custom individual throttle bodies? fab your own
 

I was looking for potential individual throttle bodies for a future motor build which will likely be a hot 3.2SS. One of the goals of this project is to investgate various EFI systems. In order to take advantage of hot cams and other typical Hp goodies I need individual intake runners. This leaves all but a few usual choices for fuel mixing...

In my search I came across some information from a honda tuning board.

http://www.homemadeturbo.com/tech_projects/itb/index.html
http://honda-tech.com/zerothread?id=775280&page=1

The listing of this project uses a Suzuki GSXR throttle body mounted to the stock Honda intake manifold. I think something similar could easily be done and the sizes are just about right.

The GSXR 700,1000 ITB have 48mm butterflys and 42mm port size. the GSXR 600 has a 44mm butterfly and 38mm ports. This could be configured easily to whichever size engine you were bulding, except for a 3.6+.

They come with 4 lined together. Two sets for 4 could be separated, shortened to 3, correctly spaced and setup for a weber/pmo manifold using a custom adaptor plate. minimal fabrication would be required.

Here's the best part. other than fab time the parts could be found for under $300. This is an order of magnitude cheaper than the other choices of TWM, etc. Of course, one would still have to find the right injectors, etc.

Since custom runners would be made, you could calculate optimum butterfly and injector distances from the intake valve. This could give you optimum flow and atomization with minimal effort.

What do you think? I am interested in some opinions from those who know more than I.

Jamie....I've been noodling that too. I've got a more low tech, low cost solution in the secret Gruppe B lab...just can't find time to finish it :(

Very interesting, Jaime.

Souk, don't hold back on us.... let's hear about it!

now the real question is, what is the measurement between the bore centers of a set of weber IDAs?

I'll measure the carbs tonight.

I hope the US military doesn't bomb the secret Gruppe B lab. .....

Seriously, keep us posted on this. It's interesting -- esp. the under $300 part.

The secret GruppeB lab....even I forgot where it is :D

And my low tech solution will not be as low cost as $300, but it will be a good alternative to some more costly induction ...that's all I'm saying...otherwise I'll be erased.

me likey low costy

Me to. Cant find a way to make it happen though.

No matter how I try to piece an EFI system together in my head I wind up with a list of parts totalling $3k-$5k.

Cool, thanks Jamie.

Are you thinking MegaSquirt? that should help a bit.

Custom ITB's for under $300 would go a LONG way towards making hotroding the CIS cars and even *gasp* the MFI cars too. I'm going to be really interested in this to see how it progresses.

Don't worry Tim, I will post some results of my experiment. Now I need to find the injection system to go with the ITBs.

I was thinking I could use some CIS runners with injector bungs. Cut them off above the bungs and weld an aluminum spacer between the runner and the TB. Should be a simple fab. I don't know about linkage though. That might take a bit of thinking. All the geometry is slowly coming back when you have to think about arc lengths through bell cranks... End result must be 90^o butterfly travel for WOT!!

Here is a drawing of the linkage for DTA throttle bodies. Hopefully it can be used as a reference.

http://forums.pelicanparts.com/uploa...1093358902.gif

HMM cable actuated. I assume there is a splitter for the cable somwhere to reach L and R bank. I like that design. I wonder how linear that cable run is.

Funny how my ideas just seem to gather information and get more complicated than originally planned.

Jamie, did you get a chance to measure the center-to-center on the carbs?

Sorry, I didn't I will go home at lunch and check. Last night I got too busy with suspension setup.

DO the CIS runners have enough of straight section above the injector bung to braze or adhear in some fashion to the throttle body?
Also alot of the cable system should be pre done if you're using preexisting throttle bodies, shouldn't they?

no worries. I'm just trying to figure out how similar the "bore spacing" is between IDAs and the GSXR750/1000 ITBs. The guy that put them on the honda said "I think it was about 80mm" on the 'Zuki throttles.

On a related note, I looked at some of the honda throttles on ebay. Most of them look less desirable because the have the injectors mounted in a "shower" configuration above the throttle plate. The problem is that the injector mounting frame seems to be bolted to the airbox, and the airbox is not the right shape for our application.

CIS runners have enough space to weld a section of Al pipe to extend the TBs. Most applications I have seen (links above) use an extension. This may only be to obtain clearance in the engine bay. The runners already have an injector bung in place.

I just had a followup post on the engine board about dimension placements.

The 911 throttle linkage is all rods and cranks. no cables involved. I just bought a single set of GSXR TBs (group of 4) as a trial part. Once they are in my hands I can comment on hooking up the linkage. If they are mounted to weber manifolds and use the stock GEXR injector ports the linkage issue may be solved. I could likely just hook up like a weber carb using a new throttle end cap arm and the existing linkage.

Cool you already bought a set of GSXRs!

I was thinking along the same lines: weber manifolds, stock GSXR injection ports (position is good IMO), and modified weber linkage. Even if people don't have them to start with, the weber linkage and manifolds aren't that expensive. it's the throttle bodies that are the killer, as you know.

It looks like there are 4 short throttle shafts so cutting one body off might not be very difficult (fingers crossed)

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.