According to my little book, standard compression ratio 6.1:1 but that was so it ran at all on the cheap petrol of the time I expect. Fit an eight head and it goes up to 7.6:1 with standard gasket but use a 20 gauge copper gasket and its whopping 8.5:1. I think one of the Ford Specials equipment companies, maybe Wooler or Buckler, made I am told a conversion of some sort for the 10hp side valve but I know little of it. I still hanker for a 4 speeder but I accept what you are all saying about the work and time required. I will chew it over and if/when I finish the current modified car perhaps I will think about it again. Cheers, Dave Incidentally, I had a Ford Rochdale special in the 60's when the craze for them was just ending and a Mini was a good alternative. It had 4.7 axle, 8 head, washers under the valve springs to reduce valve float, Panhard rods but had the standard carb. It did about 80mph and steered really well round tight country lanes.
Just found it - it was Wooler and all for £58. http://www.pop100e.com/PopWooler.php