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Old 11-02-2001, 08:58 AM   #1
SilverSubi
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Question Race gas in stock WRX

Is putting high octane fuel (say, 98 octane) beneficial (for 1/4 mile times, anyway) in an otherwise stock WRX? Does the ECU recognize something like 98 octane and make use of it?

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Old 11-02-2001, 09:13 AM   #2
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Nope. Without more boost, the extra octane won't do you any good at all.


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Old 11-02-2001, 09:52 AM   #3
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lol, Yes it will...
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Old 11-02-2001, 10:34 AM   #4
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Quote:
Originally posted by Imprezd
lol, Yes it will...
your opinion is contrary to everybody else I've heard comment on this. why don't you explain yourself further?
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Old 11-02-2001, 10:37 AM   #5
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Personally, as someone who knows nothing about anything that anyone's interested in...

My thoughts would be that it WOULD be beneficial... but not necessarily to 1/4 mile times.

Cleaner engine, better detonation, anti-knock, blah blah blah, but I don't see any perceived performance gains.
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Old 11-02-2001, 10:42 AM   #6
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Higher octane does not mean cleaner engine or 'better' detonation. Cleaner engine only comes from additives to the fuel...all fuels can have this. Higher octane fuel really gives one thing...more resistance to detonation. It is actually harder to burn higher octane fuel, which is one reason why it won't pre-detonate as easily.

So when you run super high octane fuel, it allows you to crank the boost, which gives you more power. In a sense, the fuel doesn't give you any more power, it's mostly from all the extra air (and matching fuel) that gives you more power. High octane can give some piece of mind...detonating while running 20psi is a BAD thing.

bsquare is correct...simply running higher octane fuel will NOT give you more power (unless you were previously running some type of crap 87 octane that was causing timing to be retarded, etc). If you are not tripping the knock sensor and are getting fuel timing with the fuel you have now, switching to higher octane fuel will do nothing.

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Old 11-02-2001, 10:43 AM   #7
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You know what I meant by better detonation

*edit*

Here's a good link:
http://www.motorcycle.com/mo/mcnuts/rt-fuel1.html
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Old 11-02-2001, 10:46 AM   #8
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Higher the Octane the less chance of Detonation... that means that their is more ignition advance the engine can run without pinging.

Not a truely technical answer but one that should have answered your question.
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Old 11-02-2001, 10:50 AM   #9
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The link says what I was saying but contains all the nice technical jargon.

Imprezd, agreed unless you are running fuel that already allows the car to run it's maximum timing. Most 'good' (93 octane in Jersey) allow the car to already run the best timing map, so increasing octane at that point is useless.

More interesting is the fact that I have noticed that all 93 octanes are not equal in my area. If I get my gas at Mobil or Sunoco, car runs great. When I used to buy 93 at the SuperWawa near work in my turbod DSM, the car ran like crap. I won't buy there, I stick to Mobils and Sunocos.

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Old 11-02-2001, 11:18 AM   #10
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Quote:
Originally posted by Imprezd
Higher the Octane the less chance of Detonation... that means that their is more ignition advance the engine can run without pinging.

Not a truely technical answer but one that should have answered your question.
There is only so much advance the stock ecu can use. Sure you might get a few hp over say the new 91 Cali-gas, but you really won't see the gains unless you run, or have the potential for more aggressive timing, stand alone mgmt or uni-chip or whatever...
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Old 11-02-2001, 11:41 AM   #11
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Higher octane == less power...

Using high octane gas when your car is tuned for 93 will make you loose power. The gas does not burn as well..

Now if you have a haltech/tecII and have a map for 104 Octane with timming & boost set accordinaly then you will be much higher on the HP scale..


-Zach
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Old 11-02-2001, 12:52 PM   #12
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Most of these guys know not what they say !!!!!

When my car was in stock form . . . I used to occassionaly run 100 octane CAM 2 . . . . the stock WRX cpu immeidately starts to advanvance the timing whne you put better fuel in - within 50 miles i felt and my stop watch measured the extra power - - suttle but there
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Old 11-02-2001, 01:23 PM   #13
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I would have to say the ECU will advance the timing a little after driving it for awhile... I don't have proof to this but it feels a little faster... not much though.

Unless you are turning your boost up or spraying nitrous don't bother with race gas unless you don't mind the price.
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Old 11-02-2001, 02:06 PM   #14
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Thanks a bunch, guys....just the info I was looking for.
I'm going to Cecil County Dragway in Maryland tomorrow and decided to throw my pretty-much stock WRX on the track just for fun.

Thanks again...
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Old 11-02-2001, 03:22 PM   #15
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"the stock WRX cpu immeidately starts to advanvance the timing whne you put better fuel in"

We know what we say...we say that if the fuel you are using is already ALLOWING the ECU to utilize the maximum advanced timing, the extra octane gains you NOTHING. I think 5 people said it in this thread. Such as this:

"There is only so much advance the stock ecu can use. Sure you might get a few hp over say the new 91 Cali-gas, but you really won't see the gains unless you run, or have the potential for more aggressive timing "

The ECU can only advance the timing so much (talking stock ECU here). Higher octane will not allow the magic timing fairy to show up and give you magical power from your magical race fuel. ONLY if you are NOT getting the full advancement on your current fuel can you feel a difference.

Silver, if you think you are getting the timing retarded on your current fuel, try the race gas. If you are datalogging, you can see what timing is doing, and if the race gas makes a difference.

Kevin
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Old 11-02-2001, 03:29 PM   #16
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Default Hi Octane

If you have an MBC you could play with real high boost levels with the race fuel. Ignition advance will NOT improve because of high octane fuel. You will be less likely to have your timing retarded by the detonation sensors. That is all. You will know when this happens because it totally pulls the timing out agressively.

Unichip and other tuners sap more performance by running ignition advance closer to the detonation point. Factory maps are designed to be conservative. If you really want performance, remap the timing for the fuel you are using. If you have something programable like Tec II, you can set up a programs specific to the fuel you use. This way you can modify boost levels and timing maps to accomodate the fuel octane.
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Old 11-17-2001, 01:01 PM   #17
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Can you say how much...

Suppose the following:
- Boost level is fixed;
- Safety margin is to be kept the same (with regards to detonation);
- the ECU is allowing the maximum timing advance for the current octane rating of our fuel;
- the ECU can advance timing as much as needed if higher octane fuel is use.

Can we derive a formula that would link the boost level, current and new octane rating to the power gain?

This 'formula' can only be an approximation or a upper bound or such. Like for injector size, duty cycle and BSFC.

S.

Last edited by Pollux; 11-18-2001 at 01:40 PM.
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Old 11-17-2001, 01:45 PM   #18
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In the situation you described, the gain is zero, you'll just run rich.
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Old 11-18-2001, 01:49 PM   #19
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May be it's my english that isn't clear.

If the situation that I described there isn't more fuel injected.

The new fuel can simply burn at higther temperature and, so, more power is produce because of the increase pressure (due to combustion at highter temp [PV = nRT]). I can link power with the increase pressure, but I don't know how hotter we can burn our fuel.

If I look at this in totally the wrong way, please tell me.

bsqare - "in the situation you described, the gain is zero, you'll just run rich."

Can you explain to me? (I don't know if you are wrong, but I don't understand)

S.
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Old 11-18-2001, 05:24 PM   #20
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Pollux:

Using PV=nRT is too simple as in the engine, P,V, and T are changing from moment to moment.

And higher octane gas does not burn at a higher temperature, it simply autoignites at a higher temperature. Knock or detonation, is simply the pre-ignition of the charge before the spark plug fires. Higher octane gas is intended to be less susceptable to pre-ignition because it requires a higher temp to ignite. But 112 will ignite just as well as 87 when you fire the spark plug.
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Old 11-18-2001, 06:31 PM   #21
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You WILL get better times if you use race gas. Try it, I have used VP in N/A cars and forced induction and have seen gains in all of them. Try and run with 4 gal. of VP C10 or better yet C12 and nothing else. The VP gas WILL lower exhaust gas temps, it WILL allow higher boost and timing. The stuff costs $7 a gallon but it works, its the best fuel (gasoline) u can buy.
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Old 11-18-2001, 06:49 PM   #22
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I agree, in general, with boostit's observations just above but would like to point out the pre-ignition and detonation are not usually considered to be synonymous but are, instead, two different types of malfunction.

The question, here, is did the Denso/FHI engineers believe that they had reliable knock detection? If they didn't consider it to be reliable, then they would have had to set up their maps to allow a safety margin for the worst-case scenario (engine's getting on in years, possibility of lower-than-recommended octane, focus on the most-likely-to-knock cylinder). If, on the other hand, the design engineers believed they had reliable knock detection, then they would've set up the default maps for the most optimistic conditions (new engine, Jap-spec octane, least-likely-to-knock-cylinder), and let knock detection correct the timing of individual cylinders when these conditions weren't met (and knock was detected).
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Old 11-18-2001, 07:42 PM   #23
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If you are sitting around idling waiting for your drag run, your engine and IC will get hot. You may end up with some detonation due to the hot engine. In this situation, you can decrease detonation problems by running higher octane gas. This is not making your motor run better in general, it is compensating for the nature of drag racing, which is a lot of sitting still for 12 seconds of driving.

This is why drag racers frequently run air/liquid ICs and pack them with ice.


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Old 11-18-2001, 08:10 PM   #24
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i think when it comes to race gas, octane is the last thing I look at. They sometimes come hand in hand, but like others have said, high octane is better at preventing detonation.

You basically want to run the lowest octane you can get away with without engine knock.

I think more important factors in a RACE FUEL (not a high octane fuel) is presence of lead, oxygination, and additives.

I am sponsored by VP Fuels (motorcycle racing) and use their MR-1 product which is both highly oxyginated and leaded as well, but is only about 91 octane. The engine runs nice and cool and has actually given me an extra 10hp at the rear wheel (proven on dyno--141.2hp out of a stock 750cc engine!)
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Old 11-18-2001, 08:28 PM   #25
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Lead is an absolutely atrocious octane booster (that's its purpose, btw). The entire reason lead was ever advocated as an additive is that the chemical companies developing octane boosting additives 80 years ago wanted products that they could protect with patents, so that ruled out any of the environmentally and engine friendly additives available at the time. The lead additives are extremely bad for your engine (catalyst or not, heated O2 sensor or not) and _more_ additives are required to protect the engine from what the lead additives do to it. So, chemical companies makes additives that require yet more additives and their pockets get lined.

This is a great article by Jamie Kitman (a respected automotive journalist, not a car hating tree hugger ) on the whole sordid tale.

Lead sucks, don't believe the hype.


Ben
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