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Old 05-12-2014, 07:07 PM   #1
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Default Injector sizing question.

Hey guys,

I currently am running RX8 yellow injectors, Walbro 255 lph fuel pump, running E85 fuel and an MS3 for control.

The Supercharger has been removed and sold, so currently I am running around without forced induction until my turbo system is completed and shipped.

At 6500 RPM I am at 53% duty cycle and according to the MS3 right at 13:1 A/F ratio.

Using this data, is it possible to figure out what boost pressure I will be able to run without maxing out my injectors? I know it is a long shot asking, but if someone knows how to calculate based on this data I am willing to learn

I ask because I maxed out a set of 1000 cc injectors on my old EVO VIII on E-85 on the dyno, and had to turn down my boost for daily driving to keep it around 80% duty cycle. If I need bigger injectors I would like to get them before I find out on the dyno that I am maxing the current ones out.

Thanks,

Keith
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Old 05-12-2014, 07:11 PM   #2
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you maxed out a set of 1000cc injectors on a stock evo?

as for your question, the answer couldn't be any simpler: ID1000
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Old 05-12-2014, 07:23 PM   #3
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Quote:
Originally Posted by 18psi View Post
you maxed out a set of 1000cc injectors on a stock evo?

as for your question, the answer couldn't be any simpler: ID1000
LOL, I never mentions the word "stock" in regards to my old EVO I was pushing 550 wheel HP out of it, running 127 mph trap speeds. I was only running mid 11's in it (trap speed was good for mid to high 10's) because it was my daily driver and I was babying it off the line because I didn't want the transmission to blow apart on me. It was a stock block, with stock crank, rods, and pistons. It had a full turbo back 3" V band exhaust, a GT35R turbo, huge intercooler, ported head, oversized valves, 272 durration HKS cams. ARP head studs, AEM EMS stand alone ECU, dual Walbro 255 lph fuel pumps, 1000cc injectors, and on the drivetrain side of things a triple plate clutch.

I know that the ID1000's would keep me from having to think about it, but if I don't need them, why spend the $$$? Just trying to find out if I need them or not before laying out the cash.

Keith
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Old 05-12-2014, 07:26 PM   #4
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you have an ms3, why not run the best injectors too? they idle like stock or better than stock, so what's the issue? money? the difference between them and others are within 100 bux. that's really not much money to be "saving"

But that's just, like, my opinion....man
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Old 05-12-2014, 07:30 PM   #5
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Quote:
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you have an ms3, why not run the best injectors too? they idle like stock or better than stock, so what's the issue? money? the difference between them and others are within 100 bux. that's really not much money to be "saving"

But that's just, like, my opinion....man
When I upgrade from the 425's currently in the car I will get the ID1000's... the difference between ID1000's and the competition is $100 The difference between keeping my 425's and moving up to the ID1000's is just shy of $500. That is two days of overtime I could spend on something else I need for the car like saving up for some 15x8's and 225/45/15's

Keith
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Old 05-12-2014, 07:38 PM   #6
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There are tons of fuel injector calculators, just google it. Your 425's will probably get you to 250 on e85, give or take.
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Old 05-12-2014, 07:43 PM   #7
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Probably less than 250, maybe 220.
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Old 05-12-2014, 07:55 PM   #8
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Quote:
Originally Posted by 18psi View Post
There are tons of fuel injector calculators, just google it. Your 425's will probably get you to 250 on e85, give or take.
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Originally Posted by Reverant View Post
Probably less than 250 maybe 220, .
And this is why I was hopping someone who has done it or had a really good calculation formula would chime in I know you can find injector calculators on line... they are notoriously inaccurate, relying on user inputs where the user has no clue what the efficiency, Brake specific fuel consumption, etc. of his engine is, what E85 really does to fuel requirements and many other related factors.

Oh well, I will let you guys know when I dyno the car after getting the turbo setup I am aiming for 225 lb-ft of torque through the entire rev range from 3300 RPM to 7200 RPM. If I have to back down on the boost somewhere in the rev range to avoid 100% duty cycle so be it. Then I will upgrade the injectors.

Keith
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Old 05-12-2014, 07:59 PM   #9
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Quote:
Originally Posted by Twodoor View Post
And this is why I was hopping someone who has done it or had a really good calculation formula would chime in I know you can find injector calculators on line... they are notoriously inaccurate, relying on user inputs where the user has no clue what the efficiency, Brake specific fuel consumption, etc. of his engine is, what E85 [b]really[b] does to fuel requirements and many other related factors.

Oh well, I will let you guys know when I dyno the car after getting the turbo setup I am aiming for 225 lb-ft of torque through the entire rev range from 3300 RPM to 7200 RPM. If I have to back down on the boost somewhere in the rev range to avoid 100% duty cycle so be it. Then I will upgrade the injectors.

Keith
peak IDC will always be at maximum rpm
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Old 05-12-2014, 08:05 PM   #10
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peak IDC will always be at maximum rpm
Yes, but I may hit 100% duty cycle before max RPM... that is why I phrased it as I did.

Keith
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Old 05-12-2014, 08:10 PM   #11
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You said back off the boost, not decrease the redline.

Whatever, not going to argue, seems like you're not gonna be satisfied with any answer besides "I ran them and they hit 100% idc at xxx rpm" despite that answer still not being accurate since different engines/setups/elevation will all affect this significantly.

enjoy
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Old 05-12-2014, 08:19 PM   #12
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I'm just about maxing out my yellow tops at 15 psi, but I'm running 65 psi base fuel pressure with a 1:1 afpr. I can maintain a steady 11.5:1 afr at 90% DC.

I figure I'm somewhere around 250 whp but not sure?

edit-Totally correct, I am using a churbo 2854.

Last edited by flounder; 05-12-2014 at 08:41 PM.
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Old 05-12-2014, 08:35 PM   #13
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Turbo size is gonna make a difference. Not just psi.
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Old 05-13-2014, 01:39 AM   #14
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Quote:
Originally Posted by 18psi View Post
You said back off the boost, not decrease the redline.

Whatever, not going to argue, seems like you're not gonna be satisfied with any answer besides "I ran them and they hit 100% idc at xxx rpm" despite that answer still not being accurate since different engines/setups/elevation will all affect this significantly.

enjoy
With electronic boost control you can set up the boost profile to lower boost as RPM's rise to keep from hitting 100% duty cycle. No need to lower the red line. Not trying to cause an argument here. Just not sure why you can't get what I am talking about. I already agreed with your choice of injectors for my next upgrade... so I don't know what the problem is.

Keith
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Old 05-13-2014, 01:41 AM   #15
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I get what you're saying. I don't see the point though. If you really want to push the limits of these ev6's for the sake of finding their limit though, by all means do it and post results. I've no gripe with the thread. I think you're gonna find the limit very fast after 200whp though. whether at 220, or 250. Probably closer to 220 though.
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Old 05-13-2014, 01:55 AM   #16
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Quote:
Originally Posted by flounder View Post
I'm just about maxing out my yellow tops at 15 psi, but I'm running 65 psi base fuel pressure with a 1:1 afpr. I can maintain a steady 11.5:1 afr at 90% DC.

I figure I'm somewhere around 250 whp but not sure?

edit-Totally correct, I am using a churbo 2854.
Sounds good, your setup will maintain 65 psi at the injector tips thanks to your 1:1 regulator no matter what boost pressure you run. Mine doesn't have a manifold referenced fuel pressure regulator so at the standard 60 psi with no boost would have only 50 psi dp at the injector tips at 10 psi of boost, and only 45 psi dp at the injector tips at 15 psi of boost... so I will be more limited than you on the same size injectors. I am "rods limited" for now, so I will be keeping it in the 12 psi range to start. Just have to see if I need the new injectors now or not on the dyno

Keith
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Old 05-13-2014, 06:14 PM   #17
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I have a thread somewhere in diy that explains somewhat step by step how to convert the NB to a return style fuel system so you can use an afpr.

I have a walbro 190HP pump and an ancient EMB for fuel/timing management. I can use the correction factor to idle the yellow tops at the higher base pressures without it running too poorly. I actually have it idling at around 15:1 and a perfect 14.7 in cruise. It's taken a lot of fiddling around to get it right though.
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Old 05-13-2014, 07:53 PM   #18
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Quote:
Originally Posted by Twodoor View Post
And this is why I was hopping someone who has done it or had a really good calculation formula would chime in I know you can find injector calculators on line... they are notoriously inaccurate, relying on user inputs where the user has no clue what the efficiency, Brake specific fuel consumption, etc. of his engine is, what E85 really does to fuel requirements and many other related factors.

Oh well, I will let you guys know when I dyno the car after getting the turbo setup I am aiming for 225 lb-ft of torque through the entire rev range from 3300 RPM to 7200 RPM. If I have to back down on the boost somewhere in the rev range to avoid 100% duty cycle so be it. Then I will upgrade the injectors.

Keith

The "formula" you are looking for at stock pressure (model year dependant) is "1.8".

Multiply power goals by 1.8 to get required injector size, and then round up.

Or divide injector size (in CCs) by 1.8 to get approximate potential power.

FWIW, asking "how much boost can I run?" is like dividing by zero. The answer is always infinity.
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