Porsche Enthusiasts Club Forum

Hi All,

I just wanted to know whether or not a 944 S2 can be run a higher octance of unleaded petrol? 99RON for instance. Or would this require the engine to be remapped or something?

The only reason I ask, is because these higher performance fuels are supposed to make cars run more efficently and burn cleaner. Will a higher octane fuel increase fuel efficency i.e. better mpg?

Regards,

Ben

Yes it can be run on higher octane fuel & with anti knock sensing it should run better on it. However lots report it makes very little difference to the way it runs. On the older cars it tends to make mine run fractionally smoother but absolutely no other difference.
Yes a remap would take advantage of better fuel but the difference won't be startling, remaps work better on turbos.

When I used it regularly I got better fuel consumption, and I suspect it cleaned out the insides of the engine - judging by the extra rattling noises it made!

I don't think that it is financially beneficial since the hike in fuel prices. I would work out the increase in mpg against the increase in pence per litre. If the mpg percentage increase is less than the price percentage increase then it's not worth doing.

If you want the engine insides cleaning, I find that just a touch of Fairy Liquid (none of the own-brand rubbish mind) with every tank refill works a treat - and you get some cracking bubbles out of the exhaust pipe

I have no idea about the cleaning properties of Fairy and how that keeps the engine clean.

I do know that the higher octane fuels will over time clean badly carboned valve stems and do improve the mpg. On average you pay 10% more for the 97/99 and gain about 2-3 miles a gallon about 10%. I use the higher octane fuels in all my fleet.

I have used Tesco 99 octane rated fuel in the last few tank refills of my S2 and can honestly say I did not notice much improvement in either performance or MPG however the last 80L I put in was Shell VPower and I did notice an improvement in performance (slightly) but the main improvement was on engine smoothness and the way it seems to respond to the throttle. But as has been mentioned previously you need to either want to do it or get significant mpg improvements to pay back the extra money per litre.

We'd better point out that the Fairy Liquid thing was a joke - some of the girls might have believed it

Which brand do you tend to use Sean? I was using Shell V-Power, or whatever they call it now. With a touch of careful driving I was averaging 28 - 29mpg, so 7.5 - 11.5% up on the norm of 26mpg, however when the fuel prices increased last year the difference between Shell normal and Shell fancy stuff widened making it uneconomical to continue using it.

Before the big hikes the difference used to be just 5%. Then it went up and it became more than 10% more expensive. Today in Knutsford the Shell unleaded is 93.9, and the V-Power is 100.9 - a 7.5% difference. How do they justify the increased difference?

Still, the above figures indicate that I should be using it. I'm only interested in the improved economy, any inproved performance is wasted on me.

I use Ultimate or V Power.

I don't find any improvement in performance, but do benefit from the improved mpg.

Sean - pls explain!!! Your now getting 16.1mpg from the golf instead of 16?


Rich

18.4 is my new average

Hi,

Thanks for all the replies. I know that it can take 2-3 tanks of the 'real deal' before you see any improvement.

I tend to do a lot of short journeys so the mpg takes a hammering. On average I get around 20mpg. I think part of this figure is due to some overuse of the loud pedal. I try really hard to granny the 944 but somehow I always manage to forget after a mile.

Mind you, a collegue of mine has been looking at an Audi A3?? with a 3.2 litre V6 engine and flappy paddle thingy majig. Turns out fuel economy on that is about the same as the 944 S2. Makes me feel better knowing that my 20 year old car has about the same economy as a brand new hot hatch.

Cheers,

Ben

From the middle of last year I switched to using V-Power as my S2 became "lumpy" on over-run. It was "hunting" on tick-over too, which can be caused by other issues. It's not a daily driver and I only do about 3500 miles each year. Checks on the induction, fueling and timing were all fine, so my engine man suggested a few doses of injection cleaner. At £5 to £6 a time, it is the same as putting the higher octane fuel in, which have better cleaning additives. There is a definate improvement in response, but I find no difference in my average of 29-30 mpg - as I'm enjoying the performance !
If you do have injection problems then if you can get a bottle of "Forte" Injection Cleaner (only available through the trade) - this can work wonders ! Sorted my running problems out !

Forte is available outside the trade, on E Bay for instance 120325040079
It maybe worth pulling the injectors & getting them professionally cleaned.

At the dyno day last year, octane rating made no difference to cars' outputs - we had some turbos with the same mods (inc same chips) but with 99 and 95 fuels, with almost identical power outputs. As I understand it, the octane denotes susceptibility to knock amongst other things, which allows you to run more ignition advance. Some modern cars can adjust this automatically (but not ours) so you need a different timing map to take advantage. I also understand that piggybacks don't do this so you need something like Moates' Ostrich emulator or a new chip... Problem is that timing is a bit dodgy to play with, particulary when the boost is high, so you need to know exactly what you're doing to take advantage of it.

Now that took my technical knowledge into hazy territory so I hope that's all correct!!

Paul I thought the Turbo ran knock sense on the DME? I know the S2 does. However not all management of the period can advance to a knock point whereas all ECUs can retard once knock is detected. Modern cars tend to advance tothe point of knock then back off. This is done dynamically many times a second.
I'm surprised that the Turbo guys don't map closer to knock using higher octane fuel as this would give more power. In fact LPG is around 112 Octane!

Jim,

Like I said, we're close to the point of my knowledge here!! As I understand it, the knock detection on a turbo is a safety feature - it will retard timing if it detects detonation, but only from the set point (as per the S2). To take advantage of higher octane fuels, you have to advance beyond that point. I don't believe piggybacks allow you to do that as they simply allow fuel air ratios to be changed - to get real power benefits, you have to advance ignition. A friend of mine in the US runs E85 and he uses a Maxtronic to advance ignition to get power hikes - however he datalogs knock (amongst other things) to ensure that he isn't entering dangerous territory. I guess you could remap to take advantage of the higher octane however if you were unable to find 99 (or E85), you would be left high and dry, so I would reckon that people remap to a useable setup (95 or better) - if you were only intending to put one type of fuel in, then you could take advantage. I seem to recall a comprehensive thread on Rennlist which I must try and find....