Hi Chris & Kelly + List When talking about different stages of cylinder head tuning the Moss TriumphTune Performance Manual (my source of tuning information) has the following to say for 'up to 1500cc models' i.e. spitfires:
"Work on the cylinder head centres around making the best diameter of the inlet port to suit and give maximum power potential. We have found that increasing the size of the inlet valve to 1.457" and very carefully flowing of chamber/valve throat area will produce good torque and allow top-end breathing for spring/racing use. The increase in exhaust valve sizes improves the flow of the port for maximum power. The Stage II Head - using standard valves reshaped is ideal for mildly modified engine - standard or fast road cam. Anything over this type of modification we would recommend the large inlet Stage III head for it's improved flow by the reshaped TT valves and further modifications to the chamber design. For competition use, the Stage IV head with large inlet and large exhaust valves and special shaping of chamber is essential." The various stages of car-tuning of course include much more than only changing the head. fitting your standard spitfire with a stage IV head wouldn't do much in increasing the performance I think if you do not upgrade airfilters/airintake, carburettors, silencer, camshaft etc. Anyway I think in general cylinder head tuning stages follow this pattern: stage I: factory standard stage II: reshaped and polished valves stage III: increased size of inlet valves and possible reshaping of chamber stage IV: increased size of outlet valves and definitely reshaping of the chamber probably also the valve springs are upgraded. The manual also has a picture of a stage IV head showing the enlarged inlet and outlet valves and chamber reshaping. If interested I can scan and post it to anyone individually. That's about as much as I could come up with. All book wisdom as my spitfire is still standard after ten years of dreaming about more power. But back in reality I always come to the conclusion I don't need more power for the kind of (small) roads and cruising trips that I like to take my spit on. It would only complicate things, make it (even :-) ) more dangerous. Before increasing power I would like to increase breaking power, upgrade suspension, etc. handling in general. happy spitting, Emiel. 1979 Spitfire 1500 TC Brooklands Green (just a shade more beautiful than the ordinary British Racing Green) Barcelona, Spain. /// [EMAIL PROTECTED] mailing list /// Send admin requests to [EMAIL PROTECTED] /// or try http://www.team.net/cgi-bin/majorcool /// Archives at http://www.team.net/archive /// Send list postings to [EMAIL PROTECTED] /// Edit your replies! If they include this trailer, they will NOT be sent.
