Injector Math, 55# for an F-body 3.4L w/ TBI?

[Kaos]

Lmao. Damn fat thumbs


Sent from my iPhone using Tapatalk

[carbon]

Well well, leaned something new today. I will consider this day a success. Thanks Canyonero


Sent from my iPhone using Tapatalk

"leaned" something... LOL Unintentional injector joke...

[Kaos]

Well well, leaned something new today. I will consider this day a success. Thanks Canyonero


Sent from my iPhone using Tapatalk

[Canyonero]

I have a '7747 with a chip socket, but I'm using the '8062 from the Trooper now. I could probably get it dialed in better with the wideband, but I'm pretty well invested in going MegaSquirt now.

Sent from my XT1058 using Tapatalk

[34blazer]

Was using a '7747, $42 mask and one of the 4.3 5spd binarys

[Canyonero]

What ECU are you using?

Sent from my XT1058 using Tapatalk

[34blazer]

My method wasn't nearly as scientific, but on my 3.4 and 55# injectors the fuel pressure was set at 26 psi to keep DC down. Its been a few years since I worked on it, scrapping the project anyway. LOL

[Canyonero]

Resurrecting an old thread, but I was reminded of these calculations indicating my injectors were too small. I'm configuring a MegaSquirt to run my Trooper, I keyed in the values defining my engine (displacement, number of injectors, flow rating, etc) but when I run the simulations it's complaining that the pulsewidth is too long. If I crank up my injector size in the config, things look better. Looks happy with 60# injectors, in line with these calculations from four years ago.

[Canyonero]

Still waiting on my new injectors, just now got the ship notice. I foolishly ordered an adjustable regulator for my throttle body, without looking to see how easy it is to make the stock one adjustable. There's $65 wasted, I'll have a stock one modified and installed before my fancy aftermarket one gets here. Live and learn.

If I have time to work on it today, I'll bring my pressure up to 13PSI with my 46# injectors and tweak the BPC in my BIN. See if I'm on the right track anyway.

[robertisaar]

this all sounds plausable.

[Canyonero]

I posted this up on my Isuzu forum, but you guys have more knowledge of this particular engine. Short story is that my fuel pressure and injector combo is starving my engine, based on what I'm seeing though WinALDL and TunerPro. I assumed my pressure was standard 13 PSI for TBI, but I just installed a gauge and it's actually 10.5 PSI. I'm running the same fuel pump that gave me 45 PSI for my 3.4L when it was configured with multiport. I have ordered an adjustable regulator from cfm-tech.com to bring my pressure back up, but I'm also looking into changing the injectors based on what I worked out here:

I've referenced the following page to come up with this: http://www.dynamicefi.com/TBI_Fueling.php

An important parameter in engine performance is known as Brake Specific Fuel Consumption (BSFC). It is the pounds of fuel required to generate one (1) crankshaft HP for one hour. An engine with a moderate compression ratio and so-so heads has a BSFC of about .50

I'm considering our iron-head V6's to have a moderate compression ratio and so-so heads.

So for our sanity check, we'll calculate the amount of fuel required to produce 125 HP (stock rating of the 2.8L TBI) at a BSFC of .50:

125 * .50 = 62.5 #/hr

Then factor in a maximum of 85% duty cycle for the injectors. The duty cycle of the injector is the ratio of on time to off time. (Note that this is not the best method. The required 'off' time is really tied to RPM, not a duty cycle.):

62.5 / 0.85 = 74 #/hr

OK, now we know that the engine requires 74 pounds of fuel per hour to produce the rated 125 HP. To do this with two injectors each needs to provide half that amount.

74 / 2 = 37 #/hr per injector.

We know the stock injectors in the 2.8L to be 36 #/hr, pretty close.


So now lets repeat that, but with my target of 180hp (considering I have a larger displacement, bigger cam, rocker ratio and throttle body than the stock 2.8L):

Amount of fuel required to produce 180 HP at a BSFC of .50:

180 * .50 = 90 #/hr

85% injector duty cycle:

90 / .85 = 109 #/hr

Split between two injectors:

109 / 2 = 54.5 #/hr

Fancy that. That's about the rating of a 5.7L's injectors (55 #/hr). Those might be useful, eh?


Just for kicks, lets figure the stock 3.4L (160hp) with multiport (six injectors) to see if that calculation was reasonable for my 3.4L:

160 * .50 = 80 #/hr

85% duty cycle:

80 / .85 = 94 #/hr

Between six injectors:

94 / 6 = 15.67 #/hr

Stock size is 17 #/hr each, so I think that's also reasonable.