New Intake Mani Idea

[RadoTD]

I have an idea for a new intake manifold, and as per usual, I like to get some other opinions to point out the flaws which I love to overlook. You guys are always good at that. The goal is to create an intake manifold with as little cylinder bias as possible without significantly restricting flow

Unfortunately I have no 3D CAD right now, otherwise I'd love to make a model of it, but I'll be sorta winging and probably not over engineering this one.

The design will sort of start off like a Passenger Performance intake (see here if you're not familiar with it) but with 2 big differences.

The first difference is that internally, it'll be broken into 2 plenums. One plenum for cylinders 1 & 2, one plenum for cylinders 3 & 4. Instead of rounded caps, they'll be straight making both plenums symmetrical in every way.

The second difference is that instead of the air going in one side, I'll run parallel charge pipes over the valve cover and straight into the plenums.

The idea is that I'll take my charge pipe from the intercooler and split it with a merge collector between the engine and the radiator. This will split flow evenly from my 2.5" charge pipe to two 1.75 or 2" pipes. These will then turn up together and go over the valve cover into the intake manifold. By the time the air enters the plenum, it should be far enough away from the merge collector that pressure waves shouldn't change flow and the air flow should go straight into each plenum.
By separating cylinders 1&2 from 3&4, the charge pipe can enter the manifold right in the middle of the two, in theory leaving no bias.

I can draw pictures if anyone's having trouble following. Can anyone see anything I'm overlooking though?

[Smokey Eddy]

I always wondered why no one made an intake that looked like an equal runner length exhaust manifold. But this sounds better and will look cooler. I don't see an issue with this so long as you can TIG these bits together?
were you thinking of using that MIG and going stainless?

[DJPyro]

^ I've always thought the same thing, but I think it has to do with fluid flow and how the air moves through the pipes. A design like that would work well for air flowing from the 4 ports into the one big end, but not so well the other way.

OP, that sounds kind of neat, but there are smarter minds than mine on here that will hopefully chime in about it.

[burn_your_money]

I think you would be better going to two 1.5" pipes. The surface area would be closer to equal that way, 25 in^2 with 2.5" piping to 30 in^2 for 1.5" piping.

If there are any bends right before the split I think you might end up collecting uneven amounts of air because of uneven pressure in the pipe. I'm just thinking out loud but my reasoning is how on a waterside you go around the corner and get pushed up the side of the wall. I don't know if airflow in a pipe reacts in a similar fashion or not though, or how significant it would be.

[AudiVWguy]

I thought in TURBOJ's Projrct 200 build he had come up with a great manifold design based on each intake runner getting its equal share of air. A lot of math went into it if I recall. That being said, I would Google and see what some of the big boys with Evos, Hondas and Supras have come up with. Flow into the cylinder would be slightly different, meaning I would think diesels would like longer runners than gas, but if you are going for big dyno numbers it would be a short runner design.
Just my 2 cents,
Cheers,
-Jeff

[RabbitJockey]

yeah he made a dual plenum manifold, they're pretty awesome

[RadoTD]

I think you would be better going to two 1.5" pipes. The surface area would be closer to equal that way, 25 in^2 with 2.5" piping to 30 in^2 for 1.5" piping.

If there are any bends right before the split I think you might end up collecting uneven amounts of air because of uneven pressure in the pipe. I'm just thinking out loud but my reasoning is how on a waterside you go around the corner and get pushed up the side of the wall. I don't know if airflow in a pipe reacts in a similar fashion or not though, or how significant it would be.

I get a 4.91in^2 cross section with 1 2.5" pipe and 4.81in^2 with 2 1.75" pipes. I don't want to go smaller, even if it's .1", so that's why I said 1.75 or 2".

That is a good thought about the uneven pressure from the corners, I think you're right about that. I've easily got 2ft I can work with, so the flow should straighten out by then.

The dual plenum manifolds are good in theory, but it's very hard to say how they work out in practicality. I've never seen a flow analysis on one that actually included valves opening and closing and sometimes a weird bump near the throat changed how the air flowed drastically either for better or for worse. He can do all the math he wants, but there will still be a high level of uncertainty in it.

Most people run a simple single plenum manifold. Long runners for torque, short runners for power. I'm not a fan of long runners on a diesel. Short answer is because the amount of fuel injected isn't based on how much air is actually getting into the cylinder. Longer answer here, 2nd post down http://www.vwdiesel.net/forum/index.php?topic=22737.45

[burn_your_money]

I get a 4.91in^2 cross section with 1 2.5" pipe and 4.81in^2 with 2 1.75" pipes. I don't want to go smaller, even if it's .1", so that's why I said 1.75 or 2".

Yep. It's been a while since I calculated area.