Just to confuse matters further my UK RHD SLK 320 is recommended to run on 95 RON which could be referred to as "regular" in the UK. Premium would be (expensive) 98 RON.

The engine fitted to the UK SLK 320 vehicle happens to be a California tuned M112 V6. (to reduce manufacturing complexity)

So it looks like MB recommend different grade fuel in different countries!

As I stated previously the engine will accommodate different fuels and change ignition timing to ensure that no engine damage occurs AUTOMATICALLY.

However I suspect that the MB recommendation MAY HAVE something to do with published performance and fuel economy figures. Changing the fuel impacts these results so presumably MB have to decide which fuel the vehicle is "homologated" to run on. i.e. the fuel used when performance figures were submitted to the DTP, DOT or whatever regulatory body exists in the country where the vehicle is sold.

If you want to use 91 R instead of 93 I you need to ask yourself why?
Trying to save cash?
If so do the sums and see whether the saving in fuel cost outweighs the reduction in gas mileage before you get too excited.
The gas companies "claim" increased gas mileage with premium BUT they don't point out that the claimed increase does not offset the increased price!

Stuart

 

Since the manufacturer recommended 91, I will run 91. I doubt that 93 would gain any greater efficiency. Others have stated that the dealer can tune the computer to run better on different octanes.

 

It is possible to retune the vehicle.

By this people mean insert or reprogramme the engine management system ECU.

Manufacturers OE software has to meet all sorts of legislative requirement with 100% reliability and manufacturing differences. As a consequence it is somewhat conservative and it is possible to optimise matters.

The code can be changed to improve economy / power etc but these changes CAN make the car not meet the legislative requirements AND most likely (if discovered) will invalidate warranties etc.

In some instances (including MB) the same engine unit is used in a model BUT the power output (of the two engines) is controlled to different levels by using different software. It is therefore possible to update the software and gain the manufacturers (hidden) additional performance at very low cost.

Manufacturers like to do things thru software where ever they can since it is so simple to configure such features on final production.

Other examples are things like delayed (headlamps) lighting when you leave the car at night.
In fact control of this function (which at one time was an" extra") has now been given to the customer in the form of driver configurable features thru the steering wheel controls or iDrice etc.

Clear?

Stuart.

 

Higher the compression the higher the octane needed it depends on the engine there are engines with short strokes large bores domed cylender heads that require premium with a dohc 10:1 compression ratio. I would only use what manufactor says to use if it runs it will kill econemy or the engine in long term or both. I have seen people with turbochargers say oh I was told I dont need it and they tryregular and there engine runs ruff and cause quick engine failure in few thousand miles. Racing engines have very high compression arnt expected to last as long and run everything from 100octane racing fuel to ethonol and methonol.

 

Hi Jay173.

Please read the previous posts in order to get the FACTS about this issue.

Use the RECOMMENDED fuel BUT the engine will accommodate (within reason) different fuels without damage.

Stuart