It has been awhile since I was doing this stuff. If I remember correctly it was the GT3 Cup solid lifters that were flat. The GT3 Street lifters were radius on part of the top of the tappet (like a line or strip). I also believe that after a certain year the GT3 Cup did away with the solid lifter.

What happened was when the tappets differed, Porsche varied the valve stem length to make up the difference. This lead to another issue. As the valve length became longer and the valves became wider as in GT3 Street vs GT3 Cup vs GT 3 RSR ..... the stem width became important. This is why when people started to use Manley and Forea there was an issue. On the larger valves with certain stem diameters one company made the large sizes for intake but not exhaust and visa versa on the exhaust for the other company.

 

It all depends what heads and cam housings you are using. Protomotive was the first to start having the 996tt cams reground. I believe Laurie Webb over at Web Cams started doing it for him. There was a time Webb would not touch a 996tt cam. Todd is one of the few who I shared my cam profile's with. You can only get so big of a lift profile in the 996tt cam housings. The GT3 housing is bigger. The 996tt cam housing has enough room for the GT3 street exhaust cam but not the GT3 street intake cam.

Regrinding is one thing, welding and regrinding is another as if you do not use exactly the same weld metal (hardness is the issue) as the parent metal you stand an excellent chance of flattening your lobes due to the different metals of the cam and tappets.

This is why it became so expensive to make cams ..... metal compatibility with the tappets. Now you can understand, you couldn't just make billet cams without making the tappets also.

Now it seems regrinding is what people are doing and the cam issues are not such a big deal unless you are going with big race profile cams.

 

Chad... just had confirmation to ease my mind...

The people who look after my car in UK also look after 3 RUF Nardo motors which run GT3 exhaust cams (RUF do this mod) and the question was sent to them a couple of days ago.

In dozens and dozens of engines they have done they have experienced no problems whatsoever regarding GT3 exhaust cams, they even confirmed they keep the original Turbo Tappets/Followers... what I will say is the people who do my work use the MKI (M96.76) Cams for the job.

I also fired the question to Todd Knighton, he replied - Yes the Turbo has Flat Followers, not Radius... Yes the profile slightly differs to that of a GT3 Radius Lifter, but I have not heard of anyone having problems/damage from Flat v Radius... looking at it I think it would provide a similar Ramp Up, with less Peak Lift and a Flatter Peak anyway.

I have no doubt in my mind now... I have run these in my car for 3 years now and the car has had a serious amount of abuse on track without any issues.

I'm glad this has come around, great discussion point, but I now honestly think there is no reason for some to be worried with this modification.

 

Stevo, you are using MkII exhaust camshaft or MkI?