BadAss 2.4L Velocity Stack Intake Manifold

[BadAssPerformance]

I always wanted to build a custom intake for the old 2.2L 8V in the Z but when it expired and I decided to put the 2.4L in the car, I ended up making my first custom intake manifold for it back in 2007.

It is a basic box plenum design, end loaded and with raised velocity stack ports. Not what I would call perfect but a balancing act (as usual) between function and packaging space.

OK, "Why raised runners?"

A fluid (air is a fluid) flowing in a tube (or box shaped channel) has its highest velocity in the center of a tube and slowest at the perimeter boundary layer (read: outer walls) and worst in corners if the tube has a rectangular cross section. Raised velocity stacks help pull from the higher velocity center stream as opposed to the somewhat stagnant boundary layer.

Additionally, due to packaging constraints, using raised stacks allowed me to get a little longer runner so it was a double bonus.

Well enough words, here are some pics of how I made it...

[86seeS]

amazing work man i really like the machined runner tops to bad you wont be able to see them in there

[BadAssPerformance]

Thanks, not bad for my first try? and yeah, hard to see them... the last pic is my camera shoved of the TB neck, LOL!

[turbovanman²]

I can't see how raised stacks won't cause massive turbulence! The air will go under the bell so to speak, then swirl around and cause massive air tumbling etc.



Nice work man, but I still wonder if raised stacks hurt flow? As discussed in the other thread,

[Austrian Dodge]

looks very nice!!!

[Garffus]

Nice intake. did you buy the stacks or spin them yourself?? Experimenting with venturi length/angle etc can have some interesting results. will you be posting up results?

[BadAssPerformance]

I can't see how raised stacks won't cause massive turbulence! The air will go under the bell so to speak, then swirl around and cause massive air tumbling etc.



Nice work man, but I still wonder if raised stacks hurt flow? As discussed in the other thread,

I moved your question (first part of this quote) to this thread.

Think of your example (which the way you described it is at a slow velocity) and turn it up to supersonic speed and 30 psi. High pressure high velocity air flowing down the center of the box...

Nice intake. did you buy the stacks or spin them yourself?? Experimenting with venturi length/angle etc can have some interesting results. will you be posting up results?

Thanks. CNC'd the stacks from round stock... a couple pics of them (06 and07) in process.

Results? The intake has been on the car since the 2.4L is in it... car went 10.84@130 mph (best mph 134.75) on 29psi and almost went 11's on 15psi... so it seems to work OK?

As far as variation, yes, height and angle and radiuses all come into play. Probably not as much on a boosted motor as NA, but they definitely do. I also wonder how a tapered plenum roof would alter flow... Really, I think I need an equal length header on the other side of the head before I start investigating additional intake variables.

[cordes]

IIRC Aaron Miller stated that the tapered intake like you see on some of the cars actually causes uneven filling of cyls. at what he considers high HP. I think you are heading into that territory JT. I may try and search for the post later. I'm pretty sure it is in his intake thread though.

[Garffus]

ah' i don't have access to play with CNC, have to do it the old skool way with a wooden mandrel on the lathe

Mine is for a twin-charged Lancia engine, it has not run yet, so all academic atm. i have three lengths made up with matching 7deg tapers and bell mouths and all have been on the home made flow bench with 0 measurable difference between one to the other, but know that will change on a running engine... this will have, within 5-10%, long equal length ex headers. would be very interested to see what influences varying stacks on your engine has since i want to build another for my belated hybrid..

btw, everything ive ever been told about wedge/tapered plenums is BAD!

[john1320]

Thanks. CNC'd the stacks from round stock... a couple pics of them (06 and07) in process.

Results? The intake has been on the car since the 2.4L is in it... car went 10.84@130 mph (best mph 134.75) on 29psi and almost went 11's on 15psi... so it seems to work OK?

As far as variation, yes, height and angle and radiuses all come into play. Probably not as much on a boosted motor as NA, but they definitely do. I also wonder how a tapered plenum roof would alter flow... Really, I think I need an equal length header on the other side of the head before I start investigating additional intake variables.

Yea, i would say it works, almost 11s at 15psi, in that heavy thing...awsome

[risen]

It's nice to see all the pics collected in one area, that is a sweet piece of work you put together there. However, I've got a Q and an overly-pedantic point:

First the overly-pedantic point:

A fluid (air is a fluid)

Air is a gas (or mixture thereof), no? Perhaps it can be modeled like a fluid, and fluids can be used to model airflows, but suggesting that air is a fluid is taking a good deal of liberty with that concept.

tube and slowest at the perimeter boundary layer (read: outer walls) and worst in corners if the tube has a rectangular cross section. Raised velocity stacks help pull from the higher velocity center stream as opposed to the somewhat stagnant boundary layer.

The boundary layer follows the surface of whatever the air is flowing across, correct? But the air isn't flowing across the bottom of an intake so much as through it (there's no exit but the intake ports). So wouldn't that mean that the surface the air is actually flowing across is the inlet to the ports?

I thought that was the reason the bellmouth works well in the 1st place. It allows the air to be taken from a wider area at the top and have it's velocity increased by flowing over the boundary layer. Is that not the case?

Additionally, I'd wonder what the raising of the inlets to the center of the plenum does to it's volume. And I mean this beyond the obvious 'you have to remove the volume of the inlet to find the total volume of the plenum, duh' answer. I can't imagine that the air below the inlet would want to revert back to the inlet under pressure, so wouldn't raising the port effectively reduce the volume of the plenum?

Can we get a ME in here to straighten this out, aerodynamics isn't my strong point.

[Warren Stramer]

World championships are won with setups in the links below. when I get time I will give my 2cents worth.



Click on the illustration of the port and it should animate.......I hope

[turboshad]

My 2 cents in 3.....2....1......


I think many people don't think of the flow in an intake properly, especially in "forced" induction. The term "forced" implies there is a different driving force than in an NA engine and that the flow carachteristics all of a suden change because the turbo is now "pushing" air into the runners and cylinders. That is backwards. Air, or any fluid for that matter will travel from high to low pressure. It is really the low pressure in the cylinder that is the driving force behind the air pump. The added pressure from a turbo just increases the differential between the manifold and the cylinder causing more volumetric flow.

The "continual" velocity inside a plenum is due to the multiple cylinders drawing air in short enough intervals to keep the air moving with it's own momentum inbetween intake events. Each time a given cylinder's intake valve opens it needs to start the flow of air inside that runner. It can either draw from a low velocity point and as such take more energy and time to get the air moving, or it can draw from a high velocity point where the air is already moving at a substantial speed.

The trade off is that the low velocity will be at a higher pressure than the high velocity stream. Also when drawing from the high velocity stream you will need to fight the airs momentum and change it's direction. My thinking though is that with the short time between intake events at higher RPM that you would want the situation that got the air moving the quickest which would be a raised stack.

Simon, I can see where you may see a problem with eddies and turbulance, but I think that the stacks are so close together, and sometimes touching, that it wouldn't be an issue. With the momentum of the air I would think it would almost "jump" the gap between stacks. The air running into the front of the stack is a non issue as it will just create a stagnent point at the front but since we know the cylinder is the driving force it will still be drawing from the high velocity stream. There may also be eddies between the stacks under the lips but I don't see these being issues either.

Anyway, gotta run to a meeting. Feel free to pick this apart as it helps me learn too. I should also note that in the older thread where Warren posted a great article on trumpets, it more or less concluded that as the pressure differential increased, and as such the velocity through the passage increased, the gains became less dramatic which mean that in a forced induction application the use of stacks would show a lower percentage gain as compared to an NA situation.

[rx2mazda]

Really, I think I need an equal length header on the other side of the head before I start investigating additional intake variables.

I think a ported stocker would give the best comparo.

[BadAssPerformance]

It's nice to see all the pics collected in one area, that is a sweet piece of work you put together there.

Thanks!

However, I've got a Q and an overly-pedantic point:

Ut oh!

First the overly-pedantic point:

Air is a gas (or mixture thereof), no? Perhaps it can be modeled like a fluid, and fluids can be used to model airflows, but suggesting that air is a fluid is taking a good deal of liberty with that concept.

Air is a fluid... note, I did not say liquid, I said fluid

http://en.wikipedia.org/wiki/Fluid_dynamics

The boundary layer follows the surface of whatever the air is flowing across, correct? But the air isn't flowing across the bottom of an intake so much as through it (there's no exit but the intake ports). So wouldn't that mean that the surface the air is actually flowing across is the inlet to the ports?

Yes, it follows the surface due to drag, etc.

http://en.wikipedia.org/wiki/Fluid_friction
http://en.wikipedia.org/wiki/Coand%C4%83_effect

but the effect of the boundary layer is slower flow at the surface

http://en.wikipedia.org/wiki/Boundary_layer

So the raised ports allow the ports to pull from the higher velocity center stream of arflow through the plenum

I thought that was the reason the bellmouth works well in the 1st place. It allows the air to be taken from a wider area at the top and have it's velocity increased by flowing over the boundary layer. Is that not the case?

A velocity stack bellmouth works better than a straight port no matter where it is

http://en.wikipedia.org/wiki/Velocity_stack

but the question is still at the surface in the slow boundary layer flow or int he high velocity center of the flow stream

Additionally, I'd wonder what the raising of the inlets to the center of the plenum does to it's volume. And I mean this beyond the obvious 'you have to remove the volume of the inlet to find the total volume of the plenum, duh' answer. I can't imagine that the air below the inlet would want to revert back to the inlet under pressure, so wouldn't raising the port effectively reduce the volume of the plenum?

I have a theory that the overall plenum volume effectively decreases as the velocity increases and everything reaches steady state flow.

Can we get a ME in here to straighten this out, aerodynamics isn't my strong point.

BSME-Automotive Specialy
GMI '97

[turbovanman²]

Hmmmmmmm, very interesting.

Warren, that 2nd pic is too small to decipher. Is that Viper intake forced induction or n/a?

That F1 engine is also N/A.

Maybe I am over thinking, and that the air is moving so fast and under so much pressure, it won't matter?

I see what your saying "turboshad" about high and low pressure but really, when you think about it, that intake is pressurized, so any air leak will cause the air to escape out of that hole, just like a tap, its built up until you open it up, thus the water now has a place to go,

[risen]

Just FYI, I've been looking at wikipedia most of the morning to try and get a better grasp on this. It would take months for it all to sink in, though.

Air is a fluid... note, I did not say liquid, I said fluid

Ahhh.... fluid is not a synonym for liquid. My bad. This helps: http://www.merriam-webster.com/dictionary/fluid

Yes, it follows the surface due to drag, etc.

http://en.wikipedia.org/wiki/Fluid_friction
http://en.wikipedia.org/wiki/Coand%C4%83_effect

but the effect of the boundary layer is slower flow at the surface

http://en.wikipedia.org/wiki/Boundary_layer

So the raised ports allow the ports to pull from the higher velocity center stream of arflow through the plenum

Right, but my point was more that the only place for the air to flow is out the ports. It's not like you're trying to grab air that is flowing across the ports, there's only 1 way out and that's through the port. So, the flow is actually at a 90 degree angle to the bottom of the intake, not parallel to it and therefore the boundary layer wouldn't have a large effect on the flat bottom of the intake.

I don't know if I'm not explaining myself clearly or not getting what you're saying (more likely the latter), but it seems like a 'free lunch' to me.

A velocity stack bellmouth works better than a straight port no matter where it is

http://en.wikipedia.org/wiki/Velocity_stack

but the question is still at the surface in the slow boundary layer flow or int he high velocity center of the flow stream

But isn't that flow stream smack in the center of the port opening?

I have a theory that the overall plenum volume effectively decreases as the velocity increases and everything reaches steady state flow.

Hmm, that's interesting. I've read other places (no evidence, sorry) that you want some ratio of the engine's displacement in the plenum to stop from the 'pulses' in pressure in the intake. I understand that this isn't a closed system so it's always fluctuating to some degree, but wouldn't having too small a plenum lead to a situation (in the most extreme case) where your intake pressure drops to vacuum with the valve openings?

BSME-Automotive Specialy
GMI '97

Ya know, funny thing about GMI. My Auto and Chemistry teacher tried to get me to go there after high school (which I graduated in 97). I stuck with CompSci at a regular college instead. Looks like I traded my understanding of this air flow stuff for an understanding of something like this: http://en.wikipedia.org/wiki/Halting_problem .

[turbovanman²]

Maybe you should join this conversation with the other thread or make a thread about this, lol.

I see what your saying JT but also grasp what Risen is saying. See my last comment on the other thread,

[risen]

I see what your saying JT but also grasp what Risen is saying. See my last comment on the other thread,

I didn't want to hijack fishcleaner's thread with all the stuff above.

[turbovanman²]

I didn't want to hijack fishcleaner's thread with all the stuff above.

Too late,