Turbo Intake Plenum

[MONZTER]

I started a thread a few days ago regarding the shape of air horns for the new intake plenum I am working on for my Turbo L-28. Here is a link http://forums.hybridz.org/showthread.php?t=127653

So I have begun to develop the shape and design of the plenum itself. Been doing a bunch of reading on this forum as well other sites. Seems like everybody is trying to do the same thing, get the air as smoothly and evenly into each intake runner. Ron Tyler made a nice looking manifold, but determined there was room for improvement. I have also heard Tony D talk about the internal baffles on the Japanese plenums used back in the day. This is where I began my design. Luckily, no one ever re-invents the wheel and I found exactly what I was looking for on some 80's Audi rally cars. Check the link http://www.bufkinengineering.com/intake%20manifolds.htm and pics below:







Here is also a link to some stuff BMW was doing (big Volume boxes) http://e30m3performance.com/tech_articles/engine-tech/airbox_symposium/page5.htm


So you can see in the pictures of the Audis, they are putting the air into a sub-chamber that then lets the air enter the main plenum evenly the entire length it. This will eliminate the action of the air passing the first few ports and favoring the back ports. I think this is more of a problem on turbo applications as opposed to NA.

So I designed a plenum with the same concept as above with the following specs.

-Plenum volume (without the sub plenum and air horns = 5853cc
-The area of the 3-inch sub plenum tube where it enters the bottom is 45.6cm
-The area of the slot between the two chambers is a little bigger at 57.4cm. Extra material is designed into the slot area to allow enlarging or changing the shape after testing.

Here are some pics of the concept so far:







In this cross section you can see the slot connecting the two chambers-



this view kinda looks like the inside of a turbo when looking down the outlet-



You can see the clean entry into each runner-



And the cross section of the chambers-



I saw in Ron Tylers design that someone on this forum did a CFD analysis of his design. I can provide any type of 3-D file of this idea if anybody is interested in doing some CFD work on it and seeing how it looks.

So I am looking for comments suggestions or simply holes blown in this concept. Thanks

Jeff

[RTz]

Great! I've been eye-balling the same plenum. Its quite proven and the concept seems solid.

Turbobluestreak CFD'd mine. Give him a PM... maybe you can sweet talk him into yours. Would love to see the result.

wow , smart job,
I wish succeeding for you.
turbo4ever
kuwaiti

[thehelix112]

I would be interested to see the CFD analysis.

I would have to assume that its important to ensure that the cross sectional area of the slit it atleast as big as that of the inlet pipe. Maybe even a little bigger to allow for more boundary layer loss due to increased circumference.

Do you have a mesh generated for it? If turbobluestreak (or anyone else) makes one to do CFD, I'd love a copy so I can have a play. Started mucking with this: http://caelinux.com

Dave

Dave

[Tony D]

When I knocked off the HKS Type 1 Plenum, my air entered the box on the fenderwell side, and hit an "L" Shaped baffle plate that directed it to the floor of the plenum, where it diffused through a seried of holes drilled in the 'foot' of the "L". This gave very nice drivability compared to the rough 2X4" aluminum extrusion I retrofitted to the engine years later with the air entering near the distributor end of the plenum, unimpeded. Packaging the piping was easier, but it just wasn't the same engine after the plenum change.

I feel much better now that someone has acknowledged my years of rants and howls as more than just bluster...

[thehelix112]

Sorry I didn't see that you posted specs on the areas. I would have to guess that you've got enough room in there to account for more boundary layer losses in area.

I would say though, can't really tell that well from the pics, but I'd try to get the slot to extend so that it covers each runner inlet the same. Ie, it looks like it doesn't cover the start of #1 or the end of #6.

Great idea btw, I was initially skeptical but it makes sense, I think. If I'm thinking about it correctly, the air will slow down in the pre-plenum, thus converting the majority of its dynamic pressure to static pressure. Because this air is going slower, any pressure `holes' will have time to be filled before the air slides through the gap and into the main plenum and onwards to the engine.

If you build this, please install pressure gauges in both plenums, I would love to see that plot.

Dave

[thehelix112]

So I tell this to a mate, and he says: ``I saw that over a year ago, some guy had 3d cad and cfd results.'' So needless to say I asked (very politely) mind you, for the link.

http://forums.evolutionm.net/archive.../t-196546.html

Obviously that design is somewhat limited (large pressure drop across plenums), but definitely worth the read.

Dave

[MONZTER]

Thanks for the link Dave, good reading.
Very depressing reading actually. I do not have access to the CFD, so it sounds like it would be impossible to get the right configuration with out the software. My design so far is just based on what I have seen and read. I have very little to no experience in fluid dynamics, and I would hate to build this manifold to have it be worse than a simple open plenum design. HMMM what to do, risk it and make one - possible wasting the time and money, or go with what we know and make something like a plenum used on the RB motors.

I hate problems like this when my hands are tied by my limited resources. Making it is the easy part for me. I don't think common sense will work on this project.

Thanks Jeff

[thehelix112]

Jeff,

I would probably recommend making it a sandwich design so the bit that seperates the plenums is simply bolted together between the two halves. Then you can not only adjust the shape/profile/size of the slot, but you can remove it altogether, all by undoing a few bolts.

Would also allow you to do back to back dyno testing, hint hint.

Dave

[MONZTER]

Originally Posted by thehelix112

Jeff,

I would probably recommend making it a sandwich design so the bit that seperates the plenums is simply bolted together between the two halves. Then you can not only adjust the shape/profile/size of the slot, but you can remove it altogether, all by undoing a few bolts.



Dave

Similar to what I had planned, but I was going to tack weld it together for testing on a flow bench, and then weld it up when happy with the results. You can see inthe cut away all the extra material I left in the slot area so it can be made wider if it needed to be.
I am trying to figure out how to measure the pressure loss problem with out the software??

[thehelix112]

CFD is just a somewhat educated guess.

If you have the skills, build it and test it. Will be no mistake that way.

Dave

[MONZTER]

Well good news,
A very generous person on this forum has agreed to do some CFD on this plenum design. I also met with my machinist friend, and priced out the material. He said I could run the part on his brand new Fadal 60x30 CNC. This is great news and it seems like it is going to be a go for me to build one and test it out.

Thanks Jeff

[Evan Purple240zt]

Wow, I would actually spend money on that design as opposed to the open plenum greddy that they put on RB motors.

Looks very promising.

[ktm]

Monzter, if everything works out, are you considering taking orders?

[MONZTER]

Originally Posted by ktm

Monzter, if everything works out, are you considering taking orders?

I'm not sure yet. The first one will be CNC machined in to halves and then welded together for testing. I am designing it with casting in mind. The first one is going to be pretty expensive, as it will be out of a big chunk of metal. If I cast them, I would probably make the casting patterns off the CNC prototype. I guess I will have to look into the expense for casting them. I dont know how many people would want a turbo manifold designed to work only with TWM throttle bodies.

Thanks Jeff

[ktm]

Ah, I did not see that you were using TWM throttle bodies. Thanks for the reply.

[Tony D]

Just blank the mounting face, allowing final machining to suit the end user.

As for TWM throttle bodies, most ITB's use the standard Weber/Mikuini/Solex/OER/Dellorto inlet side carburettor flange dimensions, so it should be universal.

I don't know if the TWM manifold makes any radical departure on bore spacing of the pairs either. My Cannon Manifold used the same ITG filter base with 40mm Webers as my Mikuini 44's on a Mikuini Manifold, as did the Dellortos on the JDM manifold. So that issue may well be a non-starter.

I think the biggest difference on the manifolds is length, and mounting height. Cannon/JDM/TWM seem to be straight out from the head, while the Mikuini mounts the carb bodies notably higher above the headers. TimZ has some good photos of this in some of his older posts.

My HKS ITB's have the same mounting surface print as my Mikuini 44's, so if that's any indicator the manifold would be a 'universal part' the only caveat being hood clearance on a Mikuini-Manifolded Car.

[MONZTER]

Originally Posted by Tony D

As for TWM throttle bodies, most ITB's use the standard Weber/Mikuini/Solex/OER/Dellorto inlet side carburettor flange dimensions, so it should be universal.

Tony,
Your 100% correct. The TWM spacing I used is standard mounting for all the universal manifolds out there. So really this thing could bolt up to any throttle body mounted to and triple style manifold.

I should be getting some CFD results soon; we'll se how it looks.

Jeff

[MONZTER]

TurboBlueStreak was kind enough to help out with the CFD work on this new plenum Thanks. I made some changes to the model before sending it to him. Mainly, I lengthened the slot from the lower plenum to the upper plenum. The slot now goes full length. I also modeled the rest of the intake track. You can see the throttle bodies, and how they taper down to where the flange meets the head ports. I also added the throttle shafts and butterflies to see the effect. Here are some pictures of the latest design.







Here are the CFD results:



















I can see from the results the radius going into the begining of the slot is too sharp, making it difficult for the air to get around the corner. I will modify it like this picture.



I am no expert at reading the CFD results, but it looks pretty consistent down each runner. I also find it interesting how the velocity increases down the runners due to the taper.

Anybody have comments

Thanks again to TurboBlueStreak

Best Regards, Jeff

[BRAAP]

Jeff,
Very cool. Thank you for sharing this publicly.

Just curious as to what moving the slot to the outside of the plenum might accomplish? I.e. opposite wall of the runner inlet vs dumping in the middle of the plenum in this design? Here is very crude MS-paint rendering…




*** edit ***


Looking a little closer at the Audio pictures above, it almost looks like they are dumping the air into the plenum near the runner inlet…