Does a higher fuel grade mean better performance?

[happygrump]

A buddy of mine and I were having this discussion between beers the other night. He always puts in high grade gas in his car because he says it gives him better performance. He owns a hot little Toyota, strictly stock but it goes pretty good.

I, on the other hand, am too cheap to spend the extra $$ on high test fuel. I also own a nifty little Toyota, though not the same model as my buddy, and I'm quite happy with the performance.

So I did a little test. Recently, after gas prices dropped a bit, I spent the extra bucks and put the higher octane stuff.

Now, I know that it burns hotter and cleaner and all the rest, but I frankly could not tell the difference in performance between that tankful and a tankful of the regular stuff.

This, written by a mechanic who is not beholden to the oil industry, says that it makes very little difference in most cases.

This, written by the folks at Shell, say that it makes a big difference.

This, by a journalist and citing a number of sources, says it may make a difference, sometimes, maybe.

What's your experience?

 

[auto doctor]

Fuel Injected Engines not much dif... the computer compensate for the crap gas by dumping more fuel...

Carburated engines...noticeble dif..because the fuel rate is at a preset and does not adjust for various gas quality...

but the big dif is the driving start ups and driving habits...Lead foot and brake lover.

Personally I have two vehicles with both type of fuel system and i stick to mid grade for both.

But if you have a need for speed at the top end... higher grade gas is a given..

 

[contractor]

Newer cars with computers are specifically calibrated for what ever fuel the manufacturer recomends. The higher grade may not help but it won't hurt anything but your wallet. Cars tyhat require higher octane ie., Viper,Porsch etc require the expensive stuff. Any older carburated vehical will get up and leave faster on a higher octane fuel.

 

[baci2004]

This doen't really answer your question but from what I understand every engine has an optimum octane rating (not sure where to find this) and if exceeded you could potentially damage the engine over time.

I have also heard that you get better mileage from the higher grades which actually offsets the cost. I'm not sure if this is true , but it sounds reasonable to me.

When I drove a Honda CRX si, I found the higher octane gas made the car a bit more responsive. I only really noticed it when bringing up the rpm's from idle.

 

[wrong hole]

my current car requires that I put the high end fuel (well that's what it says in the manual), so I have not tried a low grade fuel

the only thing i flutuate btwn is the ultra 94 and supreme 92 or 91

I don't really find a difference....but i've heard the ultra is too clean and burns too fast

 

[poorboy]

Sometimes a lower grade fuel will give you more energy per unit. The higher octane is to reduce knock. The higher octane fuel also contains more cleaners for the fuel injectors.

When I am at the track, I run Sunoco 116 leaded fuel. It allows me to turn up the boost from 18lbs to 24lbs without any knock.

Many of today's engines have aluminum blocks which are not as strong as iron blocks. If you use a lower octane than the manufacturer recommends and you have a lead foot, you will get knock. You may not be able to hear it either and that is why the term used to describe it is called silent knock. The computer will react, but not quickly enough since it has to detect the knock first to dial back the timing.

What will happen over time is that you will oval out your cylinders, leading to increased and maybe even excessive oil consumption.

If you don't have the lead foot, you can get by on the lower octane fuel, but if you like to open it up, go with the recommended fuel.

So to answer your question, yes, higher octane does mean better performance if the car is calibrated for the higher octane.

 

[bishop]

While it is true that modern cars through the oxygen sensor can compensate for lower octane levels, this is only true for low RPM bands. In higher RPM bands the computer disreguards the oxygen sensor information because it the sensor is too slow to respond. So if you drive in the city alot, high octane fuel should net you better fuel economy. As far as performance goes, you should get a wee more power with higher octane fuel, if you have any modifications on your car that increase the flow of oxygen into your engine, ie cold air intake, short air intake, you should probally get higher octane fuel since you are doing modifications which allow your engine to get more air than was designed for, you should add a bit more octane to compensate.

I have heard that luxury cars require you to use high octane fuel, I have never owned 1 but have heard several stories of people needing to get their fuel pumped out of their car because they accidentally put in lower octane fuel. I have no idea if these stories are true, I would tend to think they are not, a few points lower in octane should be fine for most engines for a short duration. If you had an engine that was finiky with a few percentage change in octane levels then the engine must really flip out when you rev it high or put any type of stress on it. If you drive a luxury but use cheap fuel my only advice is to not drive aggressively with the car, your engine may explode. I am not joking I had an engine explode on me, mind you this was on a heavily modified civic, but it was due to lack of fuel.

 

[freakshow]

Poorby and rub i think you hit it.......


Rub as for petro i dont like it never use it they had a problem a while back something additaves in their sensors that gm was blaming them about. I always use sunoco!!!!!!!!!

People rember your not going to notice a differnece running higher octane on a tank of gas they recommend that if you want to expirement that you should burn a few tanks that make your judgment call.


Poorboy what you boostin to 24lbs and what are you using to boost?

 

[antaeus]

So I did a little test. Recently, after gas prices dropped a bit, I spent the extra bucks and put the higher octane stuff.

Now, I know that it burns hotter and cleaner and all the rest, but I frankly could not tell the difference in performance between that tankful and a tankful of the regular stuff

What rubmeister100 says pretty much sums it up. Directly in your case, you won't notice difference in only one tankful. If you're the record keeping type, compare regular to high octane performance over a reasonable time. But I'm not a combustion engineer to recommend what that time should be, but more than one tank.

The high octane fuels burn more efficiently, that is produce less combustion byproducts, gumming up internal engine surfaces less. Plus, some of the additives rubmeister100 describes are solvents that lessen combustion byproducts sticking to engine surfaces. An internal combustion engine being an aspirated system performs better when it aspirates better, meaning it needs to be clean. High octane fuels assist this.

F1 and CART, for example, burn methanol, somewhere off the commercial fuels octane scale, as those engines require tremendous aspiration efficiency.

1. Use high octane for weeks to months then compare
2. In general, higher revving engines (your friends hot little Toyota, variable valve timing) require higher octane as they are built for it.

 

[poorboy]

Poorboy what you boostin to 24lbs and what are you using to boost?

I have an 87 Grand National. Best run down the quarter mile was 11.81 at 114 MPH on slicks. Car is full weight and air conditioned.

Turning up the boost is easy. Just switch to a performance chip and shorten the wastegate rod to the turbo.

The car has been modified with a 3000 stall convertor, 50% larger intercooler 36lb injectors, slightly bigger turbo, 3" downpipe off the turbo, stronger fuel pump and other small things.

Stock cam, headers, valvetrain and heads. Only internal engine change is stronger valve springs.

 

[james t kirk]

My hat is off to rubmeister and poorboy.

Rubmeister hit the nail right on the head.

If your car doesn't need higher octane, putting it in the tank will gain you nothing.

I have an old British car which I have increased the compression from the stock 7.75:1 to 10:1 by milling 175 thou off the cast iron head. (Yes, that's more than an eigth of an inch) and have a fast road cam in it. Also ported and polished the head, matched the intake, and balanced the engine.

I have also advanced the timing to the limit of the ping. This alone gives a remarkable difference in performance.

As a result of all this, the only fuel she can run on without knocking or pinging is Sunoco 94. I know exactly where to set the timing to the threshold of the 94.

Put 93 in it and she will start to ping.

My day to day Buick is a stock 3800 with a P.O.S. plastic intake manifold. It runs on 87 just fine.

They manufacturer generally will make an octane recommendation for the stock engine.

Stick to it.