Outer Limits 4x4 Board

(92 carby 4.2 fresh petrol motor with lukey's)

Motor runs perfect on 91 ron fuels, 95 ron yeah still good.... 98 ron and it runs like a bag of shit, backfiring and everything when on full throttle...

Tested it a few times, it is definitely the fuel that is causing it. (BP ulti)

If it was the other way (running shitty on 91 ron and fantastic on 98) I would understand...

But what would cause this???

Does it just maybe need timing done?

Or could it be something to do with the lifters?

Thanks in advance

High octane fuel will not make your car run better if you don't need it. You will make more power with the least octane fuel you can get away with.

hi octane fuel wont make an engine run worse even if it doesnt need it wont make more power but it shoudnt loose any either you could try advancing the timing by 5 deg and see if that makes a differance

rvh96 wrote:hi octane fuel wont make an engine run worse even if it doesnt need it wont make more power but it shoudnt loose any either you could try advancing the timing by 5 deg and see if that makes a differance

Of course it will!!! Higher octane means slower burning! Try putting Avgas in your mower, it will be a bastard to start, and run crap.

yeh timings not set for the higher octane .....

Totally agree with Crushu on this one.

It was like the old days when you could pump avgas from the servo. Mates would spend a 1.30/l on the shit with there reasonably modded v8's and they would be sadly dissapointed. Unless you have the compression it ran worse.

This is even more the case when you are talking a tb42 with only 8-1 compression!!!!

No need to run it and no benifit so don't bother.

My 4.5 has no real need for hi octane and I certainly can't tell the difference so I dont spend the extra.

I always ran 98ron and had an average fuel use of 22.85L to the 100 now just a few weeks ago i swapped to 95ron and get an average of 20.50 to the 100. Power wise cant tell the difference might try the standard unleaded and see how that goes.

The car has no computer for engine management so it will not recognise the different fuel via the oxygen sensor.The car is tuned for 92 so run that in it.

I think you might find the problem is that its a carberated engine and not injected. I tried high octane fuel in my old suzuki sierra once and it wouldn't even idle let alone perform better. Put 95 unleaded back in it and it ran fine. I think there is also info on the pamphlet from the servo about 98 fuel that it is only meant for efi vehicles. But I'm no mechanic so i may be wrong.

Yet i found 98 the best fuel when i had my Dual Fuel, especially Boost 98 from united with the ethanol in it.

If i ran 91 it would ping its head off up hill and no acceleration, 95 did little to stop it, Even Vortex 98 and Ultimax still had a slight ping to it. Tried the boost 98 when i was out at Cowra one time cause i wanted to fill the LPG and petrol up. man i loved the stuff, it made my patrol go like a rocket on petrol.

then again i did have it tuned for gas

8:1 compression would be best suited to the old standard 89RON fuel. Thats why it runs ok on normal unleaded. My V8 runs ok on ULP..... runs HEAPS better on PULP, runs ok on 98... but there is no performance difference, so it's a waste of time paying the extra 5 cents per litre for it. Sometimes high octane fuel will work ok on certain engines..... a guy i used to know ran his 2F motor in his 40 series on avgas because he got it for nothing it ran fine.