S_Gault
25-10-05, 06:17 PM
cam companies have to give you a few things to look over to make a choice fr each engine, they use duration and valve lift etc .
so everyone reckons a 260 deg is a road cam, and 280 ish a fast road and a 300 a competition grind.
well no.. not really, where do you start measuring your lift and duration?
Kent use a 16thou check height on most..so dont start reading anything till follower has moved 16thou.
piper use zero- so you can see that exactly the same profile will have widly different results from each manufacturer.
Then you can have 2 identical profiles ground on different lobe centres and they will have vastly different characteristics. For example some years ago I used to use a lot of crane profiles and they worked well for stage rallying very torquey for low down, but lacked top end for oval racing engines, so i got them ground on a narrower lobe centre. no other changes- dam things wouldnt do anything till 5200rpm, and were sheer useless until the cars were geared to take account of changes.
the real numbers you need to ask yourself when chosing a cam is actually what the engine is seeing as a change- the valve lift at overlap at TDC. but barely anyone uses these numbers and even then the tappet clearance or chek height must be consistant. (this is why you never see them quoted for hydralic lifters).
Steven
so everyone reckons a 260 deg is a road cam, and 280 ish a fast road and a 300 a competition grind.
well no.. not really, where do you start measuring your lift and duration?
Kent use a 16thou check height on most..so dont start reading anything till follower has moved 16thou.
piper use zero- so you can see that exactly the same profile will have widly different results from each manufacturer.
Then you can have 2 identical profiles ground on different lobe centres and they will have vastly different characteristics. For example some years ago I used to use a lot of crane profiles and they worked well for stage rallying very torquey for low down, but lacked top end for oval racing engines, so i got them ground on a narrower lobe centre. no other changes- dam things wouldnt do anything till 5200rpm, and were sheer useless until the cars were geared to take account of changes.
the real numbers you need to ask yourself when chosing a cam is actually what the engine is seeing as a change- the valve lift at overlap at TDC. but barely anyone uses these numbers and even then the tappet clearance or chek height must be consistant. (this is why you never see them quoted for hydralic lifters).
Steven