Throat % is it area or Diameter?

[frnkeore]

I don't know anything about how fuel shear acts but, in wind tunnel airfoils, in general, if you try to turn air, more than 12°, it stalls (that would be 24° included).

I see all kinds of valve seat angle talked about but, does it really matter what the valve seat angle is, when your creating a venturi for air flow?

For instance, in a 5 angle valve job, with cuts of 15/30/45/60/75, does it matter which one is the valve seat, if the curtain area is the same?

It does seem like it would effect the low lift flow, in the lift transition, if the seat was in the lower area of the bottom 3 angles, reducing overlap losses for high rpm engines but, for the upper 2 angles, using the same lift, increase flow overall but, have more overlap lose.

[SpeierRacingHeads]

I don't know anything about how fuel shear acts but, in wind tunnel airfoils, in general, if you try to turn air, more than 12°, it stalls (that would be 24° included).

I see all kinds of valve seat angle talked about but, does it really matter what the valve seat angle is, when your creating a venturi for air flow?

For instance, in a 5 angle valve job, with cuts of 15/30/45/60/75, does it matter which one is the valve seat, if the curtain area is the same?

It does seem like it would effect the low lift flow, in the lift transition, if the seat was in the lower area of the bottom 3 angles, reducing overlap losses for high rpm engines but, for the upper 2 angles, using the same lift, increase flow overall but, have more overlap lose.

Now we are talking about a NHRA Stocker valve job!

[BILL-C]

I can think of alot of applications where the throat that performs the best is not perfectly round. For those of you that are not scanning your head, how are you measuring this throat area or diameter ? How accurate do you think your measurments are? Are you trying to exactly hit a certain pre determined number?

[KnightEngines]

I can think of alot of applications where the throat that performs the best is not perfectly round. For those of you that are not scanning your head, how are you measuring this throat area or diameter ? How accurate do you think your measurments are? Are you trying to exactly hit a certain pre determined number?

I don't ever try to hit a certain predetermined throat %.
I cut the valve job to suit the chamber, bowl, lift & duration to be used & port with the same in mind.
The throat % ends up where it ends up - it just usually falls in the ranges I posted earlier.
My throats are never round either, always cut back more on the short turn & less on the long turn - the higher/straighter the port the less offset in the bowl.
On shallow ports the offset can be quite pronounced.

Flat chambers usually require smaller throats and/or larger than *normal* valves.
Deep 'pressure recovery' type chambers with high ports like smaller valves, large throats, steep angles & 50-55 deg seats.

Our job as cylinder head specialists is to assess the casting we are working with & determine the best approach to make power within the given/fixed limitations, a small part of that is throat size.

[GARY C]

I can think of alot of applications where the throat that performs the best is not perfectly round. For those of you that are not scanning your head, how are you measuring this throat area or diameter ? How accurate do you think your measurments are? Are you trying to exactly hit a certain pre determined number?

I don't ever try to hit a certain predetermined throat %.
I cut the valve job to suit the chamber, bowl, lift & duration to be used & port with the same in mind.
The throat % ends up where it ends up - it just usually falls in the ranges I posted earlier.
My throats are never round either, always cut back more on the short turn & less on the long turn - the higher/straighter the port the less offset in the bowl.
On shallow ports the offset can be quite pronounced.

Flat chambers usually require smaller throats and/or larger than *normal* valves.
Deep 'pressure recovery' type chambers with high ports like smaller valves, large throats, steep angles & 50-55 deg seats.

Our job as cylinder head specialists is to assess the casting we are working with & determine the best approach to make power within the given/fixed limitations, a small part of that is throat size.

Just out of curiosity if someone had an 89% throat but really needed a 91% throat how much power would they loose?

[KnightEngines]

I can think of alot of applications where the throat that performs the best is not perfectly round. For those of you that are not scanning your head, how are you measuring this throat area or diameter ? How accurate do you think your measurments are? Are you trying to exactly hit a certain pre determined number?

I don't ever try to hit a certain predetermined throat %.
I cut the valve job to suit the chamber, bowl, lift & duration to be used & port with the same in mind.
The throat % ends up where it ends up - it just usually falls in the ranges I posted earlier.
My throats are never round either, always cut back more on the short turn & less on the long turn - the higher/straighter the port the less offset in the bowl.
On shallow ports the offset can be quite pronounced.

Flat chambers usually require smaller throats and/or larger than *normal* valves.
Deep 'pressure recovery' type chambers with high ports like smaller valves, large throats, steep angles & 50-55 deg seats.

Our job as cylinder head specialists is to assess the casting we are working with & determine the best approach to make power within the given/fixed limitations, a small part of that is throat size.

Just out of curiosity if someone had an 89% throat but really needed a 91% throat how much power would they loose?

How was it determined that the throat needed to be bigger?
If the rest of the port cannot support a larger throat or the lift is not high enough to use more throat the net gain will be zero or negative.
If the throat truly is the bottleneck the gain could be substantial - even more than math would suggest if it is undervalved as well.
Very much 'it depends' lol, like most things cylinder head related a single variable cannot be taken on its own!

[juuhanaa]

I don't know anything about how fuel shear acts but, in wind tunnel airfoils, in general, if you try to turn air, more than 12°, it stalls (that would be 24° included).

I see all kinds of valve seat angle talked about but, does it really matter what the valve seat angle is, when your creating a venturi for air flow?

For instance, in a 5 angle valve job, with cuts of 15/30/45/60/75, does it matter which one is the valve seat, if the curtain area is the same?

It does seem like it would effect the low lift flow, in the lift transition, if the seat was in the lower area of the bottom 3 angles, reducing overlap losses for high rpm engines but, for the upper 2 angles, using the same lift, increase flow overall but, have more overlap lose.

Interesting thoughts, but if I didnt miss something that only works when all the angles are on expanding side of the venturi. Cant lift the valve if seat is at the convergent side. What does the angles matter in terms of air flow, if we get the speeds we want in different places in the port?



-juhana

[gunt]

the answer is diameter , always has being , i think [ politelly ] it could be confusion in your head ,

[frnkeore]

My question was mainly about how the seat angle effects cam timing and overlap.

I had in mind a perfectly shaped (round) port, with the ideal throat size and valve size to support what ever the ci need was.

Not how one area of the port might effect another area and the interaction involve in that.

No set angles or limit to the number but, what combo of angles might be best, too. Such as 12/24/36/48/60/72/84

Also, what angles could/should have a longer surface area

[HQM383]

the answer is diameter, always has being , i think [ politelly ] it could be confusion in your head ,

But as I demonstrated on page 2 of this thread confusion in the head isn’t hard for the non professional with quotes like “the sweet spot is where the throat area is between 91 and 92% of the valve diameter.”

[frnkeore]

Something else that I haven't seen addressed, is since we are working with, what is essentially a reverse venturi, has there been any studies in how a venturi flows backward?

[BILL-C]

Anyone have any stories about any back to back dyno testing where they only changed the valve back cut and \or valve job? NOT flow bench testing! Dyno testing.

[juuhanaa]

I was so excited about my first trip to dyno that it ended when i drove the car into a ditch while loading it onto a trailer. It was snowing and I couldnt see properly over the steering wheel. you should have seen the shop owners when they pulled me out of the ditch. Their sign language was telling me rocket scientist, go away

Sometimes less is more like the megane f7r cylinder head stock exhaust valve seats, but please note it was no a b a test.

5 pakoventtiiliä myös isommaksi.JPG

-juhana