I just dropped off a set of assembled TA Performance Rover heads (1.94" diameter intake valves, 1.6" exhaust) and Willpower single plane intake at Stiegemeyer porting, a local cylinder head and supercharger specialist near where I work. I removed the valves from one cylinder and Bob examined the ports, chamber shrouding, seat margins and valve angles and asked me some questions about the engine the heads will be going on (a higher compression 4.2L Rover), along with how I plan to use the car (TR8, purely street). He also asked if I was going to run EFI or a carb, suggesting you can get away with somewhat larger ports with EFI. He thought the size of the as cast ports were fine for my purposes, needing only detail work, and that the best bang-for-the-buck would be to work around the existing valve job. He also threaded a spark plug in and indicated he would do a little chamber work around the plugs. Looking at the intake ports, he thought they should go to 250 CFM fairly easily which would be plenty for my application. The plan is to flow bench the TA Rover head in as delivered condition then let him have a go at bowl porting and port matching the heads and intake. He indicated that getting the port floor of the intake manifold to work with cylinder head port floor was especially critical. I'm going to drop a block, gaskets (intake, exhaust and head), a header flange with pipe stubs and some bolts off this weekend so he can mock it up. I think I'll also take an OEM 4.6L Rover cylinder head along to flow bench as don't have any data on unported Rover heads. The TA heads are based upon the TA Performance Buick V6 heads. The guy who designed the TA heads also suggested:
"On the exhaust have him start by opening up the exhaust outlet, make the port wider, The port will respond by doing this. Then have him removing very little to none on the back side of the exhaust bowl. Just blend the machined throat area into the back side. He should end up with a slight bump even, on the back side. Blend the rest of the bowl how he see fit."
The exhaust port shape is way better than the Rover/Buick but has been raised 3/4" so it's not clear if off-the-shelf TR8 headers will work. He also says the intake ports should flow 250+ CFM with only minor work. It'll be interesting to see what sort of power they make. It would also be interesting to test them on the 5.0L Rover V8 I have sitting at the dyno but the valves have been relocated to the center of the bore, have a different angle and are larger so chances are there will be piston-to-valve clearance issues.
Given the bore size and chamber design, Stiegemeyer suggested no less than 11:1 compression and we briefly discussed camshafts. I mentioned the short block should handle a decent amount of RPM (cross-bolted mains, 3.03" stroke Rover nodular cast iron crank, Carrillo rods, forged flat top pistons) and I was considering running either a solid flat tappet or a hydraulic roller camshaft. He put the valve springs on a tester and said they were ideal for a hydraulic roller camshaft but recommended titanium retainers for a bit more RPM. He said they would also work with a solid flat tappet cam if offset locks were used to reduce the seat pressure. If running a solid flat tappet, he recommended using lifters with EDM holes supplying oil directly to the cam lobe/lifter face. On the tester, the springs were quite close to the advertised specifications. Note these assembled heads were delivered with TA's upgrade spring package for a hydraulic roller cam (TA p/n 1160) and have the following specs:
Dual springs without damper
160 lbs @ 1.900"
360 lbs @ 1.400"
Coil Bind 1.175"
Max Lift 0.650"
He also likes the blue Viton metal clad valve seals, mentioning the white Teflon seals don't pass enough oil to the guides for most applications (uses them in race applications where the springs are flooded with oil over the top of the guides).