Guys,
F4R valves are 33,5 mm in/ 29 mm ex. and defnitly big enough for about 270 + bhp. I did german Vauxhall STW-enines in `99, very similar to BBTC, with pretty more than 300 bhp with valve sizes 35/30, later works engines generated 320 hp with this valves.
But I would like to discuss about rocker troubles: Due to my investigations, rocker problems will occure because of the standard geometrie of valvetrain what is not designed for a high valve lift layout with revs of more than 8000. The pivot angle of the rockers is ok with Std. 8,5 mm lift, with more than 12 mm transversal movements on the valve contact area will increase and as well the friction, what tries to pull off the rocker from the ball bearing of the hydrolifter. My intensions to fix this problem is as follows:
1. Replace the hydraulic lifters by solids, adjuste the valve clearance as small as possible ( all advices just for inlet)
2. Minimise the valve stem/guide clearance to 12-15 microns ( millimeter)
3. Coat the valve stems and head with DLC to minimise friction on the contact area
4. Don`t use high load valve springs, 700-750 N for 8000 rpm is normally ok
5. Use only camshaft profiles which are professional calculated, the program has to put out side loads,ball contact loads, dynamic spring loads aso.
6. On exhaust, 2 mm less lift as inlet are no problem for power, piston pockets and compr. ration can be optimised much more along with advantage for valve train conditions.
Anyway, I would like to have a look to sodemo rockers, I didn`t find a homepage or another source as yet for their race parts.
Cheers
Udo