I want to convert a (actually convert back to) a TPI on an 89 350. I have everything except the throttle body. Will any year or size work?

I want to convert it to speed density, does that make a diference?

Thanks for a lurker,
Roy

 

All factory TPI throttle bodies are the same size. Larger after-market TBs are avaliable. It's debateable if the larger ones help much, especially if the remaining induction pieces are stock.
AFAIK, any year TB will work.

MAF, MAP, throttle body could care a less.

With a MAP however, you can install a cool looking K&N airfilter right onto the TB.

 

And suck all that nice warm radiator air into your engine....pfff....yeah right....

 

85-92....the Throttle Bodies are interchangable...but....you might have to change the throttle cable. I have an 85-88 style on my 91 Z28 (52MM BBK), and I had to change the thottle cable for it to work properly. 85-88 and 89-92, the throttle cables attach differently...

 

I believe you can't use the earler style TB with the later style plenum unless you drill the hole that the later plenum lacks for the IAC air to pass through. The later TBs route the air differently. The older plenums have a hole between the throttle bores that the newer ones don't. You can however use a newer TB on an older plenum. If I've explained this wrong then someone feel free to correct me.

 

When you say "early" or "late" style, are you referring to '92 and older vs '93 and newer?

Additionally, is there any difference between and TB from a 305 vs 350?

Thanks for the great info guys,
Roy

 

I didn't say it would run better, it just looks cool!!



In 84-85 the GM execs were planning on dropping the 350.
At the last min, they changed their mind and decided to keep it. No perf FI system was avaliable for the 350, so they used the 305 TPI sys on them.
Point is, the 305 and 350 TPI hardware are exactly the same except for the larger fuel injs on the 350's.

Humm, I was not aware abt the different IAC passages.

I'm assuming the "older" and "newer" refers to the 85-88 and 89-92 systems respectively. 92 was the last year for the TPI.

 

Thanks for clearing that up and for helping to answer a novis' questions.

Roy

 

Earlier plenums got EGR air through the small tube on the runners from I believe the drivers side runner. Later year plenums have a hole at bottom of TB for EGR air. Can use any TB for either, just have to use TB gasket for that year plenum. The TPS adjustment is also slightly different between years. IAC air flows through the TB on both models.

 

Interesting... I am running into problems on my TPI setup i installed on a 327 block. The IAC passages and TB's you are talking about. I am looking at my setup and it looks like a 85-87 unit w/9th injector, but blocked off. Yet the TB has the nipple on the underside for the tube to the EGR. I dont see any port coming off the runners...
my question is by the sound of it I have a pieced togeather unit. I dont know know what year of IAC housing I have is there anyway of telling? And if the nipple off the underside of the TB is for 90-92, that is what I might have. I am curious of what IAC motor to use???? or if there is any diffrence between 85-88(AC1) and 89-92(AC16) IAC motors except the part number and price?

 

On a TPI TB ,pass side you have top to bottom
PCV supply air to pass side rocker cover
a vac port for tank purge
and on the alum casting underneath that the IAC mounts into ,the spigots for coolant
There is also a small vac port under TB on drv side

EGR does not go to TB on any year;is by internal passage,
up the pass side runner and in the passage cast under the plenum to exit
through the 2 holes BEHIND the TB

See
http://www.hotrodlane.cc/Streetstories/choosingtpi2.htm
http://www.hotrodlane.cc/Streetstories/choosetpi1.htm