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Old 01-19-2020, 12:08 AM   #1
BurninSTI
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Default Is everyone over-sizing their injectors on staged packages?

Honestly what's the deal? We all know fuel injectors atomize better at higher pressures so what's the advantage to running 1000's, 1300's when trying to get to 350-450 hp reliably? The stock pump can't support them so u gotta go to a more powerful pump. I can see doing 750's, maybe up to 900's but to me it seems like overkill and you sacrifice superior atomization for what? Seems like 1300's can get you to around 600 whp correct? That being said I feel like having an uprated pump supplying more pressure to more appropriately sized injectors would give you a safer 350-450 hp. Just spitballing here let's put it all out on the table.
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Old 01-19-2020, 01:08 AM   #2
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Considering the factory injectors are capable of ~300whp or even a bit more or less depending on other variables, using for example 2008-14 WRX/STi injectors are 565cc, I've also often wondered why people go such high flow, especially if they aren't running alternative fuels. 300+ hp is a decent amount of go. Just because it isn't 1320 Video worthy doesn't mean it's slow.

One possible reason is E85/flex fuel. E85 needs more fuel to make the same power, so bigger injectors are handy for this.

Another reason is to keep IDC's low. Considering some guys are making the same power as a stock 2019 Mustang GT with half the cylinders and displacement. Also gives them some room to grow a little.

For some it might make them feel good when they look at their build sheet? Idk on that one, but I'm sure there's lots of owners/drivers who only browse Cobbs site, see the only two size of injectors they (currently) list and click the check out button.

https://www.fiveo-racing.com/product...nt=23105471299
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Old 01-19-2020, 09:02 AM   #3
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I guess it really depends to be honest. Some tuners prefer tuning our cars on larger injectors. Ive herd of a bunch of people over time running stock injectors to 120% injector duty cycles and i feel like that may just be maxing them out. I dont know why anyone would want to run anything at it max but to each there own. The purpose of running larger injectors usually on any set up is to support what you currently have and possible leave you with some head room. I personally wouldnt want to be on the dyno and be limited by something like injectors. Espicially when i had a chance to upgrade prior to getting the car protuned.

Injector "debates" can turn into whitch hunts on the forums. Prepare yourselves.
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Old 01-19-2020, 07:18 PM   #4
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Yeah that's kinda what I was thinking viper, people just using whatever the tuners are promoting... I get the point of leaving headroom but 2X++ oversized seems ridiculous to me, how many people are really going to be going to be running g 600+ hp. maybe I'm just lame.
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Old 01-19-2020, 07:26 PM   #5
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As they say, there's more than one way to skin a cat. I'm sure you may know most, if not all of what I've linked below, but here's an interesting thread I have book marked.

https://forums.nasioc.com/forums/sho...d.php?t=480255
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Old 01-20-2020, 01:03 AM   #6
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Quote:
Originally Posted by viper_crazy View Post
As they say, there's more than one way to skin a cat. I'm sure you may know most, if not all of what I've linked below, but here's an interesting thread I have book marked.

https://forums.nasioc.com/forums/sho...d.php?t=480255
Yeah I've read that one, was on my to do list but I decided to just upgrade the fpr vs smacking it with a hammer.
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Old 01-20-2020, 01:09 AM   #7
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Probably the better route to go, haha. I considered the hammer method but knowing my brute strength, I would have been replacing the regular.
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Old 01-20-2020, 08:36 AM   #8
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I could be completely off here... but from stock size injectors to 1050cc there are few options in between these days. especially side feeds. At least when I was putting my parts list together.

I'm a great example of over sized injectors for the HP I'm making. When I was talking to my tuner and doing injector research, I found out quickly I was going to have to convert from side feed to top feed. I didn't have any options for side feeds new and my tuner wasn't keen on tuning side feeds. I was talking to two different tuners at one time who both recommended to go to the 1050's. It was explained to me that the 1000/1050's will idle and cruise just like the stockers and tuner's like tuning with them when going up in HP. IDK if it's just a magical size or what.

For my setup. I'm running a VF37 twin scroll turbo (with ALL supporting mods). Whenever I pull the trigger to upgrade to a bigger turbo... that's all that I would need to do for me to gain more power aside from a re-tune.
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Old 01-21-2020, 11:29 AM   #9
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Some folks might also be upgrading injectors for future projects. If you're on a stock turbo now, and you want to run e85 for a while, and you think you might want to install a 20G turbo later, one might consider getting the right sized injectors for down the road.

As others have said, it's better to keep IDCs away from the 100% range if possible too.
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Old 01-21-2020, 08:50 PM   #10
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Did you re-tune after raising the FP? I've read through this thread: https://forums.nasioc.com/forums/sho...&highlight=idc where there is discussion about the pros/cons of raising pressure vs larger injectors.

Raising the fuel pressure, you should re-tune. Upping fuel pressure has its negatives as well. How beneficial would the increased atomization of the injectors be with the increase in pressure we're talking about here (for the 350-450hp daily driver scenario)?

Raising the fuel pressure and re-tuning works fine, which will lower the IDC, but there is a good argument for the less risky way being with larger injectors. This also has the benefit of leaving room to add more later, like others mentioned.
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Old 01-22-2020, 02:02 AM   #11
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to throw a counter question, why would you not want to run oversized injectors?

As everyone is saying, it leaves you room if you want to go bigger and not rebuy injectors as well as allowing the same driveability. For me, that's the ultimate win as why would I want to rebuy anything.
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Old 01-25-2020, 11:44 AM   #12
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I did some on-road tuning. Just up and down with the fuel pressure until I saw what I liked on the ap gauges. Went as high as 53-54 psi but it started missing at idle and saw some bad feedback knock during pulls. I was monitoring the duty cycle as well. I got the lowest duty cycles in closed loop at around 48 base psi as well as 0 knock of any kind regardless of how I drove it, wot gears 1-3. Was thinking that the rise in fuel pressure under 50 psi really doesn't effect latency much as when compared to the 53-54 I tried that gave it knock. Either way I'm happy now, it spins all fours soft launching at slightly under 4k on 18x9's.

Well... I do not want to run them right now if the stockers are adequate for daily driving, save me some loot. I will say that I did upgrade the pump to an AEM though, probably directly contributes to lower idc's. Who's really going wot past 3rd gear. I think the highest I saw my duty cycle at in gears 1-3 was 93%. Basically any throttle input that stays in closed loop maxes out at around 60.

On a side note, I really do wanna see someone just up the fuel pressure on the base map with all the other stage 2 mods (tbe and intake) installed. Call me selfish, I don't want to mess up the good learnin's on the ecu from the past few days.

Last edited by BurninSTI; 01-25-2020 at 11:50 AM.
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Old 01-25-2020, 12:06 PM   #13
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Quote:
Originally Posted by rhymeboy89 View Post
to throw a counter question, why would you not want to run oversized injectors?

As everyone is saying, it leaves you room if you want to go bigger and not rebuy injectors as well as allowing the same driveability. For me, that's the ultimate win as why would I want to rebuy anything.

Any time you’re operating at the extreme top or bottom end of an injector’s capacity, it can lead to issues. Basically, way oversized injectors can make your idle funky and hard to tune. ID injectors are better than some others with low range stability, which is one reason a lot of tuners prefer them. ID 1050’s and 1300’s are supposed to be really good for that.

Still, people who run very large injectors for really big power often wind up running a smaller set of secondary injectors when they need very low flow.
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Old 01-25-2020, 12:46 PM   #14
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Good discussion. Learned something for once.
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Old 01-25-2020, 07:57 PM   #15
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Quote:
Originally Posted by Stretch18 View Post
Any time you’re operating at the extreme top or bottom end of an injector’s capacity, it can lead to issues. Basically, way oversized injectors can make your idle funky and hard to tune. ID injectors are better than some others with low range stability, which is one reason a lot of tuners prefer them. ID 1050’s and 1300’s are supposed to be really good for that.

Still, people who run very large injectors for really big power often wind up running a smaller set of secondary injectors when they need very low flow.
Interesting... I was thinking something standalone and boost referenced like how they work the methanol kits.. haven't really put much thought into it other than I dont want to have to keep refilling a windshield washer sized tank with gas if I went that route and used gas instead of alky... not really too into having to buy methanol either... damned computerized everything
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Old 01-25-2020, 07:58 PM   #16
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Quote:
Originally Posted by BurninSTI View Post
Interesting... I was thinking something standalone and boost referenced like how they work the methanol kits.. haven't really put much thought into it other than I dont want to have to keep refilling a windshield washer sized tank with gas if I went that route and used gas instead of alky... not really too into having to buy methanol either... damned computerized everything
*For an extra injector
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Old 01-25-2020, 10:55 PM   #17
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Quote:
Originally Posted by BurninSTI View Post
I will say that I did upgrade the pump to an AEM though, probably directly contributes to lower idc's.
Your lowered IDC is mostly due to the increase in pressure. The pump simply helps combat the increased resistance needed to keep things flowing.

I wish I could find that thread where some tuner data logged IDC on stock vs high flow pump. They discovered IDC didn't change much at all because any increase in pressure that was caused by the increased flow was negated by the regulator. The regulator's job is to keep its set pressure. So any increased flow is being by-passed by the regulator at the higher flow rate.

Side note, a fuel pumps flow rate will be lower if fuel pressure is increased. A stock pump isn't capable of handling much more than ~18psi (safely, at least, you could probably go a bit higher if you wanted) of turbo boost at 43.5psi fuel pressure. You can imagine how high IDC will be if you increased FP and boost on a stock pump. Another reason why turbo upgrades are nice because there's more air flow at the same PSI, but that's getting into another thread topic.

I did find a reference to the above in Unabombers fuel pump FAQ.
https://forums.nasioc.com/forums/sho....php?t=1218460

"Can I run an aftermarket fuel pump by itself without new injectors/turbo/management? During the turbo upgrade path, it may be easier to purchase and install a fuel pump ahead of time. It is cheap, easy to install, and removes an eventuality from the upgrade chain ahead of time. You can run an aftermarket fuel pump with no other modifications. Adding a fuel pump will not give you more fuel (i.e. richen your car), it simply allows for more fuel to be delivered if you run higher boost or larger injectors. The stock RRFPR keeps the pressure at the stock 43 psi + manifold pressure no matter how much fuel may be available from the pump."

If it doesn't richen the AF ratio, then it isn't adding more fuel, which means IDC won't change, which also means you don't need a tune for a fuel pump.

Last edited by viper_crazy; 01-25-2020 at 11:06 PM.
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Old 01-26-2020, 06:27 PM   #18
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Thats what I was saying and was letting people know that I didn't just up the pressure to lower the idc's, I supported it with a pump. I think there are three possible reasons for the knock at the higher pressures I tested. 1. the increased pressure was increasing latency to the point where regardless what the duty cycle said not enough fuel was flowing from pintles taking longer to open. 2. the pump was running out of flow but I really doubt it on stockers. 3. the injectors were flowing enough to turn the motor into an old school batch fired set up effectively flooding the intake tracts and making fuel atomisation a non issue because it was just entering the chambers in globs. Maybe back in the day knock sensors weren't a thing so this type of injection strategy seemed okay.\

For anyone that cares, I changed my oil today because it was looking dirty and noticed that it had no fuel smell to it. Was getting worried that I would be wetting the cylinders down and contaminating the oil with fuel but this doesn't seem to have happened, especially since the motor has almost 40k on it and most definitely doesn't have the tightest rings anymore.
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Old 01-26-2020, 06:36 PM   #19
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Search for videos of injector atomization on youtube for example, may be surprised how well large injectors do, even at 43psi. Newer injectors do a good job at atomization, maybe because of the ball vs pintle style. If you're using aftermarket em, you also have more control over the injector pulse.
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Old 01-27-2020, 08:38 AM   #20
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Quote:
Originally Posted by 2slofouru View Post
Search for videos of injector atomization on youtube for example, may be surprised how well large injectors do, even at 43psi. Newer injectors do a good job at atomization, maybe because of the ball vs pintle style. If you're using aftermarket em, you also have more control over the injector pulse.
Not to mention that if you increase your base to 50 or 60 psi you're raising your fuel pressure until higher boost to 65-75+ depending on boost levels.

The higher the pressure the less your pump will flow. So that smaller injector at higher pressures may require even more pump.
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Old 01-27-2020, 02:30 PM   #21
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Quote:
Originally Posted by BurninSTI View Post
Honestly what's the deal?
Higher pressure = more heat being pumped (no pun intended) into the system and a system more prone to leaks. This temperature change is tougher to tune for than large injectors with good small IPW and latency data. A standalone system with a fuel pressure temperature sensor helps, but in terms of the stock ECU, this sensor is only for emissions purposes (the newest models may have a basic compensation table). Side note - extreme high pressure motorsport fueling systems are typically a mechanical pump, as well.

Stock injectors are sized for about 80% duty at stock peak output (approaching 90% on newer models since Subaru hasn't changed the 565 cc injectors). On a turbocharged car (not just Subaru), you almost always max the injectors out once you open the exhaust up. Pushing the stock turbo to a higher PR will net you a little fuel pressure increase but the turbo will usually be running less efficiently.

In my experience, raising fuel pressure is a crutch and the last thing I would do (compared to upgrading the pump and injectors).
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Old 01-27-2020, 04:16 PM   #22
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I got 1300s instead of 1050s as I got a killer deal...wanted to properly support ~400whp otherwise I would have kept stock as my IDCs were ~80% with 19psi on the stock and 316whp...I may not ever get to the 400 mark but I like being safe without overworking the injectors!
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Old 01-27-2020, 04:21 PM   #23
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I have a Dom 1.5xtr flex-fuel build. With 1300's and an AEM 340in the main tank, it put out 320whp/tq on pump 92 + octane booster for about 95; on E-85 it produced 340/340. This was on a Mainline dyno (stock STI = 200whp/tq).

JJ was not happy with the fuel delivery, however. It was not completely steady, and it was putting fuel into the oil. This all changed when he installed a radium 450 surge tank in the engine bay. Gas went to 345/345, and E-85 to 360/370. This is with a TMIC.

It stopped putting fuel in the oil, and I gained 2mpg on both types of fuel. JJ said my fuel was getting properly atomized now, and he frankly was amazed at the difference.

My opinion is that when you start approaching 400whp (especially on E-85) proper fueling is essential, including using a lift pump/surge tank. I've done a lot of reading in this forum over the years, and proper fueling seems to be a common denominator.
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Old 01-28-2020, 09:47 PM   #24
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Quote:
Originally Posted by Stretch18 View Post
Any time you’re operating at the extreme top or bottom end of an injector’s capacity, it can lead to issues. Basically, way oversized injectors can make your idle funky and hard to tune. ID injectors are better than some others with low range stability, which is one reason a lot of tuners prefer them. ID 1050’s and 1300’s are supposed to be really good for that.

Still, people who run very large injectors for really big power often wind up running a smaller set of secondary injectors when they need very low flow.
Or run a very tiny single oem injector in the plenum center, and tune it to only run at idle, so you can run the yuge injectors more lean at idle and their contribution wouldn't be as critical. The small injector with a very atomized mist could richen all cylinders at idle just enough, instead of having four extra injectors to tune for. Aftermarket ecus could easily handle this, or someone could build a standalone gadget that provides just enough pulse for a weak idle, something that relies solely on cam or crank pulse. People have been designing and building their own flex fuel adapters, a single injector controller would be cake for those people.
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Old 01-30-2020, 02:14 AM   #25
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Just found this yesterday
https://www.maperformance.com/produc...kaAn_VEALw_wcB

Seems like a good idea, anyone have firsthand experience with it?
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