GTI6 Ninja plans in full swing EEEKK!!!

[cwspellowe]

Out of interest, how are they timing the cams? PT81's are chuffing close when it comes to valve/piston contact and i've seen people in the past fitting the cams slightly retarded to overcome clearance issues. All it takes is a heavy head skim in an unknown service history and it's bye bye valves.

Never cammed my GTI6 for this exact reason, a PT80 or similar is hardly worth the effort for the gains but PT81 and above gets a bit brown trouser-esque when you first crank the engine over.

Sure from what I read the PT81's are too close for comfort to time properly? Again if so, defeats the purpose of fitting the cams as you get higher lift but the timing's out. If all done properly though then get on it!

Just don't come on saying the next mod is a posted throttle body or i'll cry

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Knew it

Firstly, what a lot of people do not realise when fitting performance cams you time them from the manufactures spec and not standard timing mars.
So, PT81s will work fine on standard timing marks, but won’t make full power as they need to be advanced relative to the marks. When timed correctly – it is highly likely that they will touch the pistons (there were marks of piston to valve contact in my engine).
If you want to know the exact measurements for particular engine – you have to do dry build and measure it.
The standard inlet cam has about 0.8mm lift at TDC vs 1.64mm for PT81. So you would need to deepen the cutouts by about 1mm to keep the same amount of clearance as standard. Which is what was done on my engine by Martin, (CRF450).

Of course, in ideal case I would deepen the cutouts a bit more and get the head skimmed to up the compression ratio slightly from standard to compensate for the material removal from pistons and work with increased duration of the cams...