Throttle body : a few basic questions.

[marc426]

Hi everyone, just getting in the megasquirt world.
Before i go any further, i'd like to be sure i understood everything right.
The throttle body is basically just a valve (butterfly?).
I'd like to convert my carbed car to a TBI and i've got the bottom end of a carb that fits my car and it's basically just a valve (not sure of the word).
If i machine a piece that holds my injector between my valve and my intake manifold, i'd have a TBI right? The injector has to point to the intake manifold, what angle is best?
Thanks a lot for your help

Marc

[bleoh]

I think you have it basically correct. On a TBI application the TB does double duty by controlling the air into the motor and housing the injectors. In a multi port setup the TB just meters the air. In both cases the TB is usually where the throttle position sensor, Idle controll, etc.. are located.

GM has the injectors over the butterflies and is pointed right at them. Auto-nomics makes one with the injectors at an angle but I am not sure if they are above or below the butterflies http://www.auto-nomics.com/cgi-bin/show ... 0850-002-D And I think others are making TBI's from scratch, like here http://www.customefis.com/pod.html

If you are thinking of going TBI can you just use a unit from a GM application? On most carb conversions you would just need to make/buy an adapter to bolt the TBI to your intake. With it you would get your TPS, IAT and fuel pressure regulator.

[Ralco_Be]

They list 75$ for the throttle body.
Isn't that an error?

[ChevelleFan]

They list 75$ for the throttle body.
Isn't that an error?

Nope, not an error, just the bargain of the century, at least compared to other throttle bodies, which for some reason costs hundreds of dollars.

-Dave

[marc426]

Thanks for these answers.
Got another couple of questions :

GM has the injectors over the butterflies and is pointed right at them.

I don't understand, injectors are before the butterflies? What about idle? When the butterfly is fully closed?...
For the GM conversion, i'm not sure i'd find any model that fits since the engine i'd like to convert is a Mopar Slant6. Moreover i'm in europa so it won't be that easy to find it.
What about the flow?... The "throttle body" i was talking about is from a 1bbl. carb. I guess i'd have better results from a bigger butterfly, nope?
thanks again for all your help

Marc

[Matt Cramer]

Hello Marc,

I'm also working on injecting a Mopar slant six, only mine is using a multi-port setup. Here are a few answers to some of your questions.

1. Yes, a GM throttle body has the injectors above the butterflies. Even though the throttle snaps so closed as to be almost airtight at idle, the engine doesn't use any additional injectors as a idle circuit. It may look a bit weird, but it works just fine even when idling.

2. Yes, the opening size under the carb on a slant six with a one barrel manifold is pretty tiny! It's one of the first things that most slant six tuners ditch if they are looking for more power.

3. If this isn't for a high performance application, go ahead, gut the carb (is it the infamous Holley 1945?) and put injectors in it like in a GM TBI.

4. If you want a bigger throttle opening for more performance, there are a variety of options. One, you could machine a hole in the stock manifold and weld on a new section drilled to fit the throttle body of your choice. Two, you can get a Clifford manifold which has an open space where you can make a flat plate adapter in almost any throttle body bolt pattern. That's what I did, only I'm using MPFI. Three, you can get one of the many aftermarket manifolds designed for a common aftermarket carb (between Clifford, Offenhauser, and Lynx, you can find stuff to fit Weber DCOE, SU, Holley, or Dellorto carbs on a slant six) and use an aftermarket throttle body that matches that pattern.

5. If you want MPFI, Clifford had a small batch of EFI manifolds and fuel rails built for the slant six. Price was around $300 US for a complete set - wish I'd known about that when I had mine built. You won't find it advertised on the website; you will need to email them directly.

Let me know if you want to see any pictures of my installation in progress. There's some on my blog and some others I can post.

[efahl]

I don't understand, injectors are before the butterflies? What about idle? When the butterfly is fully closed?...

Marc,

Unless you are running an idle air control valve, you never actually close the butterflies, that would kill the engine. In a TBI setup, the fuel is sprayed on the butterfly and the fuel is sheared off the edge of the valve plate and is atomized very nicely, so you get pretty good fuel distribution right at idle.

Eric

[marc426]

So a butterfly doesn't close...
GM has injectors over the butterfly but will it be better if they are under it or will i get bad atomisation at idle (in the case i make my own throttle body)?

2. Yes, the opening size under the carb on a slant six with a one barrel manifold is pretty tiny! It's one of the first things that most slant six tuners ditch if they are looking for more power.

But, if won't there be problems if i just mill my stock intake manifold? Plenum size and that type of thing? I remember having read somewhere not to adapt a 2bbl. carb on the 1bbl. intake manifold. Is that true?

3. If this isn't for a high performance application, go ahead, gut the carb (is it the infamous Holley 1945?) and put injectors in it like in a GM TBI.

Yes it is!

4. If you want a bigger throttle opening for more performance, there are a variety of options. One, you could machine a hole in the stock manifold and weld on a new section drilled to fit the throttle body of your choice. Two, you can get a Clifford manifold which has an open space where you can make a flat plate adapter in almost any throttle body bolt pattern. That's what I did, only I'm using MPFI. Three, you can get one of the many aftermarket manifolds designed for a common aftermarket carb (between Clifford, Offenhauser, and Lynx, you can find stuff to fit Weber DCOE, SU, Holley, or Dellorto carbs on a slant six) and use an aftermarket throttle body that matches that pattern.

Same question as above.

Let me know if you want to see any pictures of my installation in progress. There's some on my blog and some others I can post.

I'd love that!

Thanks for your precious help!

Marc

[sidy]

This isnt how the EFI works on most early m/cycle EFI systems, the injectors are after the butterflys, usually pointing striaght down the intake port tract.


Sid

On 1/12/06, efahl <eric@wryday.com (eric@wryday.com)> wrote:

marc426 wrote: I don't understand, injectors are before the butterflies? What about idle? When the butterfly is fully closed?... Marc,

Unless you are running an idle air control valve, you never actually close the butterflies, that would kill the engine. In a TBI setup, the fuel is sprayed on the butterfly and the fuel is sheared off the edge of the valve plate and is atomized very nicely, so you get pretty good fuel distribution right at idle.

Eric



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[Matt Cramer]

But, if won't there be problems if i just mill my stock intake manifold? Plenum size and that type of thing? I remember having read somewhere not to adapt a 2bbl. carb on the 1bbl. intake manifold. Is that true?

There are a few people out there who have tried to take an adapter where one end bolts to the stock manifold and the other end attaches to a carb, using the same, tiny hole as the one barrel manifold. This is not recommended. On the other hand, if you are willing to do a bit of cutting and welding or milling to the stock manifold, you can make a perfectly acceptable manifold for a 2-bbl carburetor or a TBI unit. The key is not forcing all the air in through the small hole in the stock piece. There's even a factory performance manual that used to recommend this prior to widespread availability of aftermarket manifolds - check out their drawing.

Here's a few pictures:

Fuel lines, regulator, and rail

Manifold and wiring harness

Manifold, throttle body, and adapter

Hope this helps!