Throttle Body design

[sbrats]

I was looking at the TB on my 16v 2L which is 64mm - there are aftermarket units that are 68mm available, however I got to thinking that a slide type TB at 68mm might flow more for given cross sectional area open vs a conventional plate style. What are the pros and cons? Why isn’t there more slide type TB used for automotive use?

Thanks

 

[patprimmer]

They give very little advantage over a slightly larger sized butterfly valve.

They are more complex to make, harder to seal reliably for a stable idle and have much higher friction and potential to stick, making power control difficult.

Regards

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[sbrats]

Thanks, makes sense, Taking it one step further then.. If the intake manifold is a 70mm bore and the TB is 64mm, what will happen if the bore is opened up to 70mm? I'm guessing low end response would change, would injector size need to be increased to compensate for increased flow? Would this type of change seriously affect the drivability? Is this why it would be presently at 64mm (design compromise)


thanks

 

[patprimmer]

I don't know without inspecting and testing your system.

If you seriously increase the airflow, you might run out of injector fuel flow.

Increasing throttle bore dia might increase airflow, depending on how restrictive the current one is compared to everything else in the system.

Increasing throttle body size at the numbers you state probably will increase airflow.

It should not prove detrimental to bottom end power.

It will most probably increase inlet tract noise.

It will make the throttle action more sensitive or touchy or snappy.


Regards

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[MikeHalloran]

You could effect a modest increase in WOT flow area by thinning the throttle shaft around the butterfly, converting the cross section from two half- rounds to two flattish rectangles, or two shallow half- ellipses.

A couple of hours attacking the shaft with a Dremel tool should do it. I'd leave the shaft at full thickness around the butterfly retaining screws, and stake and Loctite them on reassembly.





Mike Halloran
Pembroke Pines, FL, USA