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MG MGB Technical - LRP or Unleaded

I'm sure this has been asked before but...

Can you put unleaded in an original head engine?

I had a 1971 VW that you could because they have hardened valve seats.

It's a 1973 MGBGT.

Or do you have to buy an unleaded head?

Cheers
Matt
Matt Vidler

Hi Matt

There is a lot of info on this topic elsewhere, but here is a summary :

If you use unleaded there is a strong possibility that the valve seats will be damaged. How long this will take depends on how you use the car, if you drive it hard the damage could occur very quickly.

The options (in the UK) are :

Use Lead-Replacement petrol.

Use Leaded petrol (hard to find, but it is availible).

Use unleaded petrol and add a lead replacement additive whenever you fill up.

Use a fuel catalyst (eg Broquet).

Fit a head with hardened valve seat inserts.

Unleaded is about three-and-a-half star, so it does tend to increase running on and pinking. Retarding the ignition timing and fitting colder plugs helps.

Don
Don

Hi..

Take a look at the 'fuel cat conversion' thread on this board.

Don
Don

Cheers Don,

Whereabouts are you?

I'm in Newquay.

Do you know of any cheap places for parts in the area??

Ta

Matt
Matt

Matt,

Roger Parkers article gives the low down on subject.

I think BMW reckoned that 50k of LMR would last the life of engine, so I would try Optimax first as 98 Octane

http://www.mgcars.org.uk/cgi-bin/gen5?runprog=mgoc&a=&p=emg/emg110201.html

Paul
Paul

It would appear that 'strong possibility' of head damage is a bit strong, I've never heard of anyone getting VSR in an MGB even in America where leaded vanished many years ago. I use Super Unleaded or Optimax for its octane with Castrol Valvemaster as a precaution. Seems to give the same running results (YMMV) as LRP and 4-star leaded from Bayford which is still available at independant retailers dotted around the country - http://www.leadedpetrol.co.uk/ - including Cornwall. Standard unleaded even with Valvemaster plus pinks so badly that I have to retard the ignition and that badly saps power and increases running temps.
Paul Hunt

Oh yeah, LRP is on the way out.
Paul Hunt

Hi all...

Paul raises an interesting point, has anyone out there actually suffered valve seat problems as a result of running on unleaded without taking any protective measures ?.
I based my comment on what I have read rather than experience, but maybe we have all been a little paranoid about this issue, or perhaps the B engine is more tolerant of unleaded than some others ?.
How long does lead memory last ?.

I have significantly reduced the pinking and running on problems (on unleaded fuel) on my 80 BGT by fitting colder plugs, moving the front number plate up to a position in front of the bumper and providing a supply of cold air to the air filters.

Finally, if you haven't visited Paul's web site GO THERE NOW.. it's really useful.. thanks, Paul.

Don
Don

I had hardened inserts put in my head and still managed to get all the exhaust valves to sink, as a result of running the engine really really hot for quite some time (I didn't have a temp. gauge at the time). #4 exhaust had sunk about 1/16".

I put a tank of optimax in at my last fill-up, and while it got rid of my sub-2500rpm pinking (I run 20 degrees static advance!) it seems to fly through the engine somewhat quicker than 95 octane, and the car doesn't even seem as quick once I start getting some revs on. Of course, I can't back this up with any measurements so I may be imagining things. But either way I shall be sticking to cheapo 95 octane supermarket fuel.

ttfn,
--
Olly
Oliver Stephenson

Thanks Don. As another Paul has said, BMW is reported as having said that lead-memory after 40-50k should last 'the normal service life' of the engine, whatever that is. I guess that would be at least 100k on a BMW, but then I know of Bs on their 3rd or 4th time round the clock.
Paul Hunt

The best work on Valve set ressesion was done by MIRA using A series engines. They tested all the aditives and LRP. Leaded petrol gave the best protection, but LRP did pretty well, most of the adatives were ranked in terms of effectiveness. I recall Valvemaster was the best but most potassium based aditives were OK. All this work is in the public domain and I am sure I accessed it through a Department of Transport website.
I use LRP myself, it is basically super unleaded with a Potassium aditive, but it is cheaper than super unleaded so you get the protection and the higher octane. I pay 81p/litre which is only 2p dearer than unleaded.
The Mira work did show that the amount of reccession did depend on speed and load, but the trouble was that when it started it happened very quickly.
Paul Hollingworth

Castrol claimed that Phosphorus gave the best protection after lead and surprise surprise, that is what Valvemaster contains. Potassium came 3rd after Manganese and was better than Sodium, although all of them were much better than none. Most of the references I found were on the FBHVC site but now no longer seem to exist, although other sites have reprints. They only tested those additives that were submitted by the manufacturers, so-called catalyst manufacturers chose not to do so, and neither was LRP tested by them according to everything I have read. LRP is said to contain only half the recommended dosage to avoid claims for damage to catalysts if people fill up with the wrong stuff. The Telegraph published quite a good article on the situation as at April 1999. The text of this as well as summaries of information from elsewhere can be found at http://www.mgb-stuff.org.uk/wn_fuelframe.htm and clicking on 'Unleaded'.
Paul Hunt

The important thing is not to mix chemistries. If you use a phospherous additive you should never use LRP even in an emergency you would be better using unleaded. At least if you use a potasium additive in unleaded or super unleaded you can use LRP at a push. On Pauls point about the dose of potassium, most petrol companies have increased from 10 parts per million to 12 ppm, but who knows what the optimum is. I have done 8000 miles on LRP with no trouble at all and I don't know anyone else who have experienced problems either even those involved in motor sport. However there are all sorts of variables Lead memory ( I think this is more like 10 - 12kmiles) and driving style, amount of prolonged motorway driving etc. But the worst that can happen is that you will have to fit a recon head which will cost £200 and a mornings work by any competent home mechanic. There is no point in doing the head job untill something fails.
Paul Hollingworth

This thread was discussed between 29/03/2003 and 02/04/2003

MG MGB Technical index

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