Turbo + ITB's on a miata.
#61
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If I recall correctly the early 2000's (like 2000-2001ish) GSXR's have 2 paired TB's that each consist of two singles bolted together. This allows you to unbolt them and space them the same distance apart as the intake ports on the Miata head... making the manifold much easier to fab. The downside to that is some spacers need to be made and some fiddling with the linkage would also be necessary. Later GSXR TB's don't come apart... so be sure of what you're looking at.
Do a little google searching, it's how I found the info on which TB's come on which bikes.
Do a little google searching, it's how I found the info on which TB's come on which bikes.
thanks for the info man, ill be sure to use it when it come time to buy my parts.
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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.
You'd want the MAF on a pretty straight section of tube before the throttle, after the BOV.
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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.
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.
#67
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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.
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.
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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.
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.
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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.
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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.
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.
I agree that FI would have an effect on required TB size to reach xxx hp. This thread is IRTB's with FI.
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EDIT: I just measured a '99ish TB, it's 55mm.
#74
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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.![](https://www.miataturbo.net/images/smilies/smile.gif)
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
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.
![](https://www.miataturbo.net/images/smilies/smile.gif)
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
#75
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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.
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.
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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.
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