do supras need premium gas???

chefma70

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cause i read in several places they do. if the car requires premium i think il pass my really good condition mkiii to someone else soon and buy a motorcycle.latley i have been using the medium octain ?90??is this safe for the engine?

anyone in here use regular in their n/a and notice a difference from using premium.rodknock??
 

chefma70

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cool i think i stick with 89 for a year or 2 then decide if i wanna keep her.i hate gas prices so much. DUCATI 848 ftw(sf)<<
 

jetjock

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^ Your two cents adds up at the pump ;)

Assuming the engine is stock you should run what the manual says. All more octane does is allow the knock control system to push the timing a bit. If you want that extra bit of performance go ahead and cough up for it. Otherwise it's a complete waste of money.

Fwiw I've run 87 in my turbo (what the book calls out) for 95% of it's life (21 years) without issue.
 

cartel1_950

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running 90 octane here in my turbo caused pinging and when i switched to 91 it stopped. my car was a bit of princess though so that might have had something to do with it
 

Supratrbox2

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Most stations around me have stopped selling premium and plus is next. But I still buy 93+. The only time I ran less than 93 is when the dot head pumped in regular after I told him 3 times premium and my car ran like shit afterwards.
I also have a 1jz so maybe its more used to higher octanes.
 

CyFi6

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I use 87 octane in my NA and its just fine. Just make sure you have your timing at the stock 10 degrees btdc.
 

jessetooslow

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I was running 93, never felt a difference, went to 87 or whatever the cheaper is and it seems to be more peppy with no pinging, I go to the good stations, not the small guys.
 

mirage83

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Maybe a foolish question, maybe not, but for a newly rebuilt engine should I just stick with 87 octane, or would there be any benefit to the unbroken-in engine if I went to a higher octane for a few thousand miles? Just curious since I'm about to be in that situation and since we're on the subject of gas thought I would ask.
 

j3pz

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Maybe a foolish question, maybe not, but for a newly rebuilt engine should I just stick with 87 octane, or would there be any benefit to the unbroken-in engine if I went to a higher octane for a few thousand miles? Just curious since I'm about to be in that situation and since we're on the subject of gas thought I would ask.
i dont think its a foolish question at all. from what people have said in this thread, running 87 shouldnt be a problem, but for only a few dollars more you can add a little bit of insurance to your build.
 

ViR2

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in EDM manual clearly says, that running 92 (87 in the states) is prohibited. But maybe thats just for EDM supras.
 

CRE

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85 (R+M/2) + 17.5ºBTDC = :D

I am in Denver, so altitude is how I get away with 85. I don't imagine I'd need anything higher than 87 (worst case scenario 89) to keep things running strong without issues at lower altitudes though.
 

dumbo

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octane level is resistance to burn, higher compression=more heat=pre ignition EDIT(detonation, my bad, pre-igntion is hot spots i think a whole different problem) if octance rating is not high enough

has very little to do with preformance, or saftey(unless you need it) bout 9.5:1 prolly should be using 92oct. and 10:1 proll abouve 92oct. correct me if i'm wrong.

and having aluminum heads dissipates heat faster, can get away with lower octance
 
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Kosh

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octane level is resistance to burn, higher compression=more heat=pre ignition if octance rating is not high enough

has very little to do with preformance, or saftey(unless you need it) bout 9.5:1 prolly should be using 92oct. and 10:1 proll abouve 92oct. correct me if i'm wrong.

and having aluminum heads dissipates heat faster, can get away with lower octance
I was waiting for someone to post the logic behind running different octane levels...

The simplest equation is, if your running NA then you should not need more than 87, the compression isn't high enough to warrant it.

If your running a boosted application, you better be running premium (91+) or else your gunna get pre-ignition.

once again this is all explained by the post above. As the pressure levels in the engine are increased, the octane level must be increased in order to be able to handle the increasing pressures or else you will get pre-ignition which is the mixture combusting from the high pressure and heat before the spark plug fires.
 
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CRE

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I was waiting for someone to post the logic behind running different octane levels...
Then keep waiting because there's a LOT missing... hell your post was contrary to his and had more relevant info.

The previous poster (granted, much like this entire thread) was vague and relied on a number of assumptions... some are complete BS.

Octane doesn't effect power, huh? Riiiiiiight. Higher octane fuel doesn't just wait until it's more sure of itself (although it would make for an adorable cartoon).... it burns slower and is typically more difficult to ignite.

I do agree that heat + compression is the core of the issue, but you're both leaving out WAY too many other considerations... You're flat out guessing at the "right" octane and being presumptuous of the state of the engine, the plugs (yes, even they make a difference), the timing, the ambient air temps, the O2 content, relative humidity and so on.


EDIT: In case it isn't clear, I'm not saying that you two are entirely wrong... But you ARE being vague enough not to help and your octane numbers are pure guess work.

This has all been covered to excess a large number of times. If anyone cares to dig up some of the older threads on the matter it would indeed be helpful for the newbies who may not understand all the factors involved or why some of us mention things like spark advance altitude, boost numbers... hell, even carbon buildup can cause you to need a higher octane and it has nothing to do with the bump in the CR (well, it's the CR bump and more).
 
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Orion ZyGarian

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I shuddered multiple times at most of this thread. I couldnt imagine putting in 87 in a turbo (in an N/A, no doubt 87 is the way to go) on anything with more than minor mods. I know that if you can pull off 87 in a turbo and maintain a healthy engine, your car is well maintained and you are an observant driver. With 8.4:1 compression and not even 7 psi, its easy for me to believe you.

Hell for the life of me, I cant figure out why I've been able to run 18 psi on a stock fuel system (93 of course) without knocking..
 

Kosh

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Octane doesn't effect power, huh? Riiiiiiight. Higher octane fuel doesn't just wait until it's more sure of itself (although it would make for an adorable cartoon).... it burns slower and is typically more difficult to ignite.
This is such a minor factor that saying that running a lower octane increases the power is pretty negligible. It is far outweighed by the negatives that come with running too low of an octane. I agree I left out all of the factors that account for what kind of octane should be run but my point was that simply throwing different octane levels in your car will not make the engine more powerful. You have to tune it for that specific octane level.

What i said in my post just regurgitated what the owners manuals recommend for these cars and i gave a little reasoning behind it.
 

dumbo

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Octane doesn't effect power, huh? Riiiiiiight. Higher octane fuel doesn't just wait until it's more sure of itself (although it would make for an adorable cartoon).... it burns slower and is typically more difficult to ignite.

hell, even carbon buildup can cause you to need a higher octane and it has nothing to do with the bump in the CR (well, it's the CR bump and more).

well i'm pretty sure higher octane doesn't burn slower, and it is ALWAYS more difficult to ignite, ie more heat required for AUTOIGNITION-look it up-its been a while since school for me.

and carbon in a combustion chamber doesn't compress, means less volume=more PRESSURE=more heat, so clean your damn chambers out so you can go back to a healthy compression.

In A Healty Engine
fuel doesn't affect power, power affects the type of fuel you need.
 

webbs7mgte

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Kosh and cre have the legits down to it what i have been told also with the 91+ for boosted applicaitons because of pre ignitions is that higher octane gas removes the miscelanious ticka nd knocks form a motor cus i belive that every motor has some sort of knock not like rod knock or anythign bit slight ticks and everythign and i have beenn told that higher octanes remove that so thats my opinion if you have the moeny run the higher octanes and drop your balls off on the counter at the gas station but leave knowing your car is running at its prime unless you are expierenceing what most mk3 supra owners ahve at least once and thats bhg sybndrome lol but the way i see it they wouldnt tell you to run it for no reason big ups on this thread alsmot sticky material i see lots of kids looking at it with their gtes and saying im not paying that and later on running into pre ignition and in the long run rod knocks and other problems
 

CRE

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Pre-Ignition = a manic Pyrokinetic
Detonation = Pyrokinetic with Touret's


I do research stuff on my own. Naturally, given that the internet (and even published references) is horribly prone to the proliferation of rumors and "accepted fact" it is difficult to avoid completely. I've double checked the burn speed thing a number of times, I've found books, web articles and articles published by race fuel companies (yup, could be nothing but marketing behind them). Many had charts comparing the differences of burn speeds and most recommend pulling timing if knocking if you were already running the highest octane you could and the knocking was not detonation related.... I've even watched my friend's drag team pull timing to get rid of a knock when they had to use a lower octane than usual... so it's hard for me to accept there isn't a difference. It may be less common these days and it may be so small as to not really count with pump gas, but there does appear to be a lot of backing behind it. OR is this essentially a misunderstanding between the cause and the effect, the flame takes so much longer to reach a self sustaining combustion (and as such to actually create power) and as such you end up with the same result as if the fuel were burning slower? Same effect in the end but a different cause.

I find it unlikely that even if all the various octane fuels and all the various fuel formulations out there had the same burn duration from flame front to end gas that the distribution of power throughout would be identical. In which case, when compared across two identical engines there would be no difference in power output. However, in two identical engines running different octane fuels the one running the lower octane does often produce more power (regardless of how small the increase it's often there and I'm not going off of any one persons results nor am I just going off of tests published by diyers or by manufacturers. The tests that I've read I only consider if they're using the same base parameters for each batch of tests, this includes the base timing.)... now is it simply because more of the critical expansion is occurring closer to the crank's critical position whereas with the higher octane fuel the critical expansion is occurring late and as such power has already been lost? (I'm referring to peak cylinder pressure at ~20ºATDC)

If general posts of what works for others isn't enough and you feel the need to step up and clarify... fine. They're oversimplifying, go ahead and provide more info. But don't step up spit out that everyone's wrong and add enough information as to add nothing (but seem really cool in doing so).

I know dick about fuel compared to many people. I do know a bit more than most and admittedly, as we all know, there's a point where you know just enough to get into even more trouble than those who don't know a thing... with fuel... it seems I'm right there. It seems to me that there are a TON of factors which you seem to like avoiding in this, in which case perhaps it would just be better to shut up and let people discuss what works for them, under what conditions and what they've found when they've strayed from that setup. They're really not much worse off than you telling me I need to be running 92 octane based on nothing other than my engine's static CR.
 

Kosh

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It might help your case to learn the difference between pre-ignition and detonation.
Who was this directed at because i have seen no misuse of terminology here. pre-ignition is a symptom of running too low of an octane level.
 

CRE

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Probably directed at all of us for not clarifying... could be directed just at me too though, some of these terms and the difference tend to blur a bit when I start thinking about 20yo motors where not everything's cut and dry.

I'm aware as well, but for the benefit of the masses, pre-ignition is the ignition of fuel prior to the application of the ignition spark. Detonation is the inconsistent and unpredictable burning of fuel. Both can be a result of running too low of an octane depending on the shape of the motor...
 

xarewhyayen

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the higher gas prices get, the less percentage more that premium is. premium is usually only 20-25 cents more than regular per gallon. Which is like an extra $3.75 per tank. If your car is pulling timing to compensate for slight knock with lower octane fuel you're losing torque and probably getting less gas mileage. the extra 3.75 per tank is less than buying an extra gallon of regular and you will probably make up for that extra gallon by getting more miles per tank.
 

Nocheez

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*sigh*
Say you drive 10,000 miles a year, and you get an average of 20 MPG, you use 500 gallons of gas a year. I would estimate that premium is generally $.25 more than regular fuel, so it costs you a whopping $125 a year to run premium fuel. "But wait, Nocheez! I'm a poor douchebag who can't afford to spread that extra money over 35 fill-ups, which ends up costing me $3.50 a fill-up or about $2.40 a week!" to which I would tell you to sell you Supra and buy a fucking Civic.

That $125 a year is cheap insurance to make ensure you get the best performance and longevity out of your motor.
 

Kosh

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*sigh*
Say you drive 10,000 miles a year, and you get an average of 20 MPG, you use 500 gallons of gas a year. I would estimate that premium is generally $.25 more than regular fuel, so it costs you a whopping $125 a year to run premium fuel. "But wait, Nocheez! I'm a poor douchebag who can't afford to spread that extra money over 35 fill-ups, which ends up costing me $3.50 a fill-up or about $2.40 a week!" to which I would tell you to sell you Supra and buy a fucking Civic.

That $125 a year is cheap insurance to make ensure you get the best performance and longevity out of your motor.
nuff said
 

Poodles

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Exactly what I've been saying forever.

Worst case you destroy a piston and take the block with it. Sorry, but that's a WHOLE lot more expensive than paying for premium...
 

MT Photography

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In the SC400, it's about $75 a week, must run premium also, 20 gallon tank, 15mpg = owned.


That's with gas being pretty cheap (~$4.25 for premium) here in NC.
 

Orion ZyGarian

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In the SC400, it's about $75 a week, must run premium also, 20 gallon tank, 15mpg = owned.


That's with gas being pretty cheap (~$4.25 for premium) here in NC.
Running a 1UZ on 87 is probably safer than on a 7M. Also, 15 mpg means either you need a tuneup or you drive it too hard to be complaining about gas prices :biglaugh:

As was mentioned, carbon likes to negatively affect the combustion chamber. It likes to retain heat and act like a glow plug as well as act like part of the chamber to change how the combustion burns as well as raise the compression ratio negatively. Granted you'd have to have lots of it to make a big difference, its still an issue.