Injector Recommendations for Holley HP MPFI - Ford Muscle Forums : Ford Muscle Cars Tech Forum
 
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post #1 of 4 (permalink) Old 03-12-2014, 11:37 PM Thread Starter
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Injector Recommendations for Holley HP MPFI

Building a 427w, AFR 185's, 10.7:1... Holley sells the 42lb injectors, but I don't know if they are any good in comparison to similarly priced injectors. I can't get a straight answer when I call their tech line whether or not the injectors are flow matched as a set. It's like, "yeah, they come as a set".

Frustrating that they want me to spend $$$ and not have any info regarding their product. I would also like to know about idle quality and street manners.

Thanks for any info or alternate injectors anybody can give me,

Last edited by 74Bronco; 03-12-2014 at 11:40 PM.
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post #2 of 4 (permalink) Old 03-13-2014, 10:21 AM
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Re: Injector Recommendations for Holley HP MPFI

74Bronco, my 2 is about the Rochester/Delphi/Lucas Multec (Holley) large-body injectors, and general injector sizing. Rather than "yes", "no", "sometimes", I will give you more info, so you can make your own decisions for your engine and system. In any setup, the injectors must work with the application parameters. In this case, the Multecs are fine with standard return fuel systems running at 3 BAR pressure (43.5 psi) or less. This is fine with the Holley setup of course.

We have used them up to 650cc on other ECMs without any particular issues. Where folks sometimes have poor things to say are only based on trying to use them with higher pressure systems, such as returnless systems typically running at 4 BAR pressure (58 psi), or when trying to make them flow more than their rating. These particular injectors can literally not open (shut off flow) at about that pressure. While unusual, this is not a failure of the injector, as it was not designed for that.

Others fear using them in boosted applications due to this pressure limitation. This is actually not a problem, as the fuel pressure is referenced to the manifold pressure. While we have run them at 28 psig boost and 72 psi fuel pressure, the actual differential pressure across the injector is still 43.5 psi. No problem. Their spray is a bit narrower, but that's not a bad thing if you're shooting down the runner.

That leads us to injector sizing and idle quality. What camshaft timing you have and what injector control you are using highly influence idle quality. Using injectors larger than necessary is detrimental as the resolution of control is reduced. For example, let's say your should use a 36 pound-per-hour injector, but you install 72 PPH injectors. This makes it difficult for the system to control at low injector pulse widths like idle, as small corrections in flow have twice the effect from injectors twice the size. This makes achieving a stable AFR at idle more difficult.

Having said that, 42 PPH injectors will idle just fine. Yes, they are too large for your application, but they will still work. Better would be to size them to your actual requirements, and the 36 PPH versions will handle up to 575 HP, far more than your setup can make unless supercharged or dry nitrous is added.

The Holley injectors are not "flow-matched", except that they are all guaranteed to have maximum flow within X% of each other. As you have limited tuning capability and lack individual cylinder trim (altering the flow to a specific injector/cylinder), that's good enough. That may sound confusing, but intakes never flow exactly the same volume to each cylinder anyway. Without cylinder trim, super-tuning involves changing leaner cylinders to slightly higher-flowing injectors, or vice-versa. Unless you have a number of extra injectors of known flow to tune each cylinder, you'll be fine with what you get in the box. That's a lot of tuning info, but I hope that helps answer your questions.

David

PS: Gotta say this - "flow matching" is a commonly mis-used term. Most folks and companies flow the injector wide-open, measure flow, and match others to the same flow. Unfortunately, true flow-matching involves a more important test - flow during various pulse widths (opening and closing). Injectors should never be running just wide-open, so if you have a lazy injector with a slow opening or closing, that cylinder will be leaner, even if the wide-open flow is identical to the next injector. Again after all that, it's Catch-22 as the cylinders will not have even airflow anyway, and you're back to swapping injectors to super-tune. You're not doing that, so don't worry about it.

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post #3 of 4 (permalink) Old 03-17-2014, 01:29 AM Thread Starter
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Re: Injector Recommendations for Holley HP MPFI

Thank you PSIG. I've read many of your posts and have learned a ton from you.

A couple variables I'd like to know more about:
1) I'm close to running a cam sync, crank trigger, and DIS wasted spark... Does this improve my chances of getting closer to "super tune", or will super tuning require an O2 sensor at each cylinder to do that?

2) you mentioned 575hp is far more HP than my set up can make.... I was hoping for something in the lower 500's (530 or so). Am I dreaming, or is my estimate possible with my compression?

3) I'm reusing my old Edelbrock proflo manifold, essentially a multi port performer RPM. Should I be seeking a specific spray pattern for the injectors?

Thanks,
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post #4 of 4 (permalink) Old 03-17-2014, 06:54 AM
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Re: Injector Recommendations for Holley HP MPFI

Quote:
Originally Posted by 74Bronco View Post
1) I'm close to running a cam sync, crank trigger, and DIS wasted spark... Does this improve my chances of getting closer to "super tune", or will super tuning require an O2 sensor at each cylinder to do that?
Super-tuning is relative to the setup you have and its capabilities. Super-tuning is that last ounce of performance, and the sharpest level of tune a particular system is capable of under all the various conditions it may meet. So, a system with individual fuel and ignition timing trim can be super-tuned easier and a bit sharper, but a very simple system can be tuned surprisingly sharp as well using various techniques. Keep in-mind that a pro-tune or super-tune is above and beyond "average" tuning for a particular combination, and is just a term for squeezing the max out of it.

So, using a distributorless DIS system is excellent for increased spark accuracy and potentially more powerful sparks, and moves you farther up the ladder of potential performance. However, that just means super-tuning will have greater effect and results than a super-tune on a distributor system. I hope that's making sense.
Quote:
Originally Posted by 74Bronco View Post
2) you mentioned 575hp is far more HP than my set up can make.... I was hoping for something in the lower 500's (530 or so). Am I dreaming, or is my estimate possible with my compression?
I don't know enough about your combo to be specific. However, in a general sense, that type of combo might make 500+ on the engine dyno, but when loaded with 'necessary' stuff like water pump, alternator, PS, full exhaust, air filter instead of dyno ram-air velocity stack, etc. - your actual output and fuel necessary drops considerably. This is normal, but you need to plan for it.

If you were after 530, then that still fits in the 36 PPH injector range and will permit potentially better results in tuning than over-sized versions. Alternatively, you could reduce the fuel pressure to reduce the flow from 42 PPH injectors for better control, but why apply a band-aid on-purpose? That said, either will work.
Quote:
Originally Posted by 74Bronco View Post
3) I'm reusing my old Edelbrock proflo manifold, essentially a multi port performer RPM. Should I be seeking a specific spray pattern for the injectors?
You can spend a fortune buying things that would be a bit better. Sure you could get injectors that spray to the side and straight-down the runner for big bucks. It would be splitting hairs at this point. My suggestion is to get your system together in the most basic way with the options you intend. Run it. If you find unexpected weaknesses in the combination (not likely), you will know exactly what and why at that point, and how to deal with it. You are already a leap ahead by switching to a tunable EFI system. It is good to consider as much as possible but, one step at a time, and don't get too distracted along the way.

David

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