Valve Seat Angles and Flow Area

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GARY C
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Re: Valve Seat Angles and Flow Area

Post by GARY C » Fri Mar 09, 2018 11:16 am

MTENGINES wrote:
Fri Mar 09, 2018 10:30 am
cspeier wrote:
Fri Mar 09, 2018 10:12 am
So you guys don't believe the sooner you get that column of air moving the better?
Isn't that the job of the camshaft?
The head's job is to flow air the cams job is to say when?

Seat flow and seat timing would have to be adjusted accordingly but in some cases one has to be altered for the end goal.

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Re: Valve Seat Angles and Flow Area

Post by groberts101 » Fri Mar 09, 2018 1:21 pm

cspeier wrote:
Fri Mar 09, 2018 10:50 am
IMO, increasing low lift flow is the same as decreasing the ramp rate or rocker ratio.

Might just be me.
Could you elaborate?

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Re: Valve Seat Angles and Flow Area

Post by RDY4WAR » Fri Mar 09, 2018 2:07 pm

cspeier wrote:
Fri Mar 09, 2018 10:12 am
So you guys don't believe the sooner you get that column of air moving the better?
I may be wrong in this thinking, but I believe it may be a matter of wanting to get the column of air moving but not necessarily flowing... if that makes any sense. :?

Air has mass. Like anything else with mass, it takes a certain force to make it move and an amount of time for it to react to that force. In an engine running at any decent rpm, this time may be several crank degrees before the pressure drop from the now open valve is recognized by the port and the air reacts to it. So long as the pressure drop across the valve is maintained, the air will continue to speed up as the valve continues to open. However, introducing too much flow area too soon may equalize the pressure between the port and chamber causing you to lose the pressure drop. When you lose the pressure drop, you lose flow. The port stalls out. Then as the piston accelerates away, the pressure drop picks back up and has to get the air moving all over again.

On the back nine, the piston is chasing the intake valve closed as air is ramming into the cylinder from the intake wave. If the low lift flow is too high, the ramming may equalize out the pressure too soon, and allow time and flow area for the air to reverse back out of the port before the valve closes which hurts volumetric efficiency and dynamic pressure. Keeping the flow low during this low lift area may hold back the intake air just enough to keep up the pressure and keep the air flowing into the cylinder for longer.

On the exhaust side, I could see too much low lift flow causing local velocity around the valve during blow down to fall off which may hurt the scavenging strength later in the cycle. Then during overlap, too much low lift flow may draw too much on the chamber and kill the scavenging process too soon, either to start reversion or sucking intake air right out of the exhaust valve.

Though as was mentioned, the cam should be able to work around this somewhat... but then you're making compromises.

This is just my theory on low lift flow being bad. I have no testing or anything to back up this theory, just brainstorming. I don't have near the experience of most of you guys here so someone feel free to let me know if I am wrong in this thinking.

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Re: Valve Seat Angles and Flow Area

Post by groberts101 » Fri Mar 09, 2018 2:48 pm

RDY4WAR wrote:
Fri Mar 09, 2018 2:07 pm
cspeier wrote:
Fri Mar 09, 2018 10:12 am
So you guys don't believe the sooner you get that column of air moving the better?
I may be wrong in this thinking, but I believe it may be a matter of wanting to get the column of air moving but not necessarily flowing... if that makes any sense. :?

Air has mass. Like anything else with mass, it takes a certain force to make it move and an amount of time for it to react to that force. In an engine running at any decent rpm, this time may be several crank degrees before the pressure drop from the now open valve is recognized by the port and the air reacts to it. So long as the pressure drop across the valve is maintained, the air will continue to speed up as the valve continues to open. However, introducing too much flow area too soon may equalize the pressure between the port and chamber causing you to lose the pressure drop. When you lose the pressure drop, you lose flow. The port stalls out. Then as the piston accelerates away, the pressure drop picks back up and has to get the air moving all over again.

On the back nine, the piston is chasing the intake valve closed as air is ramming into the cylinder from the intake wave. If the low lift flow is too high, the ramming may equalize out the pressure too soon, and allow time and flow area for the air to reverse back out of the port before the valve closes which hurts volumetric efficiency and dynamic pressure. Keeping the flow low during this low lift area may hold back the intake air just enough to keep up the pressure and keep the air flowing into the cylinder for longer.

On the exhaust side, I could see too much low lift flow causing local velocity around the valve during blow down to fall off which may hurt the scavenging strength later in the cycle. Then during overlap, too much low lift flow may draw too much on the chamber and kill the scavenging process too soon, either to start reversion or sucking intake air right out of the exhaust valve.

Though as was mentioned, the cam should be able to work around this somewhat... but then you're making compromises.

This is just my theory on low lift flow being bad. I have no testing or anything to back up this theory, just brainstorming. I don't have near the experience of most of you guys here so someone feel free to let me know if I am wrong in this thinking.
I think your concepts use sound reasoning and cams can only do so much to correct other overages or deficiencies. And very high lift cams can only compensate for too big valve/high low lift flow so much by slowing down lobe lift accelleration rates.

I would pose a rhetorical question though.

For a mostly street oriented motor would your cam guy rather grind spec's around a cylinder head that flows like gangbusters in the <.200" lift ranges or another that flows like horsepoo in that same range because eliminating reverse flow was the entire basis for port/seat design? What differences would each grind have on the powerbands average power production?
Last edited by groberts101 on Fri Mar 09, 2018 2:52 pm, edited 1 time in total.

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Re: Valve Seat Angles and Flow Area

Post by CGT » Fri Mar 09, 2018 2:52 pm

groberts101 wrote:
Fri Mar 09, 2018 2:48 pm
. For a mostly street oriented motor would your cam guy rather grind spec's around a cylinder head that flows like gangbusters in the <.200" lift ranges or another that flows like horsepoo in that same range because eliminating reverse flow was the entire bases for port/seat design? What differences would each grind have on the powerbands average power production?
I would rather spec my own cam, or talk to a cam guy who doesn't flow spec. :lol:

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Re: Valve Seat Angles and Flow Area

Post by groberts101 » Fri Mar 09, 2018 2:56 pm

If your cam guy isn't using lift point flow data to build your custom cam then maybe you need a better cam guy. Isn't the actual measured flow window of the head matched to the cylinders demand? Then the cam pulls it all together to match the requirements?

Iow, same cam for 2.25" intake vs another with 1.94?

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Re: Valve Seat Angles and Flow Area

Post by cspeier » Fri Mar 09, 2018 3:00 pm

groberts101 wrote:
Fri Mar 09, 2018 1:21 pm
cspeier wrote:
Fri Mar 09, 2018 10:50 am
IMO, increasing low lift flow is the same as decreasing the ramp rate or rocker ratio.

Might just be me.
Could you elaborate?
Increase port pressure.
Increase port harmonics.
close the valve faster..
OR Decrease the steady state flow.

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Re: Valve Seat Angles and Flow Area

Post by CGT » Fri Mar 09, 2018 3:03 pm

groberts101 wrote:
Fri Mar 09, 2018 2:56 pm
If your cam guy isn't using lift point flow data to build your custom cam then maybe you need a better cam guy. Isn't the actual measured flow window of the head matched to the cylinders demand? Then the cam pulls it all together to match the requirements?

Iow, same cam for 2.25" intake vs another with 1.94?
Our "cam guy" was a consensus amongst the group for the 2017 EMC and we won 1st place. No flowz involved. We were hindered by an expert cam guy in our first EMC.

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Re: Valve Seat Angles and Flow Area

Post by CGT » Fri Mar 09, 2018 3:05 pm

.

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Re: Valve Seat Angles and Flow Area

Post by groberts101 » Fri Mar 09, 2018 3:13 pm

Lol.. sounds like you had some existing baseline to work from for that specific engine combo, tried a few cams, or just plain got lucky if the very first cam hit the nail on the head. Pretty rare if it's a one n done.

If I have an exceptionally well designed head that surpasses many other.. why would I want to spend the money for a custom cam designed around less efficient cylinder heads he's done grinds for in the past?

Sure seems like a stab in the dark to me.

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Re: Valve Seat Angles and Flow Area

Post by CGT » Fri Mar 09, 2018 3:19 pm

groberts101 wrote:
Fri Mar 09, 2018 3:13 pm
Lol.. sounds like you had some existing baseline to work from for that specific engine combo, tried a few cams, or just plain got lucky if the very first cam hit the nail on the head. Pretty rare if it's a one n done.
Both, lots of testing, a few cams....and quite a bit of previous testing in that basic rpm range...minus the flat tappet thing. Only the internet "experts" get the perfect cam the first time. :lol:

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Re: Valve Seat Angles and Flow Area

Post by Warp Speed » Fri Mar 09, 2018 3:37 pm

CGT wrote:
Fri Mar 09, 2018 3:19 pm
groberts101 wrote:
Fri Mar 09, 2018 3:13 pm
Lol.. sounds like you had some existing baseline to work from for that specific engine combo, tried a few cams, or just plain got lucky if the very first cam hit the nail on the head. Pretty rare if it's a one n done.
Both, lots of testing, a few cams....and quite a bit of previous testing in that basic rpm range...minus the flat tappet thing. Only the internet "experts" get the perfect cam the first time. :lol:
LOL

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Re: Valve Seat Angles and Flow Area

Post by digger » Fri Mar 09, 2018 3:39 pm

More Low lift flow kind of acts like more duration.

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Re: Valve Seat Angles and Flow Area

Post by GARY C » Fri Mar 09, 2018 3:43 pm

CGT wrote:
Fri Mar 09, 2018 3:19 pm
groberts101 wrote:
Fri Mar 09, 2018 3:13 pm
Lol.. sounds like you had some existing baseline to work from for that specific engine combo, tried a few cams, or just plain got lucky if the very first cam hit the nail on the head. Pretty rare if it's a one n done.
Both, lots of testing, a few cams....and quite a bit of previous testing in that basic rpm range...minus the flat tappet thing. Only the internet "experts" get the perfect cam the first time. :lol:
I think I have seen 5 different methods discussed on ST and they all seem to end up within a few degrees of each other, to fine tune from there you only need a lot of dyno time and start making changes a few degrees at a time.

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Re: Valve Seat Angles and Flow Area

Post by Walter R. Malik » Fri Mar 09, 2018 5:48 pm

cspeier wrote:
Fri Mar 09, 2018 3:00 pm
groberts101 wrote:
Fri Mar 09, 2018 1:21 pm
cspeier wrote:
Fri Mar 09, 2018 10:50 am
IMO, increasing low lift flow is the same as decreasing the ramp rate or rocker ratio.

Might just be me.
Could you elaborate?
Increase port pressure.
Increase port harmonics.
close the valve faster..
OR Decrease the steady state flow.
If it is the same thing, I guess that would mean that increasing low lift flow also means the valve spring requirement is not as much. I don't think so.
It is much, MUCH easier to hurt only the low lift flow than to increase the flank rates of a cam lobe profile and keep RPM in check.
When you get to the point where you can not increase the cam lobe aggressiveness any further, yet you still wish to keep your required torque while increasing horsepower ... what would you do ...?
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