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Old February 26th, 2004, 09:03
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Injectors (interesting info for nerdy types like me)

Some interesting fuel injector info that I gathered from various sites while researching injectors for my stroker (thanks to MSD, Accel, and Arlene Lanman):

ECU Compatibility:

Determining the right amount of injector fuel flow is only part of injection selection process. You also have to match the injector’s operating parameters to your Electronic Control Unit. Before we delve into these operating systems, you need to understand how an injector operates.
When an injector is energized (from the ECU), its internal parts physically move to let the pressurized fuel flow through. In the case of MSD’s “top feed” Competition Fuel Injectors, an internal ball is electronically lifted off its seat to allow the high pressure fuel to pass and go through six metering holes to form a tight 10° - 15° cone. This narrow spray angle (other injectors’ spray angle can be as wide as 30°) delivers a fully atomized fuel charge that is suspended in the intake and is kept from wetting the intake and cylinder walls.
The amount of fuel delivered is controlled by how long the injector is energized by the ECU and its driver circuit. This time is usually specified in milliseconds (ms). An injector is “pulsed” open for short periods of time at idle, and held open longer as rpm and the engine’s airflow increases, which requires a corresponding increase in fuel flow. There are two main styles of driver circuits so there are two main styles of injectors: There is a Saturated Circuit style as well as a Peak and Hold style.
Before going into the differences, keep in mind that the two are not compatible! Interchanging the different style injectors can result in slower delivery rate, overheating of the injector or driver and even engine damage!

Saturated Circuit Drivers/Injectors
Most domestic OE production EFI systems use an ECU with 12 volt Saturated Circuit drivers. These are very inexpensive, simple, and reliable. This type of driver works by supplying 12 volts to the injectors and the ECU turns it on and off to establish a fuel injector pulse. In general, if an injector has a high resistance specification (12-16 ohms) the ECU uses a 12 volt saturated circuit driver to control it. This means that the current flow in the driver and injector circuit stays low keeping the components nice and cool for long life.
Conversely, a downfall of a Saturated Circuit driver is that it has a slower response time (and closing time) than a peak and hold type. This slower time can somewhat decrease the usable operating range of the injector energized by this driver. An injector operating on a saturated circuit driver typically has a reaction time of 2 milliseconds while a peak and hold driver typically responds in 1.5 ms.
MSD offers two higher flow injectors that are designed primarily for quick response time with a 12 volt saturated circuit driver. The PN 2018 Injector is rated at 38 lb/hr with 12 ohms and the PN 2013 is a 50 lb/hr, 12 ohm injector.

NOTE: You can measure an injector’s resistance with a Digital Volt-Ohm Meter(DVOM) by connecting it across the injector’s electrical plug contacts.
NOTE: Ohm’s Law can be applied to calculate the current in the injector and driver circuit when using a high resistance injector like the PN 2018 (38 lb/hr static flow, 12 ohm). Remember, Ohms’s Law is I = E/R, where I = the circuit’s current in amps, E = battery voltage in volts available to the injector, and R = injector resistance in ohms. So, for our 12 ohm injector being supplied 12 volts, I = 12v /12 ohms, which is 1 amp of current in the circuit to operate the injector.


Peak and Hold Driver/Injectors
These type of injectors and drivers may also be called current sensing or current limiting. They are more expensive and complex than saturated circuit drivers, and are not generally used with domestic production ECUs. They are primarily used in aftermarket high performance systems.
Most high flow injectors are low resistance (2-5 ohms) and use a peak and hold driver to activate them. The Peak current is the amount required to quickly jolt the injector open, and then the lower Hold current rating is used to keep it open for as long as the ECU commands. These require the extra kick from the higher current to keep the opening and closing time of the injector stable at the higher fuel flow rate.
With this type of driver, 12 volts is still delivered to the injector, but due to the its low resistance, the current in the driver circuit is high. How high? Using Ohms’s Law we can calculate the current rating (12v/2 ohms = 6 amps). This is substantial current flow and a Saturated Injector cannot handle it.
The drivers also come in two values; 4 amp peak/1 amp hold, and 2 amp peak/0.5 amp hold.. Even though 6 amps may be available to operate the injector, the maximum it is allowed to reach is 2 or 4 amps, depending on the driver’s current limit. Note that the MSD PN 2014 (72 lb/hr, 2 ohm) and PN 2015 (96 lb/hr, 2 ohm) injectors require a 4/1 amp driver.

Question was: What is the differance between the injectors we can use in our Supras.

Reply:
There are only a few types of top fed injectors that will fit the existing fuel rail set-up. Thus, not every 550 out there will be a direct fit.

The stock 7M-GTE has P&H (Peak & Hold) hole-type injectors that have a ballasted resistor as part of the ignition system. Hole type injectors are a pintle type that have a recessed discharge hole and a distribution plate with holes. Refer to www.autoshop101.com Article 22 for more information.

Minimum cycle time for most pintle types is 2.0 Ms. for Peak & Hold (OEM) and 2.5 for Saturated units. The Disc will cycle as low as 1.0 Ms. The Lucas Disc, and I assume RC Disc, weighs only 0.4 Grams. and the Bosch / Nippon -Denso pintle is at 3.9 to 4 Grams (Ten times heavier). The reduced inertial loading of the disc, allows the Disc to overcome the hydrostatic load at excitation quicker and return to it's seat faster, providing quicker response times and more consistent cycle-to-cycle values.

So why is this important. Well, it is not, most of the time. At 3000 rpm the intake valves open and close 25 times per second. Thus, each even is 40Ms in length. At 80% injector duty, the injector is "on" 32Ms and "off" for 8 Ms. This is plenty of time for both injector types to get their job done. During those last 4Ms, the pintle would only just get closed, when it is time to open again. Beyond 90% injector duty, the injector would start to become static (open all the time) or go "semi-static" (as in "lock-up"), which would have drastic consequences at WOT - this is why Reg Riemer and others say not to go past 85% Injector Duty.

Now, at 6000 rpm, the valves open/close 50 times per second. At 80% injector duty, the injector is "on" 16Ms and off 4Ms. Thus, at 6000 rpm, the injector pintle just gets closed, when it is time to open again. At 6500 rpm (redline), the valves open/close 54.16 times per second. At 80% injector duty, the injector is "on" 14.77Ms and "off" 3.7Ms. At 6500 rpm, the valve opens/closes 54.1667 time per second; at 85% injector duty, the injector is "on" 15.69Ms and "off" 2.77Ms. During those last 2.77Ms, the pintle would only just get closed, when it is time to open again; if the pintle is "slower" than the 2Ms stated above, the injector would start to become static (open all the time) or go "semi-static" (as in "lock-up"), which would have drastic consequences at WOT - this is why Reg Riemer and others say not to go past 85% Injector Duty.

Due the short time the pintle is open at 6500 rpm, the "ramp-up" time of the P&H vs. Saturated injector becomes critical as to how much fuel is injected. The 1-1.5 Ms quicker opening time of the P&H is significant in the amount of fuel injected. It is for this very reason and the reasons first stated (consistently and accuracy) that P&H injectors are used in turbo and performance applications - the very reason Toyota used P&H injectors in the Mark III Turbo.

Next, picture the fuel curve that occurs when the injector opens/closes. The P&H ramps up steeply (as in .5 to 1Ms), then levels and then degrades very slowly for 2Ms and then degrades steeply over the next 2Ms. The Saturated Type ramps up more slowly (as in 2Ms) to a peak and then levels, then degrades very slowly over a 2Ms interval and, finally, degrades steeply over the last 2Ms. The disc types, typically, open very,very quickly then degrades quickly as well - kind of a triangular shape fuel "curve". Overall, the P&H delivers more fuel during its Duration.

In addition, the fuel tables stored within the TCCS ECU are based upon the characteristic response of the P&H injector. Basically, installing Saturated type injectors in lieu of P&H means, at high rpm, one is guaranteed that less fuel will be delivered.

With all of this said, the disc type may still appear to some to be superior to the P&H pintle type; however, HKS add-ons and stock ECU are programmed for the response time of the P&H hole type pintle and, therein, lies the reason we should stick with pintle type, specifically P&H and not even Saturated type, and not use the "superior" features of the disc type.
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Old February 26th, 2004, 09:31
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Re: Injectors (interesting info for nerdy types like me)

cool write-up

I think I'd like to build a stroker using one of each type of injector, but I'm not sure my sanctioning body allows mixed injector.
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Old February 26th, 2004, 11:49
SeanP SeanP is offline
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Re: Injectors (interesting info for nerdy types like me)

Step away from the ricer forums, geek boy.

Thanks, I found that educational. Do you think that 50lb/hr injectors might be a bit overkill for our strokers?

SeanP
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Old February 26th, 2004, 13:14
MrShoeBoy MrShoeBoy is offline
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Re: Injectors (interesting info for nerdy types like me)

Quote:
Originally Posted by SeanP
Step away from the ricer forums, geek boy.

Thanks, I found that educational. Do you think that 50lb/hr injectors might be a bit overkill for our strokers?

SeanP

Yes very over kill unliss you are supercharged/turbo'd or large ammounts of the funny gas

AARON
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  #5  
Old February 26th, 2004, 13:21
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Re: Injectors (interesting info for nerdy types like me)

Quote:
Originally Posted by SeanP
Step away from the ricer forums, geek boy.

Thanks, I found that educational. Do you think that 50lb/hr injectors might be a bit overkill for our strokers?

SeanP
I'm going 26 lb/hr on mine, with an OEM 19 lb for the auxillary NO2 flow.

You're going to need more than a stroker to move that beast of yours. I have a spare 460 that may be adequate.

CRASH
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Old February 26th, 2004, 15:49
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Re: Injectors (interesting info for nerdy types like me)

Some more very good info from RC Engineering regarding sizing injectors for a specific engine size and power:

http://www.rceng.com/technical.htm

CRASH
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Old February 26th, 2004, 16:00
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Re: Injectors (interesting info for nerdy types like me)

Quote:
Originally Posted by MaXJohnson
cool write-up

I think I'd like to build a stroker using one of each type of injector, but I'm not sure my sanctioning body allows mixed injector.
I wasn't aware that AMC or DaimlerChrysler ever built a 2-cylinder XJ. What's the engine displacement and how much torque does it produce in stock form?
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Old February 26th, 2004, 16:03
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Re: Injectors (interesting info for nerdy types like me)

Quote:
Originally Posted by SeanP
Step away from the ricer forums, geek boy.

Thanks, I found that educational. Do you think that 50lb/hr injectors might be a bit overkill for our strokers?

SeanP
Dunno what the specs are for your stroker, but Bob Salemi found 30# injectors were too large for his stroker. He backed off to either 26# or 28# and then used an adjustable MAP to fine-tune it. He posted a report about this last summer or autumn. I'm sure it's on the Strokers' site, but I thought he also posted it here.
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Old February 26th, 2004, 16:20
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Re: Injectors (interesting info for nerdy types like me)

Quote:
Originally Posted by SeanP
Do you think that 50lb/hr injectors might be a bit overkill for our strokers?

SeanP
This was said said in jest.

CRASH
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Old February 27th, 2004, 00:40
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Re: Injectors (interesting info for nerdy types like me)

So what you are saying about injector size is basically that you want to run one that will be at 80 % of it’s maximum duty cycle at WOT. So if I have a 26# injector and it’s running at 90% and I switch to a 28# injector the ECU will know the difference and slow the injector down? Am I way off base here?
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Old February 27th, 2004, 05:56
rsalemi rsalemi is offline
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Re: Injectors (interesting info for nerdy types like me)

Quote:
Originally Posted by Neil
So what you are saying about injector size is basically that you want to run one that will be at 80 % of it’s maximum duty cycle at WOT. So if I have a 26# injector and it’s running at 90% and I switch to a 28# injector the ECU will know the difference and slow the injector down? Am I way off base here?
Thats what the ECU and O2 sensor are designed to do!!
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Old February 27th, 2004, 12:15
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Re: Injectors (interesting info for nerdy types like me)

Quote:
Originally Posted by rsalemi
Thats what the ECU and O2 sensor are designed to do!!
Actually there is a lot more to it than just the ECU and O2 sensor. The ECU uses information from the CPS, TPS, CTS, MAP, CamPS, and O2 sensor. The reason I asked that question is that I am used to working on the old Bosch systems. The have a preprogramed intervial for run and cold start for the injectors. Put a larger injector in and it will deliver too much fuel. The ECU does not slow the injector down. The only way to make an injector go static is to exceed the rpm that the injector is rated (usually much higher than the engine can handle in stock form)
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Old February 27th, 2004, 13:19
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Re: Injectors (interesting info for nerdy types like me)

The Ford 24lb injectors will do fine on most strokers without needing any fine-tuning. In some cases, it may be necessary to increase the fuelling by either prolonging the injector "on time" (MAP adjuster) or by increasing the fuel pressure (adjustable regulator).
I already have Ford 24lb injectors and a homebrew MAP adjuster (set to 4.2v) on my 4.0. When I install the stroker, I'll keep the same injectors and bump the MAP voltage back up to 5.0v and maybe slightly higher until the A/F mixture's in the ideal range.
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Old February 27th, 2004, 13:30
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Re: Injectors (interesting info for nerdy types like me)

Quote:
Originally Posted by Neil
Actually there is a lot more to it than just the ECU and O2 sensor. The ECU uses information from the CPS, TPS, CTS, MAP, CamPS, and O2 sensor. The reason I asked that question is that I am used to working on the old Bosch systems. The have a preprogramed intervial for run and cold start for the injectors. Put a larger injector in and it will deliver too much fuel. The ECU does not slow the injector down. The only way to make an injector go static is to exceed the rpm that the injector is rated (usually much higher than the engine can handle in stock form)
As long as the computer has wide enough fuel-mapping parameters, it can adjust larger injectors down when it receives a "rich" signal from the O2.

The reason you want to be relatively close on the injector size is for those instances when the ECU disregards O2 sensor input. On a Renix machine, I *believe* that happens at crank over, startup, and WOT.

CRASH
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Old April 20th, 2004, 10:38
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Re: Injectors (interesting info for nerdy types like me)

I know this is an older thread but I am interested in all the info about a/f ratio measurement. Please excuse the dumb questions.

The ECU ignores the O2 during crankover, warm up, deceleration, and WOT. According to one source, the injectors are turned off duriing deceleration when RPM's are above 1500.

So based on this thread and the one about the A/F measurements, the A/F gauge is useful during these 4 modes?

So the conclusion is that one should pick the right injector based on WOT A/F at optimum and adjust MAP for idle?

WOT at what RPM? Should a sampling be done at intervals, say 1K RPM or 500? (This could be done by discounecting the O2 and TPS output signal while cruising?)

What is the range? "As long as the computer has wide enough fuel-mapping parameters"

When is the proper time to apply adjustable fuel regulator with high preasure fuel pump? I assume the stock pump is 39?

I am trying to understand when trade off decisions must be made.
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