Here's one that's been puzzling me for quite some time. It seems to me that many of the IT cars I've seen run 100, or even 110, octane race fuel. My question is...why?

Certainly it's not because of massively high compression ratios...that's not allowed in an IT engine IIRC. Could it be wildly advanced ignition timing? Here I don't really see the point...I would think that you can go "too far" with ignition timing advance.

I don't think I run my car much *less* hard than many IT cars get run...and I've never felt any need for anything other than pump 93 octane. So...anyone care to clue me in?

--Karl, who suspects the answer will be a no-brainer

 

I am sure it has to do with several factors.

First is the timing. "Too far" is subjective. Mechanical advance is usually still within range even when the distributor is all the way. The car will detonate like hell however. The high octane gas helps this.

Also, racing fuel is designed for the purpose at hand. I imagine it burns better in racing enviornments and it probably produces much less deposits. It is a quality thing. I know my cars run infinately better on Cam2 115. Of course the O2 sensors don't like it . . .

 

Yea, I believe it is so the timing can be advanced WAY up... I know on my prelude, the more and more I advanced the timing, I could feel the power as well, but the old motor running on 93octane pump gas didn't like that, cracked exhaust valves

 

I know that certain Type R's that race in SVWC use maximum physical advance.

 

I'm running at about 19 degrees, when the factory spec is +/- 2 from 15 degrees. think thats safe for the street? There are sometimes my car really bogs on the low end at partial throttle, could this be because of the knocksensor catching something I can't hear?

 

Good question. I think on some cars that are supposed to run in stock form on premium gas like GSRs, BMWs would benefit from 100 while racing given the advanced timing, etc they have done. We always ran 93 on the CRXs because by what the rules allow there's just nothing that can be done to it to make it run "better" on 100 that we've found. Plus it's a whole lot cheaper, especially when NOT buying the gas from the track!! Maybe someone running 100+ can answer this better.

 

Not sure why they did in the past, but now the ECU can be tuned to optimize the use of 100 octane gas.

 

Interesting responses.

I guess I figured it was a timing advance thing...but I wonder, is there a way to advance timing *too far*?

--Karl, who is looking for any free (or cheap) advantage he can get...because he's going to need it...

 

Another guess is that in IT you can do mods to improve air flow, but not fuel delivery. If you have a cold air intake, port it out to the max, port match, etc. you will want the higher octane fuel to keep your air/fuel ratio where you need it. Just a guess though.......

Matt

 

Kart racers use it even when not necessary for tuning because it is way more consistent than pump fuel. Every tank is the same (as long as it doesn't sit long) and you are less likely to get a "bad" tank of gas.

 

If it makes you feel any better, I run my RX-7 on the cheapest horse **** I can find. 72 Octane you say? Bring it on! And my ignition is advanced quite a bit.

But, to answer the question... I think they use it because the jacked up timing in combo with the higher compression (from shaved heads) requries it. Especially in the higher compression carbed cars (Volvo 142 and some others have well over 10:1), where there is no real-time timing adjustment for pinging.

 

Interestingly, I seem to recall reading somewhere (probably C&D a while back) that lower octane fuel actually contains more chemical (and I guess potential) energy per unit volume than higher octane gas?

 

That would be my guess as well. I have no idea if racing gas is really any better in terms of quality control but you would think it would be.

 

That is true. Regular gas is more powerful. Premium gas has additives to slow down the burning of the fuel.

 

Check this link.

http://www.seansa4page.com/resource/octane.html

and this http://www.factorypro.com/tech/fuel_..._vs_power.html


[Modified by Grumpy, 9:57 AM 12/27/2001]

 

Cool. Good stuff Grumpy (for those folks like myself that like organic and physical chemistry).