Engine / Fuel Experts - Could too high a RON damage an engine?

Gibbo · 25 Apr 2006 at 00:55

HI there

Something I have been thinking about as other owners of Mustangs have different views so I'd thought I would ask the educated car people here on the OcUK forums.

The engine in my car is a 4.6l engine, 3 valve (F.F.S.), 8 cylinders, fuel injection, catalyst, 5 speed manual. Currently running at approx 330BHP and 340lb/ft based on US fuel.

Saleen recommend using premium fuel with an Octane no lower than 91octane (I think this is US rating which is equivalent to UK 95 RON, somebody may wish to correct me).

My first question is that 91octance equivalent to our 95 RON?

Secondly would runnin Optimax in such an engine offer improvements to performance and engine reliability? I do believe the cars ECU is capable of automatically retarding of advancing the timing based on the fuel grade.......

So is running on Optimax a good or bad idea?

I ask because if the engine is designed to run on lower RON then is there any point of giving it Optimax in such a kind of engine? As higher RON fuels are slower burning and my question could this possibly cause the engine to choke up over time?

Unlike most JAP/Euro cars that have engines in higher state of tune that recommend higher RON fuels the engine in my Mustang is a big V8 that is no quite so heavily tuned.

Now I understand if I say added a supercharger that Optimax would no doubt be a good idea. But do the experts think I should keep giving her Optimax or just use regular unleaded instead, is it possible for my engine to benefit possibly from Optimax?

Anyway sorry to go on and thanks in advance.

Gibbo

Gaijin · 25 Apr 2006 at 01:09

First of all if it's tuned for 91 octane pump gas, and has the ability to advance timing then i would personally run it on 95 octane and leave it at that. 91 octane is not really equivalent to 95 octane fuel. The octane rating is the explosive rating of fuel and so 95 octane is more explosive.

JRS · 25 Apr 2006 at 01:09

Gibbo said:
My first question is that 91octance equivalent to our 95 RON?

91PON is equal to 95RON, yes.

Gibbo said:
Secondly would runnin Optimax in such an engine offer improvements to performance and engine reliability? I do believe the cars ECU is capable of automatically retarding of advancing the timing based on the fuel grade.......

Won't harm it certainly. Don't know as you'd see any difference in performance at all, as that engine isn't in a particularly high state of tune. When you go to the supercharger (not if....don't fight it Gibbo....

) then you might want to go for a higher grade of fuel. As it stands, might as well stick with 95RON as thats what it's set up for from the factory.

****edit****

Gaijin said:
First of all if it's tuned for 91 octane pump gas, and has the ability to advance timing then i would personally run it on 95 octane and leave it at that. 91 octane is not really equivalent to 95 octane fuel. The octane rating is the explosive rating of fuel and so 95 octane is more explosive.

Educate yourself mate

http://en.wikipedia.org/wiki/Octane_rating

US gas stations use PON (also known by several other names) as the fuel rating. It's derived from the RON value divided by the Motor Octane Number (MON) and multiplied by 2. So 91PON is most definitely equivalent to 95RON.

Oracle · 25 Apr 2006 at 01:14

As has been said, for monetary value, i doubt you'll see a performance increase...you can get your ECU set (however) to only accept 99RON, 95RON, etc and retard on lesser quality fuel which will only result in a flat spot (most commonly in 3rd and 4th gear).

Gaijin · 25 Apr 2006 at 01:15

JRS said:
Educate yourself mate http://en.wikipedia.org/wiki/Octane_rating

US gas stations use PON (also known by several other names) as the fuel rating. It's derived from the RON value divided by the Motor Octane Number (MON) and multiplied by 2. So 91PON is most definitely equivalent to 95RON.

Sorry, just typed what was in my head even if it was flawed

Also didnt realise the yanks used a different system

JRS · 25 Apr 2006 at 01:16

Gaijin said:
Sorry, just typed what was in my head even if it was flawed

Also didnt realise the yanks used a different system

Catches a lot of people out.

Quite why we can't actually stick to one system the world over in this day and age is beyond me.....

Baron G · 25 Apr 2006 at 01:21

In the US Octane is quoted using the average of the Research Octane Number (RON) and the Motor Octane Number (MON) - if you ever see R+M/2, this is what it means.

MON testing produces a lower number than RON so US 91 (the very best typically available) is equivalent to 95 RON. The other grades available over here (87 and 89) work out at about 91 and 93 RON respectively.

/edit - too slow

Barry Smalley · 25 Apr 2006 at 07:49

My father in law has had two 2005 Mustangs (Albeit not Saleen ones) and he ran them on 95.
Now he has just bought a C6 Corvette, and that runs on the same stuff as as his F150 Lightning........95

Morba · 25 Apr 2006 at 08:32

Barry Smalley said:
My father in law has had two 2005 Mustangs (Albeit not Saleen ones) and he ran them on 95.
Now he has just bought a C6 Corvette, and that runs on the same stuff as as his F150 Lightning........95

we are lacking pics of these beasts, get them posted up!

merlin · 25 Apr 2006 at 08:46

Gibbo - just use a good quality 95ron fuel, for the detergents.

If the ECU won't advance ignition to take into account 97 or 98 ron - there's no point using it. However, it won't actually harm the engine.

You can only harm the engine by using fuel that's significantly under or over the RON rating your ECU will advance to. There's a theory that If you put let say 102 or race fuel in a "standard" car - it may not burn instantly, this leaves a ongoing (residual) heat on the exhaust stroke. Possibly though this is a concern more with higher revving cars.

Higher RON fuel doesn't burn slower as so to speak - it's just resists self ignition a little further afaik. Maybe someone can just confirm this - in other words the flame front occurs as the same speed as it does with a lower RON fuel....

Simon · 25 Apr 2006 at 08:52

merlin said:
You can only harm the engine by using fuel that's significantly under or over the RON rating your ECU will advance to. There's a theory that If you put let say 102 or race fuel in a "standard" car - it may not burn instantly, this leaves a ongoing (residual) heat on the exhaust stroke. Possibly though this is a concern more with higher revving cars.

Higher RON fuel doesn't burn slower as so to speak - it's just resists self ignition a little further afaik. Maybe someone can just confirm this - in other words the flame front occurs as the same speed as it does with a lower RON fuel....

Yay someone gets it, no need to run higher octane on your engine tbh, it's in a relatively low state of tune. Higher octanes do effectively retard the ignition though, the flame front is slightly slower and so the mixture takes longer to burn (hence why you can run more ignition advance). Using too high octane in has a habit of killing exhaust valve seats and increasing EGTs as the mixture is still burning after it leaves the combustion chamber.