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View Full Version : octane numbers and HP gains?



Evo442
02-24-2004, 06:33 PM
I'm trying to figure out if its worth the hassel and expense of adding 1 gallon of toluene or xylene to each tank of crappy 91octane calif gas I buy. Roughly, this brings me up to 93 octane.

I know that boosting the octane will retard the combustion of the gas and reduce knocks and pings, but can anyone tell me what kind of a horsepower or torque difference I should expect going from 91 to 93 octane?

JanSolo
02-24-2004, 06:42 PM
I don't expect you to get any with the way the current ECU is set. Maybe if you had your car more aggressively tuned, it might make a difference or if you were running more boost. I ran 100 octane for a few months and then switched back to 91 and found there to be no difference at all. Granted, I don't have a dyno chart to prove my findings.

What I would recommend for proof is to dyno your car on 91 octane and then to dyno the car on higher octane to see if there is any kind of knock activity. My feeling is that on the stock ECU mappings, there will be no difference.

EvolvedDSM
02-24-2004, 07:16 PM
Coming from 93 octane, I feel a difference vs. 91. Before I could safely run 20PSI all day long. Once I got into 91 territory, I could feel the timing being pulled and had to go down to 18PSI. I have also run straight 100 w/ stock BCS and felt no difference vs 93 pump. As w/ Jan, I have no data for comparison.

Bottom line, if you want to up the boost, start mixing. Otherwise, just let it be.

jstockdale
02-24-2004, 08:10 PM
toluene or xylene

Ahhg! No!!! :)

From what I've heard, don't use octane boosters. I forget who I was talking to at the time (possibly Works) ... but basically it's not that great of a solution, and it's debatable whether or not it will help at all (I've even heard that it can be bad for the engine).

If you're going for 93, find a gas station with 100 Octane and mix the correct proportions whever you fill up ( mixed octane = ( (Gallons of 100 Octane) * 100 + (Gallons of 91 Octane) * 91 ) / (Total Gallons) )

-S ...

vtluu
02-24-2004, 10:43 PM
I've heard rumours of up to 15WHP gains due to 93 octane... And I recall Shiv commenting about performance deltas due to gas octane and/or quality. As a matter of principle I'll boost myself to 93 octane (using 100 octane gas) before each auto-x event, but I can't honestly say that I've noticed a difference.

JanSolo
02-24-2004, 11:17 PM
With better octane, you can tune the car better, for more power, etc. It's akin to running water injection. Water injection will not give you more power, but it will let you tune for more power.

As it stands, all of the ECUs you are running are tuned for 91 octane (hence why tuners sell a different flash for different octane leves). If you were running an Xede and had maps for two different fuel types, then running 100 octane would be beneficial since you could just switch maps on the fly.

But, since your car is tuned for 91 octane, you are really just helping the economy.

vtluu
02-25-2004, 12:04 AM
As far as I know, the ECU is tuned for 93 octane. There is no version of the Evo (unlike the 3G Eclipse) with a "Californicated" ECU. Even the owner's manual says to use 93 octane and 91 "in the event of an emergency." Yes, there are things about CA that suck, and crappy gas is one of them. :offrant:

robi
02-25-2004, 01:42 AM
110 leaded only the good stuff worth over 50 hp (I go from 18 lbs to 23 lbs boost) over my stock street tune...

JanSolo
02-25-2004, 09:22 AM
As far as I know, the ECU is tuned for 93 octane. There is no version of the Evo (unlike the 3G Eclipse) with a "Californicated" ECU. Even the owner's manual says to use 93 octane and 91 "in the event of an emergency." Yes, there are things about CA that suck, and crappy gas is one of them. :offrant:

Do you have proof that the ECU in the Evo is made for the entire US market, or is it just a theory? Mitsu could have easily just decided to print one batch of owners manuals to save cash, much like they could have done with the ECU.

vtluu
02-25-2004, 11:10 AM
Do you have proof that the ECU in the Evo is made for the entire US market, or is it just a theory? Mitsu could have easily just decided to print one batch of owners manuals to save cash, much like they could have done with the ECU.
While shopping around for an Evo I pointedly asked someone at a dealership if CA Evos were any different from other USDM Evos and he assured me they weren't... but given what I've heard since I think those guys don't really know much more than I do.

Do you have proof that the ECU in the CA Evo is CA-specific?

Certainly there seems to be a lack of any evidence. In my 3G Eclipse's service manual there are mentions of CA-specific differences--there are none in the Evo service manual--but then again in the case of the 3G Eclipse there are physical differences in the exhaust system.

I wonder if there's someone, say, at Mitsubishi we could ask who really knows (and could tell us)...

Maybe the folks at Vishnu/Works/etc. have experience/anecdotal evidence that points one way or the other?

:idea: We could also try dumping the contents of the (unmodified) ECU code of a CA-bought Evo and an out-of-state Evo and compare... Did anyone here buy their Evo from outside of CA?

nebolic
02-25-2004, 11:31 AM
given the fact that California is the biggest market for automakers, i would assume all specs of vehicles would be made according to "smog" levels that are acceptable in California, thus I would presume that all the ECU's are tuned to run on 91 octane. Makes more sense from a business perspective. Having the cars from the factory tuned to run lower octane gas (mininum requirement) rather than having it tuned for 93 octane where cali can only get 91 octane would only cause defects and performance issues that the manufacture would not want to deal with.

my 2 cents.

EvolvedDSM
02-25-2004, 12:06 PM
I would think all the ECUs are the same and are able to compensate (read: alter timing, etc...) for the various gasoline octanes. I believe the owners manual says it's better to use higher octane, but doesn't specifically state what the minimum is. Theoretically, you can run 87 (which is probably what the dealer put in it when you bought it) w/o worry with a 100% stock vehicle. The ECU should have the ability to make the necessary changes. BTW I bought mine in KY.