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MG MGA - Fuel Octane

The valves seats on my cyl head are not the hardened type, so naturally I have to add the instead of lead additive. I have been using unleaded 95 RON petrol all along. No issues experienced so far. I am now thinking of upgrading to 98 RON octane fuel in my tank. Will this petrol be OK to use, any harmful effects on the engine?

Frank
F. Camilleri

Frank

I use it all the time. The engine was designed around this grade and higher of fuel back in the 50s. I notice the better performance and less tendency to knock.

It's still unleaded though, so you still need your additive. Get the valve seats hardened!

Steve
Steve Gyles

PS. I guess someone will correct me, but I understand that the super unleaded 98 octane in the UK has less ethanol in it (in some cases none?) compared to 95 octane. Therefore there is less, if any, problem with rubber components.

Certainly I have never had any issues with the rubber bits since I rebuilt the car in 1997 .

Have I opened a can of worms and major controversy?

Steve
Steve Gyles

Hi Steve, thanks for your reply to my query. On this information, I shall start using 98 Octane in my Mga. Of course I will also put in the additive. As for the valve seats, I did inquire at a local engine builder to have the hardened seats fitted, they say that they will do the job for me, but I need to buy the inserts from UK as they are unavailable locally. The cost would be Eur50 per cylinder. I have no problem with the cost as I think it's quite reasonable. My only concern is the fear that one or more inserts would come loose, and damage the head, etc. What are your comments on this? The engine builder is a very reputable auto engineer Should I go ahead and get the job done?

My son dropped a spring washer inside the carb intake orifice once, and very nasty damage occured when the engine was started up.

Frank
F. Camilleri

Frank

Those costs are quite reasonable I think. I have never had any issues with any coming loose although I have heard of it happening. I guess it all comes down to the quality of the machining. I had them done on my 1948 MGTC, MGA1500 and MGB1800 engines.

Steve
Steve Gyles

Steve

I've been using Esso super unleaded as it was supposedly was ethanol free. I'm not sure that is still the case, unfortunately.
There is a current thread on the midget technical board regarding ethanol.
Dave O'Neill 2

As I understand it, the higher the octane, the longer the fuel takes to burn... hense, less 'knock'. A slower, more controlled burn makes sense.

Anyone know if this is the case?
MAndrus

Whilst a combination of factors ultimately led me to switch to an unleaded head, for long enough I used 'Tetraboost' with neither ill-effect nor complaint (albeit generally with 98RON - as now - for good measure). It helped me to keep the ignition advanced enough for spirit without tempting the odd knock at c3000 -3500 RPM under load. I couldn't find a way to achieve the same benefits with other additives. I continue to use 98RON without any apparent adverse effect - but in no more than an uninformed hope that any 'ethanol issues' are also reduced as a result.
D
D Smith

This thread was discussed between 22/04/2016 and 23/04/2016

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