saturated or peak and hold

[dannyho]

now I understand the difference between the two;
saturated injectors work by supplying voltage to the injector only durring the pulse width, and peak and hold supplies a nominal, low current to the inejctor all the time and then shoots to a high current durring the pulse width. from what i've read the peak and hold injectors turn on quicker, but it builds up heat in the ECU(?), and saturated injectors dissipate the heat through the injector.



basically does that mean that a street car should have saturated injectors? Now that you can get both in high flow rates, that's not an issue. which ones did you guys choose.

[Doug F]

I think you are a little off. A peak and hold is typically a "4 to 1" style of injector driver, creating about 4A and then "holding" at 1A. Saturation maintains about 1A.

You need a peak and hold driver in the ECU to run a low impedence injector corrrectly which most factory ECU's don't ahve and most aftermarket are.

I would say a peak and hold driver and low imp. injector give you the best opening performance.

[dannyho]

maybe i didn't write it clearly enough, but I get how they work. But peak and hold puts a heavy burden on the injector driver, which is inside the ecm, now I've read this leads to a shorter lifespan of the computer with peak and hold , while getting quicker on/off of the injector, but with saturated it's safer for the ecm, but the injectors are much more sensitive to the duty cycle. now 1500-2000 for a new ecm vs 100 for injectors. if I'm not planning on pushing 9000 rpm (ie 6k or under) is the on/off time really going to make much of a difference? worth the risk to the computer.

as an aside, I feel really dumb because going over the manualfor a couple ecms, you're right, they're all setup to run only peak and hold. so except as a talkign point, this subject is pretty moot. but thanks for replying.

[camcojb]

Just an FYI, Doug F is an EFI engineer for Holley, so you can pretty much take his stuff as gospel.

Jody

[dannyho]

noted

[Fuelie Fan]

Firstly, your ECU documentation should state what type of injectors it is compatible with, so that is your main driver. If it's designed for saturation injectors, you will damage your ecu by using P&H. Although it's sometimes possible to do the opposite, in the interest of not voiding your warranty i wouldn't do so without speaking to your ecu manufacturer.

The latest and greatest saturation injectors (bosch, denso, delphi, keihin to name a few) are approaching P&H performance, but most of the old school saturation injectors commonly used in aftermarket applications don't fall under that since they're still milking a 20+ year old design, so in your context P&H do deliver the best overall performance.

It depends on what your combination is, too. If it's pretty mild, you may not need the extra dynamic range that P&H gives you, so why pay the extra price?

Basically, both types can be sized to to flow the same at max duty cycle. The difference is, if you're running a high HP (esp boosted) engine that requires large injectors, the P&H can potentially give you a smoother idle since they work better at lower pulsewidths.

[68Formula]

[quote=Fuelie Fan]Firstly, your ECU documentation should state what type of injectors it is compatible with, so that is your main driver.quote]

No pun intended, right?
(I can't believe I just made an ECU joke.) Shoot, here come the nerd police!

[dannyho]

I wanted to add one more question, and instead of starting a new thread, hopefully someone will jump in here. For fuel injector flow testing how long do they keep the injector open. using ohms law and some resistor math it's pretty easy to maintain a desired current, but I know keeping them open for too long can fry the injectors. I saw one place recommend 60 seconds, then measure the flowrate by catching fuel in a graduated cylinder, simple enough. But how long is too long, 30 seconds, 60, or must it be run the same as it is in an engine, at some desired pulsewidth? (the third seems unlikely, because the flow testing results I've seen do not have any pulse widths listed)

[andrewb70]

Flow testing is done at 100% duty cycle, in other words fully open. With the American rating of pounds/hour I would think 30 seconds is enough. Then multiply by 120 to get the per hour number.

Andrew

[Fuelie Fan]

I always tried to keep all my testing between 30 seconds and 1 minute. On the bigger ones, sometimes my cylinder wasn't big enough to last even that long

We did do full range testing to characterize low pulsewidth performance, but this isn't usually published. It's nothing crazy, pretty much what you're imagining. Our ecus had a special "constant Pulsewidth" mode, so by varying pulsewidth and or "rpm" we could hit any duty cycle we wanted. Add one graduated cylinder and one calibrated eye (me). The results were actually pretty repeatable.

I'm sure bigger companies probably used flow meters, probably the scale type.

[Doug F]

The typical stands let you program in a pulsewidth. As mentioned I usually check at low pulsewidth (idle) and medium and static to make sure the whole range of the injectors are pretty consistent.

[rockvillespeed]

if you need to run injectors big enough to need to be low-impedance and have a saturated type ecm, you can use a variety of aftermarket boxes that take the signal from your ecm but run p/h squirters.
if i recall, even holley offers one.

[dannyho]

and an easier way than that, is to do what the OEMs do. In order to run the low impedance P/H injectors on a saturated system they stick a resistor box in series with the injectors. I know DSM's, 3000gt's and 300zx's do this.

[rockvillespeed]

not as precise, more load on ecm, changes opening/closing slew rates.

[Fuelie Fan]

Yeah I wouldn't do that unless I was in a bind. I never tested it, but i can very easily imagine the faster open/close rates going right out the window since you've cut the current running to the injector. In fact, I'd be surprised if they worked well at all. I know from testing that saturation injectors start to degrade (in performance, not physically) when you reduce the voltage to them, and i expect the same would happen here.

[Fuelie Fan]

oops double post