Optimax fuel????????

[timshap]

Re fuel question

Whilst in Germany for 4 years with my 500 chimp allways used super plus @98 RON
Since returning to the UK I had to retard ignition from 40 degrees BTDC to now 26 degrees to run on UK fuel as advised by Blackpool. I can say that the effect was a noticable drop in performance and confirmed on the rolling road at well Lane in West Yorks 300 bhp. ie not so much bite in second and third gear now although the torque characteristic was dead flat on the graph at 350-360 ft lbs which was good.
If I use optimax theoretically 98 RON should I re adjust the timing back to mid 30`s or 40 degrees again???
Views please

Tim

[Steve _T]

Optimax is 98.6 Octane according to Shell (possibly around 99 at the pump if you believe recent posts on this site) so I reckon you'd be ok. I certainly noticed a difference when I had to fill up on unleaded with my 500 in an emergency.

Steve

[MajorClanger]

Wouldn't it be nice if TVR set up two engine maps, one for 95 RON and one for 97/8 RON (maybe with a switch near the petrol cap!!!). The availability of superunleaded certainly isn't increasing and we can only hope that Shell contine to market Optimax long in to the future.

MC

[beano1197]

I thought that some of the Cerbies did this???

Switch on dash, though!??

[beano1197]

quote: drop in performance and confirmed on the rolling road at well Lane in West Yorks 300 bhp

Hang on! 300bhp at the wheels a "drop" in performance???

[shpub]

You can do it if the ECU has the facility for downloadable or customised mapping. The Rover one doesn't as it has a Pooh Bear design (one with a little brain) and was made many many years ago. To be honest it is a miracle of engineering design that it does as much as it does with so little.

The reason for Super is mainly due to the engine design requiring all the help it can get to prevent predetonation and pinking. This can be caused by many other factors as well which is why some cars can run U/L with no problem (mainly 4 litres) and others can't (mainly 500s).

The best way to retard the ignition is to adjust it until it just pinks and then add a notch or do it on a rolling road. Doing it by a set number of degrees can be a bit hit or miss especially as a couple of degrees out on the timing can make a big big difference to the overall performance.

Steve
www.tvrbooks.co.uk