High octane fuel question.
High octane fuel question. So ever since I did my headers I noticed my car will spit at a low rpm under a high load for example 5th or 6th gear at 1k-1300k. Well One day I mixed 2 gallons of 100 octane with 9 gallons of 93 and the hesitation was gone. I was wondering if it is safe to do this and if it was safe to just put the 100 octane in straight or like a 50/50 mix when I go to the track. I have no cats and the mods are in my sig. I since then ran a couple tanks of 93 octane to see if it was in my head and they all had the hesitation and every time I put a couple gallons in it solve the problem so I no im not just "thinking" that it works it is working. Thanks.
I think there might be a deeper problem that needs fixing rather than masking it with a little race fuel. I'm not sure what that problem could be though. It might just be the nature of the headers. I noticed the engine behaved a little differently at low RPM's with both the mid's and LT's. Since you are still running stock compression, there is no need to run anything more than 93 octane, unless you have some crazy timing advance! Generally speaking, you want to run the lowest octane you can without detonation to create the most power. Obviously you will want to run a little higher than this to be on the safe side though.
Well I know my car does run better with it then with out it and that it is "masking" the Problem but do you think I can run the straight 100 and see how it feels or will it hurt somthing internal? Thanks.
Me and a few of my friends have put a few gallons of older C25 (Leaded 116 mixed with 87) into our daily drivers and it didnt hurt anything. You shouldnt hurt anything, but you probably do have another problem, i'd lean towards tuning and your car being on the rich side.
I did have my car tuned by speed Inc. and the problem still happens. I think its just picky on the gas I use. When ever I use citgo gas it does it hard core but when I use bp it will only do it once in a while. Has any one else expierenced this or any similar problems?
I don't have that issue at low rpms, but when I run it through the gears up to ~6200 RPM I sometimes get a backfire right as I shift, but other than that i don't have issues.
The quality of fuel certainly matters, not just the octane. Most fuels with a higher octane rating actually burn slower than lower octane fuel; it's part of the reason you run more ignition advance. On top of the octane is the quality. I've found that if you use BP, Amoco, etc, you generally can run more timing advance than with other (lesser) fuels. In your particular situation, it sounds like you may want to run the better fuel, but also may want to double check the ignition timing at your troublesome rpm points. You may need to retard it a tad. Remember also that if you run leaded fuel you will cause damage to oxygen sensors and catalytic converters with prolonged use. Even if you don't have cats, best to keep the leaded fuel out unless you have money to change O2 sensors often.
Cheers!
Cheers!
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Thanks for all that info. I dont plan on ever running leaded fuel but and the 100 octane is unleaded. But do you think I can run straight 100 octane? and not mix it? This would be just for the track only.
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Verdad Gallardo You shouldn't have any problems running straight 100 octane. Many people do it for track use to get lower ETs. In fact, it's not uncommon to have two different tunes for your car; one for the street (on 93) and one for the track (on 100+). As long as it's formulated for automotive use, you'll be fine.
Last edited by dan@masportspeedshop; Jul 9, 2007 at 02:51 PM.
