gtred

I've got a local performance head shop that is helping me refresh a couple of NB (MSM) heads. He has a 3 angle carbide seat cutter that he wants to use, then come back and blend to the bowl.

I remember hearing discussion over the years about preferences for the valve seat angles... some opinions that the standard cutter angles don't work well with the miata heads... even one opinion that a 4 angle cutter yielded good results; but I don't remember much in the way of specifics. Has anyone here looked into this?

2004 t-miata, stainless +1 intake and exhaust valves.

aidandj

iTrader: (5)

https://www.miataturbo.net/race-prep...ing-out-82462/

hornetball

iTrader: (4)

Hah! I was just going to post about this.

What's your intended use? If it is going to see extended high RPM use on a track, then use 100% OEM specs and err on the fat side. Keep the friggin' drag-racer machinist far away from your valve seats.

OTOH, if you're just going to make a few drag passes or cruise to Cars and Coffee, do whatever you like.

aidandj

iTrader: (5)

Track car. So yes. Definitely OEM.

gtred

Just finished reading the thread. Take away seems to be: good spring pressure, wide seats; maybe: .050 intake, .060 exhaust, proper guide clearances: .001-.0015 intake/ .0015+ exhaust and then watch for wear issues by checking your valve lash. The word is not yet in on the valve surface hardening... but st seems the only readily available supplier.

Parts ordered: st heavy duals; st +1 intake/+1 exhaust, bronze guide set. Head combustion chamber deshrouded, short radius and port casting shift to be cleaned up. 3-angle valve job with a little blending into the throat and also to try to knock down some of the ridge around the seats in the combustion chamber. Back cut valves.

Thx for the "light" reading.

hornetball

iTrader: (4)

I'd go .060 on the intakes. It's really the intakes that always died on my car for some reason.

ryansmoneypit

iTrader: (6)

I agree with the above. My machinist said that there really wasn't even room for a 3 angle if i wanted to keep the seats fat. He suggested that a bunch of boost could not give a **** less about valve seat angles.