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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.
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.
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