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Old 12-14-2017, 11:20 AM   #21
Vegeta
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Quote:
Originally Posted by MilzyZ34 View Post
As I said, this rule of thumb I use comes from my personal experience since 2002 and the results of all the tuning I've done since 2004. I'm not sure how you want me to site that. I don't build cars with too small of fuel injectors, so I don't have proof to show you what happens when they are too small. I can't believe this is something that needs proven to you, that injectors fail if you use them at too high of a duty cycle. What's next, having to give you proof that engines need oil in them?

So according to you, this is a sales gimmick for me to sell 36lb injectors. If this is the case, why would I invent this gimmick and instead stock and sell the 28lb injectors. So I could sell them the 28's then they add a couple mods, and then I could sell them the 36's. Seems that would be more profitable.

If you want to stick to a rule of thumb of 80% instead of 70%, that's up to you. I really don't care.
I recommend replacing injectors at 60%. It has always worked for me and someone once told me that so I stuck with it all these years. If you want to press your luck with 70%, its your business.

For someone with no worn out injectors to speak of, and no testing to back any recommendations up, and no documentation from injector manufacturers or any other credible, scientific information to give credence to anything less than 80%, I can see why you concern yourself with my opinion of your words over facts.

You are just a salesman.
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Old 12-14-2017, 11:28 AM   #22
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For the record. I have an injector testing setup, of which an injector has been running non stop at 10,380 cycles per minute over 12 hours now without fluid running through it to keep it cool. I also held this injector at 100% duty cycle for 2 hours straight, keeping it regulated at 195-215 degrees. You thought 1 day of constant pulls with 90% duty cycle would wear them out. Doesn't look like it to me.

I've been tuning since 2001. Who gives a ****.
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Old 12-14-2017, 11:39 AM   #23
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One more. Being a sales gimmick has nothing to do with 36# injectors. Its much simpler than that. You have a car you are tuning and its hitting 70% peak. Salesman Mike tells the customer this is no good, because he doesn't like 70%. Need to do something about that.

That is what a sales gimmick is. You set the bar low and recommend parts people don't need.
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Old 12-14-2017, 12:23 PM   #24
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Quote:
Originally Posted by Vegeta View Post
For the record. I have an injector testing setup, of which an injector has been running non stop at 10,380 cycles per minute over 12 hours now without fluid running through it to keep it cool. I also held this injector at 100% duty cycle for 2 hours straight, keeping it regulated at 195-215 degrees. You thought 1 day of constant pulls with 90% duty cycle would wear them out. Doesn't look like it to me.

I've been tuning since 2001. Who gives a ****.
I don't have the luxury of intercooling the fuel injectors when dynoing a car They're sandwiched between a hot (engine temp) lower intake, and a hot upper intake, and they get hot from running them at a high duty cycle as you mentioned. testing on a bench is not the same as testing on the dyno, and testing on a dyno is not the same as testing it on the street with the hood closed.

So you're running at 10,380 cycles per minute, which is the equivalent of 20,760 rpm, but the cycles aren't the killer. Duty cycle is, which is based off of the proportion of injector pulse width and the cycle time.
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Old 12-14-2017, 12:39 PM   #25
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The fuel going through the injector cools it. 100% duty cycle is always open. What is going to wear out with nothing moving? All it tests are the electrical windings. I am not doing this for you. Its proven that you arent learning anything from anyone but yourself. If you think what I am doing to this injector is easier on the needle and seat than brief dyno runs, then more power to you. If you saw it in action, you wouldnt be saying such nonsense. Until you cite a source for 70% duty besides yourself, I am not interested in what else you think about injectors.
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Old 12-15-2017, 09:56 AM   #27
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I don't need an explanation of what duty cycle means. I even said in that post it's the ratio of pulse width to cycle time. You mentioned you ran injectors at 10,380 cycles. I said that is the equivalent of 20,760 rpm, which is around 3 times real life, so the rpm is sufficiently exaggerated for testing, but I asked what the pulse widths were during this time because the duty cycle is what my 70% rule of thumb involves, not the cycles/min.

I also understand that cold fuel running through a hot injector would cool it down. When I said ...

"I don't have the luxury of intercooling the fuel injectors when dynoing a car They're sandwiched between a hot (engine temp) lower intake, and a hot upper intake, and they get hot from running them at a high duty cycle as you mentioned. testing on a bench is not the same as testing on the dyno, and testing on a dyno is not the same as testing it on the street with the hood closed."

... I was saying that I don't have the luxury to regulate the temperature of the injectors. Their temperature is a function of their environment, and their duty cycle. When I'm talking about spending a day on the dyno hotlapping, I'm talking about running 30+ runs, pretty much back to back. With the only time between being making small changes to the tune and reflashing. I don't always spend this much time on a dyno. Usually the 2 hrs I schedule is more than enough to do even a supercharged 3800 where I do afr tuning, pulley changes to add boost, timing changes, etc. On NA cars, it's even easier. But every once in a while I'm doing something out of the box like that twin turbo'd 3900 4.2L with an engine to break in and lots of things to tune, so it takes some time. So lets say this thing is on the dyno for 30 passes over several hours. The lower intake manifold is probably around the same temperature as the coolant is. The top of the upper is a little colder, but the the bottom of the upper is just a little cooler than the top of the lower intake. Sandwiched in between are the fuel rail and injectors. If somehow the engine was at this temperature as if it was on the dyno, while the injectors were not even running, the ambient temperatures around the fuel rail and injectors would heat them to roughly 200 degrees just sitting there. In real life though, they have fuel running through them. The fuel pump pumps fuel into the fuel rail and the regulator limits the flow of the return in order to build fuel pressure. Each of these add heat to the fuel from friction and pressure. As you make pass after pass on the dyno, the unused fuel gets passed through the roughly 2.5 feet of fuel rail between the hot upper and lower, heating the fuel. Also adding to this heat is the injectors as they heat up from working hard. So heat from engine, the injectors, heat from friction, heat from pressure. The faster you're running fuel through the system, the faster everything heats up. So at it's coldest the fuel could be ambient temperature, but it could be a bit hotter than that if you are running the car hard for a while with back to back runs. This additional heat would reduce the cooling effect from running that fuel through the injectors.

Look this 70% rule of thumb I use is just to keep engines running safe and in one piece, which I personally think is crucial, especially if it's a customer's engine that you are responsible for. It's something in engineering called a "factor of safety". If you run things a little on the safe side, when **** hits the fan as it always does, you're still safe. If you run it closer to the ragged edge, you may not be so lucky. So I like my rule of 70%, but if you like 80, then do that.
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Old 12-15-2017, 11:22 AM   #28
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rule of thumb

1. a broadly accurate guide or principle, based on experience or practice rather than theory.

If its only you saying it, its not a rule of thumb. Do you understand?

80% isn't close to the ragged edge. You just say it is because you want to. Nothing to back it up.

Last edited by Vegeta; 12-15-2017 at 11:34 AM.
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Old 12-15-2017, 11:38 AM   #29
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http://www.hotshotsecret.com/symptom...worn-injector/

"Injector wear can be directly related to varnish or Stiction."

stic·tion

the friction that tends to prevent stationary surfaces from being set in motion.

Running the injector without fluid is going to increase the likelihood of stiction many times greater than any real world use...dyno....track...idling the car in your garage to commit suicide because there is no getting through to some people.
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Old 12-15-2017, 11:39 AM   #30
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This is surely enough for everyone else, so /end
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Old 12-16-2017, 09:49 AM   #31
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Quote:
Originally Posted by MilzyZ34 View Post
As I said, this rule of thumb I use comes from my personal experience since 2002 and the results of all the tuning I've done since 2004. I'm not sure how you want me to site that. I don't build cars with too small of fuel injectors, so I don't have proof to show you what happens when they are too small. I can't believe this is something that needs proven to you, that injectors fail if you use them at too high of a duty cycle. What's next, having to give you proof that engines need oil in them?

So according to you, this is a sales gimmick for me to sell 36lb injectors. If this is the case, why would I invent this gimmick and instead stock and sell the 28lb injectors. So I could sell them the 28's then they add a couple mods, and then I could sell them the 36's. Seems that would be more profitable.

If you want to stick to a rule of thumb of 80% instead of 70%, that's up to you. I really don't care.
Translation: I have no proof to back up my claims, as per usual.

Quote:
Originally Posted by MilzyZ34 View Post
I'm just trying to figure out how it would be possible that your findings for the max limit of the injectors as different than mine, and thought maybe the dyno's read differently. It could be yours read high, or mine read low, or a combination of both.

How much boost did that run with a 2.5" pulley, just curious?

So you thought it would be a good idea to use stock injectors on an engine after you added a supercharged, and now you're giving advice to people about what size injectors to use?
yeah, that's because back when I did that dyno, there were no tuners available yet for this platform so doing an injector swap was not an option dumbass. I had to make due with the modified fuel pressure regulator that came with the Magnacharger kit. I believe boost was around 7 psi with that pulley.
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