I've asked this before and didn't really reach any conclusions. Given the scarcity of V-Power and Tesco 99 RON recently, I'm asking again.

My car is getting a remap soon. It will have a 2.5 short motor with acl bearings and forged rods, bigger turbo, 740cc injectors, FMIC, and ought to be able to do 400/400. (The gearbox has been swapped for a 6-speed). Is there any mileage, (pun intended), in asking for it to be mapped for 95 octane fuel, once it's run in? I've already had one engine failure and don't want to risk another if 98/99 stuff isn't readily available. I also don't want to have to carry/mess with octane additives.

Has anyone done this?
Can anyone suggest what % of power I might lose?
And will it effect the torque?

I asked Bob Rawle this exact question recently. He flies over to Ireland (or was it Cyprus... I forget... anyway somewhere overseas) regularly where they can only get 95 ron fuel. For an engine like yours the difference would be anything from 50 to 70 bhp!!! Not sure about torque.

So I had mine mapped for tescos 99 and stopped with the questions!!!

Like Westwood said... you'd be accepting a huge drop in torque/power for the sake of filling up with 95 RON + fuel addidives... kinda defeats the point of having a modified 2.5 lump surely?

TG did a test on a standard WRX STI

95 ron to 98 ron was +36bhp iirc

sorry to hijack the thread..... but would getting your car mapped for 95 ron plus half bottle of nf booster per tank raise the octane rating to around 98 ron, is this true? some people just laugh at me when i ask them. I didnt realise there would be that much bhp difference between the 95 ron and 98 ron

Southern Ireland only has 95.
In Northern Ireland most we get is 98.

according to their website NF race raises the RON by 6, so yes half a bottle would raise the ron by 3...but at £15 a bottle (or £7.5 a fill up) is it economically viable? why not just put 98 in?

The only petrol thats available where i live is just 95. im from ireland

ahhh ok...

We did a CFR/Knock Engine octane test in a lab with South African 95 RON fuel and half a bottle of NF Race and got a result of 98.9RON.

You can't work on half a bottle = 3 RON because gains get less and less from adding more and more NF. It also varies with what base octane you add it to. Adding to 98 will not give you as much as adding it to 95 or 92.

Here's a graph to give you an idea:

Double Post!!!

If it's mapped for 95 RON anything better you put in will increase power and torque. Depending what ECU is fitted it will "learn" it's got better RON and compensate accordingly (so Rich at Powerstation told me).

Thanks for that info

Bob did also say (IIRC) that adding octane booster doesn't give as good results as using the better fuel in the first place. Something to do with the other additives as well.

I used to use octane booster as a 'get me home' if I couldn't find my preferred pump. For sure it stopped the knock link going off but I always kept off the gas pedal until I had run it low and re fuelled closer to home.

Nowadays I'm better organised.... between Shell & Tescos you have be way off the beaten track to get caught out.

Whats this talk of 98? You either get 95, 97 or 99!

Personally I would get it mapped for 97 as its readily available and I get sick of having hunt for v-power or Tesco 99

I'll have to ask Bob if the LINK on my car will do that.

Ha! When the b*ggers have stock, in my area! And that's not often, usually it's just excuses..........

I thought V-Power was 98?

vpower = 99

^^

Optimax was 98RON IIRC

Blue Dragoon......... I'm not sure that you are right. Increasing octane will not give any more power but add a safety margin for the power / torque the car was mapped for (less likelyhood of det).

Shaun

99 octane? Ah, I was thinking of Optimax, then.

Still don't undertand why it's 10+p a litre dearer here than 95, when only 2c a litre, or less, dearer in France

Guys its a fallacy to think that you can remap a car on 95 Ron then stick better fuel in and get improved performance, you won't, the limiting factor will be what ignition can be dialled in for the fuel when mapping, and thats always (or should be ) the max possible to suit the fuel, of course you could map it to det its nuts off and rely on the ecu to retard the ign and protect the engine ... but knowing what can happen thats not an option in my book.

cheers

bob

Hi Bob

My aquamist / methanol RCMS Bugeye is still alive and well on your mapping

I guess your reply was better than mine above (number 20) LOL

Cheers

Shaun

Is that right, Bob? I could lose 50-70bhp?

Try not to look at it as "losing" 50-70bhp...just never achieving it

Like 350/375 is going to be slow in a classic !

dunx