Please Explain F.I. Motors With Individual Throttle Bodies

[jyl]

I see some 911 race engines where each cylinder has its own individual throttle body, with a trumpet-like intake and a fuel injector, using an engine management system like Motec. Like this http://www.twminduction.com/ThrottleBody/ThrottleBody3006.html



This set-up looks so different from my stock 3.2 (with a single throttle body and a central intake manifold with long runners) that I'm very curious about it.

What are the advantages and disadvantages of such a set-up? Is it inherently biased toward high-revving or peaky motors, or could you get good torque too? Could you build a good street motor with this arrangement?

[svandamme]

the main advantage is throttle response
also , the high stacks work better with power in high revs
and it looks and sounds cool as well

[PorscheGuy79]

Yeah what Stijn said, it cuts the length the air has to travel to each cylinder which inturn gives you power quicker. Fastest way between two points is a striaght line kinda thing.

[porschenut]

Not including the EMS, what would it cost to convert the intake to ITB's on a 3.2?

[PorscheGuy79]

Originally posted by porschenut
Not including the EMS, what would it cost to convert the intake to ITB's on a 3.2?

Ive heard you can fab up your own system for a reasonable price if you are so inclined but I would imagine you should expect to pay $$$ for a kit or to have it done.

[svandamme]

depending on your reasons for modding the intake
you might want to consider the full package

intake... exhaust...
and no use changing those without a chip-job. ( if you re-use the EMS )

[randywebb]

Disadv.s are cost, & inability to use one cylinder to "help" another cylinder via resonance effects

[emcon5]

The biggest advantage is probably the ability to run a very agressive high-overlap cam, something that doesn't work well with single plenum systems.

Tom

[jpnovak]

There is a little more to it than the reasons posted above. Yes, it does look and sound cool.

The individual throttle bodies are important for tuning. First, they allow equal delivery of air to each cylinder. This allows better balance of the intake charge. This is usually not posstible with a common plenum system. Second, it allows equal length for each runner. While some systems come close to "equal" length they never are. The air volume from the valve to the throttle body will always be different for acommon plenum system.

The individual stacks allow for easier port tuning. This is measuring the length of the runner from the valve to opening. Changing this length affects the intake harmonics. you can use the momentum tuning for maximum cylinder charge based on length.

Another option mentioned above is power. Yes, these ITBs can have different injector and butterfly postions. The butterfly can be positioned at a node for a given intake harmonic. Also a higher injector placement can increase mixing time at high rpms. Both of these will help increase power.

There are many reasons to go to an ITB system. They are not necessary unless you have CIS or are going to install full internal modifications to take advantage of the tuning options.

[RickM]

Originally posted by porschenut
Not including the EMS, what would it cost to convert the intake to ITB's on a 3.2?

You might want to ask Souk. I believe he's working in a conversion kit.

[TimT]

what would it cost to convert the intake to ITB's on a 3.2?

$5000 give or take a few dinero, depending on what you can bring to the table

[MotoSook]

Originally posted by RickM
You might want to ask Souk. I believe he's working in a conversion kit.

Mike (the other MotoMotions guy) has actually converted his 2.7RS engine to ITB/EFI. Mike has developed the kit to utilize MegaSquirt engine management with EDIS crankl fire ignition. Our kit is well below $5000.

[PorscheGuy79]

That makes me all warm and fuzzy inside. I hope he comes out soon with it, I wanna see that thing.

[jyl]

My 3.2 has a air flow meter. I don't see a similar device in the ITB setup shown above. Is it not necessary?

[svandamme]

dunno myself

either there's a sensor in every intake, six of em

or they program the 'puter to behave like MFI
fixed fuel map, vs RPM and throttle position...

[Jeff Alton]

The fuel computer will use a map sensor instead. It will probably have to get a vacuum signal from more than one throttle body or it may be too weak. Usually a vacuum manifold is used.

Jeff

[sketchers356]

This is so hot! I definately want one of these ITB kits!
What is a vacuum manifold? The primary thing I dont understand about ITBs is how the pressure signal is obtained.

[DW SD]

To generate a vacuum signal isn't too hard. Each TB has a vacuum port (as do Webbers or PMOs). You can join the signals in a common plenum or manifold to produce one, stronger signal which averages out the six sources. You will have a throttle position sensor, temp sensor, and maybe ambient air pressure sensor. With that all of that info, you should be able to build a great fuel / ignition map. Also, either a wide band or narrow band O2 sensor can be used for closed - loop metering.

Doug

[jyl]

So . . . could one build a great street motor with ITBs? It sounds like "yes" but I want to make sure.

[emcon5]

Originally posted by jyl
So . . . could one build a great street motor with ITBs? It sounds like "yes" but I want to make sure.

Sure. Not a CA smog legal one though.

Tom