Re: TBI maunderings continue

[Darrel Kline <darrelk@domain.elided>]

>On Wed, 25 Nov 1998, Tom Harais wrote:
>
>> Roger:
>> 
>> >From what I've seen of GM TBI ('88 Trans Am - 305 TBI) I'd say you could
>> mount the injectors in or over an old carb body. The "round manifold thing"
>> you are refering to is just a set of venturis with throttle plates mounted
>> in the base. Not unlike a carburetor with no fuel connection so that jets,
>> power valves and idle circuits are defunct.
>> 
>> Whoops! I wonder if there is some type of idle circuits or anything in
>> those TBI units? 
>> 
>> Tom H.
>Hi Tom,
> The way I understand  the TBI system,the computer "tells" the injectors
>how long to open.This amount of time is determined by the information from
>the various sensors and then is compared to a preprogrammed "fuel map".So
>to get to your question NO there are no idle circuits per se.
>
>                         Dennis
>                         75,77,79 II's

  That's true about the computer determining the dwell time for the
injectors, but there *is* an idle circuit. It's called the Idle Air Control
(IAC). It's basically a solenoid which mounts on the throttle body and lets
additional air into the engine. There is also a throttle position sensor
mounted on the throttle body. 
  There are aftermarket throttle bodies available with/and without
injectors that use the Holley 4 barrel square bolt pattern, but these run
$300+. There's also an adapter available to mount the 3 bolt TBI to a
spreadbore intake, and one for the square bore. Another option is to
machine a 2 barrel intake for the larger throttle plates and drill the 3
mounting holes....this would give you more hood clearance.

Darrel Kline
Colorado Springs