Valve seat angles

[statsystems]

I'm testing on my street/strip car now. I'm close to the numbers you want. Small block Chrysler with OE heads that I ported and used a 50* seat. They lost flow below .250 (not much and not all flow is good flow...that's just bullshit) and had the same flow as the 45* seat to .750 lift.


The big difference was reverse flow and how quiet the port is on the 50* seat. Far better than the 45* seat.


Compression is 11:1 (measured, not a guess or an ishtimate) cam is 281/281 advertised 255/255 at .050 with .620 gross lift using a 1.6 rocker. Lash is .014/.016 hot.


I was more concerned with valve job life. So far, so good.

I built a new engine for my 82 suburban. 355 with dart 165 cc head ported, 2.02-1.5 valves, dual plane intake, 9.5 comp, 600 vacuum secondary carb.

It has 50* seats with a 196/206 @ .050" cam with .435" lift.
It made 380 Lbs at 2000 rpm and hung just over 400Lbs till 3500 rpm or so.

It runs very nice in the suburban, but the 700 tranny don't like it. LOL

Theory would say it doesn't have enough window area to even start.

I haven't seen seat lift be a problem with 50* seats.

Randy

I never said or implied a combination of lower performance street parts couldn't function and make decent power with steeper seats. Just pointed out the obvious and the well proven trends and limitations of each seat and throat design. Form usually follows function and most OEM head castings don't let us blow the throats out just because we think 60 degree seats will make more power in our truck motors. By the time you blend in the short side you're into water.

So riddle me this.. why stop at 50's if the results were contrary to popular and typically accepted results? Why not 55's? Maybe even 60's? More low end torqz?

There have also been some very prominent engine builders and head designers on this very site point out that they don't specifically try to kill low lift flow per se.. only that it's often a necessary trade off to increase flow in another area of the lift curve where that extra flow can be better utilized for even bigger gains. CFM is great and all but still has to be available when the engine needs it most during higher piston speed/demand.

As for specifically using steep seats to kill reversion?.. been well proven to be an effective method. But then again.. so has reducing the primary pipe size and/or running merge collectors with smaller than typically accepted choke sizes. Just because something works decent doesn't necessarily mean it's the best possible way to accomplish the task at hand.

We get it. You don't like anything but 45* seats. I've done enough testing that I very rarely use 45's on anything that is performance oriented. I know there are people using 60* seats. Certainly as you get over 50 seat life can be shorter.

I'd suggest a 30* seat if you think low lift flow is that great.

[groberts101]

I never said or implied a combination of lower performance street parts couldn't function and make decent power with steeper seats. Just pointed out the obvious and the well proven trends and limitations of each seat and throat design. Form usually follows function and most OEM head castings don't let us blow the throats out just because we think 60 degree seats will make more power in our truck motors. By the time you blend in the short side you're into water.

So riddle me this.. why stop at 50's if the results were contrary to popular and typically accepted results? Why not 55's? Maybe even 60's? More low end torqz?

There have also been some very prominent engine builders and head designers on this very site point out that they don't specifically try to kill low lift flow per se.. only that it's often a necessary trade off to increase flow in another area of the lift curve where that extra flow can be better utilized for even bigger gains. CFM is great and all but still has to be available when the engine needs it most during higher piston speed/demand.

As for specifically using steep seats to kill reversion?.. been well proven to be an effective method. But then again.. so has reducing the primary pipe size and/or running merge collectors with smaller than typically accepted choke sizes. Just because something works decent doesn't necessarily mean it's the best possible way to accomplish the task at hand.

We get it. You don't like anything but 45* seats. I've done enough testing that I very rarely use 45's on anything that is performance oriented. I know there are people using 60* seats. Certainly as you get over 50 seat life can be shorter.

I'd suggest a 30* seat if you think low lift flow is that great.

Uh.. don't think you do. Got any pic's of an LS head with 55's? What about an big olds or buick head with 50's?

The main point was that blanket statements of 55 degree seats always being better on every application regardless of the cylinder heads physical limitations.. or even intended application for that matter.. is pure bs as well. A bigger throat don't mean shit if the short turn went to hell in the process of cutting it.

[GARY C]

care to share?

The correlation between window area and reversion with your particular valve job, one thing I never see discussed is doing reverse flow at low lifts to record reversion.

This data would be tied directly to what is needed on the opening side of the cam and reduce the number of cams needed for testing.

OK I get that and what do you do when an exhaust is noisy at .200 and flows 5% better as an intake?

Can't say I have ever had a noisy ex port but all you can do is find out why and fix it, most as cast ex ports or probably to big to begin with. I am not a head porter by trade so there would be a lot of verifiable there depending on head and port.

Int, 5% where?
On the flow bench or on an already developed combo?
That would be the reason for gathering the data, if its down low on an already developed combo then you are probably going to want to reduce Int duration or retard IVO.

[induction apprentice]

My take is this. From my experience. you have to get at least .150" lift above where the curtain area and throat area are equal before 50 deg. or higher seats will pay off in anything. There is no point opening the throat and gaining area at the throat / seat area with a 50 deg. seat if on say a 2.300" valve you are only going to have .650"lift. The throat / seat area will not be the governor at that point and all you are doing is removing the radius the air desperately needs to turn the at low mid lifts when the valve head is in the way. On top of that. You have hurt seat life.

G.M. would have used 50 deg seats for sure in the ZO6 development if it was a even marginally good idea. But they did not. They also don't use a 30 deg top cut. Why? because that does not work in a performance application either.

Ok padding is on. I'm ready!

[CGT]

Got any pic's of an LS head with 55's? What about an big olds or buick head with 50's?

Resized_20170118_164953.jpg

[user-9274568]

Myself personally, I own one 55º cutter and have used it twice in 10 years. All my high end stuff gets 50º seats. Fast stuff even, like record setting. All my 23º stuff had 50º intakes and I recently changed them all back to 45º seats. I use my own custom cutter I came up with by using stones.

All a matter of opinion...

[statsystems]

Myself personally, I own one 55º cutter and have used it twice in 10 years. All my high end stuff gets 50º seats. Fast stuff even, like record setting. All my 23º stuff had 50º intakes and I recently changed them all back to 45º seats. I use my own custom cutter I came up with by using stones.

All a matter of opinion...

And also how your port geometry ends up. I'm not saying a steeper seat is for everyone. For how I finish my posts, how I determine valve sizes and the like, I use a 50 almost everywhere.

If it's blown I have a 55* and that's all I used on the blown stuff.

[Warp Speed]

Ahhhhh, the 21st Century arrives! Lol

[user-9274568]

Ahhhhh, the 21st Century arrives! Lol

So your saying if your using a 45 degree seat, your not in the 21st century?

[Warp Speed]

Ahhhhh, the 21st Century arrives! Lol

So your saying if your using a 45 degree seat, your not in the 21st century?

Not aaying that really, but take it as you see fit! Lol

[user-9274568]

Here is my biggest issue with 50-55 degree seats. You get small shops that read these posts and think a head needs a 50 degree. Then they end up trashing the chamber and killing the head. Or if you don't do that, just putting a 50 on it may hurt the performance, the port needs set up for it. It pulls harder on it. So, you might hurt low flow but your really helping a small cam.

Big difference as well as cycling parts vs guys that run them a long time.

my opinion.

[statsystems]

Here is my biggest issue with 50-55 degree seats. You get small shops that read these posts and think a head needs a 50 degree. Then they end up trashing the chamber and killing the head. Or if you don't do that, just putting a 50 on it may hurt the performance, the port needs set up for it. It pulls harder on it. So, you might hurt low flow but your really helping a small cam.

Big difference as well as cycling parts vs guys that run them a long time.

my opinion.

I agree. You don't just change the valve job and not consider everything else.

I've also found if guys aren't using carbide pilots and don't have a rigid machine and fixture they have a hard time getting a good seat with 50 or steeper valve jobs.

Also, the tool needs to be nice and sharp.

[GARY C]

Got any pic's of an LS head with 55's? What about an big olds or buick head with 50's?

Resized_20170118_164953.jpg

The seat on the right looks like it would really fill the throat.

[GARY C]

Ahhhhh, the 21st Century arrives! Lol

So your saying if your using a 45 degree seat, your not in the 21st century?

Not aaying that really, but take it as you see fit! Lol

You would think none of the returning EMC winners would still a 45 if that were the case.

[GARY C]

Here is my biggest issue with 50-55 degree seats. You get small shops that read these posts and think a head needs a 50 degree. Then they end up trashing the chamber and killing the head. Or if you don't do that, just putting a 50 on it may hurt the performance, the port needs set up for it. It pulls harder on it. So, you might hurt low flow but your really helping a small cam.

Big difference as well as cycling parts vs guys that run them a long time.

my opinion.

I agree. You don't just change the valve job and not consider everything else.

I've also found if guys aren't using carbide pilots and don't have a rigid machine and fixture they have a hard time getting a good seat with 50 or steeper valve jobs.

Also, the tool needs to be nice and sharp.

I think this is one of the biggest issue no one ever addresses when trying to do a back to back comparison, you need to start from scratch with 2 separate sets of heads so you can do ABA test.