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Old 01-29-2010, 09:41 AM   #1
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Default low impedance injectors, use resistors?

i have a 95 with the ms pnp and i was planning on running 440cc injectors from a turbo supra, from what i gather they are low impedance. So would it be better to use the resistors or the pwm feature? i searched but i didn`t really get my question answered, thanks!
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Old 01-29-2010, 11:00 AM   #2
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I would recommend using resistors.
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Old 01-29-2010, 03:00 PM   #3
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Hey this is something I may need to do soon as well. I have wondered for some time what sort of resisters will I need? Figuring out the correct resister value to reach an ohm load I can handle, but often I see people selling injectors with resisters and they have four little aluminium finned blocks. I realise those little blocks are the resisters but are they really necessary? Couldn't one just wire in normal resisters as available from radio shack and the like? How hot do they really get? What wattage will we need?

I have been around long enough to know that anything that is anodized blue aluminium Just HAS to make it go faster, and will therefore find its own buyers. But are they just snake oil or is there a real need for that level of cooling?
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Old 01-29-2010, 03:02 PM   #4
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I use 10 ohm 10 watt resistors from radioshack on my dsm 450s. I've never felt them get hot.
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Old 01-29-2010, 03:05 PM   #5
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I had a feeling that would be the case, thanks man.
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Old 01-29-2010, 04:10 PM   #6
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well if thats the case im going to the shack, unless anyone else has anything different to say
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Old 01-29-2010, 04:45 PM   #7
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Quote:
Originally Posted by chicksdigmiatas View Post
well if thats the case im going to the shack, unless anyone else has anything different to say
Note the top of my intake manifold:


Do the damn thing.
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Old 01-29-2010, 06:29 PM   #8
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Most injectors flow about 1A of current through them during use. Lets assume 2A to be safe. P=V*I=14*2=24W. Remember, you are not constantly running them at 100% duty cycle, so they will be cool at idle with no load. Not so for 4k rpm boosted. Ever touched an injector that is shorted to ground accidentaly? Its hot like ****. You can easily burn yourself. So yes, you do need the resistors with the heatsinks on them.

Jim
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Old 01-30-2010, 11:56 AM   #9
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I'm at this point too... I've got the 430cc from my 7mgte (2.9ohms?) and am trying to decide on adding resistors or using the PWM feature. Some searching said that if you use the PWM feature, you might also want to add a direct ground line (to the MS ground location) from the grounded side of R37/R38 to prevent noise... is this right? Also, can't defintetly find what our peak hold amps are for our application, so saying 2 amps is a 'safe' figure, we'd need about a 4.1ohm ~25watt resistor per each injector, or 11.1ohm for a 1amp current (according to DIYauto calculator a little more than 1/2way down the page) calculator

So far you guys are saying go the resistor route... so why NOT use the PWM feature on the MSPNP? What is being overlooked/wrong?

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Old 01-30-2010, 12:46 PM   #10
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Quote:
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So far you guys are saying go the resistor route... so why NOT use the PWM feature on the MSPNP? What is being overlooked/wrong?
If you run the Hi-Res code, the PWM feature is doa. Hi-Res uses the PWM register for the fueling calculations yielding better fueling control at the cost of no Peak and Hold injector control.

-Rouphis
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Old 01-31-2010, 02:19 AM   #11
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Those ones?
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Old 01-31-2010, 02:27 PM   #12
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I personally never liked using individual resistors and wanted a cleaner look. I have some friends with lots of Honda parts and I grabbed one of their resistor packs that come on some Hondas. Looks like this:



Wiring is simple too. Here
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Old 01-31-2010, 09:03 PM   #13
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^ thats exactly what I use , running Supra injectors. Works great.
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Old 01-31-2010, 09:46 PM   #14
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The shack resistors or the resistor box?
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Old 02-01-2010, 09:25 PM   #15
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Sorry, the Honda resistor box.
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Old 02-02-2010, 09:47 AM   #16
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Quote:
Originally Posted by chicksdigmiatas View Post
The shack resistors or the resistor box?



or



Needed when using low impedance injectors (such as DSM injectors). Gold anodized finish with solder lugs. 10ohm / 50 watt, no heat sink needed (built-in). Install 1 resistor inline with each injector on the positive side.
TA048 Set of 4 resistors- $19.99

JGS Precision Turbo

or

Honda resistor box.
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Old 02-02-2010, 01:08 PM   #17
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10 watt resistors is living kind of dangerously. 20 or 25 watt would be better.
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Old 02-02-2010, 01:38 PM   #18
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Ive been emailing Matt back and forth about this topic today. If you would like to run just a single resistor per channel you can use a 3 ohm 75+ watt in line
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Old 02-02-2010, 01:55 PM   #19
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It shouldnt matter if it is on the positive side or the megasquirt side of the circuit right? the current flowing thru the injector will still be limited .
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Old 02-02-2010, 05:03 PM   #20
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3 ohms is the minimum required to where you shouldn't damage the injector drivers in the MS. It all depends on how much current you feel comfortable running through the injectors, but prudence dictates running a bit more resistance.

It doesn't matter where the resistor falls in circuit.
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