Could someon please explain ITB's?

[Steve@Rennsport]

More ITB's:

[rsscotty]

And more.............................

[James Brown]

i don't think were talking the uber end of the engine scale, can it be done buy the DIYer, i think so but at what cost? the manifold on top of the itb's is just a fancy air cleaner, so to speak. Would velocity stacks work better?

[Canada Kev]

That manifold on top is not just a fancy air cleaner. It's actually a resonance chamber (looks like a 996?) that will increase mid range torque while maintaining the higher RPM power. This combined with the throttle response of the ITBs, and you have the best of both worlds.

However, the velocity stacks DO look cool...

[Tippy]

I think a better way to describe is ITB's don't have a plenum after the throttle butterflies, rather sometimes before as posted above. Huge difference..

[Jim2]

Originally Posted by procan

So, I am planning to do a 3.2 swap on my '69 912 (which currently has a 2.0L '69 911E in it). Originally I thought I wanted to go with PMO carbs on the 3.2, but now having looked at ITB's with EFI, I am reconsidering my options. I thought putting carbs on the 3.2 would be much easier considering I have potential access to a 3.2 motor sans motronic and all its fuel injection components.

I like the old school vibe of carbs because they are in line with the old school vibe of my car, but ITB's with EFI are tempting. Can you do ITB's with carbs at all?

Thoughts?

Back on track...


Thoughts you ask? well...

I personally don't think ITBs/efi are appropriate for a stock(ish) 3.2 unless you are wanting them for the sake of the project. If your 69 is a street car and you have expectations of good drivability then a pair of carbs will achieve those results relatively simply, jetting aside perhaps. Top end power (attribute of ITBs) can be had with larger chokes in the carbs but then you are likely to develop drivability flat spots and less bottom end. If you were planning a hot motor build, then itbs/efi might be something to consider.

My .02

[Bob Kontak]

Originally Posted by Bob Kontak

I may be speaking out of school but I believe ITB's require an engine management system and or EFI where carbs do not.

Originally Posted by Bill Verburg

3 barrel Webers or PMO's are ITBs

"Thanks the God" (as my Hungarian MIL says) that I qualified my statement.

[RWebb]

the fly in the ointment is that many use the term itb's to refer to a FI system only -- tho it is not technically correct


re which, let your camshaft be your guide ... which is Jimminy Cricket's exact advice

[JohnJL]

How is Idle Air Control achived on fuel-injected ITBs? I'm familiar and have used IAC stepper valves to 'leak' air past the throttle body as controlled by an ECU. I've seen reference to IAC on ITBs (most recently on the Triumph project) but I havent seen more detailed informaiton. Is there a single stepper that bypasses the throttles? Or is it just done like with Webers with an idle screw?

[TimT]

How is Idle Air Control achived on fuel-injected ITBs?

Yes just like air by-pass screws on Webers...

In cases where the bypass screws don't offer enough air....

There are some tricks..

open the throttles a bit and then calibrate that as zero.... and use the bypass screws for fine tuning...

Or drill a hole in each butterfly so a bit more airs passes when the throttles are closed

Depending on which software you are using there a number of ways to achieve idle and transition nirvana

[Raceboy]

Budget ITB's for 993. These are Hayabusa throttles with Pipercross air cleaners and custom made backplates (made a CAD drawing + watercut from aluminium sheet).

[JohnJL]

TimT,

Thanks, that still seems rather crude...I've tuned my webers that way and they are spot-on perfect starts and idle at the right temp, but hot or cold of that always requires some throttlework. I'd like to get the new car set up so it starts like an OEM new car.

Has anyone used an IAC with ITBs? I am envisioning a vacuum hose from a tap on each ITB below the butterfly leading to an commmon manifold. That manifold would be 'bled' air by the IAC which gets its own little air filter. Since all the ECUs I'm considering to drive injection can handle IAC then it seems to make sense to take advantage of that.

Raceboy, that's great information, thanks for sharing. A few questions if I could?

1. How did you choose the Hayabusa units? I have been lazily looking around and considering which donor ITBs might be good candidates. First consideration was airflow...if my target is to get 275 hp from my 3.0 (I already get 260 with another induction so reasonable) than I need enough air and fuel to flow 52hp per cylinder. The hayabusa's inline 4 makes 162hp, or about 40hp per cylinder. Each Hayabusa ITB services ~ 300cc whereas each of my ITBs will need to service a cylinder of 500cc. I know this is only one datapoint, and in fact I couldnt find any bikes which seemed to meet similar flow and hp. Was that a concern? What's the venturi diameter of the Hayabusa's ITBs?

2. Second consideration is mounting to the heads. Did you luck out with the hayabusa mounts matching the 993 heads, or did you need to fabricate or source an adapter?

3. Linkages...are those the stock linkages or did you build some from parts? Do you have some photos of how you linked the left and right linkages together?

Thanks!

[Geneman]

HELLO GENTS.. I AM CONSIDERING THIS SETUP FROM THE DZUG BOYS FOR MY WINTER ENGINE OUT PROJECT 3.2 UPGRADE ... PROBABLY INCLUDING RACING CAMS , CRANKFIRE ETC.. BUT MINE IS A TRACK RAT ONLY ....

DZ X-Factory ITB Setup

THERE IS A GOOD THREAD SOMEWHERE ON PELICAN ON THE DZUG SETUP CANNOT FIND IT JUST NOW.....THERE IS GUY NAMESD IKSOMAL OR SOMETHING LIKE THAT WHO SEEMS TO BE THE CHIEF MOJO HERE ON THESE SETUPS....

I THINK CLEWETT ENGINEERING HAS A SIMILAR SETUP..

JUSY MY 2CENTS GOOD LUCK FRANK

[JohnJL]

Oooohhh, how did I miss the DZug kit? I hadnt even heard this was out, but its very interesting. I've made and run a megasquirt unit before too...I see mention in the kit there is a CAI manifold and connections, so I'd like to hear more about that too.

[Raceboy]

John,

Hayabusa units are spot-on regarding size, they are tapering down and lower part matches perfectly with the 993/964 injector mount/intake flange boot.
It's not as much about the displacement but more about air flow as Hayabusa engine revs 2 times higher than regular 911 engine. Hayabusas can make 230+ hp normally aspirated with some tinkering easily. Also 'busa engine made 173 crank hp (162 was measured at the wheel).

Regarding linkages, I just extended the tabs and that retains the possibility to adjust the throttles individually with stock screws.

Originally Posted by JohnJL

Raceboy, that's great information, thanks for sharing. A few questions if I could?

1. How did you choose the Hayabusa units? I have been lazily looking around and considering which donor ITBs might be good candidates. First consideration was airflow...if my target is to get 275 hp from my 3.0 (I already get 260 with another induction so reasonable) than I need enough air and fuel to flow 52hp per cylinder. The hayabusa's inline 4 makes 162hp, or about 40hp per cylinder. Each Hayabusa ITB services ~ 300cc whereas each of my ITBs will need to service a cylinder of 500cc. I know this is only one datapoint, and in fact I couldnt find any bikes which seemed to meet similar flow and hp. Was that a concern? What's the venturi diameter of the Hayabusa's ITBs?

2. Second consideration is mounting to the heads. Did you luck out with the hayabusa mounts matching the 993 heads, or did you need to fabricate or source an adapter?

3. Linkages...are those the stock linkages or did you build some from parts? Do you have some photos of how you linked the left and right linkages together?

Thanks!

[sc_rufctr]

Originally Posted by Raceboy

Budget ITB's for 993. These are Hayabusa throttles with Pipercross air cleaners and custom made backplates (made a CAD drawing + watercut from aluminium sheet).

Cool stuff.

[JohnJL]

Originally Posted by Raceboy

John,

Hayabusa units are spot-on regarding size, they are tapering down and lower part matches perfectly with the 993/964 injector mount/intake flange boot.
It's not as much about the displacement but more about air flow as Hayabusa engine revs 2 times higher than regular 911 engine. Hayabusas can make 230+ hp normally aspirated with some tinkering easily. Also 'busa engine made 173 crank hp (162 was measured at the wheel).

Regarding linkages, I just extended the tabs and that retains the possibility to adjust the throttles individually with stock screws.

Thanks! Just so I'm clear, the hayabusa ITB has the same bolt pattern as the studs on a 993/964 head? So I guess for me one known challenge would be to adapt the 993/964 pattern to my '73 big port intakes with the 2-bolt pattern.

Any pics of an individual ITB before assembly? Did you fit a TPS on the linkage at one side?

[Jim2]

John, the bottom portion of his runner is from a 964/993. The end of the bike TB is likely round. Here is what the 964 runner looks like:

[Raceboy]

Thanks Jim for the explanation

Hayabusa throttles already have TPS on them. I have two of the throttles left (I bought two 4cyl sets of them), I can take a photos of it.

For early 2bolt intake the best route is to have the intake flange watercut from 10mm aluminium and then weld short (20-30mm long) runners to them and connect the ITB's to those with silicone hoses. Hayabusa throttles already have fuel injector mounts and one would just have to either make a custom fuel rails out of extrusion (preferred) or use a fuel rail from 3.2 or similar but those tend to be expensive and mounting can be tricky.

[sundevil64]

Originally Posted by equality72521

Anyone done ITB's on an inter-cooled turbo with EFI?

Talk to Chris at TurboKraft.

He is extremely knowledgable and his product are well thought out without beig over thought.