Restricting IAC passages

[Chewy1576]

I have a big block throttle body and bored out intake manifold I want to run on a 383. I tried running the big block throttle body on my Edelbrock intake with stock throttle bores as an experiment, and I had to back the screw all the way out to get it to even try to open the IAC when controlling idle. I don't like doing this because then you're blocking fuel during idle also because the butterflies are as closed as they can be. So when I install the big block throttle body for good, I want restrict the flow of air through the IAC passages so I can get more air going down through the throttle bores to push fuel into the intake. Does anyone see a problem with filling the yellow areas with Moroso A&B or JB Weld? Anyone have a preference on which one to use over the other?

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[someotherguy]

Before trying to modify the big block throttle body to work on a small block (even a stroker small block) I'd get a bored-out small block throttle body instead. I can't imagine you can block those passages with any degree of precision, and then you'll end up with effort invested in something that still sucks and have to chisel it all out, hoping you don't damage the thing, so that it will still be valuable to someone else.

You can get it direct from RV Morse cheaper than CFM Tech sells 'em for, and that's where they get 'em. $189 from RV

Richard

 

[Chewy1576]

I want to stick with the big block throttle body because I already have it and the wider spacer plate to get it to seal, my 56 lb injectors and adjustable fuel pressure regulator are already installed, and I have the sensors and adapters ready for it to mount on the intake and hook up. Everything worked great with it during the test, aside from the ability to control the idle. That’s why I want to partially fill the IAC passage to restrict the flow of air going through it. I know Moroso epoxy or JB Weld will be semi-permanent and will be a pain to remove, but could be done with a Dremel if needed. I’m sure the setup would be of value if sold as a set up for a small block stroker or high HP engine also.


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[89RCLB]

What about creating/fabricating a restrictor of sorts that's easier to remove than filling those channels with something that would require a lot of effort. Just thinking out loud really...

 

[skylark]

In my opinion that is going to be like trying to put a 1050 Dominator on a 4.3 V6. You're going to be putting in way too much through the IAC valve just to try to choke it down in the throttle body itself. I don't think it'll meter properly at all. It needs to be addressed in the tune.

 

[Chewy1576]

I plan on doing a lot of tuning work to get it dialed in again. Since the TB isn’t that hard to pull off of the intake, I could try to get it working as-is and re-evaluate if the idle still struggles. If I do try restricting the IAC air flow, I want something to put in the passage that will stay put with no chance of sucking into the intake and down into the engine.


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[Chewy1576]

I guess this also begs the question... is a big block throttle body overkill for a 280HP 383? I don’t plan on changing the cam or heads for a while. Right now there is a stock small block throttle body and Edelbrock 3704 intake on the engine. I’m planning on going to a big block throttle body and bored/ported stock TBI intake.


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[someotherguy]

I want to stick with the big block throttle body because I already have it

Not usually the best rationale for parts choices...unless you're building a rat rod.

Richard

 

[c1500deathtrap]

Yes That's big for a 280 horse motor. you already stated your problem isn't the IAC so why are you trying to fiddle with it? If the IAC pintle is fully closed and you are still getting to much air how is the IAC providing to much air? Its those big ass throttle plates that are the problem.

 

[Chewy1576]

The IAC is only a part of the problem, but that was the route I was going to take to try to fix it. Ok I’ll back up and try explaining what I was seeing again. Maybe I just have it screwed up in my mind...

The problem I had was that I couldn’t get the idle air adjusted with the big block throttle body so that the IAC counts stay at 5-10 when at operating temperature. To get the IAC to open few counts, I had to back the idle air adjustment screw all the way out. This created another problem because with the screw backed out, the throttle plates are almost completely closed and fuel wasn’t effectively getting down into the intake. Turn the screw back in to open the throttle plates slightly to let fuel by, and the IAC closes completely again and the idle quality goes south because the ECM has no IAC adjustment.

So my reasoning for restricting the IAC was to bias the idle air to the throttle plates so I don’t have to close them completely. More air (and with it fuel) through the throttle plates means less air needed through the IAC for idle, right? Or should I just stick with the small block throttle body?


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