Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Petrol 95/98 differece

Hello!
Until recent I have filled my 4/4 Sport 2011 with Shell V Power (98-99 octane). The 2 last fillings I used 95 octane. I found the motor runs smother and the mileage does not seem to change.
The timing of the ignition seems to adapt to the lower octane grade and got at smother run at low revs.
What is your opinion on this matter?
//Bosse

I recall this coming up before on here and others have observed the same. I recall one posting mentioning that the handbook recommended a lower octane fuel.

My older ('76) 4/4 recommends higher octane....

I always use 95 octane in our 1990 1.6 CVH engined Morgan. Last time in England, I wondered if I heard a knock from time to time. That raised the question for me, is it better to use 98 octane in our Morgan!?

By preference I use Shell V Power in my Plus 4, or other non supermarket high octane fuels if it's not available.

In theory the higher octane fuels will allow the engine ECU to run greater ignition advance which will give greater efficiency and power, particularly at higher revs. Fuels like Shell V Power also contain additives and detergents that help keep the fuel injectors clean and minimise carbon deposits on the valves and in the combustion chambers (thus optimal conditions).

Running the engine on 95 RON fuels, especially in the lower rev ranges and under load, the ECU will be backing the ignition timing off against the knock sensors (i.e. running a more retarded ignition curve) which will reduce both power and torque, and efficiency (hence reduced mpg).

The gap between the theory and practice however, can in real terms be minimal (the odd BHP or ft/lb of torque, and maybe 1 or 2 mpg) it tends to be dependant on how sophisticated the engine management system is, what you want from your car, and of course your driving style.

So, as ever in the Morgan world... each to their own

P.S. Originally a reply to Charlottendal, but Richard and Ruud got there before me... Slow typing!

It depends a lot on the engine if high compression /turboed etc the super would be the sensible option but as the recommendation for in my case (3ltr v6) is the 95, the only real benefit would be getting double shell points when buying vpower maybe cleaner internals too, 98 will probably allow it to pull smoother at lower revs.

My other car however it specs 98 and when running on 95 which it will do so happily, the down side is that it does about 7-8 mpg less on 95.

Unless doing the same journey day in day out in same traffic and weather conditions getting useful figures of economy/performance is wishful thinking at best.

The latest version of vpower (nitro+) in terms of economy has plummeted compared the the previous version so jiggling with formulations does not suit every end user.

I have no knock sensors on my carburetor CVH engine, the question than remains is spending some more money on 98 octane is wise, or just spending too much money only to be on the safe side?

But also the octane will drop when sitting in the tank.think I read some were around 2 to 3 points in a month

Erm a tank lasting 7 days might be nice all those little detours you know!

Anyone with a T16 +4 noticed a difference.. Have tried both and using 98 V Power but not sure if it is any different to MPG or performance..

My 4/4 Sport is the same year as yours and I have only ever run it on 95 octane unleaded as per the handbook and it runs perfectly. Being a humble Ford engine designed to run in the Focus 95 octane is kinder on the pocket! Somebody did suggest to me recently that it would be a good idea every few tanks to put in some 98 octane to clean it through but I haven't done it yet so don't know how it affects the performance.