Hey everyone,

This weekend is going to be the first time I tear into the GTA. Found out it needed an intake manifold gasket, not uncommon no big deal. But I got to thinking....im going to have the intake manifold off and I have a new porting kit . I already have an airfoil on the way for this thing and I decided to to the Throttle body coolant bypass. But I was reading up on porting the plenum just behind the throttle body, something about a couple of bosses back there that really block some airflow as well as casting nastyness. But is there anything else I can do to the runners or the intake manifold while I have all this stuff off not to mention other things in the plenum? Things to watch out for? Things not to do? Things to do?

Also how much HP do you all think im going to gain here? 10-15 is what im hoping for because basically its my whole weekend worth of work for trying to pull some numbers out of my butt. For basically a gasket set an airfoil and some hose hahaha.

And if anyone here has other little things I can do while im in there let me know.

 

I agree that it would be a good idea to do it while it is off.

Points of interest:

-Direct opening of Plenum, there are two 'walls' that are about 3/16" tall in either hole, on the bottom. Grind these away.

-You can siamese the STOCK runners into the flange about a 1/4". Take away metal on the plenum to match it. It won't be nearly as effective as having an aftermarket pair, but it will do something. There is a writeup here, http://rain.prohosting.com/imwhom/junk/inj/ compliments of Ed Maher on TGO.

As far as power, well I don't think you'll be making much more, but the important thing here is that you will be expanding your RPM curve. Now, the motor shouldnt fall on it's face at 4,500 rpm. You might get good power to about 5,000rpm. This will also give you better results if you ever decide to get afermarket heads and a cam. This mod will provide the additional air needed to warrant those upgrades.