Throat % is it area or Diameter?

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Re: Throat % is it area or Diameter?

Post by David Redszus »

HQM383 wrote: Tue Mar 14, 2023 5:59 am
juuhanaa wrote: Tue Mar 14, 2023 5:21 am
digger wrote: Tue Mar 14, 2023 4:54 am

i dont think you understood what i was saying, it is geometry and maths problem.

if you use 92% of area ratio the diameter ratio is 96%. if you take say a 1.5" valve and have a 45 degree 0.060" seat the ID of the seat is just about 96% already meaning there is the 45 seat and almost no room for any other angles which is not good
The question is what are the speeds through the system at different locations and how they serve us in building the engine. It depends the velocities for example at seat, throat and port on average.



-juhana
Thread title: “Throat % is it area or Diameter?”

Merely a question of terminology. Not definition or modus operandi.

Its diameter.

Just.........diameter. :D
But for every diameter there is an area present. Flow is a function of area.
Diameter defines area without fifth grade math. :)
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Re: Throat % is it area or Diameter?

Post by brad_m »

HQM383 wrote: Tue Mar 14, 2023 5:59 am
juuhanaa wrote: Tue Mar 14, 2023 5:21 am
digger wrote: Tue Mar 14, 2023 4:54 am

i dont think you understood what i was saying, it is geometry and maths problem.

if you use 92% of area ratio the diameter ratio is 96%. if you take say a 1.5" valve and have a 45 degree 0.060" seat the ID of the seat is just about 96% already meaning there is the 45 seat and almost no room for any other angles which is not good
The question is what are the speeds through the system at different locations and how they serve us in building the engine. It depends the velocities for example at seat, throat and port on average.



-juhana
Thread title: “Throat % is it area or Diameter?”

Merely a question of terminology. Not definition or modus operandi.

Its diameter.

Just.........diameter. :D
Correct Juhana.

All I wanted to do was be certain of the terminology.
I did a lot of searching of old threads and people never said the words Diameter or area. They would just reverence "throat size as being X% of the valve" Or they used both in the same sentence, making it more confusing.

There are only two options Diameter or Area. If I assumed incorrectly it could have lead to big mistake being made.
So when I started measuring a pair of heads I have, the throat was either pretty close to final size, or it was small, depending on the assumption of Diameter or Area.

It's better to ask than to ruin a pair of heads and end up with dog of an engine that is down on torque and throttle response.

A couple of people said diameter.

Chad Speier answered me over a facebook message and he was straight to the point and very clear.
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Re: Throat % is it area or Diameter?

Post by brad_m »

David Redszus wrote: Tue Mar 14, 2023 2:02 pm
HQM383 wrote: Tue Mar 14, 2023 5:59 am
juuhanaa wrote: Tue Mar 14, 2023 5:21 am

The question is what are the speeds through the system at different locations and how they serve us in building the engine. It depends the velocities for example at seat, throat and port on average.



-juhana
Thread title: “Throat % is it area or Diameter?”

Merely a question of terminology. Not definition or modus operandi.

Its diameter.

Just.........diameter. :D
But for every diameter there is an area present. Flow is a function of area.
Diameter defines area without fifth grade math. :)
Yes for every diameter there is an area present, but if people are talking Diameter because it a faster calculation, and I assumed they were talking area. Then I would have ended up with throats that were far to big. I'm working with a 4 valve head with 34mm valves, based on diameter I want an 86% throat. The head stock is 88% (not much I can do there) But if I had assumed area I would have ended up with a diameter 92% throat. which is far to big for the application, where I need bottom end torque and throttle response.

As it turns out, most people were talking diameter. I don't really care one way or the other. I just needed to clarify so that I knew how people were talking about it.

I'm just surprized we are three pages deep and no one has just said, "we are talking about Diameter because it is a faster calculation"
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Re: Throat % is it area or Diameter?

Post by treyrags »

"I'm just surprized we are three pages deep and no one has just said, "we are talking about Diameter because it is a faster calculation"

EXACTLY
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Re: Throat % is it area or Diameter?

Post by Joe-71 »

I said it was diameter on the first page. You need to read the answer, not just the first line. Joe-71
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Re: Throat % is it area or Diameter?

Post by juuhanaa »

brad_m wrote: Wed Mar 15, 2023 6:54 am
David Redszus wrote: Tue Mar 14, 2023 2:02 pm
HQM383 wrote: Tue Mar 14, 2023 5:59 am

Thread title: “Throat % is it area or Diameter?”

Merely a question of terminology. Not definition or modus operandi.

Its diameter.

Just.........diameter. :D
But for every diameter there is an area present. Flow is a function of area.
Diameter defines area without fifth grade math. :)
Yes for every diameter there is an area present, but if people are talking Diameter because it a faster calculation, and I assumed they were talking area. Then I would have ended up with throats that were far to big. I'm working with a 4 valve head with 34mm valves, based on diameter I want an 86% throat. The head stock is 88% (not much I can do there) But if I had assumed area I would have ended up with a diameter 92% throat. which is far to big for the application, where I need bottom end torque and throttle response.

As it turns out, most people were talking diameter. I don't really care one way or the other. I just needed to clarify so that I knew how people were talking about it.

I'm just surprized we are three pages deep and no one has just said, "we are talking about Diameter because it is a faster calculation"
Im just a garage guy and my stuff is from a time when i didnt have a smartphone..

34 valve with a 88 seat and a lot depends on where the minimum cross section is and what are you willing to do. You can probably make it work, but if the minimum is in the seat/bowl/valve guide region, you might appreciate the throat % more and we could be looking for a 82%. Sometimes i see the port just doesnt have enough length in it..

The same engine with the same size valves and different style heads can be like night and day.



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Re: Throat % is it area or Diameter?

Post by brad_m »

Joe-71 wrote: Wed Mar 15, 2023 9:41 am I said it was diameter on the first page. You need to read the answer, not just the first line. Joe-71

Don't panic, I did read your entire answer, not just the first line. And yes you did say "for you it was diameter" Along with other stuff that wasn't relevant to my question.
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Re: Throat % is it area or Diameter?

Post by KnightEngines »

Bigchief632 wrote: Mon Mar 13, 2023 1:11 pm I use diameter of od of valve also. And add valve stem area. This is another old wives tale that's held on for decades. 85-90% MAX!! It's all dependant on application, valve diameter, shrouding, and profile. By default, if you cut a 55 degree seat on a 2.5+ diameter valve, for example, you'll end up at close to 93%, with all the angles on the seat, 50-55-65-75. Just an FYI, some engines use seat angles even steeper, 60 or even 65. With the correspondingly steeper "bottom" angles, a 60 degree seats uses a 70 bottom angle, or more, by default the throat % ends up even larger without removing anything with a carbide. It just tips everything up, and it ends up wider. That's the reason for it too. Literally makes the hole larger under the valve. On a 800 inch deal trying to make 1600+hp at 8000+ rpm, that's just what it needs. The extra angles, vs just blowing the hole out with a carbide and destroying all the angles that help turn the air or in this case, turn it less, and helps wet flow.

I revise bottom angles all the time, no "rule" that says a 45 degree seat HAS to use a 60 bottom angle. I've changed it to 65 more times than I can count, I have a Sunnen VSC cutter I use, and I had another one made. For the serdi style blades. I'll also use a 65 single angle blade to change the bottom angle. This works well when you're valve size limited do do bore size and the engine "thinks" it has a bigger valve without increasing shrouding.
My favourite 45 deg intake cutter that I use on most things with over .600" lift is 35/45/65. Usually with 75/80 or 75/85 throat cuts.
I have no idea why everyone defaults to 60deg bottom cut.
The only issue is getting the cutters, I hang on to my old Mira ball drive cutter bodies coz I can get that cutter profile in a mira cutter. The rest of my tooling is goodson fast cut.

But to the question - it's valve diameter, not area.
And it's a rule of thumb, there are many exceptions, it's just a basic starting point.

Flat tappet lower lift stuff - 85-88%
Aggressive flat tappet or street/hyd roller - 87-89%
Solid roller decent lift - 88-91%
Aggressive roller - 90-92%

Again just a starting point.
I've used up to 91% on SFT stuff when the port design makes that feasible.
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Re: Throat % is it area or Diameter?

Post by Mummert »

65 is a good bottom angle for offset throat 3 angle. 65 doesn't seem to like a wide 75/80 IMO. 60 and 62.5 seem to work do better with wider 75/80.
Dry flow.
Wet flow looks better when you don't get too fancy with 75/80. Flows a couple less cfm but makes a couple more hp.
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Re: Throat % is it area or Diameter?

Post by steve cowan »

KnightEngines wrote: Thu Mar 16, 2023 6:10 pm
Bigchief632 wrote: Mon Mar 13, 2023 1:11 pm I use diameter of od of valve also. And add valve stem area. This is another old wives tale that's held on for decades. 85-90% MAX!! It's all dependant on application, valve diameter, shrouding, and profile. By default, if you cut a 55 degree seat on a 2.5+ diameter valve, for example, you'll end up at close to 93%, with all the angles on the seat, 50-55-65-75. Just an FYI, some engines use seat angles even steeper, 60 or even 65. With the correspondingly steeper "bottom" angles, a 60 degree seats uses a 70 bottom angle, or more, by default the throat % ends up even larger without removing anything with a carbide. It just tips everything up, and it ends up wider. That's the reason for it too. Literally makes the hole larger under the valve. On a 800 inch deal trying to make 1600+hp at 8000+ rpm, that's just what it needs. The extra angles, vs just blowing the hole out with a carbide and destroying all the angles that help turn the air or in this case, turn it less, and helps wet flow.

I revise bottom angles all the time, no "rule" that says a 45 degree seat HAS to use a 60 bottom angle. I've changed it to 65 more times than I can count, I have a Sunnen VSC cutter I use, and I had another one made. For the serdi style blades. I'll also use a 65 single angle blade to change the bottom angle. This works well when you're valve size limited do do bore size and the engine "thinks" it has a bigger valve without increasing shrouding.
My favourite 45 deg intake cutter that I use on most things with over .600" lift is 35/45/65. Usually with 75/80 or 75/85 throat cuts.
I have no idea why everyone defaults to 60deg bottom cut.
The only issue is getting the cutters, I hang on to my old Mira ball drive cutter bodies coz I can get that cutter profile in a mira cutter. The rest of my tooling is goodson fast cut.

But to the question - it's valve diameter, not area.
And it's a rule of thumb, there are many exceptions, it's just a basic starting point.

Flat tappet lower lift stuff - 85-88%
Aggressive flat tappet or street/hyd roller - 87-89%
Solid roller decent lift - 88-91%
Aggressive roller - 90-92%

Again just a starting point.
I've used up to 91% on SFT stuff when the port design makes that feasible.
I was under the impression that air does not like turning over sharp angles more than 15 degrees?
That is a statement from Darin Morgan
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Re: Throat % is it area or Diameter?

Post by juuhanaa »

steve cowan wrote: Thu Mar 16, 2023 11:37 pm
KnightEngines wrote: Thu Mar 16, 2023 6:10 pm
Bigchief632 wrote: Mon Mar 13, 2023 1:11 pm I use diameter of od of valve also. And add valve stem area. This is another old wives tale that's held on for decades. 85-90% MAX!! It's all dependant on application, valve diameter, shrouding, and profile. By default, if you cut a 55 degree seat on a 2.5+ diameter valve, for example, you'll end up at close to 93%, with all the angles on the seat, 50-55-65-75. Just an FYI, some engines use seat angles even steeper, 60 or even 65. With the correspondingly steeper "bottom" angles, a 60 degree seats uses a 70 bottom angle, or more, by default the throat % ends up even larger without removing anything with a carbide. It just tips everything up, and it ends up wider. That's the reason for it too. Literally makes the hole larger under the valve. On a 800 inch deal trying to make 1600+hp at 8000+ rpm, that's just what it needs. The extra angles, vs just blowing the hole out with a carbide and destroying all the angles that help turn the air or in this case, turn it less, and helps wet flow.

I revise bottom angles all the time, no "rule" that says a 45 degree seat HAS to use a 60 bottom angle. I've changed it to 65 more times than I can count, I have a Sunnen VSC cutter I use, and I had another one made. For the serdi style blades. I'll also use a 65 single angle blade to change the bottom angle. This works well when you're valve size limited do do bore size and the engine "thinks" it has a bigger valve without increasing shrouding.
My favourite 45 deg intake cutter that I use on most things with over .600" lift is 35/45/65. Usually with 75/80 or 75/85 throat cuts.
I have no idea why everyone defaults to 60deg bottom cut.
The only issue is getting the cutters, I hang on to my old Mira ball drive cutter bodies coz I can get that cutter profile in a mira cutter. The rest of my tooling is goodson fast cut.

But to the question - it's valve diameter, not area.
And it's a rule of thumb, there are many exceptions, it's just a basic starting point.

Flat tappet lower lift stuff - 85-88%
Aggressive flat tappet or street/hyd roller - 87-89%
Solid roller decent lift - 88-91%
Aggressive roller - 90-92%

Again just a starting point.
I've used up to 91% on SFT stuff when the port design makes that feasible.
I was under the impression that air does not like turning over sharp angles more than 15 degrees?
That is a statement from Darin Morgan
Tell Darin to think a flow over the short turn and light come on 🤣



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Re: Throat % is it area or Diameter?

Post by KnightEngines »

[-o<
steve cowan wrote: Thu Mar 16, 2023 11:37 pm
KnightEngines wrote: Thu Mar 16, 2023 6:10 pm
Bigchief632 wrote: Mon Mar 13, 2023 1:11 pm I use diameter of od of valve also. And add valve stem area. This is another old wives tale that's held on for decades. 85-90% MAX!! It's all dependant on application, valve diameter, shrouding, and profile. By default, if you cut a 55 degree seat on a 2.5+ diameter valve, for example, you'll end up at close to 93%, with all the angles on the seat, 50-55-65-75. Just an FYI, some engines use seat angles even steeper, 60 or even 65. With the correspondingly steeper "bottom" angles, a 60 degree seats uses a 70 bottom angle, or more, by default the throat % ends up even larger without removing anything with a carbide. It just tips everything up, and it ends up wider. That's the reason for it too. Literally makes the hole larger under the valve. On a 800 inch deal trying to make 1600+hp at 8000+ rpm, that's just what it needs. The extra angles, vs just blowing the hole out with a carbide and destroying all the angles that help turn the air or in this case, turn it less, and helps wet flow.

I revise bottom angles all the time, no "rule" that says a 45 degree seat HAS to use a 60 bottom angle. I've changed it to 65 more times than I can count, I have a Sunnen VSC cutter I use, and I had another one made. For the serdi style blades. I'll also use a 65 single angle blade to change the bottom angle. This works well when you're valve size limited do do bore size and the engine "thinks" it has a bigger valve without increasing shrouding.
My favourite 45 deg intake cutter that I use on most things with over .600" lift is 35/45/65. Usually with 75/80 or 75/85 throat cuts.
I have no idea why everyone defaults to 60deg bottom cut.
The only issue is getting the cutters, I hang on to my old Mira ball drive cutter bodies coz I can get that cutter profile in a mira cutter. The rest of my tooling is goodson fast cut.

But to the question - it's valve diameter, not area.
And it's a rule of thumb, there are many exceptions, it's just a basic starting point.

Flat tappet lower lift stuff - 85-88%
Aggressive flat tappet or street/hyd roller - 87-89%
Solid roller decent lift - 88-91%
Aggressive roller - 90-92%

Again just a starting point.
I've used up to 91% on SFT stuff when the port design makes that feasible.
I was under the impression that air does not like turning over sharp angles more than 15 degrees?
That is a statement from Darin Morgan
Think of that cutter as a 35/50/65, with just the 50 changed to 45.
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Re: Throat % is it area or Diameter?

Post by Bigchief632 »

steve cowan wrote: Thu Mar 16, 2023 11:37 pm
KnightEngines wrote: Thu Mar 16, 2023 6:10 pm
Bigchief632 wrote: Mon Mar 13, 2023 1:11 pm I use diameter of od of valve also. And add valve stem area. This is another old wives tale that's held on for decades. 85-90% MAX!! It's all dependant on application, valve diameter, shrouding, and profile. By default, if you cut a 55 degree seat on a 2.5+ diameter valve, for example, you'll end up at close to 93%, with all the angles on the seat, 50-55-65-75. Just an FYI, some engines use seat angles even steeper, 60 or even 65. With the correspondingly steeper "bottom" angles, a 60 degree seats uses a 70 bottom angle, or more, by default the throat % ends up even larger without removing anything with a carbide. It just tips everything up, and it ends up wider. That's the reason for it too. Literally makes the hole larger under the valve. On a 800 inch deal trying to make 1600+hp at 8000+ rpm, that's just what it needs. The extra angles, vs just blowing the hole out with a carbide and destroying all the angles that help turn the air or in this case, turn it less, and helps wet flow.

I revise bottom angles all the time, no "rule" that says a 45 degree seat HAS to use a 60 bottom angle. I've changed it to 65 more times than I can count, I have a Sunnen VSC cutter I use, and I had another one made. For the serdi style blades. I'll also use a 65 single angle blade to change the bottom angle. This works well when you're valve size limited do do bore size and the engine "thinks" it has a bigger valve without increasing shrouding.
My favourite 45 deg intake cutter that I use on most things with over .600" lift is 35/45/65. Usually with 75/80 or 75/85 throat cuts.
I have no idea why everyone defaults to 60deg bottom cut.
The only issue is getting the cutters, I hang on to my old Mira ball drive cutter bodies coz I can get that cutter profile in a mira cutter. The rest of my tooling is goodson fast cut.

But to the question - it's valve diameter, not area.
And it's a rule of thumb, there are many exceptions, it's just a basic starting point.

Flat tappet lower lift stuff - 85-88%
Aggressive flat tappet or street/hyd roller - 87-89%
Solid roller decent lift - 88-91%
Aggressive roller - 90-92%

Again just a starting point.
I've used up to 91% on SFT stuff when the port design makes that feasible.
I was under the impression that air does not like turning over sharp angles more than 15 degrees?
That is a statement from Darin Morgan

Think about it logically, and visualize it. Air turns easier and less, with say a 38 or 40 degrees top cut vs say the "classic" 30 degree. Draw the angles. 38 top, 45 seat, 65 bottom, 75 transition angle. Now draw 30 top, 45 seat, 60 bottom and 70 transition angle and tell me which one do you think turns easier around the given angles.
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Re: Throat % is it area or Diameter?

Post by Wesman07 »

I don’t see how you can determine a throat size without considering the size of the port. The throat percentage rule is an estimated maximum, not necessarily a target.
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Re: Throat % is it area or Diameter?

Post by Elroy »

Wesman07 wrote: Fri Mar 17, 2023 8:46 am I don’t see how you can determine a throat size without considering the size of the port. The throat percentage rule is an estimated maximum, not necessarily a target.
I agree. I think this regularly gets lost in the mix.
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