Injector question

[fush]

I am ordering an ecu shortly and one of the options I need to specify is whether I am going to be running low or high impedence injectors. From what I have been reading it appears one of the primary advantages of using a low impedence injector is that it has a shorter triggering time and may provide a better idle. Is there anything else I need to be concerned with in this choice?

 

-jeff

[slow4now]

Depending on how big of an injector you are getting, Low impedance will probably be cheaper. Also once you get over 440cc you may have a hard time finding a saturated injector for the size you need. 440cc and up I would go with peak and hold.

[Nitrousbird]

Now import injectors may be a little different, but here is what I've learned about the "Bosch" style used on domestics (used on GM and Ford V8's, among others).

 

Basically, how a high-impedance injector works, is that it grounds the one side, and basically pushes 12V across the injectors, causing the injector to open and close based on if voltage across it. Current draw is about around 1amp.

 

A low impedance injector is also known as a peak and hold injector. The pintle, or whatever the call it, gets heavier the bigger the injector gets. So it needs more voltage to open it.

 

Now if you would just toss on a low impedance injector onto a standard high-impedance setup, the injector would pull a straight 3-6 amps each time voltage was applied. This would burn out the injector driver, the injector coil, or both. Low impedance drivers are designed to allow that large amount of current to snap open the injector, then a constant 1 amp to keep it open (how the driver does this I'm not quite sure).

 

The reason you don't see really large high impedance injectors is because they begin to get sloppy and slow opening, due to the pintle being too heavy to snap open under just 1amp of current draw.

 

I'd assume the reasoning behind most cars having high impedance injectors and drivers from the factory is due to cost of the injectors and complexity of the driver circuit. I know for my style of injectors, low impedance are signficantly more expensive. And to run them, I need to either run an aftermarket PCM OR an add-on injector driver box. On my style, high impedance goes up to around 52lbs (rated differently than import injectors; I'm not sure of the conversion factor). Though after about 44lbs, they tend to start getting nice and sloppy, and you are better off going low impedance.

 

Not sure if that helps or not, but might give you something to think about.

[fush]

I am still trying to decide the correct size for my application. Using the calculation on the RC Engineering site it says I need something around 700cc for my application which seems rather large. Is there anything else to take into consideration when sizing fuel injectors other than the "standard" formula which they list on that site. HP X BSFC / num inj x max duty cycle

 

-jeff

[slow4now]

The best thing to do is find out what other people have had success with. Find some people making the power you want to make with the same engine and use the same injectors.

[Boost-n-Juice]

Originally posted by Nitrousbird:

Now import injectors may be a little different, but here is what I've learned about the "Bosch" style used on domestics (used on GM and Ford V8's, among others).

 

Basically, how a high-impedance injector works, is that it grounds the one side, and basically pushes 12V across the injectors, causing the injector to open and close based on if voltage across it. Current draw is about around 1amp.

 

A low impedance injector is also known as a peak and hold injector. The pintle, or whatever the call it, gets heavier the bigger the injector gets. So it needs more voltage to open it.

 

Now if you would just toss on a low impedance injector onto a standard high-impedance setup, the injector would pull a straight 3-6 amps each time voltage was applied. This would burn out the injector driver, the injector coil, or both. Low impedance drivers are designed to allow that large amount of current to snap open the injector, then a constant 1 amp to keep it open (how the driver does this I'm not quite sure).

 

The reason you don't see really large high impedance injectors is because they begin to get sloppy and slow opening, due to the pintle being too heavy to snap open under just 1amp of current draw.

 

I'd assume the reasoning behind most cars having high impedance injectors and drivers from the factory is due to cost of the injectors and complexity of the driver circuit. I know for my style of injectors, low impedance are signficantly more expensive. And to run them, I need to either run an aftermarket PCM OR an add-on injector driver box. On my style, high impedance goes up to around 52lbs (rated differently than import injectors; I'm not sure of the conversion factor). Though after about 44lbs, they tend to start getting nice and sloppy, and you are better off going low impedance.

 

Not sure if that helps or not, but might give you something to think about.

Well said!

[fush]

Originally posted by bigbabyjesus:

The best thing to do is find out what other people have had success with. Find some people making the power you want to make with the same engine and use the same injectors.

Only problem is nobody really has a setup like mine. Everyone is trying to tune with FMUs and ecu upgrades but they all have trouble with going lean up on the top of the rpm ranges. I've seen people running 440cc injectors hit about 300fwhp with the fmu/ecu chip setup but they also have very erratic a/f numbers VERY high fuel pressure and tend to break when something minor goes wrong with their setup. I'm planning to run SDS on my setup and hopefully with the correct sized injectors (as soon as I figured out what that is) and a bit of tuning I shouldnt have those issues.

 

-jeff

[SupraGlue]

EDIT: These are all ballpark numbers, btw. Actual horsepower output with a particular injector size will depend on fuel pressure, af ratio, willingness to extend duty cycle and driveline loss. But anyway...

 

Four 700cc injectors should give you enough fuel flow at high duty cycle for around the 425 safely at the wheels. Four 550's should give you enough for around 330 safely at the wheels. Four 440's is really running out of safety by around 270 at the wheels, so 300 must really be at a maxed out duty cycle, running moderately lean or some extra fuel pressure.

 

I'm assuming 85-90% duty cycle, which is a responsible maximum for top feeds, im my view. Also assuming around 40psi base, rising at 1:1 with boost (no FMU). You should go a little overboard on fuel with a boosted car anyway.

 

Hope that helps a little.

 

[ 26 September 2002, 01:46 PM: Message edited by: Stolen UFO ]