What size throttle bodies are ideal for a 1.8 ITB setup?

no one is fighting. but if its proven that they significantly enhance and increase power and its delivery we'll all be looking into doing likewise on our setups.

i was thinking what ever size comes on the 4AGE 20v that motor is a 1.6 so it should be okay for the 1.8. alot of people that have done the ITB's on a miata get them off Liter bikes.

i know its not happening right now, i just want it to be ovoided. im gonna do some more research on ITB's and see how cheap i can source parts out for this.

i can probly get away with choping the flange off a old intake manifold, source the ITBs and make a plenum. it seems simple enough right now...

As did the LS1 swap to me when I wanted to do it:giggle:

When you get ready,I will machine as much of the parts as I am capable,Just buy the material.Ive often thought about this,it seems to me that it would offer an improvement in throttle response on the same order as on a N/A motor.
(G)

thanks Greg, ill keep you posted. i have some other priorities right now but i think ill be getting my hands dirty with this one day soon!

thats why i said RIGHT NOW.... lol

1) Kind of immaterial, as I was advocating building a DIY IRTB setup not buying one. I'll stick by my contention that one could be built for $400 or less without any special discounts.

2) Welding I'll agree with, but anyone who can fab up their own DIY turbo setup should have the skills to make the pieces I'm talking about. You then take them to your favorite welder and have him stick then together. Basically you've got to make an aluminum plate with 4 holes in it the shape/size of the ports (plus the thickness of your runner tubes), four short tubes for the couplers from plate to TB, a plenum box, and some misc spacers between the TB's (early GSXR TB's come in paired barrels but they unbolt into separate units). None of it is rocket science and anyone who can run a drill, a file, and a pair of snips could make it with some patience.

3) I know and it's sort of funny because they all also complain about how M.netters won't listen to new ideas... then they do the same thing here.

In my opinion the "idea" of IRTB's and turbos is well enough proven, look at any turbo era inline-4 F1 engine. They pretty much all used IRTB's (mostly slide valve) and made upwards of 1200hp out of 1.5 liters. From my viewpoint it's a question of whether there's enough benefit to be had to make it worthwhile for our level of power. If I were to guess I'd be inclined to say you might notice a difference at about the same point as it becomes useful to ditch the stock intake.

For the record, I really meant you should try it. If you want to, and you can do it inexpensively, why not?

no promises yet. i want to see how inexpensive i can get it done first!

You're very welcome. :)

Like most things having to do with passage of air going into an engine, it depends. :)

This is stolen from someone who quoted it, on what throttle for horsepower, may or may not be right, seems to make sense to me though:

"...this guide is from A Graham Bell's Forced Induction Performance Tuning:

50mm: 250
56mm: 310
62mm: 390
70mm: 500
75mm :600"

You'd just divide the area of your intended goal by four and choose a width that gives you that opening area. i know you probably know better, but i should remind anyone reading that you'll need to use Area = pie * Radius squared, rather than a linear progression.

Honestly, most any bike throttle body will be good enough, for instance in GSXR's, the 600cc has 38mm, the 1000cc 42mm and the 1300cc 46mm. Believe this is due to keeping air intake velocity down while the bike is under high rev, but don't quote me on this.

That depends on discplacement and rpm. That is one of the advantages of an IRTB or carb with replaceable chokes. Cast intakes do not have that advantage, so it is impossible to control the speed of intake charge entering the cylinder head with a fixed intake. I currently have 40mm chokes. Forced induction cars use different chokes, but I do not know how to calculate for it.

I would like to add that it depends on what one is doing with the car. I never see IRTBs on the highest horsepower drag cars, but I see them on road race cars. I think, that it has to do with the throttle response advantage IRTBs have, which is not really necessary on drag cars.

Not 'pie' but pi. Also pressure drop, all else being equal, is inversely proportional to diameter raised to the 4th power, not diameter squared.

The misspelling was trying to type after 12 hours of working on my car, quite tired, sorry. -.-

Another OEM ITB turbo setup.

RB26DETT

http://img236.imageshack.us/img236/5751/11855mgap2.jpg

On my old RB26, the map sensor was just off the plenum. Before the throttle bodies. But stock runs two MAFS.

I was running a map sensor based PowerFC.

There is also a MAF though IIRC, so the MAP reading isn't as important for a stable idle/low load part throttle like it is in a speed density setup.

I think I might be missing something. It seems that everyone wants better flow, thus the aftermarket IMs. Wouldn't ITBs be a restrictor? I can understand how they would be better on a NA car, but a turbo? My little pea brain can't wrap itself around this.

Anyone?

I just realized I wrote that before reading second page.:facepalm:

If its been covered sorry

Lets take the 62mm TB. Area is 4.68in^2, divided by 4 that's 1.170 in^2, which is a 31mm diameter. I have some ~36mm VFR750 carbs in my garage. Hmm...