4 hole throttle bodies all too big?

[Erik88GT]

I've been looking at the accufab and bbk, etc. four hole carb-style throttle bodies for my 289, but I can't find one under 1000cfm! I think if I used one of those, my throttle would be too touchy? Does anybody make a smaller one, like 750?
I'm also thinking about taking an old Holley, gutting it and epoxying all the holes shut, then I would just have to get creative to make it turn a TPS. Has anyone had success with that?

I don't want to use a conventional Ford style TB because I want the stock air cleaner look (it's a classic mustang) and don't really want to put a throttle cable on it.

Thanks

Erik

[MegaScott]

You should look into the Autonomics throttle body, the basic body cost $75 and you add stuff from there, the standard throttle body is ~750 CFM to start and can be machined to 1000cfm+.

http://www.auto-nomics.com/index.html

[Mk1rocco]

And if 750 cfm is still too big for you, they also sell inserts that reduce the capacity down to about 450 cfm

[Erik88GT]

Thanks.
I wonder why it's so cheap?
I already modified a vic. jr. manifold for efi, so maybe I could plug the injector pockets in that autonomics TB...

edit: I see they sell a plugs. What a strange website to navigate...

[Jesse]

The Autonomics throttle bodies also feature a linkage between the pairs of bores that can be removed. So if 750 cfm doesn't trip-your-trigger then you can just remove two c-clips, pull off the linkage, and now you have 375 cfm. Both individual throttle shafts are independently spring loaded, so if you do remove the linkage the "free" bores _should_ stay closed.

(Note that one of the effects of having too big a flowrate through the throttle body is that the car accelerator is either "ON" or "OFF" - the throttle will be so sensitive that that you won't be able to accurately regulate the throttle in between the closed and wide open throttle positions).

[eliotmansfield]

I've done the convert a holley carb to a throttle body thing; www.mez.co.uk/ms2.html  - but that was before I was aware of the autonomics TB which is far easier and cheaper.  I got mine with the blanking plugs for the injectors - which I assume they sell if you *just ask*.
 
You can also convert them to a progressive throttle action, which makes controlling the power much easier. Details here:
www.mez.co.uk/turbo9.html
 
I also bored mine out to 41mm, as the std 33mm looked a bit small.
 
Eliot.

Posted by email.

[Jesse]

Wow! Eliot - Nice work!.

I am going to be running around on a Th2004R (which is very similar to the TH700R4 - same detent cable configuration) and what you have posted for the required bracket geometry is EXACTLY was I looking for!

(This has been a matter of concern fo rme since I got the TBs back in October of last year. I wasn't quite sure if that lower mounting hole would work as a viable Detent cable mounting location. But now I know it doesn't and I will be modifiying my TBs to your specifications. Again, Props to Eliot! !)

(BTW...check this site out for my installation... hehe)

http://www.cardomain.com/ride/2101029/1 )

[PSIG]

You've probably already figured this - but the Autonomics bore restrictors will not help with the throttle control tip-in problem. The restrictors only have effect once the total flow reaches their maximum level; so the off-idle power control is still an issue. You'll need to fashion a progressive system like Eliot's or other tip-in solution.
HTH,
David

[Jesse]

Here is an interesting idea for the "tip-in" problem;

Progessive throttle control is tackled by Holley through mechanical means - like the progessive linkage modification note previously.

However, the 4 barrel Rochester Quadrajets (E4ME, E4MC, etc.) handle the progressive problem with two mechanisms:

1) Progressive linkage by similar means as Holley and the modification
2) A spring-loaded air valve positioned at the top of the progessively controlled bores (now reffered to as "secondaries") and dampened by a vacuum actuator (also known as a "dashpot") with a small restrictor in the line.

#2 is a pretty clever design that only supplies air "on-demand" and has been proven successful since the 70's. (Of course now the question becomes "why not just modify a quadrajet E4ME to be a throttle body?? Hell, it even has a TPS sensor built in already!!") The force of the air rushing through the secondaries forces the air flaps or valves open, and the speed of the opening is controlled by the dashpot which alleviates the "stumble" when you put the pedal to the metal. The dashpot speed control is merely an small orifice that delays the vacuum signal applied to the dashpot. For quicker opening the orifice can be enlarged...

It would be interesting to add-on an air valve from a quadrajet to the Autonomics unit seeing as the dashpot is still available at auto parts stores. Or maybe the vacuum actuation mechanism from a vacuum secondary Holley?(see follwoing pics) Also check out this link.

http://www.tocmp.com/manuals/Carbs/Rochester/QJet/