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Influence of valve shape

Posted: February 13th, 2007, 5:28 pm
by Guy Croft
Some figures here taken from development test work on the Superflow rig with a gasflowed 1438 Twin-Cam head.

I'd like to be able to say the tests were conducted on a 'fully developed' inlet seat, but that would be a completely unsubstantiable claim, because in reality to produce an absolutely optimum result the seat would have to be reshaped and optimised for every valve, a quite impossible task really, it would take dozens of heads and weeks to do. The tests were done on an optimised seat that was certainly optimised for the early rather 'tulip' shaped valves, and all I was doing really was seeing how well the seats flowed with other - later - designs.

So, in the meantime this will have to do, and the purpose is to show how the flow can vary according to valve shape, note which valve gives better lower lift flow and which gives better high lift flow. It's interesting how the late generation inlet valve used on all the post 1973 TCs is actually a very compromise between the two.

I've done similar tests on several other heads too downdrafted ports - sidedrafted ports etc etc - sometimes making dummy valves from aluminium - and they all have their particular 'preferences'.

GC