race fuel?

[SPDRCR]

I have to disagree with the consensus so far. I've tried 101 unleaded. I added about 5 gal of 101 to about 1 gal of 92 remaining in the tank (so it mixed to something like 99 octane?).

After resetting the computer (disconnecting the battery) and driving it for a few minutes it was *significantly* stronger. Now, I don't have dyno results or ET from a track so I can't prove it, but I would bet money it gains about 15hp (yes, I can hear the laughter now...)

My understanding of what is going on is that the computer adjusts timing up to the limit of what it can based on the knock sensor. Conversly, it will retard timing if you run lower octane fuel. If octane doesn't matter, then why run 91-92 over 87? The car will still run, the computer will just retard the timing so much it will be a dog and/or it will knock.

BTW, I've tried a K&N panel filter and added a CAT back 2.5" straight exhaust and it made absolutely no difference so I think I'm pretty honest when it comes to identifying real differences verses "sensing" mental differences.

101 octane absolutely made a difference. Just my two cents from my experience.

 

[MP3-Owner]

I have 112 leaded fuel in my car right now. Never got to use it because I snapped an axle. Sometimes I go out and start the car just to smell it. Damn it smells so good.

HAHA! I need to sypher your tank!

 

[twilightprotege]

yes i was under the impression our cars knock sensor adjusts timing in the car to suit the fuel/knocking etc

can anyone confirm this is true or false?

 

[DiscreetSpeed]

yes they do^^^

 

[twilightprotege]

so if they do adjust timing to suit fuel etc, in theory spdrcr should be right (not sure about the 15hp), but there should be gains experienced due to more advanced timing?????

 

[low_psi]

If octane doesn't matter, then why run 91-92 over 87? The car will still run, the computer will just retard the timing so much it will be a dog and/or it will knock.

First, our knock senors are only so good, they can not stop constant detonation.

Secondly, octance DOES matter. You need a higher octane so that the fuel resists pre-ignition in the combustion chamber. If you ran 87 on a turbo car, the fuel would ignite prior to spark and top dead center. Octante relates to how well the fuel can withstand heat without prematurely burning.

Yes, the ecu adjusts fuel/timing due to knock, but it does not adjust it according to octane in a way that would benefit higher octane gas. It only adjusts as a preventative method of keeping minor detonation problems under control. IE: it will retard timing to prevent pre-ignition, but will not advance because of octane

 

[twilightprotege]

damn mazda ignition that adjusts for higher octane would be sweet

 

[low_psi]

yea, its a b**** eh?

 

[SPDRCR]

First, our knock senors are only so good, they can not stop constant detonation.

Secondly, octance DOES matter. You need a higher octane so that the fuel resists pre-ignition in the combustion chamber. If you ran 87 on a turbo car, the fuel would ignite prior to spark and top dead center. Octante relates to how well the fuel can withstand heat without prematurely burning.

agreed.

Yes, the ecu adjusts fuel/timing due to knock, but it does not adjust it according to octane in a way that would benefit higher octane gas.

I disagree. See Chevron Website (at the bottom) it states, "Also, higher octane may provide a performance benefit (better acceleration) in cars equipped with knock sensors. Many late model and high-performance (turbo-charged and supercharged) cars fall into this category."

it will retard timing to prevent pre-ignition, but will not advance because of octane

I disagree. See ecutek link, it uses a Subaru example but it applies to any engine management system (including a stock one like ours) that adjusts timing.

Most of the results I find support my claims and very few suggest otherwise. Additionally, consensus in my little autocross world (including Fuel Management guys at AEM) support my claims.

If those links don't convince you, then there's really nothing else I can do but let you have your opinions...like I said, I don't have the dyno results to prove it, but I'm very sure there are performance gains. They are most noticable at partial throttle. Go buy yourself some race gas for $20 bucks, reset your computer and drive it until you need gas again...you *will* notice a difference...and it's only $20.

 

[low_psi]

good stuff. here's an excerpt from the ecutek link:
At low engine loads, the ignition advance map contains no advance - this is the flat 'valley' of the map. No matter what the quality of fuel, the ECU will never advance the timing above the value in the base map. This is because the engine will not produce further power by advancing the timing - MBT (minimum best timing) has been reached. Advancing the timing further increases the chance of knock and also increases vehicles emissions of hydrocarbons and NOx.

MBT is the lowest value of ignition advance that produces maximum power.

At high engine loads, the advance map contains much larger values. This shows that the timing possible varies greatly with the octane of fuel being used. Under boost, it may not be possible to reach MBT. In other words, the more timing advance that can be run, the higher the engine power output produced - MBT cannot be reached before the engine begins to knock before the plateau is reached. This is where the active ignition timing excels - it allows the ECU to run the highest timing possible without engine knock. This results in high power output, good fuel consumption and low exhaust gas temperatures.


it appears that gains ARE possible, but higher octane gas won't be giving you HUGE gains. maybe a bit noticable, but i still don't think that there is much point in just running race fuel for the hell of it(ie. not raising the boost).

that excerpt states that the ecu will allow for the best timing within the range of ignition(pre-knock), thus making maximum power. i believe this to be true, but adding c16 to a stock MSP won't put you at 250whp just because of timing advances. i just don't see the gains being HUGE from the octane allowing more aggressive timing curves. maybe i'm dumb though

the mp3 has advanced timing, as you know, and in order to support that timing curve, you have to run high octange pump gas... i wish i knew the exact degrees so i could compare the amount of timing to the difference in pumpgas octanes.

 

[twilightprotege]

i could check my idle timing when i get home. our aussie p5's require minimum 95ron octane...i think it's 12degrees btc +- 1 or 2

 

[low_psi]

cool, i think it is 12

 

[twilightprotege]

what's the timing for the US engine?

 

[low_psi]

sorry, i don't know.

for some reason i think the mp3's were advanced 12degrees

 

[twilightprotege]

it should be on a lil sticker under the bonnet which tells you the timing and idle rpm range

 

[arkitek]

Is your car flashed?
If not, then resetting the ECU you will give the the perception of increased power with the hesitation not being there.
Just making sure that this is not the case.

I have to disagree with the consensus so far. I've tried 101 unleaded. I added about 5 gal of 101 to about 1 gal of 92 remaining in the tank (so it mixed to something like 99 octane?).

After resetting the computer (disconnecting the battery) and driving it for a few minutes it was *significantly* stronger. Now, I don't have dyno results or ET from a track so I can't prove it, but I would bet money it gains about 15hp (yes, I can hear the laughter now...)

My understanding of what is going on is that the computer adjusts timing up to the limit of what it can based on the knock sensor. Conversly, it will retard timing if you run lower octane fuel. If octane doesn't matter, then why run 91-92 over 87? The car will still run, the computer will just retard the timing so much it will be a dog and/or it will knock.

BTW, I've tried a K&N panel filter and added a CAT back 2.5" straight exhaust and it made absolutely no difference so I think I'm pretty honest when it comes to identifying real differences verses "sensing" mental differences.

101 octane absolutely made a difference. Just my two cents from my experience.

 

[MSP Chris]

10 degrees BTDC / post-flash here

 

[SPDRCR]

Is your car flashed?

It is now but my experience with race fuel was pre-flash. The hesitation was gone with race gas for sure but the real power was noticeable only after a few miles of driving after (I think) the computer had time to "learn" the fuel/octane.

The most obvious performance gain was mid-RPM under heavy load, i.e. passing on the highway in 5th or 4th. I hardly ever had to downshift to pass because the midrange was so significantly more powerful. Top end seemed to be just as buzzy and quick -- not dramatically different.

I'm very curious to see what happens with race gas now that it's leaner through the mid-range post-flash.

Everyone else should try this -- it's only a few bucks -- I'm curious if you all will get similar results.

 

[NRRfrogmanP5]

mmm smell of gas

 

[MSP Chris]

I dont live near the track and thats where I usually see it for sale, so I am out of luck. Can anyone say Octane Booster? J/P