Quote:
Originally Posted by Tom Meyer
The intake manifold has the real restriction, when you look down in the intake divider floor there is a hole that is no bigger opening than the throttle body. Air going into the engine goes threw the throttle body to a hole that drops down to lower level a goes to the intake runners. The intake air changes directions many times before it gets to the intake valve. By removing the floor it becomes a big open plenum with long intake runners. In order to remove the floor you have to cut the bottom of the intake off then weld it back on. It is not a Saturday afternoon job. I got another intake from junk yard to modify but have yet to bolt it on. At that point another trip to the dyno to see the difference. Tom
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It needs more than the plenum opened. For the engine to make good power at an RPM high enough for it to accelerate through the gears, it needs at least a 100MM throttle body, and all of the restriction removed behind it. The plenum is currently a reservoir for air, that empties rather quickly, and cannot be refilled quickly enough. Ideally, the throttle body needs to be moved back about an inch. Widen the inlet substantially, then use a throttle body spacer to mount a minimum 100MM throttle body. You can then change the duct from the air cleaner to have a larger radius, and eliminate the big restriction required to clear the shroud.
Removing the baffles, and opening up the plenum can be a double edged sword. If enough restriction is not removed, air will enter the plenum and slow rapidly, so the back half of the intake can be starved for air, you get uneven air distribution.
The runners are a bit long, even for the goal GM had of maximizing torque, even at near off idle RPM.
Also, if you move the PCV inlet and put some baffling in it, you'll get rid of a lot of the oil consumption, while also helping the crankcase breathe a bit.
I've worked with a few people who have modified the intake, with mixed results. A good example is a video Richard Holdner just put up on youtube. In looking at the intake, there were several things NOT done. The first is how the larger throttle body was installed and located. Too far forward, and too restricted. I do not think radically shortening the intake runners will work well on a tow vehicle. But porting them will.
I actually bought a spare 8.1 and an Allison from a friend of Adger's, I'm going to work on it fairly soon, and develop some packages.