Intake manifold construction

[vex]

I'm planning on constructing a new intake manifold for my Turbo-6PI as i'm tired of the cluster F*ck of lines and crap that aren't needed. I need to understand the basic principles of manifold construction and the math that goes into the proper sizing/construction of the manifold itself.

The basics prior to the start of this thread:

(I'm going to use my build philosophy as the basis of discussion)
Let's assume this is going to be for a street driven vehicle with NA S4 rotors and a T60-1 Turbo that will see track days, hpde, and Auto-x. It will be driven there and back.

This manifold will be replacing the intermediate and upper intake manifold with a minimalistic visual interruption philosophy. That basically means the manifold can be as complex as it wants so long as it's visually simple, ie: no extremely complex external shapes, no sharp bends, etc. Internally it can be as complex as it is reliable. Internal of the manifold velocity stacks, electronic runners, etc can be used so long as the probability of failure is less than .1%(just a random number).

Also consider that it will be using dual fuel system on the runners. IE: Alcohol, meth, or NOS on the primaries and pump gas on the secondaries. Assumption of enough fuel is given for any specific setup.

Turbo may be able to out put anywhere from 5psi-25psi depending on setup needs.

Assume suffcient cooling abilities from all heat exchangers (oil cooler, radiator, etc).

Any more information can be garnered during the course of the discussion.

Here are the preliminaries:

Sizing a TB--Is bigger always better?
Multi Venteri--The more the better?
Pneulum Geometry & Volume--What is the best shape and why?
Runners--Length, shape, diameter?

Ready? Go!

[drewski86]

http://www.rx7club.com/showthread.ph...ghlight=intake

This will get you started. If you do the math it will get you close enough, but you will want to plan on making adjustments if you want to pull all you can out of it; every motor is going to want something different. Don't expect to get it right the first time, but close may be sufficient for your needs.

The throttle body needs to be big enough that it's not a restriction, but not too much bigger.
By multi venturi to you mean multiple injectors?
The plenum should be shaped that each rotor gets equal amounts of air. Size depends on that application but I would guess around 1-1.5 liters.
Runners should be round since the stock lower manifold will change the shape for the ports. If you want a small taper before it hits the lower manifold will increase velocity, but you don't want to go too extreme. Length is going to depend on the application, and remember, the primaries and secondaries are going to want different lengths but you want them tuned to the same RPM.

Hopefully that will get you started. Keep in mind, all this is going to do is point you in the right direction. Testing is where you're going to get answers. Fortunately since you're turbo you can add boost to overcome a poor manifold but that will only get you so far depending on how poor the manifold is.

[vex]

Originally Posted by drewski86

http://www.rx7club.com/showthread.ph...ghlight=intake

This will get you started. If you do the math it will get you close enough, but you will want to plan on making adjustments if you want to pull all you can out of it; every motor is going to want something different. Don't expect to get it right the first time, but close may be sufficient for your needs.

Right on I'll check it out and post back my thoughts w/ math. (I heart math)

The throttle body needs to be big enough that it's not a restriction, but not too much bigger.
By multi venturi to you mean multiple injectors?

Negative. Multiple TB Plates. Is 4 Better than 2 better than 1? Or is it the other way around, or should the pick be based off of the CFM, what determines the proper CFM if the area's are the same, ie: A(4)=A(2)=A(1), which by association means that the CFM is equal between all of them. Would that mean that velocity would be increased with multiple smaller areas?

The plenum should be shaped that each rotor gets equal amounts of air. Size depends on that application but I would guess around 1-1.5 liters.
Runners should be round since the stock lower manifold will change the shape for the ports. If you want a small taper before it hits the lower manifold will increase velocity, but you don't want to go too extreme. Length is going to depend on the application, and remember, the primaries and secondaries are going to want different lengths but you want them tuned to the same RPM.

I think I understand, but could you clarify just to be safe?

Hopefully that will get you started. Keep in mind, all this is going to do is point you in the right direction. Testing is where you're going to get answers. Fortunately since you're turbo you can add boost to overcome a poor manifold but that will only get you so far depending on how poor the manifold is.

Believe me, I plan on working out the details and construction prior to even taking apart the engine for this. I'm going to be extremely focused with respect to this setup so I'm going to be doing everything possible short of shelling out $$$$$ to do a CFD model of it.

[NoDOHC]

The rule of thumb I go by is that you want 0.3 mach in the intake runners at peak torque and uniform cross-sectional area from the plenum to the port. Slight decreasing in area is acceptable as the air enters the rotor. The plenum should be 1.5X the displacment of simultaneously charging volumes (in your case .654 l).

You want to tune your manifold for 2nd harmonic at peak torque to allow for reasonable additional tuning possibilities (3rd and 4th harmonic will also assist you).

Rotary intake tuning is signicifcantly different from piston intake tuning because the chamber charges twice as often (once per revolution).

Basically, the stock manifold follows all the rules except for the mach 0.3 rule. at 100% VE we get 0.18 mach (average) or 0.33 mach during the 198 degree intake stroke at 7,000 rpm (too small).

The secondary plenum is about right for the turbo engine, the primary basically doesn't exist.

These rules are what I have compiled from reading a lot of manifold design papers and books, most of the information is for piston engines, but I think most of it can be transferred to rotaries.

[vex]

Maybe this is a silly question, but I could have sworn there were aluminum flanges for creating your own manifolds that you could buy. I can't find any except for the REW. Anyone have any websites/locations to buy it from?

[NoDOHC]

Wouldn't REW flanges work for a Turbo II (If you didn't need the coolant for your turbo)?

[vex]

Originally Posted by NoDOHC

Wouldn't REW flanges work for a Turbo II (If you didn't need the coolant for your turbo)?

It's not a TII. Turbo-6PI

[NoDOHC]

Oh, I missed that. Could you buy a manifold from summit for a holley carb and cut the runners off?

Could you cut the runners off a stock manifold? (You can buy them on eBay all the time).

You should be able to make plates for that matter. (Cut them out of sheet stock.)

I would love to build my own manifold, but I will have to wait until I get more time.

Keep up the good work!

[drewski86]

Originally Posted by vex

Multiple TB Plates. Is 4 Better than 2 better than 1?...

I don't think that any is better than the other as far as power goes. It would depend on what you have to work with. Each would have to be tuned for where the runner hits "atmosphere" whether it be a plenum, air box, or atmosphere.

I think I understand, but could you clarify just to be safe?

Which part?

Originally Posted by vex

Maybe this is a silly question, but I could have sworn there were aluminum flanges for creating your own manifolds that you could buy. I can't find any except for the REW. Anyone have any websites/locations to buy it from?

I would build off a stock S4 lower manifold as it already has good transitions to the shapes of the port runners. Depending on how big your ports are going to be, you can hone out the stock lower and it should flow plenty. The EP guys are making good power (rumors of 220+whp) with monster streetports on full S4 manifolds with only internal modifications.

[vex]

Originally Posted by drewski86

I would build off a stock S4 lower manifold as it already has good transitions to the shapes of the port runners. Depending on how big your ports are going to be, you can hone out the stock lower and it should flow plenty. The EP guys are making good power (rumors of 220+whp) with monster streetports on full S4 manifolds with only internal modifications.

Still looking for the mating flange though. I plan on keeping the stock LIM for the moment, but I'd like to re-do the Itermediate and Upper Intake manifolds so that means I'd need a flange to mate to the LIM, pipes to run to the plenum then to the TB.

I haven't been able to find the flange, even though I know I've seen them before. I just can't remember where.

[drewski86]

Originally Posted by vex

Still looking for the mating flange though. I plan on keeping the stock LIM for the moment, but I'd like to re-do the Itermediate and Upper Intake manifolds so that means I'd need a flange to mate to the LIM, pipes to run to the plenum then to the TB.

I haven't been able to find the flange, even though I know I've seen them before. I just can't remember where.

I see, for some reason I was thinking you were talking about manifold to engine flange. I don't think I've ever seen flange that you're looking for. If you don't have access to a mill, you could just cut the flange off the existing intermediate manifold and use that.