EFI Throttle Body Size?

[Woznaldo]

I have an AMC/Renault Alliance Multipoint EFI Manifold and while looking at the standard throttle body made me think what size would be optimal? The std throttle body has 2 x 32mm dia throttle butterflies that open sequentially, the 2nd starting to open when the 1st is half open and then both are fully open at the same time. The 2nd throttle butterfly is also choked down to 21mm.

Therefore the effective throttle area at WOT is 32 + 21 dia giving an area of 1150mm2

A single throttle body with a dia of 50mm would give an effective area of 1963mm2 but, is this overkill and would it be poo at low engine speeds when it comes to mapping?

This is all for a C1J with the capability to make 200 ponies approx. What size should I be looking for considering the std carb is choked to 25mm dia?

[Andrew Cooke]

I'd suggest around 1300mm2, but that's rough and ready. By choice I'd use a 45mm for that kind of power. No real science there, just a gut feeling.

Don't forget to deduct the spindle cross section when looking at areas.

[Woznaldo]

Yes, I did forget about the spindle area. So when you take the average spindle size into account, that would make the 45mm dia very close to the 1300mm2 mark.

I'll start off with the std size at first as I have all the bits but i'll start my breakers yard search for a 45mm throttle body off anything I can find. Here's a pic of the std throttle body:

https://www.rtoc.org/boards/album.php...pictureid=1255

[Andrew Cooke]

does the small one have a larger plate behind that restrictor?

[Woznaldo]

does the small one have a larger plate behind that restrictor?

Yes, they're both 32mm.

[Andrew Cooke]

Yes, they're both 32mm.

sorted then, just open the throat out and ship it

I shoulda read what you wrote to start with

[Woznaldo]

I can't open the throat out as the choke is part of the casting. See below:

[Os8472]

I've got a 55mm body on mine, its not to bad at low speeds, just gotta remember not to be enthusiastic comin off a round about lol

I would go for a 40-45mm body if I were to do it again

[Scoff]

45mm is what I would use too.

[rs250nut]

Why do w.r.c cars and the like use four individual throttles with eight injectors, is it because its easier to make more torque this way? Do people use one large throttle for maximum h.p? Sorry if these sound like silly questions

[Andrew Cooke]

I can't open the throat out as the choke is part of the casting. See below:

nothing that a tube and some good glue can't fix

[Woznaldo]

I'll measure the wall thickness and see if there is enough meat for me to open it out to 25mm? I think i've got a 1 inch reamer at work?

Does anyone know what car might be able to give up a 45mm throttle body? Ford Fiesta?

[rs250nut]

I'll measure the wall thickness and see if there is enough meat for me to open it out to 25mm? I think i've got a 1 inch reamer at work?

Does anyone know what car might be able to give up a 45mm throttle body? Ford Fiesta?

I think the throttles on early zetec cars were around 45mm so escorts mondeos focus

[Woznaldo]

I'll check the local wreckers. Thanks for all your help fellas.

[Os8472]

you want a body off a 98plate fiesta 1.4zetec, its 46mm, should do the job nicely

[Woznaldo]

you want a body off a 98plate fiesta 1.4zetec, its 46mm, should do the job nicely

Thanks Olly. I take it that's what you have?

[michael tierney]

why dont u use what u have,a small primary will give u excellent vacuum-throttle response-fuel efficiency ect.see whats its like on a rolling road...its still way bigger than a 32dis with a 25mm venturi(which u can get about 170bhp from)

[Os8472]

Thanks Olly. I take it that's what you have?

Nope I have mitsi starion 55m body, I so want to change it, I have the fiesta body but no one to adjust my manifold so it'll fit

[Harri]

I'm using clio F7P throttle body with my EFI C1J. Since it's a twin throttle body, it took a little imagination to seal&fit properly.

I'm currently drawing second version of manifold and the clio throttle body is one of the things I'm going to use on my second manifold.

pics here: https://www.rtoc.org/boards/album.php...pictureid=7229

[Os8472]

what ecu do you use Harri? And howdoes it read both butterflies? Twin throttle postion sensors or somit more sneaky?

[Rob@Backyardracing]

Would only need one sensor oli even with twin plate i would have thought..

[markey b]

yeah they are seqential butterflies, so one TPS (the red bit in the pic)

how d'ya think they do it on the clio/19 16v oliver stanley??

[Harri]

I'm using Adaptronic. Scoff helped me in making the wires and choosing right sensors. Throttle body has two butterflies; the smaller opens first almost fully and the linkage in the throttle body opens the second, much larger one, after the first is almost fully open.

check

https://www.rtoc.org/boards/album.php...pictureid=6920

[Woznaldo]

Nice work harry. Look forward to see it up and running.