4 stock TB's for ITB?

[ska69]

Hey everyone,

I have 3 stock TB's laying around and looking into the ITB idea, I'm wondering is it possible (looks so) to use stock ca18 TB's for an ITB setup (I'm worried about the TB diameter - around 55mm, whilst GSXR ITB's are 40-44mm..but on the other side BMW M3 ITB is 50mm (came across googling)?

ITB+turbo=win?

[tommey]

For moderate power levels ITB`s isnt a bad idea, but i belive 45 is a much better diameter.
55mm is pointless.
50mm on a "big" bmw NA engine isnt comparable.
Use RB26 ITB`s, they dont require much work to fit either.

[ska69]

thanks for clearing that up. I'll be looking for motorcycle itbs then, plenty of them @ ebay.

I don't think I can get rb26 itb's nor sr20det gti-r itb's cheap.

also what would be better, 38mm or 40-45mm? is there any significant difference?

[tommey]

i would go for 45mm because it matches the runner diameter pretty good.

[themadscientist]

RB26 throttles would likely be easier to use.

[ska69]

TMS, hard to get those

Tommey, thanks!

[themadscientist]

Not hard at all when you know someone who has them.....

[hint]you do[/hint]

[ska69]

are you suggesting someone? lol

they wouldn't be cheap, would they?

motorcycle itbs I found turn out to be 100-120$ shipped to my door.

[themadscientist]

The real question is the manifold. I think that is going to be the make or break part of this. There are multiple throttles you can use, but the manifold is going to be custom since the CA carb manifold is extremely rare and mine is not for sale.

Depending on your resources, are you a welder with equipment, it might not be prohibitive to make something, but otherwise you need to think hard about the way whatever throttles you get are going to attach to the engine.

Gotta bounce, time for work.

[tommey]

Cut the flange connecting the plenum to the lower intake manifold (where the injectors are).
Get some aluminium tubing and make (or buy) some "bellmouths".

Make some flanges:




You could also skip the bellmouths and use the stock plenum, but i think thats a weird solution.

Make a plenum, make it fit and get it welded.



If you know someone who can weld it should be a lowcost project, only major expense will be the TB`S.

[ska69]

Tommey, yes, that's what I was thinking of, only instead of making my own aluminum plenum, I'll order one from Ross Machine Racing (sound easier and cheaper to order a whole part + oval runners).

I'll try to make a drawing in a while.

TMS, so you may happen to have them, ol' wizard? how much would you want for these precious gems?

I have a 4 port euro lower manifold and looking to bolt on the itbs (rb26, or motorcycle) via a simple adapter plate, and put a custom manifold (as stated above) on the other end. should solve the problem?

also as this is a street engine I'm thinking some runners of 3-4" will be required..any thoughts on that?

[themadscientist]

If you decide you want them I will let a set go for $350. Two throttles and the linkage arms. No biggie on my end, I have two sets so it doesn't put me out. The nice thing about the 26 throttles is the bore spacing on them is the same as a DCOE carb, but the stud pattern is clocked out more. Carb funnels can be used as well, but the spread on the studs is wider so you will need to slot the holes on the funnels to fasten them on.

I need to go scrounging around in my storage area on Saturday. I'll try to remember to pull out the carb manifold and throttles and take a few pics to give you some idea of how that would work out. You have several potential setups that can get you the results you want, the 26 throttles are just one of them. If you want to get high-speed low-drag you could go with TWMs, but they ain't cheap and you already have a place to install injectors in the lower manifold.

http://www.twminduction.com/ThrottleBod ... dy-FR.html

[ska69]

Twm is pricey :-/
As for the rb26 itb's, thank you for the offer, but that's too much for me right now, yet I'll keep it in mind.
Is the ca18 carb manifold same as on ca20? Also is it from a ca18i?

[ska69]

Twm is pricey :-/
As for the rb26 itb's, thank you for the offer, but that's too much for me right now, yet I'll keep it in mind.
Is the ca18 carb manifold same as on ca20? Also is it from a ca18i?

[themadscientist]

No, it's an aftermarket manifold for sidedraft carbs.

[ska69]

oh, ok

[float_6969]

I bought a couple of GSXR ITB's to play with. to me, it looks like the easiest solution will be to modify the lower manifold to accept ITB's. The ITB's I have can be separated, so changing the spacing to match the spacing on the head will be easy. After looking at all of it, I really think the hard part will be the plenum.

[ska69]

cool! which ones? GSXR 1000 or 750 and what year? Looks like the later versions have dual butterflies. can all 4 throttles be separated or only by 2?

about the plenum, I was thinking this http://rossmachineracing.com/halfround.html :



from Ross Machine Racing and these http://rossmachineracing.com/runnertubing.html tube which are used for runners. they have 1.75" OD version which can be fitted to the GSXR 45mm(?) throttles.

what does everybody think?

[themadscientist]

Ross is a good company to deal with. I got some fuel rail stock from
Them.

[ska69]

nice to hear that they have good feedback. I like how they have all the required parts for the manifold - runners, end caps. etc.

[float_6969]

I got both actually, LOL. I accidentally got the set with the dual butterflies (I think those are the 750's), so I bought another set that didn't have them. I don't remember the year. I actually did a bunch of google searches for ITB setups on Honda's. It's a popular mod with them, so I followed their lead.

[ska69]

Can the ecu controlled butterflies be removed, what do you think?
As for me, I'll try the honda cbr600rr 2006-2010 itb's as they are single butterflied 40mm units, and are cheap! Lol don't see no point in overpaying almost 100 bucks for extra 4-5mm. please correct me if I'm wrong on this.

[float_6969]

Yea, they can be removed. It's actually a common mod for the GSXR crowd.

I wouldn't go with a 40mm. That's actually a smaller opening than the size of the runners going down to the sub-manifold. I traced the head port, and the upper manifold port out onto a piece of engineering paper once and counted up the area. The area of the port going into the head (on a 4 port head) is 1610mm2, and the area of the end of the upper manifold that connects to the lower manifold is 1496mm2. These 2 figures work out to have the same area as a circle with a diameter of 45.3mm and 43.6mm respectively.

[ska69]

that sounds promising might try them in that case.

is .5mm such a big difference in output results? I mean If I stick with a mild turbo, stock exhaust (yeah, 'cuz in great condition) and stock airbox, what 0.5mmm difference gonna make? I just don't get it

[ska69]

so my other option is 06 and later cbr1000rr itb's which are 44mm...and cost a few bucks more.

[float_6969]

Your .5mm x4, which adds up. The stock setup, according to the UK guys, becomes a limitation around the 350whp mark. So sizing anything down even smaller isn't going to help. It might be offest by the better plenum design, but I guess I'm of the, "do it right the first time, or don't do it at all" school of though.

[ska69]

that cleared it up, thanks! so cbr1000rr itb's it is. + I may be getting an sr20det s15 turbo in addition to itb's

[float_6969]

That's a great turbo! You'll be happy with it.

[ska69]

Thanks! ^:) you referring the gt28r or some later versions?

[float_6969]

the gt28. I ran it with the stock manifold and a mid-mount intercooler (no a/c condenser, so it was mounted in the core support, made for very little intercooler piping). It was a VERY responsive setup. I changed to an equal length manifold later and hated it. The loss in bottom end wasn't worth the small gain in top end. In hind-sight I'd have had the stock manifold extrude honed. It would have made for an awesome 275-300whp setup.