just a data point...

the people at TWM Induction recomend 44's for 2.7L and 46's for 3.0L

I have no technical data to back up the validity of this information, but they guys at TWM seem to be the biggest players in the ITB game.

That's interesting data, Alan. However, this type of recommendation should really be based on the nature of the engine (cams, port sizes, exhaust, etc, etc.), and in particular whether it is a race or street engine.

maybe one of the engineers here could post the formula for velocity. I will dig up some books tonight to get some guidelines. I picked up acouple of sets when Jamie did. Since the 3.3 has 32mm ports, porting them to match 38s seems like the right thing to do. For a turbo, you want the velocity to reach a certain # much earlier in the rpm range. Then let the turbo pack it in. I will post the formula tomorrow if nobody else does.

Jamie, keep up the good work!

Seems to me that most indicators point to using a bigger ITB than 40mm on a 3.2. Even if you use the weber analogy, opinion is divided on whether 40s or 46s are best for a 3.2 - certainly on a more highly tuned 3.2 you would opt for 46s.

Fascinated to see how this project turns out :)

Richard

Wow, what great dialogue. It seems I missed a bunch yesterday. Amazing that you miss when you stay home sick and sleep off a cold all day.

Everyone here has valid points. I am not an engine builder or engineer so all this is very helpful. I agree that these may end up being too small for my 3.2. Right now, I plan to get them working on my internal stock 3.0 to set the proof of concept.

Richard, I think that a truly track engine will require larger intakes for the fuel system. Its no surprise to me that your mechanic specs bigger TBs on his race engines. I assume these engines have lots of port work too.



John, You bring up some valid points. Sounds like the Cone shape will be best and that having the TB close to the head as the limiting point on the diameter may end up in my design. It might make fabrication easier too. btw, I tried to find your old posts with the spread sheets for calculating HP from intake speed and volume. I have had no luck. Can you email me those formulas?

Aaron, The intake velocity will be:

v = volumetric flow(cm^3/min)/cross sectional area of flow(cm^2)

Yesterday, I thought about fabrication. There will be less work to space the TBs and connect them in sequence. The linkage will be easier to setup if I mount these to the weber manifolds. The downside is that I will have to make mounts to hook up with the ball/socket arrangement. A cable operated setup may be better and easier to attach with the current config on the TBs.

Mounting them directly to the heads will be more difficult, especially since I no longer have access to a mill or lathe after changing jobs a few months ago.

This is great fun. Keep up the suggestions. Everything is being considered.

Jamie, I think you should definitely use the 38mm TBs for your proof cf concept on your internally stock 3.0. You'll learn a lot about how you want to make these work, and whether you want characteristics found in suzuki throttle bodies other than the ones you have.

I'm still not convinced that the 38mm bodies are a terrible choice for this street engine. Anyway figuring out how to use these is the hard part, not selecting the diameter. In particular, you did well by spending just a little for your proof of concept. it seems that the suzuki throttle body "architecture" is pretty consistent, so you should be able to apply your experience to another set if necessary..

I can't visualize how the linkage will hook up. maybe you can draw a diagram or take some photos as you get closer to setting that up. It would be cool to hook directly to the heads, but getting this set up in some way is the most important part. Did you get the rubber boots with the TBs? They appeared to hook right up to the alfa ports, which don't look too different than porsche ports.

Get well soon, Jamie!

The required size is pretty much about the amount of HP needed, so using the HP per cylinder of the bike as a guide should let you know if it will be suitable for your monster 911 project!

I will try and get some pics of potential linkage mounts this weekend. I need to measure the throttle shafts and see if they are the same as the webers. That would make finding linkage parts easy - especially if they are the same size as the VW versions.

From "Maximum Boost" by Corky Bell

"For race applications where one throttle plate per runner is employed, it is quite adequate to sum the throttle plate areas and calculate accordingly, or simply to use one cylinder and one throttle. The 300ft/sec figure should still offer a suitable guideline."

"Simply making the throttle bigger will alleviate the problem, but low speed driveability can become an on off, jumpy proposition. A big throttle plate open a small amountcan let in a lot of air, and smooth low-speed throttle respnse will suffer. A maximum air velocity of approximately 300 ft/sec will keep flow losses acceptable."


I don't know if 300 ft/sec works for n/a engine, but I thought I would post.

40mm ports at 6Krpm is about 65 ft/s. Should be within the limit of a boosted engine. What does the target of 300ft/s give you? throttle response? cylinder packing/filling efficiency? air column momentum? Just looking for more context.

Funny you bring up the large TB opening and letting a small amount of air in. I chased a high idle problem when I first started up the 3.0. Turns out that two plates were out of adjustment and not closing. they only let a sliver of light through on one bank and it was enough to drive the engine at 3K rpm. This example just shows that it doesn't take much air to get things going.

Jamie

My guess is for throttle response. He doesn't get specific as to his findings. I'll look around for books on intake design. That should hold more info.

What is the dia of you original throttle? That should be a good starting point.

I am currently running weber 40IDAs. So 40mm is the trottle body. This size should also be good for a 3.2 unless its a full race application. the 38mm throttle plates should not give up too much for this first shot at building them.

Jamie;
For street use, I agree that 38 mm TB's should fine for a 3.0. As far a HP/port size formula, I'm not aware of one -- although some would disagree. I've rarely found a non-CIS's 911 (carb'd, MFI'd) that generated peak HP much above 100 m/s (about 300 f/s). I've come to the conclusion that peak torque gas speed is more important. In the case of non-CIS'd 911 it tends to occur at around 80 m/s. If the speed is much below 60 m/s you start to lose low end performance. Above 80 m/s it seems that torque tends to trend downward (off set by the increase in rev's) until the peak HP engine speed.

Where you put the butteflies and the injectors also makes a difference. In general, the further upstream that you place the injectors, the better the performance at peak rev's. If you put the injectors down close to the head, the engine runs better at low revs.

I don't have any definitive conclusions on where you put the butterflies except that I believe that the total volume of air downstream of the butterflies will have some sort of affect on idle quality. But if they are no closer or further then the standard MFI butterflies, it shouldn't be an issue.

Now if someone like a Steve Weiner weighs in here, I'd take his $0.02 over mine. I'm not of any observations that agree with Corky's conclusions. I don't think that it's a safe assumption that a common intake of 6x is the same as 6 separate intakes of x diameter or area. Look at the performance the smaller Le Mans Prototypes who have a fairly small single intake restricter of about 32-35 mm's.

Check out these two threads for some explanation of what I'm trying to describe. Here are the rest of the videos. They may start to give you something of an idea of the way that intake designs work.

I've run across some info on the GSXR 750 TB's for anyone that is interested. I am looking for similar info on the 600's

There was a change in configuration from '99 to '00. Something to check on when buying two sets of TB's. It may be a good idea to buy from the same model year or confirm that the design is the same between years.

http://forums.pelicanparts.com/uploa...1094239725.jpg

http://forums.pelicanparts.com/uploa...1094239831.jpg

Thanks Mike, I know there are many changes year to year on these systems. What I measured was different than the info I found on the web. I guess a factory manual would be the only way to find correct info, unless you happen to know a good Suzuki tech/engineer.

John, That information about intake speed vs Hp/torque was what I referred to previously. I guess I was searching for the wrong topics. Now I can go back and reread the previous threads.

Jamie, the main throttles are in the wider part of the cone, right?

John, That 911R inspired thread was very interesting, thank you for your research. I will probably ressurect that thread once I get some time to think about it.

Best Regards,

No, the primary plate is in the narrow section, at the bottom. The secondary plates, which I have not figured out yet, are in the wide section. Interestingly, the secondary plates have a diameter that is about 4mm smaller than the body at that point, 2mm/side.

That's odd. it seems like the injector would spray against the throttle plate at WOT, from the picture I posted in the other thread. it might be important to use injectors with a similar spray pattern if you replace the suzuki ones. You ought to have more HP/cyl than the suzuki even with a stock 3.0, but sometimes there's lots of margin.

here's the picture I was thinking of. It's a 1000 throttle body (of some year, not sure which year), maybe Jamie could note if there's any significant difference versus his.'

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

I believe the secondaries are computer contolled . There is a vacuum sensor also.Now here is the leap I made, the throttle bodies are oversized to take advantage of high rpm performance. The computer monitors vac and other sensors and modulates the secondaries to keep velocity at the lower rpm range. Sorta like varioram....are you buying it? 38mm throttle bodies are pretty big for a 600cc engine.