Joined: Aug 2017 Posts: 1,334 Threads: 34
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Location: Cheshire
Car type: Race Ulster, 1926 Special, 1927 Chummy, 1930 Box
It’s not the lift,as such, it’s the acceleration as the valve opens. Theoretically at least the acceleration at opening with flat tappets is infinite. It probably isn’t quite but you get the idea. Nippy cams, likewise, have very sharp ramp angles. I agree with Dave. My trials car, when I did such things in the 70s/80s was on a standard cam with 3/4 radius tappet blocks. It was quite successful. My advice would be to sort out the inlet/exhaust manifolds before you even think of the camshaft, but when you do, talk to Paul Bonewell and listen to his advice.
Alan Fairless
Joined: Aug 2017 Posts: 1,530 Threads: 60
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I bothered to measure a handful of cams and plot the duration, lift, acceleration and jerk (the derivative of acceleration) on charts using some clever software. If I can find them on my laptop I’ll share one or two.
What it did tell me is that Paul Bonewell’s cam grinds are very clever at minimising the valve train loads whilst giving very much improved breathing.
And never use a standard Nippy cam.
Joined: Aug 2017 Posts: 925 Threads: 74
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Location: Essex
Was that from an engine you are stripping for refurbishment Ruairidh or something in your rogues gallery?
Joined: Mar 2015 Posts: 5,436 Threads: 231
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Location: Scotchland
I recalled someone asking about them, perhaps it was you?
They were in a box of spares - would you like them?
Joined: Aug 2017 Posts: 925 Threads: 74
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Location: Essex
It was me who asked if anyone had ever tried it. Interesing that Chapman's design made them concave. I would like them Ruairidh, like those cast wheels, but I'm trying to quit the habit.
Joined: Mar 2015 Posts: 5,436 Threads: 231
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Location: Scotchland
They will be sent south next week…