LRP is unleaded with an industry standard potassium based additive. In fact, the amount of additive does not justify the price differential, and it would have been far cheaper to use standard unleaded and add your own, although obviously less convenient.
Rover V8 engines were not fitted with hard exhaust valve seats until October 1985 with the advent of the EFI Range Rover. Before this, they were all fitted with chilled iron seats, and this includes the SD1 and Vitesse models. Only the last few SD1 vehicles had the silicon chrome seats.
It is a common misconception that engines built from 1976 on (SD1) had hard seats. This is not so. Rover themselves stated that all engines from 1970 would run on unleaded with appropriate adjustment to ignition timing, which is true, as indeed will ANY internal combustion engine ever made. What they cleverly DID NOT state however, is that you would NOT suffer exhaust valve seat recession, because the fact is........you will.
Without getting too technical, valve seat recession will only occur when a certain localised temperature is reached. This will only happen when the engine is either under load or running very fast or both. The exhaust valve itself is made from an alloy steel, so is not a problem. Under hard use it will actually be glowing red hot, and is cooled by touching its seat mometarily many times per second, and to a lesser extent heat conduction up the valve stem and out through the valve guide. Because the chilled iron valve seat is relatively soft and has a lower melting point, tiny particles of material will stick to the valve head, to be burnt away when the valve is open. This causes the valve seat to gradually wear away and the valve to sink into the cylinder head.
HOWEVER......In practice, you really have to thrash the nuts off the engine to do this, and by and large very few people drive a Rover V8 that hard. The rev limit is a modest 5500 anyway, and you would have to be cruising at getting on for maximum speed to do it. Driven normally, it will still occur of course, but only over a long period of time. This is how Rover have manged to get away with it, coupled with the fact that the hydraulic tappets with automatically keep the valve clearances adjusted, so you tend not to notice the gradual drop in performance and fuel economy. What you WILL notice though, is unexplained overheating.
In a vehicle with conventional manually adjusted valve clearances, the gaps will close up until there is no clearance at all and you end up with no compression if it goes unchecked.
In an ideal world the solutions are.........
1. Fit 1985 on Range Rover cylinder heads. This will give you the unleaded capability, plus give you the opportunity to fit later composite head gaskets to drop the compression ratio slightly. This will both help to stop pinking, and provide a much better water jacket seal, helping to eliminate another big V8 problem......oil contamination, and camshaft wear. You will also get bigger valves and improved porting. Your camshaft will have a couple of the lobes worn anyway, so you might as well do that at the same time ;D
2. Have your own heads fitted with hard valve seats. This will probably entail new valves and guides too, and will probably be more expensive that fitting the later heads. Dont forget those composite gaskets !
3. Use an additive.
The only one that I think will work properly in the long term, is a product called Tetraboost, which is actually tetraethyl lead in a bottle, so you are making genuine leaded petrol. You can even make up five star too ! Only trouble is, this stuff is expensive.
Of the others, I think Red Line is the best of the bunch. But that of course, is my opinion based on experience.
You will also need to retard the ignition timing slightly using a bit of trial and error.
4. Just retard the ignition and see how it goes !
All these options depend on milage covered, expense, personal circumstances etc etc, and how the owner considers the long term life of the car
Another item which I recommend without reservation is a product called Red line Waterwetter. It reduces localised heating and promotes heat transfer and can only help with this, and other problems.
You can still get proper leaded petrol at some garages, and at a price. Tap into your computer " Bayford Thrust" and use their outlet locator.
.Anyone heard of the 2nd product which seems a better deal?