Radius contact valve seats

[sbcharlie]

I’m curious if many of you car guys use a radius contact seats in your cylinder heads. I started using this in our flat track motorcycle cycle cylinder heads. Seen gains in air flow on flow bench and horsepower gains in our Husky 450 race engine s

[Alaskaracer]

I've been told it's ok on exhaust, but a big no-no for intakes. The sharp edges on the angles of the valve job help with shearing the fuel and keeping it in suspension, where a radius does not....that's how I understand it anyway.....

My new heads have a five angle valve job on the intakes, three angles on the intake valves, and a similar deal on the exhausts.

[fastvette]

I believe you are talking about where the valve actually contacts the seat. Would that not wear into the valve or flatten out the seat pretty quick?

[BCjohnny]

No, I've never used them, as the evidence I've seen would indicate a 'flat' seat angle that exactly matches the valve angle is the best way to seal the valve, transfer heat, and flow air/fuel into and out of the chamber ..... in the majority of cases

It would be a convenient way to seal up a valve/seat that has less than stellar machining, much like an interference angle, but I doubt it could be run successfully, especially on the exhaust, unless it quickly bedded out the radius on the seat ..... and then you no longer have a true radius

Is the extra power you are seeing from improved sealing rather than flow, and what are the gains you are seeing ?

A lot of very clever people, much, much sharper than me, have tried all sorts of stuff over the decades and we basically come back to multi-angle intakes and radius throat exhausts ...... predominantly if not exclusively ....... so as a simpleton I'm happy to accept the cubic man hours of research, instead of trying to re-invent the wheel

[mag2555]

How much of a power gain are you seeing ?

My first guess would be that such a seat set up has its biggest effect on the exh side, by improving low lift flow.

This makes for faster blow down and that in turn produces higher VE.

[sbcharlie]

On intake we offset seat 1mm and have 4 angle breaks on long side of seat contact is 1mm on exhaust .6mm offset with radius on long side 69 hp no valve or seat recession

[Tom68]

How much of a power gain are you seeing ?

My first guess would be that such a seat set up has its biggest effect on the exh side, by improving low lift flow.

This makes for faster blow down and that in turn produces higher VE.

Single cylinder 450cc's probably talking fractions of a horsepower change depending what the radius seat is getting compared to, dusted flogged out factory seat with too much clearance.

[sbcharlie]

You know what you guys crack me up

[sbcharlie]

You know what you guys crack me up

[digger]

are you talking about a radius VJ or radius contact angle i.e. instead of a 45 it is concave seat and convex on valve?

[Warp Speed]

Waterbury Hall used to make a radius valve seat grinder. We used them to do the exhaust seats in our superstock drag engines back in the 80s.

[TMSJoe]

I used a radius on the EX seat for dirt track engines. After cutting the seat I would take a stone and hand lap the seat to prove it's concentric. There would only be a thin ring where the marker was wiped off. No abnormal wear on the valve or seat. SS valves, 150# springs, flat tappet, iron head no inserts, gas, 2bbl carb.