| Flow bench |
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We've been using the flo pro quick flow bench at QEP now for over 6 years and have built up an extensive list of flow figures from different heads, valves and port/chamber shapes. Its not the be all and end all of engine tuning, but certainly a considerable benefit when deducing which valve shapes and profiles work in both pre and crossflow cylinder heads. Of late we have managed to port and tune precrosflow heads to as good a flow rate as a crossflow head, right up to very high lift situations where the straigher tract of the crossflow is less restrictive and the lack of shrouding/turbulance caused by a bowl chamber means the crossflow head will continue to flow whilst the precrossflow head will stall due to the tight turn in the port, this with a lot of work has been minimised to smooth the flow through the valve lift and maximise low and midrange lift which is where the valve spends a vast majority of its time. We have also proved to customers that money spent on correct porting will invariably gain more than the 'pub talk sales pitch' of big valves, we've seen better results per £ spent on porting with standard valves than we have by poorly ported, and even unported heads which have been brought to us with big valves fitted. Heres an example of a full race big valve precrossflow cylinder head we flowed recently 0.1 - 63.5cfm We have a standard callibration plate for the flow bench which is used every time we set up, the flow bench runs at 25" water gauge We also always mount our heads on an 83mm bore liner to as accuarately simulate an installed situation, likewise with the crossflow heads, simulated/published flow gains can be claimed by using a large bore on the bench which de-shrouds the inlet valve, what I'd call cheating! This is a similar full race specification flat faced crossflow head with big valves. 55.8cfm
@ 0.1" This
goes some way to explaining why Crosslfow engine repond better to
higher lift cams (like the Kent range) and make very cammy motors
by comparisson to precrossflow ones.
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