Thanks to you guys' advice I'm not going to try updating a 1.5 manifold to my upcoming 2.2. Doesn't look like the math works really well either but I need to do something or I won't have a class to teach this winter. What I'm locked into doing now is building an entirely new manifold from the ground up, or rather, having my students build an entirely new manifold from the ground up.

The plan is to make the manifold as adjustable as possible, since we are unlikely to be able to design it correctly first try. To do this I was planning to build it in three pieces:

a) A base with weld-on injector bungs and a place to bolt the fuel rail.

b) Four round tubes that bolt onto the base plate.

c) A plenum that will mount a vacuum block and bolt to the four round tubes. 

 

With this design I can swap the tubes any time I like for different runner lengths. Maybe even end up with a torquey street set and a higher rpm track set. 

Does this sound like an intelligent approach? 

Should I just copy the plenum volume of the stock manifold or is there a rule of thumb for plenum sizing?

I've seen three styles of plenum on four cylinder engines. A sort of blob that looks like this:

A log style manifold like this:

And finally, a sloping log like this:

There are also snail type manifolds, but I lack the tools and skills to build them.

 

Any ideas on which type of plenum I should use?

 

 

i've never had any luck building intakes.

Kind of afraid you'd say that. Guess I'd better hang on to the stocker while we're building the new one.

I have never had luck building intakes for NA engines either,  Neither have some engineering firms I know with CFD, GT Pro and other powerful engineering tools.

If you want to try some general stuff is you want the plenum walls to be 4" from the runners ends, you want the pmenum volume to be 1.5x engine displacement and you want the plenum walls not to be paralle. This might make the manifold more one degree of freedom and sort of easier to model.  It will still probably end up being cut and try.

In the end you will probably spend a lot of time and money for little or no gain at least that's what happend to me.

 What's the engine? Can we have some facts and figures to work with? Bore, stroke, N/A or F/I, cam duration? Size of intake valves? etc. How about intended RPM range and where the engine will spend most of its time.

These are just a few of the tidbits that should be used to give even a vague bit of feedback on what design parameters to follow. 

IMHO That last manifold is not bad for a turbo car. For an NA car it's likely crippling unless you run at stratospheric RPM all the time.

The engine is a 2.0L Holden D-Tech. The engine code is TS20D. hIt's a square 86/86mm design. It is FI and NA right now. The cam specs are 254 degrees with .394 inch lift on both intake and exhaust.

Posted By Mike Kojima on 11-27-2011 07:37 PM

I have never had luck building intakes for NA engines either,  Neither have some engineering firms I know with CFD, GT Pro and other powerful engineering tools.

If you want to try some general stuff is you want the plenum walls to be 4" from the runners ends, you want the pmenum volume to be 1.5x engine displacement and you want the plenum walls not to be paralle. This might make the manifold more one degree of freedom and sort of easier to model.  It will still probably end up being cut and try.

In the end you will probably spend a lot of time and money for little or no gain at least that's what happend to me.

Time, probably. Money, nope. The science highschool is buying my donor manifolds and all the aluminum sheet we're going to cut and shape. 

 

Here's what my students came up with. 

 

 

Me and the kids took measurements of the engine bay and built prototype models out of cardboard. We'll check to make sure our models fit during the next meeting.  We also looked at the stock manifold (I've bought two extras to chop up and use as the bases for our competing designs) and decided how to improve upon it. Honestly, improvement shouldn't be that big of a challenge. The 180 degree, sharp radius turn can't be good for flow and the runner length of 790 mm is clearly biased towards low end torque. My test drive with the bone stock 2.0L has borne this assumption out. The car pulls hard from as little as 1700 rpm but is completely out of breath by 5500 rpm. I'm shooting for a power peak around 6000 rpm and useable power up to the fuel cut at 6600 rpm. 

 

 

You can see just how huge the OEM part is by looking at it attached to the engine.

 

The middle school kids came up with something pretty conventional for their design. Basically they shot for small size and good flow. If I had to bet, I would assume this design actually ends up dynoing better, although I think it's going to end up killing low end torque. You can see the pictures below, but they essentially made a triangular box that is biggest near the TB and tapers towards the number 4 cylinder. This design is only 10 cm thick and will probably cut the weight of the stock manifold by 60%. Just looking at it compared to the old one, I'm guessing this manifold will be considerably more high rpm intensive. 

 

 

 

The highschool kids, on the other hand, came up with something really trick. I hope this works better because if it does, it could be such a neat proof of concept.

 

 

As for the aforementioned concept, the idea is to build a reasonably compact manifold with short runners that still maintains good mid range power and a flat torque curve. The high school kids are trying to do this by separating the airflow from the reversion waves as much as possible. In theory, the airflow moves largely undisturbed from the very low mounted (close to the flat floor of the plenum) TB and then under the triangular cutouts, but each triangular cutout  is designed to reflect the reversion waves at a 90 degree angle and off a flat surface before bouncing them straight back down to the runner. This effectively lengthens the duration of the reversion wave heading back to the intake valve with only a tiny increase in the size of the plenum and no increase in the length of the runner. I was playing with some ideas and think I might take this concept further by trying echo chambers of varying sizes attached to the vertical faces of each triangle. If the concept works, it should be a simple matter to make the manifold more low RPM biased by increasing the size of the echo chamber. 

 

The students then decided to flatten the torque curve by staggering the distances of the reversion wave reflectors (what I'm calling those triangles). This should result in each cylinder having a slightly different torque curve. Since it has the longest distance between the intake valve and a reversion surface, cylinder one should make the best low end torque. Cylinder four should make the best high rpm power.

 

Here's how the highschool manifold will work in theory, explained via my incredibly crude drawings.

 

Like I said, I've never seen anything like this and I'm not sure if it will work, but the idea is so creative and interesting I'm really rooting for it.

 

BTW, is there any particular reason I should avoid parallel walls in the plenum? It's easy enough to change at this juncture. 

 

I usually try to do trapezoidal walls to keep things to one degree of freedom. The high school design looks too complicated but it would probably work for getting rid of reflected waves.

Here are some links that might help, I would pick and choose some info from each and make sure put the calculator to the test.

http://horsepowercalculators.net/intake-manifold-design/intake-manifold-design

http://www.popularhotrodding.co/tech/0602phr_sheetmetal_intake_manifolds/viewall.html

You might try finding some hose that fits over the runner pipes you are using and clamp the hose to the metal pipe. Start with the hose at the longest you can fit, then test and trim them down, and so on.

 

To visualize why the walls should be asymetrical, think about drops of water hitting the center of a circle, the waves going out are causing turbulance with the waves reflecting from the walls. Then the same with an asymetrical shape, and see which cancels out first. You can't really do the exact shapes with water but it will make a good visual for the students and maybe help them think about how the air in the intake acts as a fluid.

Here is a sheet metal how to book that might help with some of the crazier designs ie your "snail manifold" for example. You would be set if you could sneak into the wood shop at the school if they have one. 

http://www.google.com/products/catalog?q=sheet+metal+hand+book&hl=en&safe=off&client=firefox-a&hs=wop&rls=org.mozilla:en-US:official&prmd=imvns&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=620&um=1&ie=UTF-8&tbm=shop&cid=14342390703585032910&sa=X&ei=yMkLT7uJDqrq0gHki_CVBg&ved=0CHMQ8wIwAQ

 

 

Also the plenum volume should be at least 1.5x the displacement.

Posted By jere on 01-09-2012 11:06 PM

Here are some links that might help, I would pick and choose some info from each and make sure put the calculator to the test.

http://horsepowercalculators.net/intake-manifold-design/intake-manifold-design

http://www.popularhotrodding.co/tech/0602phr_sheetmetal_intake_manifolds/viewall.html

You might try finding some hose that fits over the runner pipes you are using and clamp the hose to the metal pipe. Start with the hose at the longest you can fit, then test and trim them down, and so on.

 

To visualize why the walls should be asymetrical, think about drops of water hitting the center of a circle, the waves going out are causing turbulance with the waves reflecting from the walls. Then the same with an asymetrical shape, and see which cancels out first. You can't really do the exact shapes with water but it will make a good visual for the students and maybe help them think about how the air in the intake acts as a fluid.

Here is a sheet metal how to book that might help with some of the crazier designs ie your "snail manifold" for example. You would be set if you could sneak into the wood shop at the school if they have one. 

http://www.google.com/products/catalog?q=sheet+metal+hand+book&hl=en&safe=off&client=firefox-a&hs=wop&rls=org.mozilla:en-US:official&prmd=imvns&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=620&um=1&ie=UTF-8&tbm=shop&cid=14342390703585032910&sa=X&ei=yMkLT7uJDqrq0gHki_CVBg&ved=0CHMQ8wIwAQ

 

 

Thanks for the information. Good stuff. 

I did have one question though, I thought part of the point of a manifold was to get the waves in sink so that at the correct RPMs they resonate at the right frequency to ram air into the intake valve right as it opens. Is this true, or do you want to cancel out the sound waves as soon as possible?

 

@Mike,

Just out of curiousity, what cars have you and those big companies been building intakes for? 

My understanding is that's why building intakes tends to be hit or miss and it's where everyone's different theories start coming up.

The most common theory (although not without debate) is your idea. Intake air that is on it's way into the combustion chamber suddenly gets reflected when the intake valve closes. Then travels back and forth to the plenum side of the runner many times at around the speed of sound until the intake valve re-opens. The reflection is said to have to due with the Helmholtz resonance theory, and only has an effect in certain RPM with certain airflow speeds. Then if the timing of the wave pulse is just right, and the runners have the right diameter, the pulse getting back just as the intake valve is opening adds a boost of air pressure is delivered into the intake chamber. That is where changing the length of the runners comes into play also. Different lengths change the timing of the wave bouncing off the plenum air and back towards the intake valve.

In other designs there are some intakes that feature a small plenum (smaller than the engine displacement)paired with long runners, to keep waves coming from each runner from disturbing the next. This idea is aimed minimizing the turbulence in the plenum as all of the different cylinders' valves take turns sending their own waves in different order back to the plenum like four people on a waterbed effect. This design doesn't try to take advantage of the wave effect rather, it just tries to avoid it.( A better solution for a race car might be individual throttle bodies but then there would also not be as much vacuum for stuff like the brake booster.) And there are other designs that incorporate all kinds of different ideas from runners that extend or collapse based on the RPM, to dual runner manifolds. This goes to show it's not a completely predictable science yet.

doesn't the exhaust system do more for NA scavenging..
than any intake could hope to achieve with sound wave pressurizing??