Why do ppl say that octane doesn't make a difference?

Echoi17 · #1 08-21-2005, 05:37 AM

I can't figure out why people are saying that cars don't perform better on higher octane gas...Technically, if you think about it, when you dyno a car or race a car through a quarter mile, the cars running on 100 octane gas perform so much better...especially more so when they are turbo charged cars. So whats the deal with that?

somewhereinla · #2 08-21-2005, 06:31 AM

that's because a race car engine is tuned to perform better with 100 octane, bmw;s engine are tune to perform at their best woth 92 premium gas.

Ajogu · #3 08-21-2005, 12:33 PM

My manual says to use 98 octane unleaded if not performance gets worse

Over here, 98 octane costs approx. $1.65 a liter while 95 is 20% cheaper.

Now, in my previous car (Opel Vectra GTS V6), I used 95 octane while my brother's 330i was on 98 and we drove to Greece (4500km both ways) in both cars. Gotta say we were going quite fast on those highways and my bros car's fuel consumption was 10% lower than mine and once a filled up 98octane somewhere in the alps, my fuel conasuption dropped by 10% and could feel better response in the alps.

My conclusion: Higher octane gives better performance and lower fuel consumption.

03Topazbluex5 · #4 08-21-2005, 01:39 PM

Quote:

Originally Posted by Ajogu

My manual says to use 98 octane unleaded if not performance gets worse

Over here, 98 octane costs approx. $1.65 a liter while 95 is 20% cheaper.

Now, in my previous car (Opel Vectra GTS V6), I used 95 octane while my brother's 330i was on 98 and we drove to Greece (4500km both ways) in both cars. Gotta say we were going quite fast on those highways and my bros car's fuel consumption was 10% lower than mine and once a filled up 98octane somewhere in the alps, my fuel conasuption dropped by 10% and could feel better response in the alps.

My conclusion: Higher octane gives better performance and lower fuel consumption.

The Alps!!!! The elevation might have had something to do with it?!?!?!?!

MikeB · #5 08-21-2005, 01:53 PM

The purpose of octane is to slow down the rate the mixture ignites. The higher the octane, the slower the fuel mixture ignites. High compression engines require high octane because the heat and extreme pressure will cause the mixture to ignite prematurely. A high compression engine running low octane fuel will not produce as much power. A normal compression engine running high octane fuel will not run better. It is a waste of money. Only a high compression engine will benefit from high octane fuel. The petroleum companies explain this in the fine print.

High octane pump gas is not the same as race fuel. Race fuel is oxygenated among other things. It will help most engines run better. It costs over $5 per gallon.

Thunder22 · #6 08-21-2005, 01:59 PM

I don't think that octane is computed the same in the US as it is in europe is it?

lanbrown · #7 08-22-2005, 07:08 PM

Quote:

Originally Posted by WagnerX5

WOW..if I could get 98 octane I would be excited....

Engines are designed around a specific octane level. Thus an engine that requires 98 octane will run worse and can possibly detonate early on a lower octane fuel. Higher octanes are essential for FI vehicles because of the increased air flow and heat.

You'll see with many Turbo cars that detonation is a HUGE problem (causing the piston to hit the valve).

You can, just look at the RON value, which is what most of the countries use, the US uses R+M/2. All engines have detonation, that’s what makes them run. I think you mean pre-detonation and that’s when the fuel mixture ignites early. Detonation and pre-detonation have nothing to do with the piston hitting a valve, that's a different problem.

Octane has nothing to do with if an engine is FI or not.

Quote:

Originally Posted by MikeB

The purpose of octane is to slow down the rate the mixture ignites. The higher the octane, the slower the fuel mixture ignites. High compression engines require high octane because the heat and extreme pressure will cause the mixture to ignite prematurely. A high compression engine running low octane fuel will not produce as much power. A normal compression engine running high octane fuel will not run better. It is a waste of money. Only a high compression engine will benefit from high octane fuel. The petroleum companies explain this in the fine print.

Octane requirements have nothing to do with compression. You can have a low compression engine and still require high octane, just because the head is inefficient. You can have an engine with a CR of 8.9:1 that takes regular, or an engine that has 11:1 that takes regular as well. Engine displacement, head design and compression ratio are just three factors in what octane will be required.

Ajogu · #8 08-21-2005, 02:05 PM

Quote:

Originally Posted by 03Topazbluex5

The Alps!!!! The elevation might have had something to do with it?!?!?!?!

Yeah, driving in the alps does change characteristics of the car, but to worse. I noticed the higher I drove (altitute), the worse the power, torque, everything. So loosing 10% on fuel economy is a good thing

I took the X5 to Italy in July through the alps and experienced the same thing (loss in power, etc) using 98 octane all the way. So I assume that in the opel I had higher octane gave me better fuel economy.

ifly · #9 08-21-2005, 02:09 PM

I live in Europe and use 95 octane in the X. So why do you get lower octane gas in the mile high city of Denver?? The lowest Octane I have seen at a gas station is 84 to 85 and sometimes the premium gas is 89 to 90?

Just a question and maybe it relates to performance as I had the same issue driving back to Poland from Nice last year going through the Italian Alps.

Bavarian · #10 08-22-2005, 08:35 AM

Quote:

Originally Posted by Ajogu

My manual says to use 98 octane unleaded if not performance gets worse

Over here, 98 octane costs approx. $1.65 a liter while 95 is 20% cheaper.

Now, in my previous car (Opel Vectra GTS V6), I used 95 octane while my brother's 330i was on 98 and we drove to Greece (4500km both ways) in both cars. Gotta say we were going quite fast on those highways and my bros car's fuel consumption was 10% lower than mine and once a filled up 98octane somewhere in the alps, my fuel conasuption dropped by 10% and could feel better response in the alps.

My conclusion: Higher octane gives better performance and lower fuel consumption.

But in Europe the octane rating is measured differently...

So 98 in Europe is NOT 98 in North America.