06-09-2020, 11:33 AM
(06-09-2020, 10:38 AM)Alan Wrote: Tony is right in what he says. For a quick Austin 7 two things matter. Gearing and breathing. But, you have to consider them as a package. It’s no good having big valves if you are breathing through a 12mm carburettor choke. It’s no good having good breathing if the gearing means you can’t get it on the cam. The thing that’s not been mentioned is the importance of the exhaust manifold. If the cylinders can’t get rid of the burnt gases they can’t breathe in fresh. A standard manifold simply will not do.
Endorse everything Alan says. As an example, my Trials car has a four branch under the bonnet exhaust manifold. On a Derbyshire Trial a few years ago we managed to break it and, as the Herefordshire Trial was the next weekend, substituted it with a standard exhaust manifold. With the exception of that and the log type inlet manifold, everything else stayed the same including the 1 1/8" SU that was mated to the standard manifold. The thing was hopeless indeed it was something of a revelation to us the negative difference it had made.
I don't have any four speed Sevens but I've been on holiday with my absolutely bog standard 3 speed SWB Saloon this last two weeks and have used it pretty much every day. The engine has no tuning enhancements whatsoever but will cruise on the flat at a happy 40 - 45 mph and, if you give it time to get there, 50 mph is available. I really do think your engine may be too far retarded, Duncan, as even as you've described its specification, it should be able to beat that handsomely . An easy thing to check. Advance it and see what happens.
Steve