91 vs 95

[muddymatt1973]

Hi All,

I run a 2003 Discovery 2 V8. Handbook and inturdnet specify 95 ron so that's what I use. I have put 91 in (actually the missus did by accident) and I'm pretty sure it took more right foot to drive and so would have used more fuel.

I think research backs this up but I was wondering what your guys experiance is?

Does your motor spec 95 but you always use 91 or the other way round? Do you notice any change?

Lastly - the wife put $30 of 91 in by accident then remembered she had a supermarket voucher for Gull. So she drove across town and added another $30 of 98 to even it up! So does it work like that? Did we end up with $60 of 94ron! lol

Cheers Matt

[parriehunter]

Not a 4wd but when i had my Celica running a 3SGE, i paid less for 95 per km than if i ran 91 per km.

I am not sure if it was a mind thing that made it seem like it had less power but i spent a month on 91 and a month on 95. It was definiely worth while for me to run 95 in it. I also tired 98 but that just cost more for no gain.

[Ralfie]

I always use 95 octane in my petrol vehicles.

The 95 refers to octane rating and you get more bang for your buck with it.
91 maybe 4% cheaper than 95 but you get 5-10% better performance and mileage out of 95.

91 won't hurt the engine but as you say it needs more right foot to get up and move thus using more fuel and therefore costing you more in the long run. Not an economical practise for the sake of trying to save a few dollars at the pump.

[tweake]

91 won't hurt the engine.

depends on the engine. old ones will blow.
most modern ones will just retard the timing when it knocks. its not good for it to keep knocking and the timing will always be out a bit. it will run poorly.
the good cars that are built for variable fuel will change ignition maps and give the correct timing. they will run fine on just about anything.

[Ralfie]

Yes, thanks for clearing that.
However I was only referring back to the vehicle in question, but guess didn't make it clear enough.

[churchill]

It should be alright if you drive it easily. I drove my airtrek turbo on 91 for a whole tank, just didn't gun it and it was fine. You've done the right thing by blending the fuel, you can also add octane booster if your still worried.

[prado_boon]

you can also add octane booster if your still worried.

Octane booster is a total myth, there have been many test conducted. Check it out: http://www.youtube.com/watch?v=2jbcCr2ll3c

Also, 91 vs 95 is not going to make much of a difference. Don't worry about it unless you have an old V8 pushrod engine timed so advnaced it "just" doesn't ping on 95 at WOT.... then you might get some pinging on 91...

Use 96 or 98

I have heard many many people say shell petrol is the best. But then again... it's all the same!

[churchill]

Octane booster is a total myth, there have been many test conducted. Check it out: http://www.youtube.com/watch?v=2jbcCr2ll3c

They didn't even change the timing in that test as the higher octane fuel burns slower. They also measured power output not octane rating.

Have a read of this. Looks like they do work.

http://members.rennlist.com/951_racerx/OctaneBoosterComparison.html

[polaarbear]

I always thought the RON number is an indication of how much you can compress something before it will combust. So in an engine with high compression you'd need to use a higher octane fuel so to make sure it doesn't knock. Whereas a low compression engine won't compress the air/fuel mixture as much and therefore doesn't need a high octane fuel...

[churchill]

Exactly though some people think their low compression engine runs better on high octane gas. Never done the stats on that myself.

[bang-thud-thump]

race cars use race gas.
Its a solution to a problem (high compression) rather than a performace boost. using Av or c16 wont help your 1972 corolla.

But I agree with using 95. usually better results.

[cornflake]

in my mazda i have 260-300hp depending on gas
non turbo 13.1 comp
use both 91 95 with no detonation or pinging 98 is just as fun
and have advanced timing of 14degres

[churchill]

Interesting, if I remember correctly F1 cars used fuel closer to 91 due to the fact it combusted quicker which suits engines reving to 20000rpm.