Intake Manifold Questions

[TJ530]

Hello all,
I am in the middle of building a 2110 Turbo Type One. My goals for the engine are 100HP-ish per liter, and good daily driveability/ autocross on the weekends. Turbo is a Holset HE-221W with a Turbosmart Universal Wastegate. Heads haven't been decided just yet and cam is a DRD Turbo Grind. For engine management I'm going to be running MS3 pro. I have some CB IDF manifolds I'm going to use for the lower intake manifolds, the upper part is where I'm currently undecided. Onto the questions/discussion about intake manifolds. I have determined that to boost torque I would like to use a dual plane Manifold. The questions start coming in while determining throttle body size and plenum sizing. Using some maths I've determined that a 48mm TB for each side of the engine should be close to ideal. Unfortunately finding a single 48mm TB locally hasn't been easy. There are some internationally on a Rover and aren't expensive. The questions I have is
1. If I use a 48mm throttle for each side what should I do for plenum volume? I've read anywhere from 50%-200% of engine displacement.
2. Where should the throttle body be in relation to the plenum? In my research moving the Throttle Body away from the plenum allows the air to slow and helps with air distribution. However putting the Throttle Body on the plenum and moving the plenum further from the Lower intake manifold would allow longer runners and boost low end torque.
3. If I use a larger than calculated Throttle Body how does that affect plenum sizing. From my understanding having too large of throttle makes it more a on off switch so can that be offset by larger plenum sizing to essentially slow down that change? On the other hand too large of a plenum causes slow slow throttle reponse due to loss in velocity so that may cause more of a issue.
Any thoughts and discussion would be appreciated.

[ps2375]

I would think most of your questions are going to really depend upon when and how quickly you can build boost. The sooner you build boost, the less you'll need a well tuned plenum.

[TJ530]

I would think most of your questions are going to really depend upon when and how quickly you can build boost. The sooner you build boost, the less you'll need a well tuned plenum.

That is true. Once on boost the engine wants as much well distributed airflow as it can get. Proper plenum design also must ensure equal airflow to the individual Cylinders as well. Sizing and tuning do have a part to play in that regard as far as I can tell. I'm hoping the HE-221W turbo and a good equal length exhaust manifold build boost rather quickly but there will be times where the engine is not in boost and that does have to be taken into consideration as well. Thanks for the input.

[ps2375]

If you are doing dual TB's, I doubt a plenum will matter at all.

[sideshow]

Your question is hard to follow, where is local, why are you running an IR intakes into separate split throttle plates, are you splitting front/rear cylinders?

[TJ530]

Your question is hard to follow, where is local, why are you running an IR intakes into separate split throttle plates, are you splitting front/rear cylinders?

Local is California.
The idea is by seperating the cylinder banks into their own plenums you gain low end torque.
I don't plan on seperating the front and rear Cylinders but instead splitting the engine by cylinder banks.

[ps2375]

With TB's at the top of intake runners, like where they would be on a dual carb'd motor, "air distribution" from a plenum above them is all but done. I would sort of , but not very, be concerned with "air distribution" with a manifold setup that had the TB feeding the plenum and then the runners off of that to each cylinder(more like a modern subi manifold). But then that concern would only be to get the most out of motor that was not boosted. Unless you have found some data that shows otherwise, the difference in airflow to each cylinder would be small and nothing to worry about.

[TJ530]

With TB's at the top of intake runners, like where they would be on a dual carb'd motor, "air distribution" from a plenum above them is all but done. I would sort of , but not very, be concerned with "air distribution" with a manifold setup that had the TB feeding the plenum and then the runners off of that to each cylinder(more like a modern subi manifold). But then that concern would only be to get the most out of motor that was not boosted. Unless you have found some data that shows otherwise, the difference in airflow to each cylinder would be small and nothing to worry about.

I am envisioning something like the second option with the plenums coming after the TB and then splitting into the intake runners. This allows for more freedom with the intake runner length, and plenum design. Ideally the idea is that you have a engine that makes good power and torque throughout the RPM range regardless if it's on boost or not.
I remember seeing a picture that Mario at the dub shop had showed about how different the airflow was between Cylinders with the stock injection pieces which isn't exactly apples to apples but Is why im trying to figure all this out. Also because it's a fun experiment.

[ps2375]

The only way I know of to measure airflow in a manifold is to mount it on a flow bench. Unless you have one, or have access to one or are willing to pay for those services, this "experiment" is all guess work. You might be able to get useful information with a WB or EGT sensor mounted in each exhaust tract.

[TJ530]

The only way I know of to measure airflow in a manifold is to mount it on a flow bench. Unless you have one, or have access to one or are willing to pay for those services, this "experiment" is all guess work. You might be able to get useful information with a WB or EGT sensor mounted in each exhaust tract.

True until this is somehow verified through data all of this is just a thought experiment. I'm also planning to model some of this up in solidworks. It's not exact but should show general ideas and concepts.
Any thoughts on throttle size vs plenum sizing?

[ps2375]

not a clue. I suppose a 48mm on each side should give you plenty of control for modulation and still be open enough at the upper RPM's for good power.

[sideshow]

Well splitting the engine L & R is normally done for packaging reasons, firing order being what it is.

I/R is the best overall cost verses performance, it almost sounds like you are adding stickers to over come sound design.

Get the best N/A manifold you like, size it small (autocross is not a WOT event, you need down low drivability leaving turns), then add pressure pipes.

[TJ530]

Well splitting the engine L & R is normally done for packaging reasons, firing order being what it is.

I/R is the best overall cost verses performance, it almost sounds like you are adding stickers to over come sound design.

Get the best N/A manifold you like, size it small (autocross is not a WOT event, you need down low drivability leaving turns), then add pressure pipes.

So your thought is to run ITBs and runner lengths sized for drivability and torque then let the plumbing take care of itself? So that brings up the question do people see improvements enlarging the "turbo hat" above the ITBs?
Thanks for th input!

[ps2375]

So that brings up the question do people see improvements enlarging the "turbo hat" above the ITBs?
Thanks for th input!

Seems like that could be a simple thing to vary and test. Or the simplest, anyway.

[Clonebug]

My feeling is you are making it more complicated than needed with ITB's.
Just run a single TB and put the boost to it.
My 1679 has a custom homemade intake shaped like the stock intake but a little larger tubing due to matching the CB FI inlets outside diameter. I think it is either 1 5/8ths or 1 3/4 inch tubing. That is the largest that will fit without interfering with the alt stand and having to flatten the tubing to fit underneath it.
I have great low end and good top end.
The way to more HP is in RPM's I have found. If you limit rpm to 5000 you limit hp. Turn it up to 7000 rpm you will gain a lot.