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I have just started recommissioning a time warp 970 racer, not run for possibly 40 years it’s full Longman spec/ jack knight . Pulled off head then water pump as seized but to my surprise it is a shallow impeller type with a screw on the body for lube hole. It’s the same colour blue like the rest of unit so it’s been on along time. My question. Was this fitted for a reason of lowering drag/ reducing cavitation bearing in mind they rev to 9K or more or just fit deep impeller type

Hiya,

Can't say for 100 per cent certain but funnily enough, our 970 racer had a shallow impeller type pump. I fitted a deep one but don't race it to test its effectiveness.

When running at such high rpm it "may" make sense, but I suspect that cavitation wouldn't be reduced "that" much as the impeller is still spinning at a heck of a rate.

Another possible reason could be to reduce the drag from the water pump to make sure as much power gets to the wheels as possible.

Yes Mark , that what I thought but as it will never be used in anger so normal pimp will be fitted and try to get it I assembled for for Blyton (not for track) just a runner/ display. Peter

what size pulley was fitted ?

Small pulley as 850 , Larger 1275 Pulley rubs the head

To reduce the water pump speed even more a cut-out can be made in the underside of the thermostat housing accommodating a larger pulley, about one millimetre gap is sufficient. Assembly has to be with the belt around the pulley.

A 970 can rev to 9000 rpm however the torque falls down considerably after 7500 rpm due to the restricted breathing of a five porter. Better to tune for torque band and stay in the torque band and shift typically around 7500 rpm with an 649.