reprofiled cam

Hi all
I am thinking of getting a re profiled cam for my TF160 [ exhaust only ] What I don't under stand is how do they add to the profile when they are taking material off the cam or lobes, surely the lobes need to be bigger to get a longer duration ?
Just a thought I have

The opposite side of the cam lobe is ground away and the hydraulic cam follower extends and makes up the difference so the height thats been ground away now becomes the extra lift on the high side of the lobe.

Obviously with this method there is a limit to what can be achieved due to the allowance that can be made up with the cam follower.

Many decades ago I raced motor cycles (only at club level) and Piper Cams re-profiled the cams on my 305 Honda with stunning results.

So have I got this right piper take off on the closing side of the cam making the hydraulic tappet stretch so when it starts to open again there is a thou + more in the tappet and it's not the cam but the tappet which makes the difference

The centre line axis of the camshaft cannot change so if you remove material from the opposite side of the lobe and re-adjust the follower to the new closed height then you have moved the eccentric of the cam lobe up by the same difference of the material that has been removed from the underside.

The material that is removed is reducing the base circle of the cam which gives a greater lift and a sharper opening and closing action.

So, is the performance improvement due to the increased valve overlap, or what I'd call the exhaust scavenge/gas evacuation effect during the inlet stroke?

Back in t'day we'd go for a higher kick on the inlets to get a bigger fuel air charge and a re profiled exhaust to increase the overlap for better scavenge.

Been mentioned for being too technical on the coolant thread so hope this query is ok.... :whistle: p

Hi John. As I read it, the tappets are made bigger by taking material of the lobes on the closing side of the cam only 1-2 thou and the hydraulics take this up so the opening cycle is started earlier giving a longer opening time

John and Sue wrote: So, is the performance improvement due to the increased valve overlap, or what I'd call the exhaust scavenge/gas evacuation effect during the inlet stroke?

Back in t'day we'd go for a higher kick on the inlets to get a bigger fuel air charge and a re profiled exhaust to increase the overlap for better scavenge.

Been mentioned for being too technical on the coolant thread so hope this query is ok.... :whistle: p

Hi John,

You missed the original thread: the question was how can you increase valve lift by removing material from the cam.

Brian.

Badger wrote:

John and Sue wrote: So, is the performance improvement due to the increased valve overlap, or what I'd call the exhaust scavenge/gas evacuation effect during the inlet stroke?

Back in t'day we'd go for a higher kick on the inlets to get a bigger fuel air charge and a re profiled exhaust to increase the overlap for better scavenge.

Been mentioned for being too technical on the coolant thread so hope this query is ok.... :whistle: p

Hi John,

You missed the original thread: the question was how can you increase valve lift by removing material from the cam.

Brian.

Yep, I get that. My point was that the main point of exhaust cam tuning is to better evacuate the exhaust gas by increased valve overlap.