WonTon

iTrader: (17)

i sold that unit and im building a MSII unit, so it should be able to do that and more. there are a few reputable shops around that i can take my car too, ill look into that aspect more when that time draws closer.


thanks for the info man, ill be sure to use it when it come time to buy my parts.

Nagase

iTrader: (6)

Well, if you can setup the MS2 to use a MAF, you'll be worlds happier when it comes to tune your car.

ZX-Tex

iTrader: (15)

Not to be difficult here, but you cannot assume that 4 throttles with area X each will flow the same as one throttle with area 4X. It does not work that way.

WonTon

iTrader: (17)

when you say MAF i think about this:



will i have to use one before the turbo? man this is gonna be a PITA!

Nagase

iTrader: (6)

It's a good point, and that is a bit of a gross simplification, though is should effectively work out. In any case, i'd say four 38mm throttles will flow more than the single stock 48mm, unless something is grossly off, wouldn't you agree?

Could you provide a more accurate equation that involves flow properties of the system? Because i'd be glad to be more accurate, but i can't come up with that myself.

Yep, like that. Putting in a bit of tube and setting it up to work with your MS2 will be hard now, but some people just... give up on ITB's if they try to take shortcuts in the initial process.

You'd want the MAF on a pretty straight section of tube before the throttle, after the BOV.

ZX-Tex

iTrader: (15)

That is a rough approximation that will get you in the ball part. The more precise way to do it gets into incompressible fluid flow equations, Reynolds charts, etc, engineering stuff.

I believe there are some online fluid calculators for like flow through a pipe, assuming they let you substitute in density and viscosity for air. If you keep pressure drop constant for both configurations this may tell you what the equivalent diameter for the 4-throttle setup should be. This method still neglects the drag caused by the throttle plates and shafts. Not sure how significant this is. You might also be able to find some flow tables somewhere that someone has posted for smooth body restrictor flow (not orifice plates).

Simple answer is yes, you will probably have more flow with four 38mm throttles than one 48mm throttle.

miata2fast

iTrader: (2)

I am not so sure that a 38 mm throttle is nearly enough. Like I said earlier, I have 45 mm throttles, with 40mm chokes. I started out with 36mm chokes, and they were not enough. I am now maxed at at the 40mm chokes. The difference in performance from the smallest choke I first tried, to the current choke was very significant.

I know that IRTBs will be a bit different than a carb, because carbs flow wet, and may need a little more volume.

There are currently 2 versions of IRTBs developed specifically for a Miata from Weber; 40mm and 45mm. The 40mm is for pretty much stock motors. From what I have learned so far, I would be willing to bet that a high rpm and or stroker BP could benefit from a 50mm. To put 38 mm motorcycle throttles on a miata maybe a great novelty, but will not cut the mustard for all out performance.

TurboTim

iTrader: (9)

But it does get you in the ball park.

ZX-Tex

iTrader: (15)

Well, thinking about miata2fasts empirical argument, no it probably does not get you in the ball park. His point is a good one. A Hayabusa makes ~200 BHP and uses four 44mm throttle bodies (varies slightly with year maybe). So if you are going FI, and will be more like in the 300 BHP, then even a 44mm may not be enough.

But then again, we are comparing FI to natural aspiration, another complication.

Short answer, find some FI (turbo) throttle body setups from some other setups and see what works for them.

miata2fast

iTrader: (2)

Because of this discussion, I contacted Pierce Manifold to see if forced induction would have any thing to do with choke selection on an ITB set up. He said that discplacement and rpm are the only real determining factors in choke size, whether normally aspirated or forced induction. That should make things easy. Just get the proven set up that N/A racers are already using, then add plenum and turbo.

WonTon

iTrader: (17)

awesome!

that helps out alot! so i should be looking at running between 40mm and 50mm?

TurboTim

iTrader: (9)

Somewhere in this thread it says the factory throttle body is 48mm. You are hinting that 4 44mm ITB's might not be enough for 300 BHP?

I agree that FI would have an effect on required TB size to reach xxx hp. This thread is IRTB's with FI.

TurboTim

iTrader: (9)

Between 40 & 50mm may be the factory throttle body. I would not recommend putting 4 OEM throttle bodies (or something of similar size) on a miata engine, ever.

EDIT: I just measured a '99ish TB, it's 55mm.

Nagase

iTrader: (6)

Do have to apologize, i got the 48mm from an incorrect source. Assuming Tim is right, the OEM TB is actually 55mm, according to this post:

https://www.miataturbo.net/showpost....90&postcount=1

Here's a 4x 48mm ITB setup, but it doesn't tell what horsepower range it's for:

http://www.streetunit.com/TWM_Indepe...-fslash-48.htm

Edit: Tim edited his post while i was quoting his old post.

Edit x2: This is a pretty interesting site, though it's for naturally aspirated engines with a redline of 9,000 and just an outline, but another data point: http://extrudabody.com/TechInfo/Sizing.html

Sparetire

A MAF is not neccesarily that hard to do. A GM unit off any LSX will handle any airflow we will throw at it and they are very precise and reliable. They do however work on a HZ signal (0-12V square-wave IIRC) where the stock AFM and most other MAFs from the 90s work on a analog 0-5V signal. Luckily there is a translator:

http://www.maftpro.com/

Lots of DSMs still use these.

Another option would be a MAF off a Mustang or preferably a Lightning, which will run on a 0-5V signal and also will be basically 0 restriction.

If you put the MAF pre-turbo, just make sure to recirc your BOV outlet to a point right before the turbo inlet and maybe a few inches (or more) away from the MAF.

If it were me, I would want to try a signal line off each runner post TB to a single source and run that to the MAP sensor. I think that would work and be a lot easier.

ZX-Tex

iTrader: (15)

Really I have no idea without running some real numbers and/or looking into it more so right now it is all an ---- extraction.

Empirical data is a good start for this. Surely there are some others running IRTB turbo setups. Find some with good results and see what they are doing.