I have an 87 IROC that I have installed a GMPP 383 engine with GM aluminum vortec heads. I have installed a comp cams cam, vortec TPI base, Edelbrock runners, Accell cdi ignition, Motovation custom prom, 58mm throttle body, Edelbrock shorty headers and Flowmaster 3" catback system. It has a 5 speed and 4.10 gears. It runs good, plenty of torque. I'm afraid to put any tire on it due to the flimsy 10 bolt rear. The engine feels as if it flattens out at rpms above 5000. Is this the nature of the TPI? Is there anything I can do to the plenum to improve this?

 

If you use the stock TPI intake then yes. It will be able to support the engine until 4500-5000 RPM. Of course you can port the whole intake and that may help a little. Other choice is to use an aftermarket intake for your setup.

 

Typical of all TPI intakes
Read this and compare the graphs
http://xtremecarzone.com.au/index.php?showtopic=386

 

The Vortec TPI base is known for poor flow. Also, the Vortec heads, unless ported do not flow enough to support high RPM. Which Comp Cam do you have? To make power above 5,000, any engine needs to flow well. Also, cam duration plays a big role here. You can make power to and beyond 6,000rpm, even with long runner TPI, but its not cheap. High flowing heads, a high duration roller cam, ported high flow base and big runners are just the beginning.