[Capt_Hazzard]

Hey everyone, I just wanted to document this build for anyone in the same boat as me, or if you're just interested in DIY. Over the last few weeks I've been working on a RWD intake for a K swap I'm doing. Since the cast one from Kpower didn't really appeal to me , and the Skunk2 two piece ones are out of my price range, I decided to design and build my own. I'm kind of starting this log in the middle of the project, but I'll try to lay all the steps out as best I can. Unless otherwise stated, all material is 6061 T6 aluminum. If you plan on duplicating this, you WILL need access to a lathe and mill, a TIG welder, and a good working knowledge of how to use them. Also, I'm pretty used to eyeballing most of my measurements, so I might not have exact numbers for everything. You've been warned 😆

DISCLAIMER: This thread is not intended as a set of instructions, and the methods shown are not guaranteed to be safe in any way. I will not be held responsible for any damage or injury sustained to you or your property by attempting to recreate this project.

Basic Designs

After reading a lot of papers on manifold design, I was able to layout a rough sketch in Fusion360. I went with a parabolic curve in the velocity stacks on the inside, and curved the outside to reduce turbulence at entry as much as possible. I decided against a tapered runner since I didn't have the tooling for it:

This is going on a street driven build, so I went with longer runners than most of the performance manifolds I've seen. They measure ~322mm from runner entry to the intake valve, and are made from 1.75" ID seamless tubing. The plenum volume is approximately 3L, but this might change as I go. The throttle body will be mounted on a separate adapter plate that mates to the flange shown below, similar to the old four barrel Edelbrock adapters. This will allow me to change throttle bodies without having to modify the manifold itself, and instead only having to make a new backplate. Max TB diameter is 90mm:

Note that this drawing is for measurement and layout only, and doesn't accurately show the finished product (injector bungs, vacuum ports etc.). I skipped drawing the injector bungs since they were very simple to make.

STEP ONE: Velocity Stacks

These were a bit tough to make on a manual two axis lathe. They are normally done on a CNC machine, so I ended up having to cut and heat treat my own cutting die to get the inner and outer curves. Using a 3D printed pattern, I cut a 1/4" piece of mild steel bar to the shape I needed, then hardened and tempered it to make it hold an edge. After cutting a piece of round aluminum stock to the inner and outer diameters of my drawing, I shimmed the new tool into my toolpost and used it like a form cutter. This worked well, but cutting speed was slow since my lathe is pretty small. I then sanded the cutting marks out (do not do this without a mask) and polished them:

On the back they have a lip on both sides, one that fits tightly over the runner end, and one that will be set into the plenum wall:

STEP TWO: Runners

The runners were fairly simple, but needed to be formed into an oval at the bottom to match the head. After struggling with it for a bit, I found that annealing around 2 1/2" of the runner end with an oxy/acetyl torch (look up "torch soot annealing") and squeezing it around a die in the bench vise worked very well. Note that 6061 will crack if it's not annealed. You can see this in the example below:

STEP THREE: Head Flange

This was and probably will be the hardest part of the build. I strongly recommend having this done on a CNC mill if possible. The way I did it is difficult, and fairly dangerous too.

After laying out the shape of the flange using the OEM intake gasket, I mounted the plate in the mill and drilled all the bolt holes. Note that the small holes for the IACV are not needed, don't drill them by accident like I did . I then centered the mill over the first runner hole and plunge cut the rough shape using a pilot hole and an end mill. After getting as close to the line as I could, I set a flyhead cutter to the max diameter of the runner and used it in the same fashion to cut the radius the rest of the way out on both ends:

I don't have any pictures of the flange itself, but here it is with the runners welded in:

Again, I don't recommend this method, but it worked for me. After that I sanded it smooth and moved on to welding.

(Continued)

 

[Capt_Hazzard]

I will update this thread as I go.

 

[Capt_Hazzard]

STEP FOUR: Welding in the Runners

Biggest thing I learned here is don't do this without bolting the manifold to a heat sink. Bolt the flange down and use this heatsink to also clamp the runners flat. I'm talking a good sized chunk of aluminum here, at least an inch thick and the same footprint as the flange material. If you just clamp it down in one spot like I did it will warp more and more with each weld. Luckily the warp was an even radius all the way across with no twist, and I was able to put it in my press afterwards and bend it back into shape, but DO NOT rely one being as lucky as I was. This is what I ended up with:

I'm considering only welding them on the outside since the runners will seal all the way round the stock gasket once they're milled flat, and I'm not planning to turbo charge this.

STEP FIVE: Injector Bungs

The injector ports are simply made from a 3/4" piece of round stock, drilled to 7/16" and counter bored to 9/16 by 9mm deep to fit the injector seal. I don't have metric end mills, so do this with a 14mm bit if at all possible. I then milled them to a 45 degree angle, making for a total length of 1" at their longest point. This gives my modified stock injectors just enough recess out of the runner to keep them from fouling:

Props to LotusElise for his input on these.

After making the bungs, I set the manifold in the mill and milled a flat spot for them on the top of the runner. This will only work on pipe with 1/8" wall or thicker. Any less and you will cut through the wall before getting to the right width:

Welding them on was very difficult because of the thin walls. I ended up having to mill two of them off and re make them because I blew through the wall of the bung while welding. My advice is to start out with at least 7/8" stock for the bungs so the walls end up thicker. Notice that I have them mounted further up the runner than stock manifolds, and at a bit more of an angle. This is mostly for ease of construction, but be sure that they are still aiming as close to the intake valve as they can get. Putting them too far up the tube on a non high performance engine can cause issues with idle and cold starting.

After welding them on, I clamped the intake in the mill at a 45 degree angle and milled the hole through the runnner. This needed to be done after welding as I didn't have a good way to drill them beforehand. Once drilled they just need a bit of deburring and polishing:

And that's about all I've got right now. I'll update as I get further along, but its a slow process. I honestly spend more time making custom jigs and tooling than the actual manifold 😆

Also, I'm either going to use the stock 270cc injectors that I've removed the the IACV caps from:

... or I'm thinking about using these 364cc Volvo injectors that have the same seal sizes:

I would think they would work with kpro, but I could use some advice on the impedance. The stock ones are ~12ohms, and these ones are 15ohms. Is this a problem, and is there a way/reason to compensate for it in tuning? I'd really like to have the extra output for later when I upgrade cams without dumping money into aftermarket injectors, so any advice would be appreciated.

Thanks for reading!

 

[LotusElise]

Thanks for starting a thread about your IM DIY project, which I really appreciate. That's an impressive work you did and you find some nice simplifications to get it finished cheap and with a few tools. I really like that 😍.

The Autodesk Fusion360 is a great 2D/3D CAD program for this job. I've used it also, as it is for free for hobbyists and small entrepreneurs and have an huge tool package, starting from easy free form modeling till simulation tools. I've started this for the first time of my CAD experience, so I have no comparison to other programs. How did you like it Capt_Hazzard?

I have some Design Questions if you don't mind to answer:

• Did you include the port inlet angle into your runner angle or is it just 90° to the flange?
• What let you decide to go with an parabolic bell mouth curve?

The idea to adapt the oval port inlet shape from circular shape is a real money safer. Otherwise a 5-axis CNC machine has to be programmed and run to get that into shape and it has likely to weld or to be integrated into the flange. Very nice idea! Will you run it as FI'd or NA'd application?

I am sorry, but I can't see the pictures from step 4 and on. Could you please load them again, maybe there is a limitation of pictures per post?

I am curious how your '50 Willys Wagon look like. Do you mind to share a picture?

 

[Capt_Hazzard]

How did you like it Capt_Hazzard?

I like it quite a lot, especially becasue of the price tag lol. I'll admit I'm super spoiled coming off of using Solidworks in university, but 360 has had every feature I need or want so far, even rendering. Definitely recommend to anyone using it for hobbies/small production.

Did you include the port inlet angle into your runner angle or is it just 90° to the flange?

I thought about it, but A: I don't have a good way to mill and bend all the runners to the same angle (I don't have a tubing bender), and B: I don't have a way to clamp them all in the same position for welding and keeping them from warping apart. But I doubt it will have much impact for what I'm doing.

What let you decide to go with an parabolic bell mouth curve?

I read up on some velocity stack theories that were used for motorcycle tuning, and a research paper by Blair and Cahoon. While they were working mostly with carbureted two strokes, the concept of smoothing the intake charge is identical. They found that a parabolically curved V-stack, raised out from the plenum wall and given an additional curve on the outside of the mouth, gave the best increase in intake efficiency.

Will you run it as FI'd or NA'd application?

It will be NA for now. Though I will probably be turboing it in the future, this manifold would need some slight modifications before I'm confident it will hold boost.

I am sorry, but I can't see the pictures from step 4 and on.

I could see all of them on my screen, but they were all thumbnails for some reason 🤷‍♂️. I reuploaded, let me know if its fixed.

I am curious how your '50 Willys Wagon look like.

It doesn't look like anything yet, just a stack of body panels and a frame wrapped in a tarp . I can't really do anything with that side of it until the spring, so I'm just working on the engine for now. Which is arguably the most important part imo. So far I have a BMW 5-speed lined up for it, and a set of front and rear independent suspension from a VW Passat to get it as low as possible. I'd love to be able to drift it some day, but I know it's a bit too top heavy for that, so I'll settle for just looking cool.

 

[Capt_Hazzard]

Also, a trick I learned about Fusion360: you can export .STL files without saving or uploading to the cloud. Get your model where you want it, then go to File>3D Print, select the model, and uncheck the "Send to 3D print utility" box at the bottom of the print settings window on the right, then press OK. This will allow you to save the .stl directly to your desktop without uploading or saving anything. It's great for making quick templates or saving test models for later, or in my case running in and taking a set of measurements from paper and quickly printing a template from it.

 

[LotusElise]

I would think they would work with kpro, but I could use some advice on the impedance. The stock ones are ~12ohms, and these ones are 15ohms. Is this a problem, and is there a way/reason to compensate for it in tuning? I'd really like to have the extra output for later when I upgrade cams without dumping money into aftermarket injectors, so any advice would be appreciated.

Yes, you can compensate this on almost any ECU, even KPro. You need to check for their dead times or delay times specification over supply voltage and fuel pressure (at least for your fuel pressure).

I like it quite a lot, especially becasue of the price tag lol. I'll admit I'm super spoiled coming off of using Solidworks in university, but 360 has had every feature I need or want so far, even rendering. Definitely recommend to anyone using it for hobbies/small production.

Sounds good, I totally agree with you.

I read up on some velocity stack theories that were used for motorcycle tuning, and a research paper by Blair and Cahoon.

G.P. Blair, was one of the best in the field of race engine design (2-stroke). His paper about bell mouth design was likely more read then any other in this field. He definitely had a heard for race engineers who need those information's and design criterias.

It will be NA for now. Though I will probably be turboing it in the future, this manifold would need some slight modifications before I'm confident it will hold boost.

Oh, it will show some nice VE support in part load and low engine speed WOT on NA.

I could see all of them on my screen, but they were all thumbnails for some reason 🤷‍♂️. I reuploaded, let me know if its fixed.

Many thanks, I really appreciate it.

...So far I have a BMW 5-speed lined up for it, and a set of front and rear independent suspension from a VW Passat to get it as low as possible. I'd love to be able to drift it some day, but I know it's a bit too top heavy for that, so I'll settle for just looking cool.

You won't AWD it?

 

[Capt_Hazzard]

You won't AWD it?

I was really torn on this, but I'm leaving the option open until I actually start assembling this. I'd love to have it, but he big problem with all wheel drive is space limitations at the front of Willys jeeps. The nose narrows pretty quickly, and I'm trying to keep this as low to the ground as possible, so I need to get the engine mounted before I'll know if I have space for a differential/front driveshafts. The other problem is finding a non-computer controlled AWD setup that will handle the extra weight. The Willys Wagons weren't crazy heavy, but they still weigh more than the average AWD sedan. I looked into the transmission from the BMW X-drive, but it's unreasonably massive, and I'm not sure it would fit in the transmission tunnel . The option is open since I'm using the all wheel drive Passat running gear, I'm just leaving the front driveshafts out for now.

 

[LotusElise]

...The option is open since I'm using the all wheel drive Passat running gear, I'm just leaving the front driveshafts out for now.

An Audi Quattro RWD transmission for your setup...und upgrade for every AWD .

 

[Capt_Hazzard]

An Audi Quattro RWD transmission for your setup

Do the Quattros have a manual AWD transmission option though? I'm not familiar with the Quattro at all.

EDIT: Looks like they do. Thanks for the tip, I'll definitely look into it

 

[Capt_Hazzard]

Got some good progress this weekend, and another big step done.

STEP SIX: Plenum backplate

This is really two steps here, cutting and welding the backplate, and welding it to the runners. I did some calculations for plenum size off of what little information I could find and will be aiming for a volume of 3 liters. The backplate is made of 3/16" x 4" "bar" stock. Though I could have made it out of sheet, it is much easier to use bar stock as you get to have factory edges on both long sides. I marked the hole centers by standing the manifold body on the plate, then scribing the centers using the circles I traced:

After that I rough cut the holes using a 2 3/8" bi-metal hole saw on a drill press. If you use this method, be sure to push the saw through very slowly, as the aluminum catches easily and the saw will hog out the hole too much if it starts to wobble. I do not recommend doing this with a hand drill, you'll never get it square and its super dangerous with a hole saw this big. The V-stack's rims were made slightly larger than 2 3/8" to allow for space to smooth out the holes with sandpaper and a Dremel tool until they were a very tight press fit (by hand). If they are off center from your original center marks the runners will not drop in, and it will be very difficult to put together:

I then clamped and welded the V-stacks into the backplate, which caused significant warpage. While I'm sure this is due to my welding technique and lack of heat sink, it was easy to bend the thin sheet back into place. It is also very important that the holes are deburred and chamfered before welding so the stacks can fully seat against the plenum wall. If they are even slightly crooked then there will be a gap between the stack and the runner, which is exactly where you do not want a gap:

At this point I was ready to put the two pieces together, which was pretty suspenseful. I had machined the V-stacks to fit each pipe as tightly as I could make it, and I was worried that they would be skewed and not fit since they were assembled separately. But my eyeballing didn't let me down and three of them fit perfectly, with only one being off about a 32nd of an inch and easily pulled into place. Not bad for not using any jigs :

I will likely do some extra sanding around the seams to get rid of the slight inner ridges you can see in that last picture. But none of them have seam gaps, which is the most important part in my opinion, and none of the ridges are over half a millimeter. If I were to do it again though, I would also mill an outward chamfer into the base of each velocity stack on the outside in order to smooth the transition to the wall. But that's mostly a pet peeve, and I highly doubt it will noticeably effect the airflow. Overall though I'm extremely pleased with how close I was able to keep all these measurements, and its super satisfying to see all the parts snap together so tightly. Even before I welded it there was virtually no movement.

But of course I'm not nearly finished, so stay tuned for more

 

[LotusElise]

Very good progress and looks like a very good result. This IM will be a real low end torque enhancer 🤩.

 

[Capt_Hazzard]

That's a nice solution. However I'm working with the K24A1 block which has a separate colant outlet on the right side instead of the integrated one like yours. It wouldn't work for the A1 without cutting that part off and welding it shut, and buying a blockoff plate for the hole. Not sure about cheaper though, I'm only into this about $60 on aluminum stock not counting tools. Also, I take it you just did this to move the TB to the other side? The exit angle seems like way too much for a RWD engine. It would definitely hit the fender in my setup.

 

[Kr4nG]

Im not sure what you mean by your coolant situation. I have a k24a block which is pretty much the same thing as yours. And yes, I need to move my throttle body to the other side and I want to keep all of my accessories. I will be putting my k24a with s2000 trans into a volvo 240 so I have plenty room between fenders.

 

[Capt_Hazzard]

Im not sure what you mean by your coolant situation

Some of the K24 intakes had the coolant outlet cast into the manifold like below. You can see there's a big difference in the block (k24a1 on the left):

That part of the manifold has to be cut off to work with the earlier A1 blocks found in the CR-Vs. And yeah, a 240 probably has a lot more space than my Willys does

 

[Kr4nG]

Ok your getting a bit confused about the coolant and the blocks. The blocks have nothing to do with the coolant ports. The Heads do. The image on the left is not a k24. That is a k20a3 engine (Unless that is a JDM k24a1 CRV which is the only engine that came looking like that from factory only in Japan though.) The image on the left came in the civic si hatchback 02-05. No vtec on the intake and k24 style oil pump. Most of the k20 heads had that bigger looking port for the coolant jacket. But dont get confused with the k20z3 engine from the civic si 06-11. Those heads were like the k24a2 tsx heads with the smaller ports that require the intake manifold to be longer for the coolant jacket.

I have a k24a JDM and 07 tsx k24a2. Both engines are identical besides the intake valves and cams.
But they sell the cheapo manifold with or without the coolant jacket. So people can still do what I showed earlier by cutting it from one side and welding it to the other. It fits very close and not much patching is required.

Sorry to keep you off track.

Cool build!