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Old 03-23-2009, 02:08 PM
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TBI injector flow rates

I've been trying to research the flow rates of various GM TBI injectors and I'm finding conflicting information on the web (imagine that). Most sites quote this data:

Quote:
Engine | Bore ~~~|FI color| Flow ~~~| Part #
_________________________________________________
2.8L~~ | 1-3/8 ~~|Blk/Wht |33 lb/hr |GM5235430*RPD
_________________________________________________
4.3L~~ | 1-11/16 |Yel/Blu |45 lb/hr |GM5235203*RPD
_________________________________________________
5.0L~~ | 1-11/16 |Grn/Wht |40 lb/hr |GM5235279*RPD
_________________________________________________
Pickup
5.7L~~ | 1-11/16 |Orn/Blk |55 lb/hr |GM5235206*RPD
_________________________________________________
Cop car
5.7L ~~|1-11/16 ~|Yel/Brn |65 lb/hr |17084327-ACR
_________________________________________________
Late big block pickup
7.4L ~~| 2" ~~~~~|Blu/Blk |80 lb/hr |GM1708430*RPD
_________________________________________________
big block pickup
7.4L ~~|2"|Drk Red/Drk Blu|90 lb/hr|GM5235231*RPD
I'm confused that the injectors from the 4.3 V6 apparently outflow those on the 305???

Then I found this:

Quote:
For injectors they come in various flow rates. The common injectors that are found in the above TBI units are:

* 2.8l and 3.1l engines: 33 #/hr
* 4.3l engine: 45 #/hr (note: some units have different flow rate injectors. This is done to help with fuel distribution.)
* 5.0l engine: 55 #/hr
* 5.7l engine: 61, 65, & 68 #/hr
* 7.4l engine: 46*, 75 & 81 #/hr.

*Just watch for the '94 - '95 BBC truck units as the injectors only flow 46 #/hr at 13 psi. Which is 74 #/hr at the 30 psi these TBI units use. On the up side they come with a 30 psi FPR. The down side is that the injectors are small.
So which is it for the 305 injectors, 40 lb/hr or 55 lb/hr? Thanks.

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Old 03-23-2009, 03:53 PM
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Quote:
Originally Posted by joe_padavano
I've been trying to research the flow rates of various GM TBI injectors and I'm finding conflicting information on the web (imagine that). Most sites quote this data:



I'm confused that the injectors from the 4.3 V6 apparently outflow those on the 305???

Then I found this:



So which is it for the 305 injectors, 40 lb/hr or 55 lb/hr? Thanks.
The 4.3 should be 40 lb/h at 9-13 psi

The 5.0 should be 45 lb/h at 9-13 psi

The 5.7 uses two
- standard 55 lb/h at 9-13 psi
- heavy duty at 65 lb/h at 9-13 psi

7.4 uses two
- standard 85 lb/h at 9-13 psi
- heavy duty 90 lb/h at 9-13 psi

For every psi you bump the line pressure, the injector will deliver about 2 lb/h above its rating. But 18-20 pounds is about the limit before the wheels come off the injectors. The stock pump will not deliver more than 14-16 psi, if that.

There are two tricks to getting more flow without changing to a higher flow injector, the first is the afore-mentioned increase in pressure. The second is to reprogram the computer for a longer open/on period. Typically injectors are flow rated at 80% duty cycle. The off time used for solenoid cooling. You can eat into this by keeping a lower rated flow injector on for say 90% of its rated duty cycle. Yes this reduces their life a little.

Bogie
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Old 03-23-2009, 05:15 PM
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Thanks. Your list certainly makes more sense. Unfortunately, that now makes three conflicting sets of data. Does yours trace back to either factory data or test data? Thanks.
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Old 03-23-2009, 05:58 PM
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Quote:
Originally Posted by joe_padavano
Thanks. Your list certainly makes more sense. Unfortunately, that now makes three conflicting sets of data. Does yours trace back to either factory data or test data? Thanks.
Factory data and screwing around with them, here's some of the GM part numbers.

- 4.3 uses 17111468, 17112521, or 5233203

- 5.0 uses 5235279, or 5235307

- 5.7 regular duty uses 5235206
heavy duty uses 17084327, or 17112412

- 7.4 regular duty uses 5235231
heavy duty uses 17112560

There may be other GM P/Ns I'm not aware of. Also keep in mind that Holley is a big supplier of these things as is Bosch and others. Another good outfit to look for service and parts is Turbo City.

edit:

Keep in mind that when hot rodding these things it's better to use a too high of a flow injector and run the computer chip to select a shorter on time, than it is to run too small and injector that has the computer programmed for more on time, with-in reason. You don't want to run a 7.4 injector on a 4.3 with a real short on time as that provides a crummy spray pattern.

Bogie
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Old 03-23-2009, 08:20 PM
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Oldbogie, i read your post, but then got to wondering, why wouldn't the 4.3L- with the same per cylinder displacement as the 5.7- use similar injectors and flow rates?

I'm sure there's an obvious reason and I'm not contesting your info, just curious.
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Old 03-23-2009, 08:36 PM
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Quote:
Originally Posted by cobalt327
Oldbogie, i read your post, but then got to wondering, why wouldn't the 4.3L- with the same per cylinder displacement as the 5.7- use similar injectors and flow rates?

I'm sure there's an obvious reason and I'm not contesting your info, just curious.
We're talking TBI where 2 injectors are feeding the entire engine. The 4.3 is only 262 inches the where the same type of paired injector is feeding 305, 350, and 454 respectively they have to be bigger or online more or operate at higher fuel pressures.

So while the 4.3 has the same per cylinder volume as a 350, the injectors have to feed two more of those 43.7 cubic inch cylinders with the V8.

Bogie
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Old 03-23-2009, 08:44 PM
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Thanks, my bad. I was seeing TBI and thinking individual cylinder injectors.

Last edited by cobalt327; 03-23-2009 at 08:49 PM.
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Old 03-23-2009, 08:59 PM
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Quote:
Originally Posted by cobalt327
Thanks, my bad. I was seeing TBI and thinking individual cylinder injectors.
I've done it more than once, then you catch yourself as you switch back between TBI and TPI or multiple TBI systems like the Holley 4 barrel or dual 2 barrel or dual 4 barrel systems.

TBI....errr, rather TPI..... injectors tend to run around 19 to 30ish pound per minute. But they have to come on faster, run for a shorter time and operate under higher pressure. So they appear to be oversized in terms of flow because of the way they cycle they need more instant flow and when the engineering design for that gets tested the standard way for electronic injectors, they end up looking too big or conversly the TBIs look too small. But it all works for the applications they're intended for.


Bogie

Last edited by oldbogie; 03-24-2009 at 10:44 AM.
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Old 03-24-2009, 01:34 AM
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It has been a long day...

Spent a couple hours this evening after work R&R'ing my lawn tractor's carb to clean it out, had started up but ran like stink.

Carb cleaner fumes may have gotten to me, so anything I say tonight needs an asterisk next to it...

Last edited by cobalt327; 03-24-2009 at 01:20 PM.
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Old 03-24-2009, 07:57 AM
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Here check this site this guy at this place is pretty sharp. He helped me out with my problem on my TBI.

www.cfm-tech.com
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Old 03-24-2009, 10:44 AM
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Quote:
Originally Posted by cobalt327
Or is that TPI injectors? Now I got you doing it!

It has been a long day...

Spent a couple hours this evening after work R&R'ing my lawn tractor's carb to clean it out, had started up but ran like stink.

Carb cleaner fumes may have gotten to me, so anything I say tonight needs an asterisk next to it...
Sometimes the finger is faster than the brain, got it busted once in a biker bar for that reason.

I'll edit

Bogie
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