Radius shaped valve seats
 

Opinions on this type of valve seat compared to multi-angle seats. Some time ago I took my heads to a nearby shop to have a multiple angle valve job on my #15 heads, gave him the specs but the machinist took it upon himself to grind in radius seats. Don't know if this type of seat is any good but we were done after that move. He didn't do anything to the valves thankfully.
If I leave the seats as is how are the valves to be ground? Thanks.

The big question is 1) is your main seat on the intake valve still a 30 degree?

And then 2) what did he give you for the bottom radius out of the bowl and into the main seat, and then what did he give you for the radius leading out of the main seat blending into the chamber floor?

If he gave you a 15 degree top cut / radius above the main 30 leading into the chamber floor then that’s no good.

That top cut will make for very unwanted reversion and a loss of low speed throttle response and torque even though it picks up some cfm @ .100” lift.

Also if a intake port has wet flow issues a radius valve job can exacerbate that condition and once again make for a loss of power that could have been had, and even worse it can make for full throttle detonation when that wet flow lights off at a later time then when the main burn started in the chamber.

On the exh side a full radius valve job is never a problem unless doing such leaves the main 45 degree seat too narrow, like less then .060”

In terms of myself, I will live with the intake flow I have being 3 cfm less then what I could have had from not running a full radius seat and enjoy possibly better overall power being made from my cylinders burning all the fuel they receive on the intake stroke.

Steve.. any recommendation for the angle or angles below the 30 degree seat cut (in the head)?
And is a 15 degree top cut about as good as it gets?

Man, I'm not even sure how to measure all of this. It will take some time. Nothing given on my receipt. I appreciate your help!

HO Racing used to talk about the benefits of doing a full radius seat.
 

I don't have the Engine Design booklet in front of me, but I'll dig it out.

You are probably fine as long as he stayed with the factory valve angles. It might be great valve job, definetly takes some skill to perform a good radius seat using stones. I've seen a lot of screwed up jobs from guys using multiple angles. Concentricity and seat placement are more important than the angles of the top and bottom cut.

Some aftermarket aluminum Pontiac heads come with radius valve jobs.

Are you sure there was not a misunderstanding and the fellow used a radius cut on the exhaust seat?

After you help the OP , and Since there some knowledgeable guys in here what was angles and Mc carthy talking about with an “elliptical valve job “ back in the old days on their book?

If you have a flow bench you can play around with valve jobs all day as long if you have enough mule heads to eat through..

It’s very important to have a highly worked out valve job, and David Vizard points out why this is.

He states two rules for this, one for Intake valves and one for exh.

The rule for the intake is OD x .18 which gives a lift value.
For instance a 2.11” valve gives a value of .380”
This means that up to .380” lift the valve job and head shape of the valve is the main factor in the amount of air flow seen, not whatever the port shape may happen to be from the end of the valve job on back to the intake flange.

If your running a 2.11” valve and a .500” lift cam then 76% of the total air flow is likely being produced below .380” lift!

This change over point can in fact clearly be seen during a flow test on the vertical Manometer, especially if your testing in increments of .050” lift.

In terms of maxing out power once your running a Cam of over .500” lift and over 230 to 240 duration @.050” then you want the intake flow numbers from .200” on up to be as healthy as they can be, especially if you have a full race motor with a solid roller cam.

If you making flow numbers of 140 cfm or more at .200” lift your doing pretty good.

Exhaust valve wise a different rule comes into play.
This rule is valve OD x .35.

For a 1.66” valve the valve job and shape of the valve head have a influence right up to .580” lift.
So a well researched radius valve job is aways a benefit to exh flow.

If you have a shop giving you a radius valve job that has no flow bench and has not done before and after flow test on a head such as your then it’s a crap shoot if the work you paid for helped or hurt you.

As I posted yesterday, you never ever want a top cut of any kind on a intake valve that has a 30 degree seat.

Yes, having such will show a low lift flow gain, but the intake valve will then act as one heck of a big exh valve in terms of reversion .

Later today I will post some flow test that all too clearly show this, reversion issue.

also adding a top cut to a 30 seat or even a 45 degree seat valve makes getting a good flowing valve job done for a oversized valve difficult since your using up needed meat in the chamber floor.

I elliptical valve job with its different width cuts on the exh valve side and common wall side of the port is a plus in a wedge type chambers that we are dealing with which have the intake valve on one side of the chamber and the exh on the other.

This helps because at high lift the largest mass of the air flow wants to move over to the center of the cylinder bore and the exh valve side of the bore in terms of a intake valve since this is the flow path of least resistance.

The best bottom cut to use changes with the ID of the valve bowl throat, especially with factory heads that start off small in stock form and then get enlarged when ported .

The stock set up is a 60 degree bottom cut running into the as cast 70 to 75 degree valve bowl walls which depends on core shift.

You will never go wrong with using this 60 degree bottom cut, but how wide it needs to be changes with the throat ID and air flow rate.

The depth of the bottom cut can be used to stabilize high lift air flow and if used for such your definitively at the point where your trading off low lift air flow for high lift high rpm air flow.

Any one know of any off the shelf aftermarket Pontiac head that was designed with the specific aid of wet flow techniques?
I don’t.
Why are we still behind the 8 ball in this way?

Isnt part of valve to seat contact to transfer heat from valve to head?
Seems to me by definition a radius would provide less contact surface area than a seat
Might not be an issue with todays valve materials or maybe advantages for short term drag racing not so good for 100's thousand mile engines

About a month ago, I took a course in Atlanta taught by Darin Morgan as the lead instructor and John Kasse as secondary. Of course they are talking about engines in general and Pro-stock specifically. It was interesting though, that of all the possible engines to talk about, the 30 degree factory seat angle on a Pontiac head was discussed briefly. As Steve said, a radius above the 30 degree seat cut is not a good. Below .475 lift, of course, they recommend keeping the 30 degree seat with distinct 15 degree cuts above, (very narrow), and below as needed to bowl blend. Morgan said there is no situation he can point to where a radius intake seat improves the heads he works on. On the flip side, they recommend a radius seat on virtually all their exhaust seats. Of course they recommend flow testing but in general, they are big proponents of back-cut valves. As always, another excellent learning experience, even if not Pontiac specific. All the heavy hitters were there, Kasse, Morgan, Warren Johnson, Tony Bishoff and others. I felt like a midget among giants!

The actual sealing main seat be it 30, 45 or the flat out high rpm full race 55 degree type is not radiused, only the lead in or lead out parts can be radiused.

That being said the narrower you make the main seat the more it blends into the others to form a radius.


Of course once you start doing that then your living closer and closer to the edge of pounding out and or burning the seat.

All I am saying is for me I like to go with distinct cuts / angles and reap the benefits of atomizing the fuel better and having that on my side more then having more peak air flow as can be had by a radius valve job.

That had to be a very interesting class. Bet it was hard to take in all the info. Did they let anyone record it ? Audio only maybe ?
Was it expensive ?

Here’s the results of a reversion test I just made.
The head used was a stock 6X-4 and the intake valve used was a 2.11” stock one for that head.

The stock seat is a 30 degree and it’s width is .070” and it’s OD is 2.090”

On the second flow test I recut the 30 degree seat to a OD of 2.10”.
This then left me with the area to cut in a .030” wide 15 degree top cut and also brought me back to a .070” wide main seat.

This is as close as your going to get to a Apples to Apples test.

The first column is the flow of the stock configuration on a exh flow test setting.

The second column is with the 15 degree top cut added.

The third column is the change in flow.

.050”. 38.5. 40.5. +2

.100”. 80. 86.7. +6.7

.150”. 126. 129.1. +3

.200”. 148.8. 149.5. +.6

.250”. 161.3. 161.3.

Pics
 

I hope these pics will help to explain what I have. I know I will have to blend back into the ports some. I should have explained these were small valve heads ground into big valves.

I would leave that unblended.
That minor step will act as a fuel sheer point .

He plunged pretty deep into the intake bowl, but I don’t think his work picked you up much flow above about.400” lift.

One way to tell would be if you still have one of the original 1.66” exh valves.

Can you drop one of those into the intake bowl down to the point where it will sit flat on top of the valve guide boss.

I am willing to bet by the looks of things that your exh ports are fitted with a 1.77” valve that they now flow way better then what’s needed to keep up with the intake valve flow.

If you have not picked out a cam yet I would really try your best to get at least a intake and a center exh port tested.

It was an incredible deal. Offered to AERA members. (Automotive Engine Rebuilders Association). $40.00 a head and that went to charity. Mr. Anonymous and I made a bonsai run from Dayton to Atlanta where the seminar was. All day Saturday. Then we made an all night run home . It was worth it. About 150 attended. Just my guess. The host was CWT Balancers.

Yes the exhausts were enlarged to 1.77. Thanks so much for your input!

Here's picture of what I mean to try out with the old valve.

I am using a template here, not a valve but still the same thing.

I'll see if I have the old valves, and I do have a couple templates I made quite a while ago.

'Nuther pic
 

This valve is ground down to 1.61+/-. It fits into the bowl about 3/8 to maybe 1/2". Plenty material underneath it.