Do these pictures need captions? (32V Intake Manifold Study - HP)
#271
Rob Edwards found an interesting bit of information on Speedtalk about the Helmholz resonance thing. I'll see if he can post it, here.
There is some real knowledge on Speedtalk. Of course not everyone is an expert, but the following people I think are credible sources of high-quality information on intake manifolds:
Stef -- makes intake manifolds for living
SchmidtMotorWorks -- consults car and aerospace companies. One of the early employees at Bryan's crankshaft firm
Vannik -- wrote a full engine simulation software suite himself, it's for sale for about $400
SWR -- a lot of practical data on turbo engines, source for many of the turbocharger files in the EAP
Nitro2 -- sells equipment to measure the intake port, cylinder, and exhaust port pressures over the engine cycle
Edit: Erland *** also, if you get anywhere close to the intake port and the valve.
Stef -- makes intake manifolds for living
SchmidtMotorWorks -- consults car and aerospace companies. One of the early employees at Bryan's crankshaft firm
Vannik -- wrote a full engine simulation software suite himself, it's for sale for about $400
SWR -- a lot of practical data on turbo engines, source for many of the turbocharger files in the EAP
Nitro2 -- sells equipment to measure the intake port, cylinder, and exhaust port pressures over the engine cycle
Edit: Erland *** also, if you get anywhere close to the intake port and the valve.
Thanks for the list Tuomo- I have been perusing Speedtalk for a while but don't know the players, most of the conversation is wayyyy above my pay grade.
I was struck by the following quote in one of the longer threads on plenums (plenii?) and airboxes volume calculations and their design.
This whole Helmholz resonance thing seems to be hugely misunderstood by a great many people.
If you have a column of air contained in a pipe, the air in that column has mass.
If you have a SEALED chamber, the air contained within acts like a spring. (think of airbag suspension).
Couple the mass of air in the pipe, to the stiffness of the air spring located at one end, and it will resonantly bounce at a very specific frequency.
That is Helmholz resonance.
As soon as you cut a big hole in your air spring, it is no longer a fully sealed chamber, and no longer a simple spring.
So an open airbox can never behave as a Helmholz resonator.
And a plenum with a big wide open throttle body fitted to it may be almost as bad as a wide open airbox.
If you cut seven more holes in your plenum air spring and connect them to seven other inlet runners which are ALL pulsing out of phase, and cut another big hole which is a wide open air entry, the situation becomes extremely complex, and not a nice clean helmholz resonator.
It probably will resonate, and do strange things at certain engine speeds that may end up being either good or bad, but the situation is very complex and really defies simple analysis, and the more cylinders you have, the more complex it all becomes.
Only way to know for sure, is build it, and run it on a real engine on a real dyno.
Rinse and repeat........
A really simple basic formula to calculate "optimum" plenum volume does not exist.
If you have a column of air contained in a pipe, the air in that column has mass.
If you have a SEALED chamber, the air contained within acts like a spring. (think of airbag suspension).
Couple the mass of air in the pipe, to the stiffness of the air spring located at one end, and it will resonantly bounce at a very specific frequency.
That is Helmholz resonance.
As soon as you cut a big hole in your air spring, it is no longer a fully sealed chamber, and no longer a simple spring.
So an open airbox can never behave as a Helmholz resonator.
And a plenum with a big wide open throttle body fitted to it may be almost as bad as a wide open airbox.
If you cut seven more holes in your plenum air spring and connect them to seven other inlet runners which are ALL pulsing out of phase, and cut another big hole which is a wide open air entry, the situation becomes extremely complex, and not a nice clean helmholz resonator.
It probably will resonate, and do strange things at certain engine speeds that may end up being either good or bad, but the situation is very complex and really defies simple analysis, and the more cylinders you have, the more complex it all becomes.
Only way to know for sure, is build it, and run it on a real engine on a real dyno.
Rinse and repeat........
A really simple basic formula to calculate "optimum" plenum volume does not exist.
#272
I don't see a sea change?
Similar cams (ish) = similar peaks with more flow.
Rob's engine has reached a limit somewhere (heads or valves or...) so HP flattens out/can't make the same percentage gain.
6.5 - 30% = 5.0
466 - 30% = 326 TQ (336 ~28%)
453 - 30% = 317 HP (368 ~19%)
Similar cams (ish) = similar peaks with more flow.
Rob's engine has reached a limit somewhere (heads or valves or...) so HP flattens out/can't make the same percentage gain.
6.5 - 30% = 5.0
466 - 30% = 326 TQ (336 ~28%)
453 - 30% = 317 HP (368 ~19%)
I prefer to think about it slightly differently. Air flow is proportional to displacement, rpm, and volumetric efficiency. My starting point is that a 5 liter engine will make the same power at 6400 rpm as a 6.4 liter engine at 5000 rpm, if the volumetric efficiency is constant. Volumetric efficiency isn't constant, but it's a useful starting point, especially if the intake valve area in the two engines is about the same.
In other words, one could take the power curves and shift the rpm axis of the 5.0 L engine by dividing it by the 6.4/5.0, then compare the curves. If they look different, then it's things like runner length etc. changing the volumetric efficiency.
#273
Rob --
I don't think that simple spreadsheet formulas or simulators like EAP are going to get the Helmholtz resonator volumes exactly right. However, some notes: First, they probably do get one to ball park as a starting point. Second, once you have one experiment done on dyno, the formulas appear fairly accurate in predicting the peak rpm changes in response to plenum volume changes.
Third, the manifold we're talking about in this thread is a single plenum manifold with all eight cylinders being fed from the same plenum. The usual Helmholtz equations are probably not a productive way to think about this manifold, because the pulses cancel inside that manifold. Instead, the equations that are used for individual isolated runners seem like a better way to think about it.
In contrast, if there were two plenums and the pulses would be separated correctly (think S3 manifold, but just bent and tucked in the valley), then some Helmholtz equations might be useful. I think I posted some months ago the formulas that I used to try to figure out how much the lower torque peak rpm drops in the S4 manifold if a spacer is added.
(Digression: I think that those individual isolated runner equations are themselves also derived from the Helmholtz equations, it's just the resonating cavity is the cylinder itself and the volume is taken as an approximation the volume at half stroke. The plenum manifold Helmholtz formulas are in fact derived from a two-chamber resonator. I think this might be the original reference from 1953, it's Engelman's dissertation: http://minds.wisconsin.edu/bitstream.../Engel1953.pdf)
I don't think that simple spreadsheet formulas or simulators like EAP are going to get the Helmholtz resonator volumes exactly right. However, some notes: First, they probably do get one to ball park as a starting point. Second, once you have one experiment done on dyno, the formulas appear fairly accurate in predicting the peak rpm changes in response to plenum volume changes.
Third, the manifold we're talking about in this thread is a single plenum manifold with all eight cylinders being fed from the same plenum. The usual Helmholtz equations are probably not a productive way to think about this manifold, because the pulses cancel inside that manifold. Instead, the equations that are used for individual isolated runners seem like a better way to think about it.
In contrast, if there were two plenums and the pulses would be separated correctly (think S3 manifold, but just bent and tucked in the valley), then some Helmholtz equations might be useful. I think I posted some months ago the formulas that I used to try to figure out how much the lower torque peak rpm drops in the S4 manifold if a spacer is added.
(Digression: I think that those individual isolated runner equations are themselves also derived from the Helmholtz equations, it's just the resonating cavity is the cylinder itself and the volume is taken as an approximation the volume at half stroke. The plenum manifold Helmholtz formulas are in fact derived from a two-chamber resonator. I think this might be the original reference from 1953, it's Engelman's dissertation: http://minds.wisconsin.edu/bitstream.../Engel1953.pdf)
#274
Tuomo- Just for purposes of discussion, if you wanted to reality test the equations on a plenum design that only feeds four cylinders (say, the Threshie CF intake), and for which there are lots of dyno runs and info on the engine configuration, what measurements would you need to have? I can't do math, but I can measure stuff.
#275
Third, the manifold we're talking about in this thread is a single plenum manifold with all eight cylinders being fed from the same plenum. The usual Helmholtz equations are probably not a productive way to think about this manifold, because the pulses cancel inside that manifold.
In contrast, if there were two plenums and the pulses would be separated correctly (think S3 manifold, but just bent and tucked in the valley), then some Helmholtz equations might be useful.
In contrast, if there were two plenums and the pulses would be separated correctly (think S3 manifold, but just bent and tucked in the valley), then some Helmholtz equations might be useful.
I would imagine that the box has two levels, with the same cylinders feeding a layer as they would a S3/4 plenum.
Packaging aside, it would be sweet if the two levels could have a flappy connection to restore the first torque peak.
FWIW, when I had my S4's intake off I thought that more common plenum space could be created by putting a spacer between the upper and lower parts of the S4 manifold. (Would need to find a smaller TPS.)
#276
Gentlemen, don't get me wrong, I'm not any specialist just tried to explain the reason for those lows and highs of torque curve.
As Greg pointed out, those lows and highs are probaply undetectably in driving, whereas the stock S4 intake effects are.
Playing with intake port CSA and port shape is different thing to tune flow and velocity. My heads are made and designed by this guy:
https://www.facebook.com/pages/anorr...38511279525280
I'll stop here
As Greg pointed out, those lows and highs are probaply undetectably in driving, whereas the stock S4 intake effects are.
Playing with intake port CSA and port shape is different thing to tune flow and velocity. My heads are made and designed by this guy:
https://www.facebook.com/pages/anorr...38511279525280
I'll stop here
#277
Plenum, full of holes, weird or no Helmholtz.
Cylinder, less holes, Helmholtz effects maybe more likely.
The way I think about it is two fold; most of the flow is filling the cylinder as the piston drops, and what happens in the immediate time vicinity of BDC and intake valve closing. The first part is like HVAC ducts, so much pressure differential, length, cross section, gives X amount of cfm. The second part is more about velocity, mass of air, speed of sound and distances within the cylinder and within the intake system.
Cylinder, less holes, Helmholtz effects maybe more likely.
The way I think about it is two fold; most of the flow is filling the cylinder as the piston drops, and what happens in the immediate time vicinity of BDC and intake valve closing. The first part is like HVAC ducts, so much pressure differential, length, cross section, gives X amount of cfm. The second part is more about velocity, mass of air, speed of sound and distances within the cylinder and within the intake system.
#278
Tuomo- Just for purposes of discussion, if you wanted to reality test the equations on a plenum design that only feeds four cylinders (say, the Threshie CF intake), and for which there are lots of dyno runs and info on the engine configuration, what measurements would you need to have? I can't do math, but I can measure stuff.
For Threshie's CF intake, the optimal plenum volume is as large as possible. This is because the pulses are combined into two plenums with unequal spacing. The plenum resonance will never be right, so it needs to be minimized. The two ways to minimize is to add cross-over pipe(s) between the plenums and to make those plenums as large as possible.
For GB's custom intake manifold, the plenum volume is close to irrelevant. This is because all eight pulses are spaced so close to each other that the plenum pressure about averages out. All that the plenum needs to do is to be large enough to slow down the air enough to give equal cylinder filling with steady state flow.
For a dual-plane manifold, such as the stock S4 manifold with the flappy closed or the S3 manifold, the plenum volume matters. Increasing plenum volume will move the peaks to a lower rpm and reducing it will move them higher up. Once you know the volumes and the current peak, the formulas are pretty accurate on how much the peak moves for a given change in the plenum volume.
Just speculating, the fabrication difficulties are likely related to the entry angles of the runners to the plenum. The fabricator probably wanted to have the runners enter normal to the cover, and each runner has a slightly different entry angle. Otherwise, the stories about small aluminum pieces wouldn't make much sense.
An alternative construction method would be to measure the entry angles from this manifold, then cut a flat plate with holes that correctly project the hole shapes when a round runner intersects the flat plane at that angle. Then, one could just push the bellmouth pieces thru from below and weld them in place. This is what I would try if I were reconstructing this manifold.
Another difficulty I see in this manifold is that there's about 90-degree turn for the air flow near the throttle plate. For this reason, one should probably use a throttle plate on the bigger side and also large diameter pipes on both sides of the throttle plate. If I were reconstructing this manifold, I'd try to fabricate the piece between throttle and the plenum from bent pipe section. If it won't fit, then it's more involved project of welding together an angled box (like a piece of a periscope) to feed the plenum.
#279
Just speculating, the fabrication difficulties are likely related to the entry angles of the runners to the plenum. The fabricator probably wanted to have the runners enter normal to the cover, and each runner has a slightly different entry angle. Otherwise, the stories about small aluminum pieces wouldn't make much sense.
The straight sections for prototyping hose connections did not help matters. I doubt they will be there in the final version.
#280
Chronic Tool Dropper
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If the cams are the same in terms of overlap area, then my bet is it's the intake tract air speed. The GT moves less air per second than the stroker at the same rpm. Thus for the same intake runner diameter, the stroker has a higher air speed at the same rpm, which is perhaps the single most important number on the intake side. The engine works the best at certain, relatively high air speeds. If the air speed is too low, then the cylinder doesn't fill well ABDC. If the air speed is too high, then the intake tract goes to sonic choke and declining cylinder pressure no longer increases the flow. So there's a sweet spot for the air speed.
If my internet-engineering theory is correct, then the torque curve peak should move to higher rpms in smaller displacement engine, holding the runner ID constant. The character of the stroker torque curve should be recoverable in the GT by making an intake with smaller ID runners. Ball parking the reduction in the cross sectional area about equal to the reduction in displacement.
If my internet-engineering theory is correct, then the torque curve peak should move to higher rpms in smaller displacement engine, holding the runner ID constant. The character of the stroker torque curve should be recoverable in the GT by making an intake with smaller ID runners. Ball parking the reduction in the cross sectional area about equal to the reduction in displacement.
I often use a Slinky to illustrate the effect, with the downstream end oscillating in sync with flow changes as the valves open and close. The upstream end is linked to the other Slinkies sharing the plenum. How they are coupled depends on the relative positions of the other intake runners and the flow/firing order of those coupled runners.
The Good News, at least for me, is that my little process modeling package is used for no more than four sources with one destination, and is looking at only one on-off flow condition at a time. No wildcards like fuel spray expansion to convolute the calculations.
Back to our regularly-scheduled car stuff...
#281
bob --
That's not how I've understood the physics to work.
http://en.wikipedia.org/wiki/Choked_flow
However, I don't know what I am talking about. I have no idea whether the intake port flow ever goes sonic or not. Maybe it's just turbulence starting to choke off the flow. I don't know. The point was that at some air speeds the frictions start growing fast with increases in air speed, and there's effectively a speed limit on how fast air can flow in the intake tract.
That's not how I've understood the physics to work.
http://en.wikipedia.org/wiki/Choked_flow
Choked flow is a limiting condition which occurs when the mass flow rate will not increase with a further decrease in the downstream pressure environment while upstream pressure is fixed.
For homogeneous fluids, the physical point at which the choking occurs for adiabatic conditions is when the exit plane velocity is at sonic conditions or at a Mach number of 1.[1][2][3] At choked flow the mass flow rate can be increased by increasing the upstream pressure, or by decreasing the upstream temperature (assuming high temperature, flash-boiling flow).[citation needed]
The choked flow of gases is useful in many engineering applications because the mass flow rate is independent of the downstream pressure, depending only on the temperature and pressure on the upstream side of the restriction. Under choked conditions, valves and calibrated orifice plates can be used to produce a desired mass flow rate.
For homogeneous fluids, the physical point at which the choking occurs for adiabatic conditions is when the exit plane velocity is at sonic conditions or at a Mach number of 1.[1][2][3] At choked flow the mass flow rate can be increased by increasing the upstream pressure, or by decreasing the upstream temperature (assuming high temperature, flash-boiling flow).[citation needed]
The choked flow of gases is useful in many engineering applications because the mass flow rate is independent of the downstream pressure, depending only on the temperature and pressure on the upstream side of the restriction. Under choked conditions, valves and calibrated orifice plates can be used to produce a desired mass flow rate.
#282
My heads are made and designed by this guy:
https://www.facebook.com/pages/anorr...38511279525280
https://www.facebook.com/pages/anorr...38511279525280
#283
The price depends on what else needs to be done for the heads( valve work, seats etc.) But roughly less or little more than 200/cylinder is what Andre is charging. If you are interested, I can send you more details.
Better to send them asap. as those race quys usually are priority #1 customers and they starts their projects some time after Christmas.
Andre also welded some hooks to bottom of the port as an extra safty to keep epoxy in place next thenths of years. That was my extra requirement.
Tested heads at last summer with my partially flow enhaced and balanced intake and the difference was amazing what came to torque and power increase.
Didin't dyno as intake was so badly balanced, but was very happy since cylinder #5 was knocking together with #2 and #6. I did hell lot's of work to make #5 to get better statc flow
I have also contacts to other guy who's doing plasam welding and re-grounding to cams, the Viiala guy doesn't wnat to do it anymore
You need to give some details of your project and he always want's to measure the cams to make heads to work perfectly with them.
EDIT:
Here is series of fluid mechanics lectures from 70's, wery informative.
http://www.youtube.com/playlist?list=PL0EC6527BE871ABA3
Better to send them asap. as those race quys usually are priority #1 customers and they starts their projects some time after Christmas.
Andre also welded some hooks to bottom of the port as an extra safty to keep epoxy in place next thenths of years. That was my extra requirement.
Tested heads at last summer with my partially flow enhaced and balanced intake and the difference was amazing what came to torque and power increase.
Didin't dyno as intake was so badly balanced, but was very happy since cylinder #5 was knocking together with #2 and #6. I did hell lot's of work to make #5 to get better statc flow
I have also contacts to other guy who's doing plasam welding and re-grounding to cams, the Viiala guy doesn't wnat to do it anymore
You need to give some details of your project and he always want's to measure the cams to make heads to work perfectly with them.
EDIT:
Here is series of fluid mechanics lectures from 70's, wery informative.
http://www.youtube.com/playlist?list=PL0EC6527BE871ABA3
Last edited by simos; 11-15-2013 at 06:56 AM.
#284
I have also contacts to other guy who's doing plasam welding and re-grounding to cams,
the Viiala guy doesn't wnat to do it anymore
You need to give some details of your project and he always want's to measure the cams to make heads to work perfectly with them.
#285
Chronic Tool Dropper
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Two glasses of wine after a very long workday. Not a good combination with the keyboard.
The ratio of upstream and downstream pressures are a good yardstick way to determine at what point the flow is 'choked'. As downstream pressure changes, the sonic velocity changes with the density of the gas. Once the flow is sonic/choked, changes in downstream pressure change the mass flow only as it affects the density of the gas. Changes in upstream pressure directly affect the volumetric flow. Discounting the change in temperature as the gas expands beyond the choke point, flow is almost perfectly related to changes in upstream pressure.
The ratio of upstream and downstream pressures are a good yardstick way to determine at what point the flow is 'choked'. As downstream pressure changes, the sonic velocity changes with the density of the gas. Once the flow is sonic/choked, changes in downstream pressure change the mass flow only as it affects the density of the gas. Changes in upstream pressure directly affect the volumetric flow. Discounting the change in temperature as the gas expands beyond the choke point, flow is almost perfectly related to changes in upstream pressure.