Brosky said:
I'd be really concerned about putting that kind of power on a 30+ year old engine, without doing some serious overhaul work and beefing up of the bottom end.
That is a very good point, adding extra stress to any older engine will just accelerate the wear. Which is probably covered in Moss' "limited warranty" that you have to request separately.
Just about any engine out there can take a 6-8psi boost from a supercharger as long as its in good shape. The stock bottom end of the TR6 engine is plenty strong for that amount of boost. It can actually take a lot more boost than the Moss kit offers before you have to worry about it failing. The big weakness of the stock TR6 is more RPM related (long crank and only four main bearings). Turn up the 'wick' a bit over the standard 'kits' and you venture into newer territory.
Raising compression on a supercharged car is tantamount to suicide for the engine without the sophisticated timing and engine management systems to control knock. The supercharger is already stuffing more air into the cylinder than would normally be there so the compression is already effectively increasing with the boost. And yes, a supercharged car is more sensitive to gasoline octane than a non-supercharged engine.
Big cams on forced induction engines are also detrimental to performance. Where the overlap of exhaust and intake valves being open at the same time will help a naturally aspirated engine, on a forced induction engine it sends a bunch of your boost right out the exhaust port.
The draw of a supercharger over the cam/compression/ extra carburettor routine that some of us have done (guilty /bcforum/images/%%GRAEMLIN_URL%%/blush.gif ) is the ability to have a decent and docile idle and very easy drive-ability at lower rpm and the extra power when you stab the loud pedal. /bcforum/images/%%GRAEMLIN_URL%%/driving.gif I still prefer my lumpy idle and loud bark when I succumb to the red mist and 'gently' press my volume control lever. /bcforum/images/%%GRAEMLIN_URL%%/cheers.gif