Molotovman

iTrader: (49)

I can get some of this for free, Will it benefit me at all with my N/A, or is it just bad for it? I'm talking like 2 gallons, good Idea, or bad idea? Will I see any sort of power increase, or will It just be useless like putting 93 octane in the car?

-Ian
EDIT: This would be on an 87 S4 motor with 175k original miles.

I love my 87 se.

hornbm

totally useless

Alot of the N/A racer guys have special LOW octane fuel brought in. A natualy aspirated rotary is said to run best at something like 82 octane

zinx

iTrader: (3)

No, you want as low of octane as you can get in an N/A. Mazda ran 85 in all their N/A rotary race cars.

ddub

Worst idea ever, it will only hurt you not help.

Molotovman

iTrader: (49)

Thats what I thought. I just wanted to check. Does 104 octane blow up pretty good?

ddub

Blow up? The higher the octane the less chances of detonation, if that's what you're talking about.

Evil Aviator

The 104 octane fuel would probably add some power if you tuned for it (aftermarket fuel computer required). The octane rating itself doesn't do anything for you, but since there is no 104 octane pump fuel, it is obviously some type of race fuel that will most likely have more power. Do you know what kind of fuel it is?

Wankel7

At least your asking first...good job

James

87turbomkiii

Running 104 octane fuel in your stock(i assume) s4 is not going to do anything for you in terms of performance. Your motor was not built or tuned to run 104 octane thus making it a complete waste to put it in your tank.

Molotovman

iTrader: (49)

thanks for the info, i figured it wouldnt do anyhting, because its higher octane fuel and i know its better to run 87 than say 89 or 93. My firend just told me his friend left about 5 gallons of 104 octane race gas at his house, and I could have some of it. I didn't get any yet I figured it would just make my car run like crap.

Icemark

It would probably run ... okay... but there would probably be considerable build up on the rotor combustion faces.

totallimmortal

what if ignition timing were changed for the higher octane fuel? and would thre be more of a benifit in a s5 NA with higher compression?

Tofuball

Changing the ignition timing effectively . . . and I guess leaning out the mixture some . . . But I donno if it would really be worth it in the end.

SonicRaT

iTrader: (6)

Most race gases are leaded as well. Just run on the lowest and you'll be fine, even if you ran it and it did help, it wouldn't be worth the cost on an N/A.

Tofuball

I know the lead in gas helps keep non-hardened valve seats in good condition.
I think it is supposed to 'fill in' small scratches and act as a lubricant at times . . .
I think it kills cats and O2 sensors . . .

I wonder what leaded gas would do for a rotary.

veryblacksquare

would lower octanes such as 87 be better for turbos as well? or is there some sort of difference?

RotaryWeaponSE7EN

iTrader: (6)

Valve seat? Ur not suppose to say that in here.....

sar

iTrader: (1)

The reason why higher octane is needed to prevent pre-detonation.... when the compression and temperature of the combustion mix don't need a spark to ignite. This is why the s4 rx-7s could run 87 octane with 8.7:1 rotors, low compression on stock turbo == okay to run low octane.... but the moment you increase boost you need to make sure that your gas is higher octane.... you might need 104 octane gas if you're pushing like 30pounds of boost all day. As you increase air temperature and compression you will need higher octane. Pre-detonation spins the rotor in the wrong direction and breaks apex seal when the rotor won't move backwards.

High octane in piston engines is also actually bad for a car that does not need it. The higher octane gas will burn less which will produce less power and leave more residues.

So.... turbo rx-7 would depend entirely on how much boost... if tons, then yes, high octance.... if stock... then stick with what is recomended

Evil Aviator

There are too many variables involved to answer that question.

If it helps, the octane rating is an anti-knock rating. The octane rating can be raised by either "watering down" the fuel, or "hopping up" the fuel. Without knowing the other statistics of the fuel, there is no way to know if the fuel will be "better" for your engine. All you really know is that a fuel with a higher octane rating will generally resist knock better than one with a lower octane rating. Generally, higher octane means less power, but that's not always the case.

Pump gas usually has the same power (18,000 to 19,000 BTU/lb), regardless of the octane grade. Often, the lower octane grade has slightly more power (18,500 vs. 18,400 for example), but I don't think most people are going to notice a 0.5% difference. Race fuel may or may not have more BTU/lb than pump gas, depending on its composition.

Detergents are also good for your engine, and race gas doesn't usually have detergents. The US government requires a certain level of detergents in pump gas, and most manufacturers use the same detergents in all of their octane grades. However, the new Shell V-Power is supposed to have the industry-leading detergents.

A stock TII is rated for 87 (R+M/2) octane.

veryblacksquare

thanks for the clear up guys, i just recent got a TII a month ago and wasnt to sure about subject. anyhow, thanks.

totallimmortal

I was wondering the same thing about leaded gas in rotaries, when the first rotaries came out leaded gas was still being use i think so was it used in rotaries?

Icemark

Probably not, as I would guess that the build up of lead would probably eventually cause apex seal sticking.

No proof on that however as I have never seen a rotary engine that was popped open after running leaded gas.

KingCobraV9

iTrader: (2)

my car runs like *** on 87 octane but a ok on 89 why is that? its just N/A not a turbo

Evil Aviator

If the engine is worn, out of tune, and/or full of deposits, it may run better with a higher octane grade that reduces the knocking caused by these types of engine problems.

KingCobraV9

iTrader: (2)

o. could be true it does have 126xxx miles on it i was going to do the watter trick this weekend think that will help it?
(done thread jacking now)