I have been wondering and searching and I have come to a dead end.

What is up exactly w/ the receding strip line on some of the TPI plenums?? When I say receding strip line I mean the stripes on the plenum start way back instead of in the front. I have made a few interesting finds on this plenum

1. My friend has a plenum of an 89 350 TPI w/ the receding stripe line, BUT my friend has a 90 350 TPI and he doesnt have it. My other friend has an 88 350 TPI and he doesn't have it either, so was it an 89 only thing???

2. Amazingly the runner blocks in the plenum look as if they are ported from the factory! They are very small and almost flush to the plenum. The bottom front blocks on the TB entrance are there but the side blocks that usually have to be radiused are already radiused!

3. The top part on the front of the plenum where the TB holes screw in and there are little banks that Mike in AZ talks about grinding them down so it looks smooth aren't there, they are just about flush to the plenum.....


This is wierd, GM obviously used a different casting to make these, but why? why in 89? and why all the significant differences???

anyone with knowledge on this please enlighten me.

 

The shorter lines on top of the plenum started in 89. Your friends 90 should have the same plenum. If it doesn't then its either not the original plenum, or somehow an old stock plenum came up in the parts bin and they slapped it on there.

And yes, the later plenum is a much nicer piece than the early one, but it can still be improved upon.

 

guess its not a mistery anymore