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We don't need no saturated injectors!

Old 07-19-05, 10:52 PM
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Lightbulb We don't need no saturated injectors!

First off, let me say that this idea might be totally off the wall. I'm brand new to rotarys, so you never know.

Anyways, let me say that I have been a honda guy all my life. I have love for any kind of tunable car, but hondas were/are just my thing. One thing you learn from working on different brands of cars is different tricks...and i'm typing this so maybe I can help you HARDCORE rotary drag enthusiat out (maybe.) Most of you guys will know the difference in the main 2 types of injectors, but i'll break it down for the rest of you.
Peak and Hold-
Running in the lower ohmz range, this injectors have quicker response, but can also provide added heat.
Saturated-
Running in the higher omhz range...10-15omhz, these have a slower pulse time, and usually cannot support as much fuel as Peak and Hold, but have lower heat temps. Good for your civic

Rx7's are of the saturated type. If your running 9's in the 1/4th, I figure the extra little response might be make or break. To use peak and hold on an origanlly saturated type setup, you need resistors. 10 ohm, 10watt resistors should do the trick.

Anyone have any input on my idea?
Thanks,
Nick
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Old 07-19-05, 11:15 PM
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Mazda used peak and hold injectors with resistors in the S4 (86-87), so your only 20 years behind them. This is also a well known trick in the standalone EFI world. But welcome to the site, enjoy your stay.
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Old 07-19-05, 11:38 PM
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Originally Posted by 13bdreams
First off, let me say that this idea might be totally off the wall. I'm brand new to rotarys, so you never know.

Anyways, let me say that I have been a honda guy all my life. I have love for any kind of tunable car, but hondas were/are just my thing. One thing you learn from working on different brands of cars is different tricks...and i'm typing this so maybe I can help you HARDCORE rotary drag enthusiat out (maybe.) Most of you guys will know the difference in the main 2 types of injectors, but i'll break it down for the rest of you.
Peak and Hold-
Running in the lower ohmz range, this injectors have quicker response, but can also provide added heat.
Saturated-
Running in the higher omhz range...10-15omhz, these have a slower pulse time, and usually cannot support as much fuel as Peak and Hold, but have lower heat temps. Good for your civic

Rx7's are of the saturated type. If your running 9's in the 1/4th, I figure the extra little response might be make or break. To use peak and hold on an origanlly saturated type setup, you need resistors. 10 ohm, 10watt resistors should do the trick.

Anyone have any input on my idea?
Thanks,
Nick
we already do that with larger injectors though.. old news


Thanks though
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Old 07-20-05, 12:45 AM
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Cool- Like I said I wasnt sure. I saw on a site that all rx-7's were saturated...but thanks for the insightful input!
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Old 07-20-05, 04:11 AM
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Go back to Hondas.
You don't know what you're talking about.


-Ted
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Old 07-21-05, 04:52 PM
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running a low impedence injector with a resistor is the same thing as stock, its still being driven with ~0.8A. a peak and hold driver slams the injector open with 4A of current, then backs off to 1A to limit the power dissipation of the injector.

i have been planning on making a peak and hold driver box for when i upgrade to 1600cc injectors as the peak and hold method causes the injector to open faster and sooner, providing benefits such as smoother staging and more time to inject fuel.

if you used a driver like this you could also get a smoother idle when using big primary injectors.
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Old 07-25-05, 03:55 PM
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Ted, are you saying that saturated style of firing injectors is better than the peak and hold method? Please explain.


-s-
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Old 07-25-05, 09:18 PM
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Originally Posted by scotty305
Ted, are you saying that saturated style of firing injectors is better than the peak and hold method? Please explain.


-s-


Not to answer for Ted, but my impression was that he was simply saying STFU to the know-it-all Honda boy.

After all, despite the fact that this is the ONLY section of RX-7club.com that has a general tone of civility and tolerance, it is also a place populated by people who know RX-7s inside and out - some of whom may not take kindly to a self-professed Honda guy giving us basic and not very in-depth lessons on fuel injectors for drag racing.

But please, let the highly technical discussion continue - let's see if 13bdreams can hang with it... good luck, Nick.
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Old 07-26-05, 03:18 AM
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Originally Posted by scotty305
Ted, are you saying that saturated style of firing injectors is better than the peak and hold method? Please explain.
No, my point is that both can be made to work.
We can argue till we're all blue in the face, but the fact of the matter is that either or will work fine.

You can get around the "slow reponse time" unless you're trying to fire really small pulsewidths for idle on a very large primary fuel injector.

Bottom line is...I doubt you'll feel a difference from either.


-Ted
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Old 07-27-05, 11:40 AM
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OK, thanks Ted.


From the brief research I've done ( http://www.msdignition.com/fuel_3.htm ), and my electronics background, it seems that using a peak-and-hold (low-ohm, high current) injector in our stock setup shouldn't provide any gains (given equal flow rates, etc..), unless you change the way the ECU drives it.


Simply adding a resistor will cause it to act like a standard saturated (high-ohm, low-current) injector, if not worse because the resistor could be causing the injector to see less than 12 volts. It's even possible that your peak-and-hold injectors are not opening as quickly as your saturated injectors, because of that 10-ohm resistor limiting the current.


I'll do more research and work a few calculations, and get back to you.
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Old 07-27-05, 06:30 PM
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Scotty,

You have it right. If you want the benefits of peak-and-hold injectors you must have peak and hold drivers. Unless you are using single stage injection with huge injectors (one injector per rotor like a peripheral port) peak-and-hold isn't necessary. Where peak-and-hold shines is with turbo engines that have a very wide dynamic range and need a very short opening time at idle, but big flow under high boost and high RPM.
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Old 07-27-05, 10:03 PM
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Originally Posted by scotty305
From the brief research I've done ( http://www.msdignition.com/fuel_3.htm ), and my electronics background, it seems that using a peak-and-hold (low-ohm, high current) injector in our stock setup shouldn't provide any gains (given equal flow rates, etc..), unless you change the way the ECU drives it.


Simply adding a resistor will cause it to act like a standard saturated (high-ohm, low-current) injector, if not worse because the resistor could be causing the injector to see less than 12 volts. It's even possible that your peak-and-hold injectors are not opening as quickly as your saturated injectors, because of that 10-ohm resistor limiting the current.
Bingo!
That's pretty much summarizes it in a nutshell.
It's NOT the fuel injector; it's the DRIVER tha controls the fuel injector!


-Ted
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Old 07-28-05, 01:43 AM
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Originally Posted by RETed
It's NOT the fuel injector; it's the DRIVER tha controls the fuel injector!
Exactly. There's no such thing as a 'peak and hold' or 'saturated' injector, those labels refer to the actual driving technique. You can saturate a low-impedance injector, you just won't like the results (unless you like the smell of burned electronics).
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Old 07-28-05, 07:05 PM
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So it's no surprise that the Mazda ECU uses a saturated driving method. The FD's electrical system has a few snafus that I've found, including the use of high-current wires in the interior headlight switch, rather than low-current wires (safer and lighter weight) and a relay. Plus, why are there 3 separate fuse boxes in the engine bay???

I can also see why Ted jumped on the Honda guy for calling low-impedence injectors "peak and hold" style.



The use of low-impedence injectors would be necessary if you were to attempt a direct-injection setup in the rotary engine.

-s-
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Old 07-28-05, 10:49 PM
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Awesome info and link - thanks guys.

Hmmm.... where's the original poster?
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Old 07-28-05, 11:10 PM
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Originally Posted by JEC-31
Awesome info and link - thanks guys.

Hmmm.... where's the original poster?
I think he melted in the flames. They sure don't make Honda guys like they used to....


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Old 07-29-05, 02:37 AM
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Originally Posted by scotty305
I can also see why Ted jumped on the Honda guy for calling low-impedence injectors "peak and hold" style.
It goes beyond that.
To be discriminating between fuel injector types at the level is a royal waste of time.
Even with the increased dwell time on the high-impedence units, I want to see someone prove they are inferior in terms of performance.
These cars can't take advantage of the different types of fuel injectors - and neither can a Honda.
So the original poster is full of ****.

Assume a 9,000 redline, that allows for a 150 revs / second or ~0.007 seconds between each revolution.
That's about 7mS (milliseconds).
Fuel injector dwell time is measured in uS or MICROseconds, which is a thousand times smaller!
So your fuel injector dwell time factors in about 0.1% of the pulsewidth at 9,000RPM - who cares?!?!?

Bottom line, it really doesn't matter.
A high-impedence versus a low-impedence fuel injectors is not going to really make a difference here, period.
To argue otherwise shows ignorance on the whole matter.


-Ted
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