I don't know my injector flow rate, now what?

[zorb847]

I want to use a throttle body from an 89 GM truck 350 motor but don't know what size injectors are in it. Where do I start? Anyone out there using this TBI or similar?

[Bernard Fife]

I hope you will be able to find your injector flow rates. If you can't find published specs, you can estimate the flow rates from the applications they were originally installed on.

What you might do is assume that the factory used them at about 80-85% duty cycle for the horsepower the original engine made, and work backwards to the flow rating.

For example, in my AstroVan, the 4.3 V6 (with two injectors) makes 160 HP, so the flow rate would be 47 pounds/hour if they are actually at 85% duty cycle.

There is a calculator for this here:

http://www.megasquirt.info/manual/minj.htm#size

Once you get your engine tuned, you may find you have VEs that are too high say, 145% for a naturally aspirated engine. In that case, you can use the 'Scale VE table' function in MegaTune to increase your Req_Fuel and decrease your VE table numbers automatically to a more reasonable number (say 115%, which is about 98%VE at 12.5 AFR). And obviously you can do the opposite if the VE numbers seem too low.

This will depends both on your engine configuration (i.e. high or low specific oputput), and the state of your tune. You should be able to narrow down the actual req_fuel number (and hence your injector flow rating) quite quickly this way.

Lance.

[colinnwn]

Hi zorb847,

Your injectors should be
injector engine flow lbs/hr throttle one GM
color code size at 13 psi bores part #
Green/White 5.0L 40 43mm 5235279

Thursday, June 24, 2004, 2:11:30 PM, you wrote:

z> I want to use a throttle body from an 89 GM truck 350 motor but
z> don't know what size injectors are in it. Where do I start? Anyone
z> out there using this TBI or similar?

Some info on GM TBIs and using them here
http://thegebharts.com/msindex.html

Later,
Colin
mailto:colin@thegebharts.com
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[Ricardo_Penteado]

Lance, which is the standard that is used for the measuring of the flow rate? 100% duty cycle under 43PSI of pressure? Which liquid is used in this measuring?