I'm in the final stages of planning my intake manifold design (pictured below) and I have a couple of questions before I begin fabricating. Is equal air distribution between the runners a major concern on a turbo application? If so, on my design, would it make a difference which way the throttle butterfly opens into the plenum? Should the throttle body be angled downward like I see on many similar designs, is that for air distribution or just for packaging reasons?

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Nice Topic!

Lots of advanced theory here.

1) The throttle blade angle WILL have an effect on where the air distribution goes.
Most Throttle Bodies that have a Blade Design that makes the blade into a
"Ski Jump" for the air to land near the rear cylinders unless at WOT.

2) Also the velocity of the air through the Throttle Body will send more air to the rear cylinders vs the front ones. Boost is "Increased Density per CFM" of air. If more cfm is available to the rear ports vs the front ports the rear ports will have more mass density, will be leaner, and will require more fuel at those locations.

3) So you add more fuel to the rear cylinders and your engine is now basically two engines making different power levels. The "fix" is to try and make the cylinders the same by stopping more air going to the rear cylinders.

4) Some GOOD boost intake manifolds have a "Hump" in the roof of the intake after the throttle body flange. The "Hump" slows down the air with a large expansion and less air goes to the rear.

5) Moving the Throttle Body farther upstream will increase the manifold volume (not a bad thing on a engine that typically wants more volume). The farther upstream the more likely that the air flow will be even when it arrives at the Intake Plenum.

More to come.

Tom Vaught

 

Thanks Tom, you just confirmed what I was thinking. I'm using a 90mm LSx throttle body which opens like this when used on an LSx application:
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I don't really want to change my intake design so could I just flip the throttle body over like this to increase the air distribution to the front runners?
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It has been done before, "flipping" the Throttle body.

Typically you have to tip the Throttle Body out at the top (Wedge Plate) to take away a little bit of the extra airflow to the front but the overall distribution is better when the Boost/ Velocity goes up.

Keep after it

Tom Vaught

 

Interesting subject. I spent some time working on a DIY intake, too. I'll post pictures when on my desktop.

At lower throttle angle, the engine has low air velocity. As such, I would think that the plenum is completely capable of feeding each cylinder equally and adequately.

The throttle blade's angle is 90* at full throttle. It seems that the manifold should be designed to work best under that condition. when I was in the design phase of my intake, I found many efi intakes with a large taper leading to the back of the manifold. Imagine this: half way back, the plenum is only feeding half as many cylinders. 3/4way back, the plenum is only feeding two cylinders. Obviously, you do get some back flow...

If the cross sectional area remains constant while your volumetric flow rate reduces, your velocity also drops a proportional amount.

Is there an ideal air velocity in the plenum?

Have a good day!
Michael

Disclaimer: none of my statements are being stated as fact. I am not an expert.

 

Here is the kit I designed and had machined. It had several flaws in it (20/20 hindsight).

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You may have seen these already...

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Your profile says you live in Tulsa. I'm in Broken Arrow. Like my disclaimer above says...I'm no expert, but I did a lot of research and learned a lot during my DIY intake project. I'm willing to lend you a hand.

Can you show a cut-away view of the inside of the plenum?

Have a good day!
Michael

Disclaimer: Nope, still not an expert...

 

That looks pretty good, what flaws were there? I wish I could use bellmouths, having them greatly improves air distribution and flow but they would complicate my build a lot because of my port layout (EIIEEIIE). I chose a design that was as simple as possible since this is my first attempt at fabricating my own intake.

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I shaped the runners as a perfect transition into the intake port.
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Runner taper, floor/roof shape (tapering down as you move towards the back of the engine), lack of distributor clearance, and transition from TB to the plenum.

Can you put some separation between the runners to allow for a bell mouth? Sorta like the front two runners on the intake below? A square edge there can't be good...

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Have a good day!
Michael

 

Say that you have a rectangular port shape at the plenum.

Typically you would like to have a minimum of a 3/8" radius on each side of the runner.

So you take some 3/8" round stock and machine a flat on one side using a jig to hold the round stock. You can make this "jig" by using a ball-end mill to make a 3/8" "trench" in a piece of flat stock 3/4" thick.

You drop the 3/8" aluminum rod material into the trench and clamp each end and you can mill a flat on one side.

You cut the milled round stock into lengths that match the port dimensions at the plenum. You put a 45 degree angle miter in each corner of the lengths and you now have a nice rounded radiused entry into the individual port. You do this for each port.

You can use a single rounded piece in the middle of two ports if they are close together.

Weld everything in and you have a proper entry.

If the ports are split apart, then each port gets 4 rounded mitered pieces.

Bell-mouths inside the plenum need to be designed properly and typically only work with an EFI intake. Otherwise you have fuel collecting in the bottom of the intake.

The radius entry design is used on many carbed tunnel ram intakes and will pull any excess fuel into the runners.

Tom Vaught

 

This thread is awesome! I had no idea it existed until yesterday.

Michael - your design looks pretty awesome, why not just run it? (That, and it looks like most of the hard work is done.)

Re: chasing down 1st order harmonics - who has seen (or remembers) the Chrysler Long Ram stuff? Those things actually DID have 20" length runners. They were also mostly impossible to fit practically into cars. I'm not an expert either, and I know this attitude sucks, but I have a feeling that people would be doing it / chasing it if it made such a huge difference (like, for instance, 180 degree headers, etc etc). Or, the payoff isn't worth the trouble. Yes / no?

Tom (and everyone else of course), would you mind nitpicking / throwing out some predictions for Shaun's intake here? I tried to include as many of the dimensions as are outlined in some of the pictures Michael provided. As you can see, we don't have any of the criteria for ultimate runner magic, but for good reasons:

- The entire idea was to get something which breathed O.K. and which had a forward facing inlet all under the stock hood. The intake flanges are in red, and the top of the "octagon" is about where the hood comes down....you can see there isn't much room for anything.
- The bore size was us literally thinking: "2 1/4" will probably be fine."
- The inlet radius was determined by how big the bellmouths could physically be while still allowing assembly.
- The runner lengths were, again, limited by how much assembly room we had.

Any thoughts on flow dead spots within the plenum? Distribution problems? It's all built and put together so there's no going back now, haha......

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If I had more fabricating experience and access to a CNC machine then I would go all out and make runners like this:
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On my current design, I'll probably just build up material for a radius by stacking beads and then grinding it into a smooth transition.

 

I am not a big fan of "Large Taper" Intake Manifold Runners. I have recommended "stuffing blocks" in a couple of intakes to reduce the taper due to the large taper angles and the engines ran better with the "stuffer blocks" installed vs with the as made large taper intake runners.

JMO

Tom Vaught

 

If I remember right, high RPM setups often get 6*+ of taper while lower RPM setups get 0* - 3*.

Here are some photos of my first attempt at fabbing the straight runners for my DIY intake. You may find that it'll work well for you.

I bolted together several of the drop outs from the intake flanges.



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Here is a method I was planning to use on an intake that had tapered runners and a shape change.

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Have a good day!
Michael

 

I wasn't doing any math when I quickly drew up that rendering, I just picked a 2.5in diameter opening because it looked good. A 2.5in diameter opening gives me a cross-sectional area of 4.9in^2 and with a cross-sectional area at the flange of 3.15in^2 gives me a 56% increase in area which is WAY too much. If I decrease the opening to 2.25in that gives me an area of 3.97in^2 which equates to a much more acceptable 26% increase in area.

Here are the revised runners:
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That method has seriously crossed my mind but then Ross Machine Racing released a new product meant for the Ford 3 valve and Chevy LS3 which also happens to fit my Mopar Max Wedge ports. To achieve the desired taper I'm going to cut one piece straight down the middle and the other piece at an angle then weld the two halves together.

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I'm getting ready to start on my second intake manifold design. Here's my first. Small taper, short length runners. Eliptical flare runner entrances.
I picked short runner lengths to flatten and broaden the torque curve.
The 100mm throttle body is also my design.

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i thought this might be relvent pic here this is my runner for the mani im starting build atm.,

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I went with the 100mm throttle body size to cut down the speed of the intake charge as it entered the plenum. It required me to make the throttle linkage pull progressively to tame down the off idle and light throttle opening response.
I figured that if I could get the charge speed down, it would provide better distribution. Particularly to the front runners.
The throttle body was mounted to the upper plenum cover with a slight angle that would promote flow to the forward runners.
The upper plenum cover flared outward just after the throttle body, again to further slow down the speed of the charge to promote equal pressure distribution.

I tried to keep the intake runners as straight as possible. Not hard to do with such a short runner. I also aimed the intake runner straight down the middle of the runner in the head. I wanted absolutely no turns or corners that the airflow would have to maneuver around.

The amount of taper I used with the intake runners was 5.4 degrees.

The next intake I make will mount the throttle body further from the main plenum body, and the plumbing will taper out from the throttle body to the width of the main plenum body over a fair length to slow the charge speed while preventing turbulence from occurring.

 

Here's a better look at how I mounted the throttle body to the upper plenum cover. I hammer formed the upper plenum cover. Not fun.
The second pic shows how the runner entrances are unrestricted on all sides. Fluid would build up in the bottom of the plenum, but with enough run time, it would evaporate away. I did end up running a drain to a catch can that I would drain out once right after the first cold start of the day. After the warm up, it was unnecessary to check the catch tank for the rest of the day. Running alcohol, a lot of ice would collect in the intake at first cold start, that would later melt to water. That was the majority of the liquid that would collect in the intake plenum catch tank.
If I happened to forget to drain the catch tank, and enough run time had passed, nothing would come out of the catch tank when I went to drain it at the end of the day.
I like the idea of catching all that water, rather than letting it flow through the engine to contaminate the engine oil.

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Even with my upper plenum cover design, testing the flow into the manifold showed that the flow favored going to the rearward runners. I added a flow dam to the upper plenum to disrupt the flow as it entered the plenum and force a more equal flow to each runner.