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Discussion Starter #1
I was just wondering if your fuel octane can ever be "too high". Assuming you have full control over your timing and fueling, does it ever make sense to use say 100 octane when 110 octane is availabe at the same price? Does higher octane fuel always make you lose some power (even after re-tuning) ? If so, about how much? Thanks.

-Paul
 

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You only want as much octane as you need. I can't say for sure, but the common thought is that ~100~104 is about all you need for stock twin boost levels. Though Matt A. recently put down 449hp/46Xtq (@1.3bar) on 100 octane with minimal tuning (S-AFC) on his basically BPU++ car, so the extra octane wasn't killing too much power if any. I guess an interesting experiment would be to dyno back to back on the same dyno's using a lower octane race gas and see if you picked up, lost, or had the same output.

But another consideration of course is that running 100% leaded gas will significantly decrease the life of the stock O2 sensors.
 
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Ok, thanks. I don't think the stock ignition system can even ignitre more than 50% leaded gas properly. I have an HKS DLI. I'm not sure if that would make a big difference or not, or if the coilpacks are the limiting factor.
 

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Stock ignition has no problem even with 100% 110 octane leaded fuel. That is all that is ever run in my car with the hose pulled on the stock twins and will continue to be run that way with the single to come shortly. BTW my car is a TT Auto and recently made 404RWHP and 437RWTQ. on 1.5 bar. (downpipe,intake,catback,and frontmount) Drew
 
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You run 100% 110 leaded?? No way. I tried that several times and the car would barely run. It felt completely dead and was probably making 80 hp less. It was horrible. The egts went form 1650 to 1400 F as well; a little TOO cool I think. That was with a completely stock ignition system. I thought you're not supposed to use more than 50% leaded gas? What kind of ignition system are you running? Maybe I should try straight 110 leaded next time?? That would be better (except on my o2 sensor) and much more convenient for me if it works!
 

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AZMongoose said:
100 percent leaded fuel will NOT harm our 02 sensors. I've personally ran over 200 gallons of 100% leaded fuel with NO problems..
I've run it a couple of times and ended up getting a trouble code for the primary O2 sensor right after I ran 100%.

It isn't good for them, that's a known fact, but you are right that many people (including yourself) have run a good amount of leaded before having any problems.
 
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LOL, you guys aren't making any sense to me. Since when does leaded fuel not harm o2 sensors?? I hope you're right, because I have my FJO permanently installed in my midpipe and I run leaded gas pretty often, but from what people have told me in the past lead kills o2 sensors pretty quick. Anyway, I'm more interested in the fact that you can run straight 110 leaded. Like I mentioned, I tried that in the past and the car felt so dead it was ridiculous. The stock ECU can correct for it?? Or are you using a standalone? When I tried it last, I was using the stock ECU, and now I have an AEM so I can probably adjust for anything. So I guess there's no reason for me to mix 50/50 anymore? I'd rather just run straight 110.
 

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Yes, I run straight 110 leaded all the time. Have been for the past 3000-4000 miles with no problem. I have the stock ignition system (no DLI, Ect....) I have a stock ECU with a Greddy Emanage. I have yet to replace any O2 sensor in the car (knock on wood) As I said earlier it made that power level at a 11.0:1 AFR until 6000 Which fell to 10.5 (Before the emanage) after 6000. Car went [email protected] On %100 110. (on street tires 2.5 60'ft.) I believe the computer learns the curves and makes up for it. My car will not run on pump gas now with out pulling timing even on 1.1 bar (unless I reset the ECU) I guess my car just has expensive tastes. ;) LOL
 
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Discussion Starter #10
Very strange. Well if it works it works. That's sweet. I'll try straight 110 leaded next time and see what happens. I bet I'll lose a ton of power though, like last time. How do you know your o2 sensor isn't bad though? Maybe it's just dead and you don't know it? Your car won't run any differently when it's dead, you'll just get bad gas miliage. My a/f went down one full point with a bad o2 sensor vs a brand new one I put when I had the stock ECU. I bet it's dead/dying and you just don't know it. Either way, it doesn't matter much... if you can afford straight 110 leaded then I think you can afford to lose a few miles/gal while cruising around hehe. I'm just hoping my wideband o2 sensor doesn't get screwed up because I rely on it.

-Paul
 

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I think the point here is to understand that you'd be working with a fixed timing map and you only need as much octane to safely run this amount of boost and timing.

If you had a stand alone with this same setup, you could use more octane because of added timing.

RSA Supra said:
You only want as much octane as you need. I can't say for sure, but the common thought is that ~100~104 is about all you need for stock twin boost levels. Though Matt A. recently put down 449hp/46Xtq (@1.3bar) on 100 octane with minimal tuning (S-AFC) on his basically BPU++ car, so the extra octane wasn't killing too much power if any. I guess an interesting experiment would be to dyno back to back on the same dyno's using a lower octane race gas and see if you picked up, lost, or had the same output.

But another consideration of course is that running 100% leaded gas will significantly decrease the life of the stock O2 sensors.
 

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I haven't had any major issues running leaded gas with my standard O2 and my wideband O2 so far although I only run off of the wideband now.

However, keep in mind that leaded gas WILL slowly damage the sensor over time and the damage causes the sensor to react slower and not just outright act broken. I was told that periodically using a bottle of techron cleaner will help keep the O2 sensor clean after leaded use.
 
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Discussion Starter #13
Ok oh, so it mainly causes the sensor to react slower? I was concerned that it might actually change the whole calibration/reading. So that's cool... it's nice to have it as accurate as possible for tuning, but more importantly when I'm going through 5th at 25 psi and it says 11.8:1 I want to be pretty confident it's really at 12.2 and not 13.2 heh. Thanks.
 

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Well, I take some of what I said back. It's possible for the sensor to outright stop reading correct values in some cases. This isn't the common problem I've herd about with anyone I've talked to but it's possible. Remember, we're apply coats of crap over the sensor makingit unable to take proper readings. Cleaners like regular fuel or straight Techron help clean off the build up.

The Forbidden Supra said:
Ok oh, so it mainly causes the sensor to react slower? I was concerned that it might actually change the whole calibration/reading. So that's cool... it's nice to have it as accurate as possible for tuning, but more importantly when I'm going through 5th at 25 psi and it says 11.8:1 I want to be pretty confident it's really at 12.2 and not 13.2 heh. Thanks.
 
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Ok, I'll keep that in mind. Maybe I'll try some techron once in awhile. I usually don't use race fuel for more than a day or two at a time so hopefully during the week it'll clean itself off a bit.
 

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Wideband O2 sensors are much less sensitive to lead than the OEM sensors are.

The question is whether or not the stock ECU can give enough timing to take advantage of 110 octane, and the answer is probably not, but is it killing power too? And if so, how much?
 

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Ok, I may be crazy, but I thought standard race gas was unleaded anyway...
Aviation fuel is leaded, but you guys arent using that are you?
 

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Aviation fuel isn't that great for cars.

SNOOP said:
Ok, I may be crazy, but I thought standard race gas was unleaded anyway...
Aviation fuel is leaded, but you guys arent using that are you?
 
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