What octane gas for my 88 sc mk1?

[8589]

user's data (non "technical")

I do a lot of miles weekly = lot's of fill ups = (with engine cold) car fire up like a ford model T with 93, like TS said 93 is slow burning, with 87 car fire up like a champ, case solved for me.


I always start with manufacture suggestion then I do my trials, the ping/low octane mentioned is the best simple method to adjust octane to necesities..there is the timing/low octane method but that's another story

[jasenklems]

I miss the days here in cincinnati that you could get 98 octane at any gas station but not any more it is a shame that has changed now I have to get fuel at the track or at the airport for aviation gas ( it is like 120 octane I mix that 50/50 with the highest octane at the pump)......

[filonin_2]

Toyota recommends at least 91 for the SC, good enough for me. Running a higher octane can let you run more advance without the threat of detonation.

[scottohno]

i once heard from someone that it said somewhere to use E85 from your local farmer if you could... it wasnt even invented yet, so i call BS on this guys story whom i probably quoted wrong but shall remain anonymous until he happends to stumble upon my post.

i wonder if we could get an E85 compatible fuel gauge sender... i know where to get a pump thats e85 safe... then we could advance to 14* or so jumpered, and have more go-go

[mr2tim]

Scooto-we do have E85 compatible fuel gages, the mechanical float characteristics do not change with fluids.

Here is a definition of octane I found:

Octane rating does not relate to the energy content of the fuel (see heating value). It is only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where octane is raised by blending in ethanol, energy content per volume is reduced.

Therefore buying 98 octane rating for energy compacity is false thought.

So is getting better performance like I previously thought I felt in the seat of the pants on race gas. Oh well...

The picture I am now getting is that if you buy 10% alky gas you are going down in available energy.

So 328's Aussy 91 octane and my 91 USA (10% alky) octane are not alike? His has more power available.?

Jeez..just when I thought living in America was so great..

[scottohno]

is this true for the NA cars? would i have to advance my ignition a bit?

i can save 50cents a gallon by using e85. this would go great with a supercharger on the 9.4:1 because of the burn control, but fuel economy will suck.

maybe 1/2 and 1/2

[griffin2020]

Originally Posted by scottohno

is this true for the NA cars? would i have to advance my ignition a bit?

i can save 50cents a gallon by using e85. this would go great with a supercharger on the 9.4:1 because of the burn control, but fuel economy will suck.

maybe 1/2 and 1/2

The manual for my 88 SC states specifically to not use any gasoline with a methanol level of greater than 10%. There are probably several reasons for this, not the least of which being that methanol burns much less efficiently than gasoline, as well as the fact that it eats the rubber hoses on vehicles that were not designed to run it.

Also, my manual states that the recommended octane level is 96 (US). It is impossible to find 96 octane in my part of the country, so I add octane booster.

I notice increased fuel efficiency with it. I get around 180 miles per tank on 91 octance, and around 220 miles with octane booster.

[BlackWidowMR2]

You only get 200 miles to a tank? That's ridiculous. Does the SC really make that big of a difference?

[dirocyn]

Alcohol has 60% as much energy as gasoline. The 10% ethanol gas we get most everywhere in the States has 96% as much energy as real gas.

E85 has much higher octane than pump gas, but it has 66% as much energy as real gas. If your engine is set up for it (higher effective compression, more advance, and flowing a lot more fuel) it can make a lot more power. But you'll get less power on an engine set up for gasoline.

As far as octane rating--there are (at least) 2 different methods of calculating octane, the RON and the MON, in the U.S. the octane listed on the pump is the average. Most pumps list "R+M/2" somewhere on them. Here in Tennessee, 87 is low-octane, 89-90 is mid grade, and 92-94 is high octane. Before R+M/2 was mandated, you might find the same gas listed as 66 or 108 (random numbers pulled out of the air).

You can run with more spark advance on higher octane fuel, and that can net you more power.

Edit: Many countries outside the U.S. list RON on the pump, and I'm adding some equivalencies:

U.S. "regular" 87 octane =91=92RON and 82/83MON. U.S. 90 =95RON and 85MON. U.S. "premium" 93-94=98RON 89MON.

If the manual says minimum 95, I bet that's RON. If your pumps list R+M/2, look for 90 octane.

[AURMEND]

adding 10% ethanol would make the gas companies 10% richer

[toyotaspeed90]

Originally Posted by griffin2020

Also, my manual states that the recommended octane level is 96 (US). It is impossible to find 96 octane in my part of the country, so I add octane booster.

I notice increased fuel efficiency with it. I get around 180 miles per tank on 91 octance, and around 220 miles with octane booster.

that seems odd..... octane has nothing to do with how much mileage you will get.

an octane booster is just a way to get your money. it doesn't do anything. it might raise the octane value... maybe 1/10th of a point.


the octane rating, as I've said time and again, is just a rating of how easily the gas can ignite -- lower rating and it's easier to ignite. Higher rating and it's more difficult to ignite. Boosted engines and those with high compression have to use higher octane -- it's more difficult to pre-ignite (more heat in the combustion chamber in these types of engines and more likely that during compression the gasses will self-ignite).

And again... as I've said this over and over and over (.......) you want to run the LOWEST octane that your engine doesn't pre-ignite on. The more difficult the gas is to ignite the higher possibility that it isn't completely burning upon each ignition.

[dirocyn]

Originally Posted by toyotaspeed90

..... octane has nothing to do with how much mileage you will get..

It can, actually. If you have an engine that sets spark timing based on a knock sensor, your engine will run more advanced timing on high octane gas and more retarded timing on low octane gas. That can effect both hp and mpg. But the difference is marginal.

Originally Posted by toyotaspeed90

The more difficult the gas is to ignite the higher possibility that it isn't completely burning upon each ignition.

Gotta disagree again. The octane number has to do with the autoignition temperature, not the burn characteristics once it's lit. Gasoline autoignites at 475-576 degrees F, depending on its octane and fuel mix. In a high-compression engine, or one that's overheating, it's not hard to get there. And it burns at about 1650 degrees. You could raise the auto-ignition temp to 800 or 1000 before incomplete burn becomes an issue.


The reason to buy lower octane gas is it's cheaper. Running gasoline that's higher octane than you need won't hurt anything--it won't cost you power, it won't cost you mpg. If 95 octane was cheaper than 87 octane, I'd buy it. You want your octane to be just a touch higher than your engine's knock temp on its hottest day.

[toyotaspeed90]

The first part -- I don't entirely agree. If you're concerned about MPG then you're probably not driving at high rpm in 3rd gear everywhere you go. The amount of power to keep a car in motion at a set speed (say 60 or 70mph) is typically 30-50hp... not much. That's a low load, low rpm's and low temps -- if you're having issues with your knock sensor at cruising speeds then you're driving like an idiot in 3rd gear at 70mph or there's another serious issue with the car.

and the 2nd part.... if that were completely true then you would never see carbon build up (unless, again, there are other issues at hand and you're burning oil) It's been years... but the flamefront, performance, and octane was something we went over for a good few days in one of the automotive engineering classes I had (at one of the top VRI's in the country)

[scottohno]

dirocyn, you make some good points, but i too have to disagree.

the fuel MAY NOT burn all the way through. higher octane fuel does burn "slower" than lower octane fuel. this is WHY you can advance the timing more. if the flamefront hits the piston any time AFTER top dead center, youre pretty much golden. somewhere around 120* the burn is complete and the downward force on the piston is little to none.

according to you, you can advance your timing more with higher octane because it wont detonate. detonation is fuel igniting under pressure and heat, without the help of a spark. a detonating (hi comp, overheating, etc) engine can run (albeit for a short time) without an ignition coil IF you were to tune it just so (the flame front from the detonation would have to hit the piston after TDC.) dont believe me? look into how a diesel engine works. (diesel burns slower so it doesnt do as much damage to the pistons and rods even with compression ignition)

[toyotaspeed90]

Originally Posted by scottohno

according to you, you can advance your timing more with higher octane because it wont detonate. detonation is fuel igniting under pressure and heat, without the help of a spark. a detonating (hi comp, overheating, etc) engine can run (albeit for a short time) without an ignition coil IF you were to tune it just so (the flame front from the detonation would have to hit the piston after TDC.) dont believe me? look into how a diesel engine works. (diesel burns slower so it doesnt do as much damage to the pistons and rods even with compression ignition)

Diesel's run at an insanely high amount of compression... they also have pistons with special coatings to withstand the knock. Preignition/knock on a gas engine will literally burn/melt away pieces of the piston as it ignites... the big problem with this is that as it makes these pinholes in the surface they become hot points (instead of just a flat surface that the flame moves across it's something that the flame can 'grab' or move around)... which then will in turn increase the likelyhood of preignition. Temperature across the face of the piston isn't actually even.... there's higher temps along the edge where the pistons 'ride' against the block, which is why you will see preignition pitting usually along the edges of the piston.


Diesels and pre-ignition are what are known as uncontrolled (or chaotic) ignition.... the igniting point isn't always the same place

[traintech86]

Holy cow, this is a civilized argument... keep going haha.

[dirocyn]

Originally Posted by toyotaspeed90

The first part -- I don't entirely agree. If you're concerned about MPG then you're probably not driving at high rpm in 3rd gear everywhere you go. The amount of power to keep a car in motion at a set speed (say 60 or 70mph) is typically 30-50hp... not much. That's a low load, low rpm's and low temps -- if you're having issues with your knock sensor at cruising speeds then you're driving like an idiot in 3rd gear at 70mph or there's another serious issue with the car.

Hey, no fair bringing the real world into a theoretical discussion... I was talking about a theoretical engine that bases timing entirely off a knock sensor. I'm not an expert on ECU programming, but I suspect our ECU has only a narrow range of control over timing advance--if your base timing is wrong, the ECU can only correct it to get you so close. I'm thinking spark timing like on OBD2 and future theoretical things that haven't been invented yet.

Originally Posted by toyotaspeed90

and the 2nd part.... if that were completely true then you would never see carbon build up (unless, again, there are other issues at hand and you're burning oil) It's been years... but the flamefront, performance, and octane was something we went over for a good few days in one of the automotive engineering classes I had (at one of the top VRI's in the country)

Doesn't carbon buildup usually happen when an engine's running rich? If there's not enough oxygen in the cylinder for the fuel to combust, nothing you do to spark timing will fix that.

[dirocyn]

Originally Posted by scottohno

higher octane fuel does burn "slower" than lower octane fuel.
...
(diesel burns slower so it doesnt do as much damage to the pistons and rods even with compression ignition)

(quotes taken out of order)
Diesel has 15-25 octane. Octane rating and speed of combustion are separate things. It's plausible, maybe even likely, that in real-world gasoline the higher octane gas burns slower.

Originally Posted by scottohno

according to you, you can advance your timing more with higher octane because it wont detonate.

Ok, you got me. I see the logical fallacy of my argument. Yes, higher octane must burn slower, otherwise you could not run more advanced spark timing. However, the octane rating itself is not what causes the fuel to burn slower. The octane rating is a measure of resistance to auto-ignition, not a measure of combustion speed. Unfortunately, combustion speed is not printed on the gas pump where we can see it.

[dirocyn]

Originally Posted by toyotaspeed90

Diesel's run at an insanely high amount of compression... they also have pistons with special coatings to withstand the knock.
<snip>
Diesels and pre-ignition are what are known as uncontrolled (or chaotic) ignition.... the igniting point isn't always the same place

I don't know about insane. Road diesels run 16:1 to 25:1 compression. My pickup truck has a Detroit Diesel 6.2, it's got 21.5:1 compression. They don't all have special coatings on the pistons, though. Diesels don't do the same way gas engines do, they don't have to worry about flamefront. The way that works is, there's no fuel in the cylinder on compression. No risk of detonation, because it's just air. Air that's well over 600 degrees F, by the time the cylinder reaches TDC, just from compression (after the engine's running and warmed up, cold start is a whole separate set of issues). Then the injector opens, and sprays high-pressure fuel into that 600+ degree chamber, where it ignites instantly. Flaming fuel sprays in, and combustion is more like a flamethrower than like a grenade. There's really not much of a shockwave, and the piston's already pushing against pressure when combustion happens.

With diesels tuners do worry over injection timing--but it's not at all the same thing as spark timing.