C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

3 "Where do these connect" questions.

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Old Aug 4, 2010 | 01:20 AM
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Default 3 "Where do these connect" questions.

On my 1990 coupe, on the back of the plenum, drivers side, there is a large threaded port that opens up into the plenum cavity. Where does this connect too?

Also, where does the middle port right behind the TPS go?

And lastly, on the intake manifold near the distributor there are two ports, one of them connects to the passenger exhaust manifold, the other is much smaller and has a pipe that sticks out about 6" or so. Where should I hook this up?

I am getting this engine back together after 2 years and lost all my reference photos.
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Old Aug 4, 2010 | 01:30 AM
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Originally Posted by jdraughn
On my 1990 coupe, on the back of the plenum, drivers side, there is a large threaded port that opens up into the plenum cavity. Where does this connect too?
The large threaded port goes to the Brake Booster.
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Old Aug 4, 2010 | 01:42 AM
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Originally Posted by jdraughn
On my 1990 coupe, on the back of the plenum, drivers side, there is a large threaded port that opens up into the plenum cavity. Where does this connect too?
Brake booser as indicated in post #2 (There's a metal line bracketed to the rear of the DS head,,,then a rubber hose to finish the bends over to the booster).

Originally Posted by jdraughn
Also, where does the middle port right behind the TPS go?
Largest vacuum line coming from the DS fender well. Fuel cannister IIRC.

Originally Posted by jdraughn
And lastly, on the intake manifold near the distributor there are two ports, one of them connects to the passenger exhaust manifold, the other is much smaller and has a pipe that sticks out about 6" or so. Where should I hook this up?
That's got water running thru it. There should be a small 1/4" pipe that splices into your heater hose line. They connect with that size rubber hose and small hose clamps.

Last edited by GREGGPENN; Aug 4, 2010 at 01:45 AM.
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Old Aug 4, 2010 | 09:52 AM
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Here are a couple of pics of my 91 right after I got it home. Hope this helps a bit.
I will also go out to my garage and take a pic of the intake manifold that I am preparing to install. All of the fittings are on it now (except EGR and gooseneck). Getting ready to put the gaskets and sealer on it and plop it back on today.

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Old Aug 4, 2010 | 10:14 AM
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Here you go. Hope this will help. I am working lots of hours so will probably take me about a week of spare time to get it all back together. I will post pics as I go along.





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Old Aug 5, 2010 | 07:09 PM
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Thanks for all the info and the pics too. I pretty much have the whole together, I was hoping to start it up today but I spent too much time trying to figure stuff out.

I found a few vacuum diagrams on the web, not sure if they were my exact year and model, but they had to be pretty close, but they never showed everything.

Part of the problem is that I bought an 87 parts engine along with the pretty much everything else that goes in the engine bay, so I have brackets and hoses all mixed up, and most of the vacuum hoses are cracked or broken.

If someone can point me to a decent vacuum diagram that shows cruise control and all, and I also need a cooling diagram, so many heater hoses, they are all over the place.

Thanks again.
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