TBI Throttle Body Tear Down and Rebuild.

[Jims86]

sounds good to me then because I was unsettled on even trying to mess with the FPR besides changing the thing out.

Well, this is what I ran into. My AFPR would only go as low as 11.5 psi. My stock regulator was supplying 10psi...you wouldnt think that would make much difference, but it did...stuck my stock regulator back on, and things settled down a little.
Since all the tuning here recently, and finding un expected **** wrong with my throttle body, and repairing those problems, I finally have a pretty smooth idle(im picky, I like a Cadillac smooth Idle) and great power.
Believe it or not, we ended up taking a shitload of fuel out at idle, and adding in the mid range, because of my "Mild" cam.

 

[austinado16]

Subscribed!

Excellent thread.

 

[Swims350]

I think i'm done with the tb smoothing now lol..

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[89Suburban]

Nice work man.

 

[austinado16]

Is it of value to blend the transition from the upper "funnel" shape, to the more cylindrical area that meets the throttle plates? There's sort of tight turn there that it seems like would create a restriction.

In other words, can you make it more velocity stack shaped, right up to the throttle plates? Or do you risk breaking through? Or would it not make that much difference?

 

[Swims350]

I thought of the same. I don't see why it wouldn't work but you would definately want to stay away from being too close to the blades. Then again on tbi could cause issues, bigger holes and when the blades open some there hole is biggher, like it was opened further but it's not, thus causing some lean issues or something?

 

[Jims86]

Is it of value to blend the transition from the upper "funnel" shape, to the more cylindrical area that meets the throttle plates? There's sort of tight turn there that it seems like would create a restriction.

In other words, can you make it more velocity stack shaped, right up to the throttle plates? Or do you risk breaking through? Or would it not make that much difference?

I thought of the same. I don't see why it wouldn't work but you would definately want to stay away from being too close to the blades. Then again on tbi could cause issues, bigger holes and when the blades open some there hole is biggher, like it was opened further but it's not, thus causing some lean issues or something?

you sure can, but I think they use a custom made sanding drum/mandrel to make the initial grind, then polish it up.
Per CFM-Tech, their porting brings the cfm from 480 to 620, that tells ya just how much the injector placement plugs things up, and I think the plates are a little bigger too.

 

[austinado16]

I just ment taking that "hump" out, so the funnel shape transitioned to the cylinder shape better.

 

[Jims86]

I just ment taking that "hump" out, so the funnel shape transitioned to the cylinder shape better.

you mean around the circumfrance, right before the factory polished area before the plates?
I have seen that done...there is more than enough material...After all, they do bore these units to 2" from the 1-11/16" that they are now.

 

[austinado16]

Yes.

When I do porting, either in heads or throttle bodies (I've never done a TBI unit) I blend out all the "transitions." Not that I'm some sort of pro or anything, it's just how I was taught.

 

[Jims86]

Yes.

When I do porting, either in heads or throttle bodies (I've never done a TBI unit) I blend out all the "transitions." Not that I'm some sort of pro or anything, it's just how I was taught.

I think that hump would actually speed up the air, instead of hinder.
With TBI, Bernoulli principal is our friend!

 

[89Suburban]

Wouldn't that hurt the venturi effect and design?

 

[Jims86]

Wouldn't that hurt the venturi effect and design?

Not really...the venturi was to help draw fuel into the airstream from a carburetor, where fuel was not injected. if you look at boosters in a carb, you may notice that they are kinda shaped like an airplane wing, only the wing is a loop(the throttle bore its self was the booster in early carbs) the air going over the internal surface(kind of a hump) travels faster, causing an area of low pressure(lower than atmospheric pressure) drawing fuel into the air stream, via a hole in the hump.

 

[89Suburban]

Not really...the venturi was to help draw fuel into the airstream from a carburetor, where fuel was not be injected. if you look at boosters in a carb, you may notice that they are kinda shaped like an airplane wing, only the wing is a loop(the throttle bore its self was the booster in early carbs) the air going over the internal surface(kind of a hump) travels faster, causing an area of low pressure(lower than atmospheric pressure) drawing fuel into the air stream, via a hole in the hump.

Yeah, I understand all that, let me rephrase it. Wouldn't the curved tapered bore be preferred rather than a V shaped bore that would have more of an edge where it transitions into the straight bore section of the butterflies?

You get what I am asking? Like it's a smoother flow? I don't see what advantage you get from increasing the size of the upper bore when the lower bore diameter @ WOT is the ultimate decision maker of the CFM entering the intake. I don't see how a large, v shaped bore would benefit at all.

Nut I ain't all that smaat so....

 

[Jims86]

Yeah, I understand all that, let me rephrase it. Wouldn't the curved tapered bore be preferred rather than a V shaped bore that would have more of an edge where it transitions into the straight bore section of the butterflies?

You get what I am asking? Like it's a smoother flow? I don't see what advantage you get from increasing the size of the upper bore when the lower bore diameter @ WOT is the ultimate decision maker of the CFM entering the intake. I don't see how a large, v shaped bore would benefit at all.

Nut I ain't all that smaat so....

The injectors up top block air flow pretty good, so the only other place to get more air, is from around them.