wrong gas
03-11-11, 04:53 PM
#1
wrong gas
so i wasnt paying attention when i filled up a bit ago and i accidently put about 9 gallons of 87 into my TII i then once i noticed what i did i stopped the pump and put 5 gal of 91 so there was another 4gals of 91 in the tank so half 87 half 91. stock motor fuel exhaust. will it be ok. should i drive like an old lady or siphon all the gas out.
03-11-11, 04:56 PM
#3
CC of L-Squared Shots
I'm a touchy kind of person and I would siphon it out...
It won't blow up your motor but it'll run like crap until the fuel is gone. Just be careful when driving it...
It won't blow up your motor but it'll run like crap until the fuel is gone. Just be careful when driving it...
Last edited by w0ppe; 03-11-11 at 04:56 PM. Reason: oops
03-11-11, 06:33 PM
#7
If it's stock, it will make no difference at all - and next time, you can just fill up on regular and save your money, throwing premium at an engine that doesn't need it/isn't tuned for it is just wasted $$$. It doesn't improve performance, and stock there is generous allowance so it's not giving meaningful extra margin against detonation even.
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03-11-11, 06:40 PM
#8
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Why are you using 91? 
Anyway, if you are wondering about mixing, half 91 and half 87 would end up pretty much like 89 once it is mixed thoroughly. It is a little more complicated than that, but that is the basic overview.
Just to clarify, 87 is the minimum recommended octane. You can use higher octane if you like, but unless the engine is in poor shape or overboosted then the higher octane will make no difference other than costing more money. In many cases the higher octane yields slightly less power and slilghtly worse gas mileage, but it is negligible.
If the engine is stock and in good shape, it will run just fine since the TII is rated for 87 octane. Sometimes 87 will even run better than 91, depending on the mixture used by the fuel vendor.
Anyway, if you are wondering about mixing, half 91 and half 87 would end up pretty much like 89 once it is mixed thoroughly. It is a little more complicated than that, but that is the basic overview.
Just to clarify, 87 is the minimum recommended octane. You can use higher octane if you like, but unless the engine is in poor shape or overboosted then the higher octane will make no difference other than costing more money. In many cases the higher octane yields slightly less power and slilghtly worse gas mileage, but it is negligible.
If the engine is stock and in good shape, it will run just fine since the TII is rated for 87 octane. Sometimes 87 will even run better than 91, depending on the mixture used by the fuel vendor.
03-11-11, 09:44 PM
#13
talking head
the result is not as expected,, and the discussion on the matter was lively
( i will point out this bloke was teaching us the petroleum industry processes )
i was at that point advocating what you wrote,, but apparently it is not so ,, and the reasons complicated
( something to do with hydrogen bonding / van der waals ratios )
for the OP,, it will not matter that much,, drive it for a short distance conservatively ,, and refill with your normal choice
where i am in western austraila,, octane is rated in RON ,, and so the numbers don't co-relate with your grades
-- however,, on any aftermarket tuned rotary,, using the standard 91 RON
( about 86 combined ron/mon )
can be engine lethal in hot ( 100 F + ) conditions
here,, the better tuners tune for 8/10's cause the petrol quality from the pump can vary in hot conditions
- pulling 2 degrees out of the optimum timing is considered normal practice
03-11-11, 09:47 PM
#14
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Higher octane will not cause more carbon build-up. That is just an urban legend based in the misconception that the octane rating is related to the burn rate, which it is not. Higher octane fuel may cause poorer gas mileage, but the amount is usually insignificant. Pump gas from the same vendor is all pretty much the same, with the only real difference in grades being the knock resistance and price.
03-11-11, 11:37 PM
#16
Now With 10th AE Fun!
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What fun is driving on stock boost? I have posted it before, but I have a stock sticker on my 10th AE that says run 92 octane fuel or higher... It says it on my filler cap too which is stock. Very weird. Not like you can get 92 in Ca anyway I don't think, and my car has always been a Ca car. I run 91 always, but I run 11-12psi too. 
03-12-11, 11:31 AM
#19
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For the most part, you don't need to worry about the octane of the fuel with an NA rotary engine unless the engine is running very high compression rotors, highly advanced ignition timing, a very lean fuel mixture under load, or highly contaminated with carbon deposits. I am not aware of any professional rotary race cars which require high octane fuel, so your street RX-7 should be fine unless you really screwed something up.
That's actually also a misconception. In the book, "How to Modify Your RX-7" by Dave Emanuel, Rick Engman stated that he found better results with "very low-octane fuel" and conservative (optimal) ignition timing as opposed to high octane fuel with highly advanced timing. People misconstrued this to mean that a lower octane rating always means higher performance. What it really means is that advanced ignition timing is not optimal, and that lower octane fuel tends to have more energy content. Since the energy content of pump gas does not vary much throughout the various octane grades, the main point here is to focus on tuning the ignition timing for optimal results. Simply dumping low octane fuel in your fuel tank will not make much performance difference if you have not fine-tuned your engine with an aftermarket fuel computer, however you will at least save money.
For reference *:
Chevron UTG-91 (86.8 R+M/2): 18500 BTU/lb
Chevron UTG-93 (89.3 R+M/2): 18300 BTU/lb
Chevron UTG-96 (91.6 R+M/2): 18400 BTU/lb
This shows that the high octane test fuel actually has more power than the mid-grade in this case. The power difference between the low grade and high grade is only about 1/2%, which works out to less than 1hp on a stock NA RX-7. Other brands of pump gas will have different statistics, blends also vary with specific regional standards, winter fuel is different than summer fuel, and race fuel is totally different.
* Chevron has since changed their test fuel from what is listed above, but they no longer publish the energy content, so I used the older 01/30/07 stats.
This is a very confusing subject. I have experience running a fuel farm and international fuel contracts, but I do not have the level of understanding that my chemists did. Those guys are something else, and it isn't reasonable to think that the average forum members would have that level of education and comprehension. However, you would think that the forum members would at least open the owner's manual to see what it says about fuel.
03-12-11, 01:23 PM
#21
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Stock = how it came from the factory. Once you start screwing with the boost level, fuel system, and ignition timing then it is no longer in the original stock form. Since your car has a modified fuel system and probably a higher boost level, then you should use whatever fuel was recommended by the tuner.
03-15-11, 11:42 PM
#23
so heres an update car actually got about 50miles more out of the tank with the mixed gas. only prob now is ive been overboosting for a bit and today i gave it a little to much pedal in third and ping ping boom. now i need a rebuild sucks *** to beacuse this motor only had about 30k on the rebuild now. :0(
03-15-11, 11:46 PM
#24
You have to port the wastegate, even with an S5 turbo. Opening up the exhaust will lead to creep. http://fc3spro.com/TECH/HOWTO/KWG/kwg.html
03-16-11, 06:17 AM
#25
Right near Malloy
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so i wasnt paying attention when i filled up a bit ago and i accidently put about 9 gallons of 87 into my TII i then once i noticed what i did i stopped the pump and put 5 gal of 91 so there was another 4gals of 91 in the tank so half 87 half 91. stock motor fuel exhaust. will it be ok. should i drive like an old lady or siphon all the gas out.
Case in point everyone... COMMUNICATION!
Proper punctuation and giving as much info as possible will help others help you.
Someone mighta caught on earlier had you said the exhaust was modified.
Sorry for your loss man.