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MG ZR ZS ZT Technical - Super Unleaded in a ZS180?

Well, it's only 4 days 'til I get my new toy and I've started wondering. A friend of mine with a Scooby Impreza runs on Super Unleaded petrol and gets sufficiently improved fuel economy to make it cost effective plus extra power when he is in the mood. Obivously, to get these gains, the ECU needs adaptive anti-knock so that it can use the extra octane. Does anyone know whether the ZS180 is able to adapt to the higher octane fuel?

Cheers,

S.
Steve H

Steve, most cars with high revving engines, or ones that are considered performance engines, will benefit from 97 Octane rather than 95. I don't believe you have to make any adjustments at all. 97 Octane fuel just has improved lubrication qualities, and over time this results in smoother pickup across the rev range and a marked improvement in economy. I run the 'F', the VERY high revving Integra and a 2.5 V6 Mondeo all on 97 Octane and have noticed great improvement in all 3. Of course I got all this info from the Ford dealer's. so I do stand to be corrected. Some people say 1 fill-up in 4 is enough, but I disagee. My 'F' has gone from 320 miles per tank to an average of 350, since i started filling up with 97 every time. it's smoother too.

Cheers

Kieren

ps I'm gonna put 97 in my next MG - whether its a ZS180 or ZT-T...
Kieren

Roger Parker - for whom I have the greatest respect as the most knowledgeable and helpful poster on this board, always reckons 97 is only wasting your money.

However I always use this when in Europe and am sure I can feel a difference in terms of smoothness and pick-up.

I also thought that the ECU on the K series can be modified by a garage with the correct test book system to set the engine to ONLY handle 97/98 petrol. I only read in on this board some years ago and have not tried it.

Cheers

Patrick
Patrick

When it's available locally, which is not always the case, I fill up with Super U/L in preference to LRP for my MG Montegos originally designed to run on old 4 star. Tested over many tankfuls in my cars involving several thousand miles; although more costly, I find that economy is improved with an overall cost saving of 7%.

I sometimes fill up with straight unleaded. Here the mpg is ALWAYS reduced by around 12-15%. When I last checked prices, on average Super U/L was approximately 8% more expensive than straight U/L.

John McFeely.
John McFeely

I have used Super Unleaded in my race car occasionaly and have had problems while running the stuff (the worst stuff came from Silverstone race circuit). There seems to be a huge difference in performance and quality between different brands of unleaded, and even a difference between different batches from the same manufacturer.

I know of a few racing friends (who are very skilled engine builders) who have questioned the quality of super unleaded and are going to do some tests with different batches of the stuff. They also mentioned that they expressed there concerned to the manufacturers who replied that the shelf life of super unleaded is very short (around 2 weeks) before it starts losing its octane (I thinks it is octane, but not sure.. it does lose something though).

Regards,

Peter
Peter Dignan

> There seems to be a huge difference in performance and quality between different brands of unleaded

This is certainly true of regular UL. I used to fill up at Tesco when I was getting some shopping there. One time they were out of UL so I filled up in the Esso station next door and I found that I got more miles out of the tankful. I have since experimented with Tesco, Esso and BP and found that Esso UL gives 5-10% more miles from a tank than Tesco, with BP being somewhere between the two.

On the other points raised, I'm not interested in having the timing advanced so that it will only run on SUL as it is not sufficiently common to always guarantee availability when needed. I was curious as to whether, like the Mk2 MX-5 and the Impreza Turbo, the ECU monitors the engine for predetonation and adapts the timing accordingly.

Finally, for those who use SUL, the Impreza boys are currently getting all excited about Shell Optimax. This will be replacing SUL at Shell stations and, unlike SUL which is now a by-product of producing LRP and is only 97RON, Optimax is a direct result of Shell's racing fuel development, is engineered for maximum performance and is 98.6RON. Of course, all that comes from the Shell web-site so a large pinch of salt is required but it'll be interesting to hear how much difference it makes to the Scoobys.

Cheers,

S.
Steve H

Well, I filled up with optimax last night, only cost a few quid more per tank than the regular UL, but it certainly does seem to make a difference, a lot more lively. *touch wood* no problems yet.

Steve.
Steve Childs

Who remembers 'Formula Shell' and the short lived life of that product which also came from racing development (alledgedly)

Kelvin
Kelvin

Patrick,

Thanks for your comments. My views are applicable to the circumstances present when I made them and in the recent past we have seen some changes to fuel make up which HAS made some percieved differences. Many classic cars now run hotter and have problems with running on and generally poorer operation. Newer cars do not seem as 'crisp' or responsive as they used to be, my F included.

I feel that there has been some changes to the fuel make up of late (mention of low sulphur fuels comes to mind) and whilst I haven't been able to quantify this at all, the indications are with altered engine response.

Overall though the changes will be to engine response and 'throttle feel' only. There will not be any worthwile change in measurable power. However bear in mind that I expect to see a variable of around 10% in delivered power from variations in atmospheric and weather conditions. These have a far greater real impact on power and torque than the relatively minor fuel make up changes.

John makes a valuable reference to the O series engine which is very sensitive in fuel efficiency terms to fuel changes. His experience mirrors some testing I did in 1988(ish) and then twice in the mid 1990's. The O series has a terrible design of combustion chamber so needs all the help possible to obtain an efficient burn. I also tried the uleaded ignition ECU and mirrored the factory fuel consumption figures,which was the same 15% worse than standard leaded operation.

Originally intended for leaded and the result was the most fuel efficient. Change to unleaded (and retaining the original advance settings) and the efficiency dropped by around 15% with power the same. Change then to super unleaded and the efficiency was within a couple of percentage points of leaded, with the same power. The throttle response was however sharpest with a mix of leaded and base unleaded.

I have done the same comparisons with an MG Metro which has a high static compression ratio (10.5 to 1) and several 16 valve Rover engines including a Turbo. What was clear is that all these have efficient combustion chamber designs and the actual fuel efficiency between all types of fuel drops to very small levels, although the throttle response is apparently sharper on the higher octane unleaded. Measured power on the occasions I was able to measure this was still so close that any difference was insignificant.

All of these engines, and all those in the Z range too, have fixed mapped systems without adaption to timing change from fuel quality changes. (Saab EPC for example, and to a lesser extent the Knock sensor system on Lucas managed Rover engines) This means that when the engines are said to be mapped for 95RON fuels that means just that. Using a fuel of a higher grade will alter the combustion characterisics slightly, but without the opportunity of optimising the physical engine spec or the mapping details to suit, you will not achieve any worthwile improvments other than the changes to the throttle response. Experience also says that with an efficient combustion chamber design the fuel economy is not likely to move more than perhaps 2 to 3% which can be easily written off against sligtly different driving or weather conditions.

Mind you that won't stop me from trying out the higher octane fuel in the ZS180 in due course after I pick it up Saturday.

Rog
Roger Parker

I am surprised that the ECU has a fixed mapping. I thought most modern engine ECUs would adapt to different fuels. I know the one on my Volvo does...
Mark Frost

Unless there is a knock sensor or other specific combustion sensor variable control on ignition timing is both impractical and postively dangerous towards engine longevity. One of the first applications ever done was in 1984 when the Maestro, Montego and Rover 216 all had models with such a system. MEMS is now light years ahead of those systems but when there is more than adequate production control on the fuels sold in the markets where MGR sell cars there is no direct need for any additional system complication.

Rog
Roger Parker

This thread was discussed between 28/08/2001 and 02/09/2001

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