Project ITBs: Part 1-parts arrive

[jpnovak]

Some of you already read the thread about building some individual throttle bodies. Here is the link to the first idea thread

custom individual throttle bodies? fab your own

Today the parts were waiting when I got home. Here are a few sizes and pictures of the tear down.

Here is the entire assembly as received. This is a 2001 Suzuki GSXR 600 throttle body setup. I bought it from a motorcycle parts dealer on ebay for $20. You can see that it comes with four individual throttle bodies bolted together in a complete setup.


the first thing to do is strip the vacuum lines, electrical connectors and fuel rail. There are two #2 phillips screws that secure the fuel rail. These were tight but the injectors just pulled out after removal.

Next we look at the parts that are usable. This system as two internal butterflys. One set is hooked up to an electronic actuator (silver plates). I assume this is part of a choke system for low speed response. To remove lock the 17mm nut and spin off the 10mm nut shown to the right of the photo. next remove all of the small screws that secure the throttle valves. These slide out of the trottle shaft.



Next its time to split the TBs. on the end plate there are two really long allen cap screws that tie all of the throttle bodies into one unit. These simply unscrew and the trottle bodies will fall apart. The throttle shaft you disassembled above will then slip out. Careful to catch the bushings and springs that set the clearance and adjustment.



You are now left with 4 throttle bodies like this. There is one end unit that contains a TPS and the actuator for the secondary butterflies. I doubt I will use this and focus on the other three.



How do they measure up? This setup has 41mm upper openings(45mm OD) which will make them comparable to the 40IDAs that I currently have on my 3.0. I will be building a 3.2SS so this size is comparable. The TBs neck down to 38mm throttle plates and this size continues to the bottom side(44mm OD) where I will adapt to my heads. I really think this will be a fantastic match for this engine. Andy, I think you will agree here. The overall height is 83mm.



Next, I will start to think of how to adapt these to fit on a 911 motor and also design a linkage. I think I am going to fab up simple plates that will bolt to the heads. I will use a PMO CIS to weber insulating plate as my template. To this will be welded a section of aluminum pipe (near 40mmID). Once I decide on the total length of the system the TBs will be added to the top.

I would like to use the stock injector ports on these TBs. I don't know if there are injectors that fit. There is a 21mm diameter with 14mm hole on the step. Can anyone help ID some injectors?

There will be more progress soon but don't look for daily updates. I am trying to finish my ST for its DE debut in 3 weeks.

Jamie

[tsuter]

GSXR600 is basically a debored GSXR750. The injectors are Mikuni.. widely available. I'd guess you'll need more fuel though. 4 into 600 vs 6 into 3200.
Well at least your RPMs will be lower. Good luck.

[KobaltBlau]

Very cool! Yes Jamie, with stock ports I think those are a good match, especially for a street car. $20 seems like a cheaper than usual price for these, nice work.

what's the center-to-center measurement on these before you take them apart?

[jpnovak]

OOPs I had that measurement written on my diagram but forgot to post.

the stock ITBs come with 80mm on center spacing.

I will have to widen them a bit to get them to fit the 911 head spacing. Even less if I use a weber manifold or make my own. One main issue is how to connect the butterflies between adjacent TBs. They use their own internal spring setup. There is a setscrew on one side and an L bracket on the other. They are arranged so that the set screw seats on the L bracket. The setscrew is spring loaded and serves the purpose of syncoronzing the TBs, sorta like the majic 140mm number for MFI but much simpler.

[KobaltBlau]

Hi Jamie,

Thanks for that on center measurement. In the alfa or honda thread I think someone said that some of the suzuki bodies have 90mm on center spacing, as well. I don't know which ones. With the construction they have it shouldn't be too big of an issue either way.

I remember that one of the guys just lengthened the L brackets when he spaced them out by welding some stock on. I think he showed pictures, they came out nice.

I would encourage you to investigate using a carrera 3.2 fuel rail unless you already have that figured out. It should certainly have the correct spacing and if you can fit some injectors to the 'zuki TBs and to the Carrera 3.2 fuel rail it would show you exactly how to space them. This is, as you probably saw, what some of the honda guys did with things like a prelude fuel rail. It's possible, though, that there aren't injectors that fit the carrera fuel rail on one end and the 'zuki ITBs on the other, but I bet there are.

I also want to clarify my statement above regarding a good match with "stock ports". I was referring to stock early SC 39mm intake ports. We discussed this more in Jamie's initial suzuki ITB thread.

and I want to know if you're going to that chile festival!

[Randy Webb]

$20 !! These are exciting threads -- and I already paid $3,000 for PMO's...

[911-32]

I am no expert, but my mechanic is. When I was recently looking at some third hand ITBs, we talked about sizing. His comment to me was that when you have fuel and ignition controlled by an engine management system (ie., Motec, DTA etc) you don't have to worry about air velocity like you do with carbs. So while a 40mm Weber/PMO may be correct for you engine, 40mm ITBs while workable are too small. Perhaps less than ideal is a better way of describing it. On the engines he is building, he is using 46mm ITBs on 3.2s and 52mm ITBs on 3.6/3.8s.

He has built about a dozen ITB engines in the last 4/5 years all for race applications. I guess for street use, YMMV.

Just trying to be helpful...

Richard

[Mike Bonkalski]

The guy on the Alfa board used toyota injectors with the throttle bodies. He didn't mention any additional machine work. I may contact him to see if they were a direct fit.

Custom fuel rails are relatively cheap at $10 - $12 per linear ft. of extruded aluminum. Some of the place I contacted will also machine the injector ports at any spacing requested. Those will run about $85 each.

[KobaltBlau]

I believe the honda guys are using honda injectors with no machine work as well.

Richard, it would be interesting to know what intake port sizes his 3.2s had. Race and street engines are definitely different, as you noted. If anything, a throttle body should be effectively bigger than an equvalent total diameter carb, because you don't have the venturi. Unless I'm missing something. I do think that you still need to worry about port velocity. Please don't think I'm slamming you but the difference between race and street may be the major factor here.

[jhelgesen]

Jamie, we need to get your some clean calipers......

[Tim Walsh]

Andy,
My first impression is that the throttle body should be about the same as the carb body, since the carbs neck down in the venturi area. AKA my 2.4T motor needed ~32mm venturi, but the carb size would be a 40mm and throttle plates on the MFI are 38mm. My first impression is that the throttle plate size should be the same as the carb body sized, and have nothing to do with the venturi size, but I might just be repeating what others have said.

I think when it comes to port velocity, port size is more important than throttle plate size. I'm basing this on the MFI data, where the 2.4T used 29mm ports, but had a 38mm plate size,and the 2.7RS, which used 36mm ports still had 38mm plates.

[911-32]

Originally posted by KobaltBlau
I believe the honda guys are using honda injectors with no machine work as well.

Richard, it would be interesting to know what intake port sizes his 3.2s had. Race and street engines are definitely different, as you noted. If anything, a throttle body should be effectively bigger than an equvalent total diameter carb, because you don't have the venturi. Unless I'm missing something. I do think that you still need to worry about port velocity. Please don't think I'm slamming you but the difference between race and street may be the major factor here.

I am fairly sure they are standard port sizes.

Certainly no slam intended or taken I only contributed because he specifically said that velocity is not really important compared to carbs - which seems to differ from the consensus here.

I have alot of respect for my mechanic - his training and experience are impeccable and the results his clients get are amazing. On the extreme side, he is building 800hp TT engines that last a race season not just a weekend. Among other things, he has built engines for podium finishing Le Mans 24 hour cars. I have every reason to trust him.

Anyway, I was just throwing the comment into the mix for you all to digest and consider. I have no axe to grind.

ciao,
Richard

[KobaltBlau]

Richard, thank you for sharing all that. Your mechanic has more experience than me, that's for sure! That surprises me that the engines had standard 3.2 ports!

Originally posted by Tim Walsh
Andy,
My first impression is that the throttle body should be about the same as the carb body, since the carbs neck down in the venturi area. AKA my 2.4T motor needed ~32mm venturi, but the carb size would be a 40mm and throttle plates on the MFI are 38mm. My first impression is that the throttle plate size should be the same as the carb body sized, and have nothing to do with the venturi size, but I might just be repeating what others have said.

I agree.

Originally posted by Tim Walsh
I think when it comes to port velocity, port size is more important than throttle plate size. I'm basing this on the MFI data, where the 2.4T used 29mm ports, but had a 38mm plate size,and the 2.7RS, which used 36mm ports still had 38mm plates.

true BUT you want to make a smooth transition from the throttle plates to the ports. For this reason 45mm throttles on 39mm ports don't make much sense to me, but the T example you used is even worse. How is this transition made (smoothly?) on a 2.4T?

[Tim Walsh]

Andy,
Right after the throttle plates, the throttle bodies themselves neck down to 29mm from 38 just before the port on the head. The strange thing is interface from the stack to the throttle body itself isn't smooth. If I remember right the bottom of the stack on a T motor is 34mm or so and the opening of the t body is 38mm. Kinda strange but they do this consistantly between all of the stacks and t-bodies across the range.

[jluetjen]

Here's my two cents -- there are two important things to keep in mind...

TB size: If your TB chokes down to 38 mm's at the butterfly, your effective diameter there will be much less then 38 mm's since you will have the shaft running right through the widest part of the TB (ie -- across the diameter). Just guessing, the effective diameter might be down in the 35 or 36 mm area, so these TB's may not be any better then running a 40 mm weber with 36 mm chokes. Weber wasn't stupid - by putting the butterflies downstream from the venturi where the body has a 40 mm ID, they avoided this issue. But as far as peak HP is concerned, your intake is only as good as it's weakest link -- or most restrictive element. On the webers it is the venturi. According to what I understand of your TB's, it will be the butterfly area. From a peak HP perspective, whatever happens upstream and downstream of the restrictions is secondary.

The shape of the intake. Ideally, you want to have something of a cone aspect to the intake. So that the smallest ID is close to the valve. I've posted previously information about the acoustics of closed tubes versus closed cones, and for engines cones appear to have a number of benefits from a tuning perspective. As a general rule of thumb, I've seen something like a 5 degree angle to the cone is enough to get the affects. If you've got your restriction at the beginning of the intake track near the butterflies -- you don't have a cone.

I really like the idea for this project, but I think that you're starting out with TB's which are too small. In order to maintain the relative performance of your engine, you are going to want to use TB's from an engine which shares roughly the same cylinder capacity as your 3.2 -- so about 533 cc's. Figure that your 3.2 at peak RPM (say 6500 RPM) will be drawing about 1.733 million cc's or 1733 liters of air per minute through the TB. The GSXR600 has about a 150 cc cylinder. If it generates peak HP at about 10,000 RPM, you're talking about 750 liters of air per minute through the TB. Using these "back of the envelope" comparisons, it looks like the TB's are going to be pretty tight for your application.

[}{arlequin]

Well, the largest four I can think of is the 1300cc Hayabusa. Don't know the dimensions of the tb's though. Either way, this is one of the more interesting threads, right up there w/ Noah's EFI conversion.

[Tim Walsh]

John, one question for you since your numbers add up and yet at the same time don't.

Does suzuki and porsche assume the same mm of diameter/ liter of air required in fitting their throttle bodies? It seems that the suzuki's are really large compared to the porsche versions. 38mm plates are the same size as a 2.7 with a 7300 rpm redline. that's about 440cc's per cylinder @ 6800rpm, that seems alot closer to 1733liters of air than 750. (I'm pulling all these example numbers from the top of my head)

[jluetjen]

I don't think that it's a question of either company's assumptions. One difference is that I suspect that the Suzuki spec'd considerable overhead into their TB's given a number of reasons.
1) The boundry conditions within the TB make up a larger percentage of the TB's area in a smaller TB then a larger one.
2) As engine speeds go up, pumping resistance apparently becomes a larger issue.
3) Having a relatively smaller TB on an engine will increase velocity and turbulance at lower engine speeds. Given the relatively light weight of a motorcycle, I suspect that pulling off of idle is a smaller issue in a bike then in a car. So the bike engine is most likely designed to have a relatively "peaky" motor since it is less of a handicap then in a car.

I'm not an engine designer, but those are my suspicions of what is going on.

[Mike Bonkalski]

The ITB's on the GSXR 1000 are 41 mm.

I wonder if we can come to some kind of consenus on which would be better to bolt up to the weber manifolds that I have on my 2.7, the 600 or 1000's?

Maybe I'll just try the 1000's and post my results.

[KobaltBlau]

Here are the sizes I collected, might not be accurate but I did my best. GSXR 1000 should be 42mm:

http://forums.pelicanparts.com/porsche-911-technical-forum/179053-custom-individual-throttle-bodies-fab-your-own-post1481866.html?highlight=hayabusa#post1481866