50 degree valve seats in modern hot street builds: is it finally time?

[MadBill]

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?

[digger]

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?

[RevTheory]

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.

[GARY C]

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.

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.

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?

[CGT]

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

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.

[zums]

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

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.

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 VE
Tom

[GARY C]

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

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.

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 VE
Tom

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=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.

[digger]

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.

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"

[CGT]

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.

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"

So starve the cylinder earlier for a greater depression later.

[groberts101]

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.

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"

So starve the cylinder earlier for a greater depression later.

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.

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.

[pcnsd]

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.

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 VE
Tom

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=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.

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.

[RevTheory]

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"

I addressed that when I said David apparently didn't reference atmospheric pressure.

[GARY C]

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 VE
Tom

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=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.

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.

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.

[digger]

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.

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"

So starve the cylinder earlier for a greater depression later.

dont know where you get starve from, that is not what i interpreted it as.

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

[GARY C]

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?