racing 99+ fuel issues

[ALKISPAN]

Had a talk with the local dealer the other day
He insisted that I should avoid using racing 99+ gasoline in my mk1, because on long term it will generate engine problems. Instead I should stick on old plain unleaded fuel. Any ideas why? Is this correct?

[alunr]

The engine doesnt have a knock sensor so it ignores the extra abilities of the fuel you are putting in.

One would assume that the extra richness of the fuel must come out somewhere but I don't know enough to tell you more!

[DanH]

99 fuel apparently has lower calorific value than standard fuel. The only way you get an advantage is by advancing the timing which allows you to run the engine more aggresively and get a net benefit (requiring a knock sensor to be done without reprogramming ECU). Otherwise, as far as I can tell its actually inferior.

As mentioned, the k series lacks a knock sensor, so even if what I said above is in fact bollocks, the petrol is a waste of money

[ALKISPAN]

thank you all ,valuable information

[DanH]

Just to clarify, if you _always_ use racing 99 fuel, and have a programmable ECU, you could get the car setup for it. If you were then forced to put in standard unleaded, you would then have a problem as it would probably lead to knocking and potential engine damage.

Suppose you could always carry a laptop loaded with the different mappings in the boot

All a bit pointless though imho.

[tonykart]

so what about 95 vs 98? I can get both, easily. Are you saying the is no effect in getting 98? Even for an S2 111s?

[Nightmare]

'fraid so.....as far as i know they havent made any intrinsic changes to the K-series even now...hence no knock sensor.

That said, I run my S2 on Optimax, for the simple reason that all the independant tests showed it genuinely does keep the injectors in better shape. And seeing as it works out at less than 2 quid difference each tank....

N

[bogie]

The difference in bhp, even if you have a map for 98RON fuel on a 160bhp engine is around 3bhp. Some TVR Cerbies have a button IIRC for 98 RON mapping and it does make a 20bhp or so difference to them ...but thats on a 400bhp engine