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Old 03-15-2009, 01:13 AM   #1
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Default Higher Octane

Just curious if any of you guys run higher octane fuels from time to time and how you tune for it? I think I'm going to the drag strip this week and I'm absolutely determined to get in the 12's. If I can't do it on 93, the track has unleaded 100, as well as leaded 100 and 112. Any advise on what fuel to run? I've got no cat, so I'm thinking the leaded 112 would be the best bet. Also, any advise on how to tune for the higher octane? Would you just crank the boost up a few psi, or bump timing up a few degrees?

Motor is a stock '95, currently running 12psi. I'd certainly prefer to not sling a piston through the hood, or 'nading my '90 tranny w/ 169k on it, but I am trailering the car and it's not a daily or so if it happens it won't be too traumatic. Given that, what kinda boost would you feel comfortable running? I really have no idea what I'm doing in this area so any advise you can give is greatly appreciated.
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Old 03-15-2009, 01:16 AM   #2
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running higher octane without tuning for it really wont do much imo. leaded can still destroy your o2 sensors, or so I've heard.

throw some unleaded 100 in there, add a bit more timing and lean it out (safely of course) and it should definitely put down a bit more power


*edit: run whatever fuel/timing/boost the car will like. there is not "set" levels for certain octane.
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Old 03-15-2009, 01:37 AM   #3
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Throw it on the dyno and have a tune done up for the higher octane fuel.
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Old 03-15-2009, 02:38 AM   #4
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Tune with the good stuff, then make det cans and listen for knock at lower octane levels. Then, the car is "tuned" for each octane.
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Old 03-15-2009, 03:03 AM   #5
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Blahhhh, you guys would seriously get your car retuned so you can make a pass at the dragstrip? Certainly with higher octane there are some assumptions that can be made in reference to boost pressure, timing, fuel that will still be conservative, but will allow for more power than pump gas.

If no one else has been bold enough to make those assumptions, I guess I'll go ahead and make them myself and report back with the results.
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Old 03-15-2009, 03:10 AM   #6
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good Idea

I have done this, but with a wrx, therefore cant really help much
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Old 03-15-2009, 03:36 AM   #7
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Originally Posted by pdexta View Post

If no one else has been bold enough to make those assumptions, I guess I'll go ahead and make them myself and report back with the results.
Let us know how your upcoming motor build goes. If you aren't tuned on 100 octane, adding it to the tank and assuming you can add X boost or X timing is an awesome way to add a fancy new crankcase ventilation port next to your fourth cylinder.
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Old 03-15-2009, 03:54 AM   #8
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Let us know how your upcoming motor build goes. If you aren't tuned on 100 octane, adding it to the tank and assuming you can add X boost or X timing is an awesome way to add a fancy new crankcase ventilation port next to your fourth cylinder.
Like I said earlier, if it happens, it happens. If you don't think that assumptions can be made then we've obviously got some very different opinions. Hopefully the plans go through and I can either post a timeslip or a pic of the carnage.
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Old 03-15-2009, 04:05 AM   #9
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or both

the timeslips and what it took to attain them lol
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Old 03-15-2009, 04:33 AM   #10
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If you have no worries, then crank it up to about 17-18# and see how she does. If there's any detonation, pull a little timing. Have fun and post up your slip.
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Old 03-15-2009, 11:38 AM   #11
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Quote:
Originally Posted by pdexta View Post
Blahhhh, you guys would seriously get your car retuned so you can make a pass at the dragstrip?
If no one else has been bold enough to make those assumptions, I guess I'll go ahead and make them myself and report back with the results.
You're ******* fantastic with reading comprehension...like a god damn 8-year old. Read my post, again, because you're obviously too hung-up on your homosexual fantasy bullshit to comprehend what I posted. i gave you the ******* assumptions, fucktard. Die of aids. No one loves you.
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Old 03-15-2009, 01:12 PM   #12
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According to Corky's book, 2 RON = 1psi.
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Old 03-15-2009, 02:04 PM   #13
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Originally Posted by hustler View Post
You're ******* fantastic with reading comprehension...like a god damn 8-year old. Read my post, again, because you're obviously too hung-up on your homosexual fantasy bullshit to comprehend what I posted. i gave you the ******* assumptions, fucktard. Die of aids. No one loves you.
It's hard for me to get aids when you're ***** is too small to get any penetration.

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According to Corky's book, 2 RON = 1psi.
Good info, thanks man. Something around 15psi is what I had in mind so that sounds pretty close.
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Old 03-15-2009, 03:21 PM   #14
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If you don't think that assumptions can be made then we've obviously got some very different opinions.
The difference between our opinions is that you don't know how to tune for high octane and I do. In fact, your comment asking whether we all have our cars retuned for a single pass leads me to believe that you don't know how to tune at all. Instead of calling you an idiot and telling you to have fun blowing your **** up, I'm going to go one step further and make our search function a little more worthwhile by explaining you in relatively simple terms exactly WHY you are an idiot.

Higher octane fuel has a couple of characteristics that make it more advantageous to lower octane fuel. It does not make more power in and of itself - in fact, it makes less power than lower octane fuel provided the lower octane fuel can be used safely. It is more difficult to ignite, which means it can endure higher cylinder pressures and higher temperatures than lower octane fuels can. This suppresses detonation and allows you to increase boost and/or timing.

Increasing either one *****-nilly is a recipe for disaster, though. What high octane fuel DOES NOT DO is add MORE fuel to your motor. In order to increase the boost levels, you have to ensure your AFRs are tuned safely in those cells. The high octane fuels will not magically provide MORE fuel; all it does is provide more protection against detonation, which enables the motor to deal with the increased internal pressures that come with increased timing and boost.

Increasing boost and maintaining AFRs is a relatively simple thing to do for someone with even the most basic grasp of tuning theory, however; you click buttons until the number on the screen is between 11 and 12 and away you go. Timing maps are an entirely different ballgame, however, and unless you happen to have a dyno tucked away in your garage they are difficult, if not impossible, to tune on the street. If your tuner was intelligent, he set your spark map up to massively retard the timing map in case of overboost; you'll add that high octane fuel, get your AFRs dialed in, make a pass, and melt **** because your EGTs spiked.

Assumptions are the mother of all fuckups. Adding boost, timing, and octane without any sort of checks or tuning of any kind, lining up on a dragstrip, and making a pass is a ******* terrible idea. If you want to do it safely, get a FULL TANK of 100+ octane, spend some time getting it at least safely tuned on the street, and then make your passes.

BTW - If a tuner I paid for was caught assuming that 2 RON octane points meant he could add 1 pound of boost to my motor, the only thing he'd be getting any money for was labor for removing my car from his dyno.
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Old 03-15-2009, 05:08 PM   #15
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FWIW, I never said or tried to imply that higher octane fuel adds more fuel to the motor. I never said anything about running high octane fuel without making any changes to the current tune, hence the whole point of the thread. The car has been tuned on 93 up to the 212kpa row, but I choose not to run that much boost on a stock motor with pump gas.

I think I have a high 12 second car as it is right now, if I don't I would like to make use of those higher boost levels. I could run 15 pounds on pump gas, but it seems to me that it would be safer on racegas. If that makes me stupid, then so be it, but I'm pretty sure that I have some very basic comprehension of what I'm doing and that I'm not quite as retarded as you seem to believe I am.

Like I said, we will see what happens. If I am as stupid as you think I am then go ahead and start getting your "I told you so" post ready, but there is really no need for name calling and personal insults, IMO.
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Old 03-15-2009, 05:44 PM   #16
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Most who ask this question DO assume that they can run more octane and more boost without addressing AFRs. Sorry to lump you in. Keep in mind that your AFRs will get leaner as you add timing. Build yourself a set of detonation cans and make your assumptions on the street before you get to the drag strip, so if you hear a little knock you aren't wasting a run or wetting down the strip with a fine spray of coolant/oil.
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Old 03-15-2009, 07:07 PM   #17
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Resistance to knock won't help an engine that doesn't have active knock/boost control. The same timing, same boost, higher octane won't do anything at all. I think the actual energy per gallon is less with a rise in octane, mostly due to additives to keep knock down.
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