern cali, you can find octane 100 at these locations:

http://www.m3forum.net/m3forum/showt...ighlight=verne

[FStop7]

That list is a little out of date but a lot of those are still around.

[dcstep]

Ok, interesting news. I tried Chevron-Phillips RaceTek 105 and actually lost power on the dyno (about 5 peak whp). Their site says it's 100% petroleum based, so I thought it'd be hunky dory, but it did indeed lose power vs. 91-octane.

They've also got a 100-octane, but it shows 13 - 19% ethanol, by weight, so I wouldn't try that.

I've found a supplier of Sunoco 260 100-octane (100% petroleum based), so when I finish the current tank of 91-octane I'll run a tank or two of Sunoco and then do a dyno run to compare to the 91-octane.

Dave

[SoCalM3Mang]

Originally Posted by PencilGeek

Almaden Expressway & Foxworthy -- San Jose. 100 Octane is usually about double normal prices.

Here's a list of others:
http://www.davebarton.com/Unleaded_R...ral_and_NorCal

WHOAAAAAAAAAAA! WHAT?????

There is a Union 76 Competition Station on Arroyo Parkway just before the 110 Freeway in Pasadena.

There really are gains to be had here? In combination with an ECU Tune? What is the risk to the engine mixing half .91 and 100 Octane?

"Cautiously Optimistic"!

Details please.

[mvagusta]

Would 115 octane. Hurt the engine?

[dcstep]

Originally Posted by mvagusta

Would 115 octane. Hurt the engine?

I doubt it, BUT I'm almost certain that it'll lose power, based on my experience with 105-octane at 5400-ft above sea level, which lost over 10-hp.

We can't be certain until someone does some dyno runs, but I'm betting that anything over 100-octane at sea level will be wasted money and you'll actually start losing power somewhere not far North of 100.

We're not certain what's happening, but many suspect that the higher octane is delaying ignition past the ideal spot and the engine ECU isn't designed to adjust beyond 100-octane. Nothing bad happens, just you lose power and waste money.

Dave