Andy, yep, the ITBs should be on teh way today. It was only a $35 investment. No big loss if this whole thing doesn't work. I went with the 600 size. it chokes down to 38mm which still may be a bit big for my 3.2 project. I could always make it to fit a weber choke from below.

The trottle bodies just unscrew. Its like removing the throttle plates from a set of webers. a few set screws on a short throttle shaft and you are done. I just plan on removing on TB, then shortening/lengthening the housings to get the correct spacing. I think you and I have the same idea for manifolds and linkage.

Mount a TPS on the other end, O2 sensor and map away.

oh, I see. so you don't have to worry too much about the spacing, then. I was about to object that the 600s might be spaced closer together but maybe it won't matter to you. perhaps you could measure the spacing before you cut them apart just in case.

I will have full specs before doing any mods. I think a tech article is in the makings.

The honda board thread that I posted a link to has a description of pulling them apart. Its on pg 16 or so. all four are separte bodies. The throttle connecting shafts hold them together. They can easily be fit to whichever spacing you need. Very cool!

Here is a guy on the Alfa board who also used the GSXR throttle bodies. The rubber mounts have the same bolt pattern as Webers so you can mount the TB's in the proper orientation.

http://www.alfabb.com/bb/forums/showthread.php?t=1561

Thanks for the link Mike. It was good to see how they mounted to a weber manifold. There was also a good link to a DIY wide band O2 sensor on the last page.

I really need to find time to read the Megasquirt board.

Did you guys see the other "profiles" of the home-made turbos on this site listed above? http://www.homemadeturbo.com

Most of these tools blew their motors! No BOV, no idea how much boost they were running, broken wastegate, etc. Each of them did things like this: (edited profanity out)

Tools!

DAve, That's a pretty funny excerpt. I will go read more. its one of those days. I need a laugh.

We all know there is a good way... and a bad way to do things. The educated way is always the best.

Andy, I measured an extra weber 40IDA manifold. The carb body openings are 94mm on center.

Is there enough material and length to the pipes under the throttle plates so these things could be bored to hold webber choke tubes?

This looks like a good alternative.

David Duffield

I don't think there is enough length. They can probably be added in some custom fab when you integrate the stacks and/or manifold. Of course, I won't know for sure until I have them in my hand.

Thanks for measuring the manifold, Jamie. I'm working through the alfa thread, and also the honda thread. Both are very interesting and informative, too bad the honda thread has so much drivel in it as well. I have great respect for honda engineering, but while some honda enthusiasts are knowledgeable and articulate, many are not. I'm just glad we have such a great collection of people here on this board.

Also Jamie, I plan to buy this book:

Four-Stroke Performance Tuning
by A. Graham Bell
ISBN: 1859604358

which 125shifter recommended in my "injector mounting outside the box" thread.

I have a few other engine books but this one seems to be a nice balance between theory and practice, where most of mine are on one side or the other.

You are absolutely right about the drivel in some of those threads. I have to laugh at some. At least there were no computers when I was going through school. I could have learned short hand for text messaging instead of all the really cool things that make owning and wrenching on cars a lot of fun. I digress...

Let me know what you find in the books. I am interested to know what good placement for injectors and butterflys would be. Brian had some interesting info in the engine forum. This would affect a final design for the ITBs. I was thinking that a long butterfly distance with a short injector distance might be the best.

I asked the seller of my manifolds if he had two sets. He did and combined shipping. I spent about $60 for both manifolds shipped. They went out fedex ground yesterday. I should have them beginning of next week. More info to come...

here are some sizes from the honda thread, information may not be accurate but it was at least taken from posters with respectable english, not posts like this "can you wgive me asite addr plz?":

Suzuki:
Hayabusa 45mm
GSXR 1000 42mm
98/99/2000 GSXR 750 42mm
later GSXR 750 40mm
GSXR 600 38mm (I think, not sure on years)

Note that the honda motorcycle throttle bodies I've seen are in paired castings rather than individuals, so probably are not usable in groups of 3, at least not without major surgery. The suzuki ones are really perfect.

Jamie, I think you might want to think about skipping the weber manfiold and mounting the throttle bodies directly over the intake ports, and also trying to run as tall of a stack as you can in the 911 engine compartment, then fine tuning to where you want to make power. If you haven't read this article on intake runners, you should!:

http://www.hotrod.com/projectbuild/113_9907_efi/index.html

Here is an interesting calculator done by the megasquirt guys, but I am sure there are some assumptions built in, you will understand what I mean after you read the hot rod article:

http://www.bgsoflex.com/intakeln.html

OOPS: just realized you posted these in the injector thread:

http://forums.pelicanparts.com/911-engine-rebuilding-forum/179179-optimal-injector-throttle-plate-placment-post1481719.html#post1481719

anyway future searchers can find them here as well.

Andy, you and I must have been doing the same things this morning. yes, I already posted my theory on the engine site and did not want to cross post. I guess these two threads could be combined into one but some of the information may get lost.

There was also a link to an Excel spreadsheet that has a full Helmoltz Resonator theory calcs. I just clicked and saved. I am in the process of backing out the equations from it. I will post some results for those who like numbers.

One other point is that 98-99 GSXR 750 throttles don't have the second throttle plate that I guess some of the others do. However, the second plate can be stripped out and the shaft holes plugged.

http://www.alfabb.com/bb/forums/atta...tid=2669&stc=1

there is some speculation however that the injector is supposed to spray against the second plate in certain circumstances. I'll be interested to see if your 600 plates have this or not.

On a related note, with EFI ITBs, it seems that you would want your throttle bodies to be no smaller than your intake port at the bottom. Then whatever manifold you have between the throttle and the head should transition between those two sizes. based on the specs of your 3.2 project that you posted in the other thread, I would be surprised if you wanted ports smaller than 38mm.

here is the image

http://forums.pelicanparts.com/uploa...1093539275.jpg

I will likely have to open up the heads a bit. Now they have 39mm ports (published figs for 78SC), My information in the TB says there is a 46mm throttle plate necking down to a 38mm body. Looking at the picture I can see this. I just don't know which is primary and secondary throttle plate. I will once I get them in my hands.

From the calculations in BAs bood the choke on webers should be about 35mm for a 3.2. I assumed that the 38mm TBs would then be close and flow well at high rpms. I was acutally thinking about a way to close them down to help with low speed drivability.

I still have lots of learning and planning to do before the engine teardown. right now I am just trying proof of concept stuff for later. At least the buy-in price for experiments is cheap enough. Heck, I wasted lots more money than this trying one-off experiments in grad school.

The 600 specs will likely be too big for my current stock config test mule. I would like to compare the webers currently and the EFI on a dyno before starting to mod internals.

Here is another thought to ponder while doing this. Could the bungs be tapped for MFI injectors? I know this would not be as tunable but power output would be fantastic, and don't forget that fantastic throttle response. this method would bypass the expense of having custom bored TBs. You will still have to pay for a custom space cam.

Nice photo - somebody should calculate the detriment of having the screw heads stick up into the airstream. Maybe they are low enough not to matter... maybe not.

I don't think you should really compare directly the weber venturi size to an FI manifold. In particular, people try to use 38mm MFI stacks on slightly bigger engines, just because that's the biggest they can bore out the mag stacks. Henry Schmidt makes custom MFI stacks for bigger engines, he would know what a good size would be for a given app.

The primary throttles are the ones higher up. But keep in mind the photo is of GSXR 1000 bodies: 42mm at bottom

Also, the honda guys are running 42s on 400cc cylinders. Sure, their VE is quite good, but I wouldn't worry about 38s being too big for a SS 3.2 with hot cams.