50 degree valve seats in modern hot street builds: is it finally time?
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Re: 50 degree valve seats in modern hot street builds: is it finally time?
Seems to me the preceding attributes and references to low lift flow are actually addressing flow capability at various crank angles. In other words, lets say port 'A' has 10% less flow at lifts below 0.250" than port 'B' but cam 'B' has enough more lift at any given crank angle in the overlap range to fully compensate. Ditto as IVC is approached. Would the pressure graphs in these regions look any different?
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Happy is he who can discover the cause of things.
Re: 50 degree valve seats in modern hot street builds: is it finally time?
if the low lift flow is lower then yes you can simply alter the EVC and IVO to achieve the same mass flow by virtue of more lift, the question would be is this a better a worse choice for a street motor that needs a really wide powerband? for example at an rpm where the exhaust isn't "in tune" or at say light load will the negative consequences be more severe than a head that flows more at low lifts but uses more moderate cam events?
Re: 50 degree valve seats in modern hot street builds: is it finally time?
Ok Bob, I read your post twice, slept on it and read it again this morning. It appears as though all Clint is saying is that the graph posted didn't come from his software so David must have compiled the sensor data and fit it to the basic template, if you will, that matches all of the other charts and graphs in his books which allowed him to overlay several things on one chart.
David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.
What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.
Obviously not everyone sees it that way.
David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.
What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.
Obviously not everyone sees it that way.
Re: 50 degree valve seats in modern hot street builds: is it finally time?
Davis's charts and graphs are the way they are because of the software he uses to illustrate his books and articles, when he submits a book or article it is fully illustrated and edited so he doesn't have to depend on a mag editor that may be good at editing but knows nothing about engines and ends up editing out something important to the info he is presenting.RevTheory wrote: ↑Sat Jul 21, 2018 9:20 am Ok Bob, I read your post twice, slept on it and read it again this morning. It appears as though all Clint is saying is that the graph posted didn't come from his software so David must have compiled the sensor data and fit it to the basic template, if you will, that matches all of the other charts and graphs in his books which allowed him to overlay several things on one chart.
David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.
What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.
Obviously not everyone sees it that way.
Very likely this data came from previous test that led him to contact Clint, DV was writing about the benefits of this technology long before he knew Clint and possibly before this equipment was available to the public.
The one question I still have is, If air flow starts before TDC and is clearly filling the cylinder at TDC while the piston is motionless then why wouldn't an engine benefit from low lift flow if the mid lift and peak lift is equal or better than a steep seat?
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THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
Re: 50 degree valve seats in modern hot street builds: is it finally time?
Ive seen conflicting data on the flowz before tdc, who knows. But...their isnt technically a cylinder or much of one at tdc to fill.GARY C wrote: ↑Sat Jul 21, 2018 11:46 am The one question I still have is, If air flow starts before TDC and is clearly filling the cylinder at TDC while the piston is motionless then why wouldn't an engine benefit from low lift flow if the mid lift and peak lift is equal or better than a steep seat?
Re: 50
Re: 50 degree valve seats in modern hot street builds: is it finally time?
Seems to me thats where all these low lift lovers seem to get hung up, exhaust .7bar pull, great low lift, overlap blah blah, they are looking at the wrong end of the cylinder when it comes to high VECGT wrote: ↑Sat Jul 21, 2018 2:00 pmIve seen conflicting data on the flowz before tdc, who knows. But...their isnt technically a cylinder or much of one at tdc to fill.GARY C wrote: ↑Sat Jul 21, 2018 11:46 am The one question I still have is, If air flow starts before TDC and is clearly filling the cylinder at TDC while the piston is motionless then why wouldn't an engine benefit from low lift flow if the mid lift and peak lift is equal or better than a steep seat?
Re: 50
Tom
Re: 50 degree valve seats in modern hot street builds: is it finally time?
You guys may have already seen this video inside a working cylinder showing from TDC through exhaust, the piston is at TDC for a very brief point before piston movement increases the volume to fill. https://www.youtube.com/watch?v=sEf8va1S7Swzums wrote: ↑Sat Jul 21, 2018 2:46 pmSeems to me thats where all these low lift lovers seem to get hung up, exhaust .7bar pull, great low lift, overlap blah blah, they are looking at the wrong end of the cylinder when it comes to high VECGT wrote: ↑Sat Jul 21, 2018 2:00 pmIve seen conflicting data on the flowz before tdc, who knows. But...their isnt technically a cylinder or much of one at tdc to fill.GARY C wrote: ↑Sat Jul 21, 2018 11:46 am The one question I still have is, If air flow starts before TDC and is clearly filling the cylinder at TDC while the piston is motionless then why wouldn't an engine benefit from low lift flow if the mid lift and peak lift is equal or better than a steep seat?
Re: 50
Tom
Maybe to much to soon causes a stall in the intake system, although in the video it is very active or so it appears?
Just always curious to figure out why somethings work better than others.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
Re: 50 degree valve seats in modern hot street builds: is it finally time?
You missed the part where nitro2 said "Usually the greatest depression (relative to atmospheric pressure) will be part way down the intake stroke and it can be several psi at high rpm. Flowbench tests are typically in the vicinity of 1 psi, which is not nearly enough"RevTheory wrote: ↑Sat Jul 21, 2018 9:20 am Ok Bob, I read your post twice, slept on it and read it again this morning. It appears as though all Clint is saying is that the graph posted didn't come from his software so David must have compiled the sensor data and fit it to the basic template, if you will, that matches all of the other charts and graphs in his books which allowed him to overlay several things on one chart.
David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.
What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.
Obviously not everyone sees it that way.
Re: 50 degree valve seats in modern hot street builds: is it finally time?
So starve the cylinder earlier for a greater depression later.digger wrote: ↑Sat Jul 21, 2018 6:39 pmYou missed the part where nitro2 said "Usually the greatest depression (relative to atmospheric pressure) will be part way down the intake stroke and it can be several psi at high rpm. Flowbench tests are typically in the vicinity of 1 psi, which is not nearly enough"RevTheory wrote: ↑Sat Jul 21, 2018 9:20 am Ok Bob, I read your post twice, slept on it and read it again this morning. It appears as though all Clint is saying is that the graph posted didn't come from his software so David must have compiled the sensor data and fit it to the basic template, if you will, that matches all of the other charts and graphs in his books which allowed him to overlay several things on one chart.
David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.
What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.
Obviously not everyone sees it that way.
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Re: 50 degree valve seats in modern hot street builds: is it finally time?
Better have one hell of an intake port/valve sizing and induction system capability to make that all work out in the end. If that were truly the be all solution then most race engines would not be using such long cams. All boils down to a time limitation and we just do what needs to be done to gain the desired power curve.CGT wrote: ↑Sat Jul 21, 2018 7:48 pmSo starve the cylinder earlier for a greater depression later.digger wrote: ↑Sat Jul 21, 2018 6:39 pmYou missed the part where nitro2 said "Usually the greatest depression (relative to atmospheric pressure) will be part way down the intake stroke and it can be several psi at high rpm. Flowbench tests are typically in the vicinity of 1 psi, which is not nearly enough"RevTheory wrote: ↑Sat Jul 21, 2018 9:20 am Ok Bob, I read your post twice, slept on it and read it again this morning. It appears as though all Clint is saying is that the graph posted didn't come from his software so David must have compiled the sensor data and fit it to the basic template, if you will, that matches all of the other charts and graphs in his books which allowed him to overlay several things on one chart.
David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.
What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.
Obviously not everyone sees it that way.
Personally, I think most street guys are not leveraging the exhausts velocity capability anywhere near its potential. Get that closer to right and you can boost cylinder filling from both ends.
Last edited by groberts101 on Sat Jul 21, 2018 8:23 pm, edited 1 time in total.
Re: 50 degree valve seats in modern hot street builds: is it finally time?
Thanks for the link Gary. It is interesting but missing ~180 degrees from the end of exhaust blow down to TDC. The most interesting part of overlap is not there.GARY C wrote: ↑Sat Jul 21, 2018 4:51 pmYou guys may have already seen this video inside a working cylinder showing from TDC through exhaust, the piston is at TDC for a very brief point before piston movement increases the volume to fill. https://www.youtube.com/watch?v=sEf8va1S7Sw
Maybe to much to soon causes a stall in the intake system, although in the video it is very active or so it appears?
Just always curious to figure out why somethings work better than others.
- Paul
Re: 50 degree valve seats in modern hot street builds: is it finally time?
I addressed that when I said David apparently didn't reference atmospheric pressure.digger wrote: ↑Sat Jul 21, 2018 6:39 pm You missed the part where nitro2 said "Usually the greatest depression (relative to atmospheric pressure) will be part way down the intake stroke and it can be several psi at high rpm. Flowbench tests are typically in the vicinity of 1 psi, which is not nearly enough"
Re: 50 degree valve seats in modern hot street builds: is it finally time?
Yes thats the bummer part, I tried to find the original from the video company to see if it was on that one but I didn't have any luck.pcnsd wrote: ↑Sat Jul 21, 2018 8:22 pmThanks for the link Gary. It is interesting but missing ~180 degrees from the end of exhaust blow down to TDC. The most interesting part of overlap is not there.GARY C wrote: ↑Sat Jul 21, 2018 4:51 pmYou guys may have already seen this video inside a working cylinder showing from TDC through exhaust, the piston is at TDC for a very brief point before piston movement increases the volume to fill. https://www.youtube.com/watch?v=sEf8va1S7Sw
Maybe to much to soon causes a stall in the intake system, although in the video it is very active or so it appears?
Just always curious to figure out why somethings work better than others.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
Re: 50 degree valve seats in modern hot street builds: is it finally time?
dont know where you get starve from, that is not what i interpreted it as.CGT wrote: ↑Sat Jul 21, 2018 7:48 pmSo starve the cylinder earlier for a greater depression later.digger wrote: ↑Sat Jul 21, 2018 6:39 pmYou missed the part where nitro2 said "Usually the greatest depression (relative to atmospheric pressure) will be part way down the intake stroke and it can be several psi at high rpm. Flowbench tests are typically in the vicinity of 1 psi, which is not nearly enough"RevTheory wrote: ↑Sat Jul 21, 2018 9:20 am Ok Bob, I read your post twice, slept on it and read it again this morning. It appears as though all Clint is saying is that the graph posted didn't come from his software so David must have compiled the sensor data and fit it to the basic template, if you will, that matches all of the other charts and graphs in his books which allowed him to overlay several things on one chart.
David also apparently didn't reference atmospheric pressure to his cylinder pressure sensor so he must have been comparing cylinder pressure relative to the intake and exhaust pressure sensors. Perhaps that leaves a little to be desired. This is my ASSumption without talking to David so I could be chewing on both feet here.
What it definitely shows is just how much depression the exhaust pulls across the chamber and into the intake port during TDC and that happens during low-lifts and that's probably why he harps on IVO/EVC relative to low-lift flow so much with IVC being a close second.
Obviously not everyone sees it that way.
i personally dont think you need much flow to evacuate the clearance volume when you pull 100-200" on it. when you look at the engines of proponents of killing low lift flow they still have the exhaust communicating with the inlet alot during overlap they just arent chasing the most cfm on the bench at that low lift point
Re: 50 degree valve seats in modern hot street builds: is it finally time?
It seems like it's a matter of matching the incoming pressure wave of the intake to the negative pressure area in the chamber/cylinder.
If the incoming pressure wave overcomes the negative pressure area of the cylinder what happens in the intake runner?
If the incoming pressure wave overcomes the negative pressure area of the cylinder what happens in the intake runner?
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!