Questions for devilishdesigner / Pigeon

Cellulose thinners is a mixture of xylene and toluene (sometimes with a bit of methanol as well) and has an octane rating of at least 108 depending on the blend and the mixture of xylene isomers. Ordinary petrol already contains some xylene and toluene to increase its octane so all you're doing is adding more of the same. Environmentally, your contribution to the concentration of aromatic hydrocarbons in the atmosphere pales into insignificance compared to what's kicked out every day by millions of cars running rich and retarded before the cats have warmed up. As for the high-compression engine comment - that was something of a joke; I wouldn't really consider an engine that couldn't be run on pump fuel to be suitable for a road vehicle in everyday use. I've raised the compression on my bike engine such that it is not happy on 95 octane and really wants 97, and that itself is a pain when I can't find a petrol station with 97.

With LPG I can run very high compression ratios without trouble. LPG is over 110 ron but I do not feel its worth taking the engine to the comprssion limit and perfer to keep a bit of spare.

Hi Dai, I had a good chat with Mike the other day about LPG for the Rover. Ends up I didn't buy the rover, but instead bought a 960! The car I had in mind in this post is an 1800 and not used reguarly. Think I'll just 'suck it and see' with the head. I didn't want to risk taking any more material out of the chambers and spoiling gas flow around the valves. Gordon

one thing you could try if are willing to give it a go is grooving the head as lesslightlylimp has done with the 240 head. On the 240 I have personlay found it to make a difference and expect you should work on the B18/B20 heads. Could be worth a try.

I ordered the 'Speed pro' series book on headwork but it hasn't arrived yet. I'd be interested to know what groovin' (use to do that back in the 70's) a cylinder head intails. Thanks Dai. Please tell me more...

While you're waiting for the book to arrive here's some links to a little light reading. Follow some of the hyperlinks in the articles on the last one. Includes head porting amongst other things.