how close do you have to be for high impedance on a MS?

[Beagle]

I'll go read the manual but thought I might toss this out here since I can't do that right this second.

14.5 ohm are what most of the High impedance injectors I see are. I also see some that are 12.5 ohm - is that close enough?

I'm wondering if there is any wiggle room on that.

[Matt Cramer]

Anything over 10 ohms can be treated as normal high impedance injectors.

[Beagle]

Thank you sir!

[BigBlockMopar]

Maybe the following would be better in it's own topic, but...

How much does high/low impedance-number impact the opening/closing rates of injectors?

[dieselgeek]

Maybe the following would be better in it's own topic, but...

How much does high/low impedance-number impact the opening/closing rates of injectors?

It varies completely by injector type. The newer injectors like Injector Dynamics sells, are high impedance with ridiculously awesome opening times, well under 1 ms at typical operating voltages. Older ones like the 160 lb/hr Ford units so popular with turbo cars (until ID showed up) have longer opening times.

Honestly, it's the system voltage that affects open time more than anything - which is a good reason to have your car's system voltage well sorted out. A lot of cars have bouncing voltage that wreaks havoc on tuning... and many of their owners have no idea (even though it also affects your MSD/jacobs/etc ignition quality).

Finally, what really matters especially when you need large injectors, is the linearity of their fuel delivery at low pulsewidths. The newer ID injectors are awesome, they have a video of a Honda 1.8 liter engine idling happily with 200 lb/hr injectors. Many injectors do not have linear fuel delivery with decreasing pulsewidth, which is where tuning skills, *and having a good, tuneable system* become important. You'd be surprised how many "popular" EFI systems don't allow you to map open/dead times, which sucks to find out after you spend $2000 on one. They never tell you this in the marketing literature...

[BigBlockMopar]

...
Honestly, it's the system voltage that affects open time more than anything - which is a good reason to have your car's system voltage well sorted out. A lot of cars have bouncing voltage that wreaks havoc on tuning... and many of their owners have no idea (even though it also affects your MSD/jacobs/etc ignition quality).
...

Makes sense.
In my case, the cars I have, Mopars from the 60's, all have pretty much lousy alternators and voltage regulators at idle.
I'll definitly want to upgrade to a newerstyle charging system (with suitable wiring).