3400 #36 injectors

[AaronGTR]

If you were running a bigger cam and higher rpm you could get close to maxing out the stock injectors. Plus if your engine was bored for more displacement, ported heads and headers etc... I could see it getting enough air flow. Depends on a lot of factors and scanning is really the only way to tell for sure. Even GM changed the injectors on the 3400 from 19# to 22.5# in 2000. I'm boosted of course though , which is why I'm using 42#'s.

[MMGT1]

I flow 268cfm through the heads and will put down a 14.5 qm all day long at 95mph! My 36's hit 57% duty cycle at 6400 RPM. Still lots there for the addition headers and nos.....

[HayesPerformance]

I hope I can help!

Hey Everyone,

I got some pointers that I hope can help you out. First off, rememeber that obtaining the correct amount of fuel flow from a group of injectors in an EFI system is similar to determining the right size jets for a carbureted engine. The fuel flow of both systems must be matched to the airflow requirements of the engine over a broad rpm operating range.
A carburetor may have three or more separate control circuits such as idle, mid-range, and power, to deliver a fuel curve over the engine’s operating range. An injector also must be able to supply a small amount of fuel to support engine idle, a large amount at wide-open throttle to prevent high-rpm lean-out, and transitional amounts to cover all of the operating conditions in between. These wide operating boundaries demand that an injector have a wide ”dynamic range” of operation.
The amount of fuel delivered by an electronic injector is controlled by how long it is held open by the Engine Control Unit (ECU). It is “pulsed or energized” open for short periods of time at idle, and held open longer as rpm and airflow increase.
Just as the wrong-sized jets in a carb can cause driveability problems such as rough idle, surging, poor throttle response or even high-rpm lean-out, so can incorrect injectors. Following is a guideline equation for approximating fuel flow per injector based on estimates on engine Horsepower (HP) and Brake Specific Fuel Consumption (BSFC). Take note of these conditions for equation accuracy:

1. Engine HP must be realistic estimate of engine output.

2. BSFC is determined from engine dynamometer measurements. It typically ranges from 0.4 - 0.6 for gasoline powered engines. A BSFC of 0.5 is a reasonable initial estimate for most engines.

3. The 0.8 multiplier of the "Number of Injectors" helps us derive a practical, maximum "Injector Flow Rate" for each injector based on an effective real world injector operat-ing pulse time and fuel flow. It's unrealistic to establish the fuel flow to the engine based on an injector operating pulse time of 100% (wide open all the time). This formula uses an injector operating cycle based on 80%. Some full race engine management systems may operate at 85 - 95% duty cycle, but doing so for some time increases the likelihood of overheating the injectors which may cause irregular fuel rates or a decrease in low rpm operation.

[HayesPerformance]

For example, to calculate the individual injector size for a 650 HP V8 using eight injectors and assuming a BSFC of 0.5:

[HayesPerformance]

Use a Fuel Injector rated at 50 lb/hr static flow at 43.5 psi (3 barometric) fuel system pressure.

If you have a known injector fuel flow rate you can solve the above equation for a rough estimate of fuel system capacity like this:

[HayesPerformance]

NOTE though:

Keep in mind your application and other mechanical modifications that have been made to your engine. The number of cylinders or extremely high rpm engines (such as rotary engines) may require larger injectors due to on/off times.


Regards,
Dave

[HayesPerformance]

One thing too, REMEMBER Bigger Isn't Always Better.

Stock, street driven EFI engines using an O2 feedback, closed loop control system rarely exhibit a performance gain simply by installing higher flowing injectors. During closed loop operation, the stock ECU will try to adjust for the greater amount of fuel being delivered. If the replacement injector is not too large (about 10 - 20% greater flow at most) the ECU might be able to make the correct compensation. If the induction system has been left stock and the ECU cannot compensate for the increased fuel volume, unburned fuel will all but pour into the exhaust. This in turn will cause the Check Engine Light to come on, the catalytic converter could overheat and other problems will occur. In applications looking for just a little more performance it my be easier and more cost effective to raise the fuel system pressure to get a 10%-20% fuel flow increase at the injectors.
Remember that installing larger flow injectors only has technical merit if substantial modifications have been made to the entire induction system. Plus, the stock ECU will undoubtedly have to be re-programmed for the increased injector fuel flow.

Best Regards,
David

[prophiseer]

I understand the need for larger injectors with boosted apps, but, IDK . . . I'm kinda confused by our stock setups, then . . . so the multec2's were rated at 22# as compared to the 19# on the multec1's? Was there any real difference in intake volumn that showed a need for the larger ratings between the year models, and is there an actual performance difference between the '99 and '00+ year models? If so I might just go ahead and bump up my injector sets (I run 19# during the warmer summer months and 21# during the colder winter months) a size. I'm kinda looking that route anyway once I get my spare 3400 upper end finished.

But anyhow, I was under the assumption that as long as you don't go radically bigger than stock on a N/A setup, and as long as the PCM is noting enough air flow into the motor, at WOT the injector dwell time is a set value; and as long as you're not at WOT the PCM can compensate the dwell time based on the various inputs to achieve 14.7:1. Also, I thought that if you increase the fuel pressure at the injectors too much, you can bog them down.

[AaronGTR]

I understand the need for larger injectors with boosted apps, but, IDK . . . I'm kinda confused by our stock setups, then . . . so the multec2's were rated at 22# as compared to the 19# on the multec1's? Was there any real difference in intake volumn that showed a need for the larger ratings between the year models, and is there an actual performance difference between the '99 and '00+ year models? If so I might just go ahead and bump up my injector sets (I run 19# during the warmer summer months and 21# during the colder winter months) a size. I'm kinda looking that route anyway once I get my spare 3400 upper end finished.

The '99 injectors aren't multecs. '99 and earlier used bosch injectors rated at 19lb/hr. '00 and later used delco injectors rated at 22.5lb/hr @55psi. No performance difference that I know of between the years. I know GM changed the upper manifold design slightly for the EGR, and they did change the pcm calibration for the different injectors.

But anyhow, I was under the assumption that as long as you don't go radically bigger than stock on a N/A setup, and as long as the PCM is noting enough air flow into the motor, at WOT the injector dwell time is a set value; and as long as you're not at WOT the PCM can compensate the dwell time based on the various inputs to achieve 14.7:1. Also, I thought that if you increase the fuel pressure at the injectors too much, you can bog them down.

You would need some extreme fuel pressure to have any effect on the injectors. It's usually fuel flow and the fuel pump that suffer from bumping the pressure too high. If you don't increase the injector size too much, yes the pcm can compensate slightly at idle and cruise by using the O2 sensor and changing the fuel trims. That is only so accurate though, and there is a limit to how much it can adjust. Also constantly having the fuel trims way to the negative means you are always running too rich until the pcm has time to adjust (it takes some time to react) so your gas mileage will suffer and your O2 sensors will foul up faster. At WOT you will always be running too rich and will actually lose power. Even a change from 22lb to 28lb is enough to throw things off from running optimally. Basically any time you change injectors you NEED to program the computer to compensate.

[prophiseer]

so, following along with this now, as long as you don't change the flow rate of the injectors by anymore than one size, you should be alright? Although, I wouldn't think you would need to reflash the PCM if you kept the flow rate the same, but just installed more efficient injectors (different spray pattern). Although, like I said, I change injectors between seasons, I've never had any problems (actually, the car runs phenomenal by feel, and by the info I grab off the scanner). Question, though, does a 5ms injector dwell time at 100% throttle angle, 100% load, 4,900 RPM @ 83mph sound reasonable on 19#?

[AaronGTR]

Oh yeah, 5ms is pretty short. I run 2-3ms at idle with my 42#'s and 14-16 at higher load and rpm under boost. My stock 22#'s on the other hand where in the 24-26ms range at 80% throttle and 5k rpm. Thats maxed out. Usually if you're under 18ms at redline you should be ok.

[prophiseer]

I thought that was a decent spec. I gotta say though I love the numbers I pull off the scanner every now and then; no cylinder misfire counts current or in history (seriously . . . 0 for all 6), 0* KR, lt and st fuel trim are always low; blah blah blah (just tooting my horn, )

Anyways, while on fuel in general, I'm back to a stock pump assembly and motor. I think I'm going to sell the Walbro unit I had, along with the t-fitting for the fuel line and the pre-wired short harness for the pump motor and fuel sender. I'm just tired of the extended crank times, leaking pump assembly (that REALLY pissed me off), etc. Pump runs great, never had any running issues with it. Pressure has been regulated around 46-47 so it hasn't been under a lot of stress, fuel tank was always kept above 1/4. A buddy of mine dropped the pump motor before I installed it, but I never noticed any damage to the unit and it ran fine for the 5 months it was installed. If I do sell it I'm thinking $80, maybe a little less. Opinions?

[jabartram]

i ended getting L32 injectors, but now i need to find the harness connectors?

[MMGT1]

I think Milzy has the harness for sale:

https://www.milzymotorsports.com

contact him through there

[jabartram]

he has connectors for L67 injectors, i already have a set of those, i'm using 04 L32 injectors, they use different connectors.