Cvh Turbo Valve Seat Shape ?

[leeuk]

Hi Guy

I am porting a Ford CVH turbo head i have the ports opened out to 35mm and bigger 43mm valves

Can I just ask you a question about valve seats have you ever tried a 1.5 mm wide seat that is just totally cut straight into the valve throat but this would make the valve throat very wide around 40 mm (over 90%) would this be ok for a 43 mm valve ?

I was thinking this would be ok because its a turbo engine I read somewhere on here that a turbo engine is also flow restricted by throat diameter

Regards

Lee

[Guy Croft]

Lee, hi

sorry to be slow.

No is the short answer and I never do parallel throated seats even on downdrafted heads because you're left with no metal to recover a new seat on an overhaul (the seats distort in service). No, for the most practical of reasons I don't agree with the practice.

The best flowbench results I've had on that head are 2mm contact face, 70 deg into near parallel (2/3 of seat insert at 70 deg, lower section parallel) with Burton 43mm race valves. Very good combo giving 24% over standard flow at 12.6mm lift (102.6 cfm at 10"), which is huge. The port was 32mm across at narrowest section. Some might better that - certainly claim too - but that's huge for a 1600 and certainly plenty for well over 160bhp on a well-built race engine.

The flow restriction will either be the valve throat or port dia. For the practical reason I cited I would not go bigger than throat size 37.4mm (like the head that I mentioned above) and in that case the 35mm port is the restrictor - but 35mm is huge on that 1600 (I assume) and I would not go bigger.

Making the valve throat bigger doesn't necessarily yield a benefit on its own. I've tried that in vain many times only to discover that the port configuration (especially on sidedraft ports like yours with that critical valve-port axis change just below the seat) just won't allow any more in.

A big port like yours will certainly tend to be less responsive off-boost than a smaller one, but the bigger port will be a lot less likely to choke in the critical valve pressure region just above peak torque where there is still some useful boost and the piston speed is very high, thus giving an engine capable of higher-rpm performance.

GC