GM TPI manifold -- description

[John S Gwynne]

Greg Jestico sent this to me a while ago, and I thought others
may be interested. (reposted w/permission from Greg)

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From: pbjorn at sirius.UVic.CA
Subject: TPI manifolds

John,
remembering an article from Car Craft magazine a year or so ago, I can give you 
this Info.

If the manifold was originally from a Corvette,
The manifold, runners, plenum, throttle body etc. remain identical from 1985
to 1989. These have conventional bolt hole angles, and as such will bolt to
any earlier small block. the Corvette uses an external tube from the header
to the manifold to supply the EGR. 1990 to 1991 manifolds have a boss for 
mounting the Map sensor at the right rear of the Plenum. These manifolds 
still have conventional mounting bolt angles.

If the manifold is from Camaro/Firebird,
The manifold is the same from 1985 to 1987. These have conventional bolt angles.
The manifold has an internal passage from the head to supply the Egr. The 
remaining parts are the same as Vettes' , and it will bolt to any earlier
smallblock. In 1988 GM changed the angle of the center two bolts on each head
to a more vertical angle, and it remained that way until 1993.
I have heard that these holes can be elongated and spot faced to match up with
the earlier design, but have not seen how cleanly it can be done.
In 1990 the same boss for the Map sensor was added to the plenum as the Vettes.


The 1985-1988 TPI on all models used a cold start enrichment valve. The plenum
and runners have passages for this. After 1988, the valve was eliminated.

All this means that there are ;

3 possible manifold bases- internal Egr, external Egr, and angled center bolts.

2 possible runner tube pairs- With cold start passage or without.

3 possible plenums- early whith cold start passage, mid. without cold start 
                    passage and late with Map boss.

GM also made a revision to the Throttle cable attaching design on 1989 and later
TPI systems.



Greg Jestico
at
pbjorn at sirius.UVic.CA

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