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Old 01-19-2007, 12:38 AM   #1
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Default RB20DET Injectors

Hi,

I'm wondering if anyone knows if the 270CC injectors from a RB20DET engine are plug and play? All I know about them is that they are 10ohm High Impedance injectors.

Thanks!
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Old 01-19-2007, 08:07 AM   #2
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10ohm might be high impedance compared to, say, 1ohm, but the Miata/RX-7 high-impedance injectors are typically 13-15ohms, I believe. Not an electrical expert, so I don't know if that's enough to cause a problem, but it sure sounds like a decent ohms spread.
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Old 01-19-2007, 09:34 AM   #3
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They aren't on my list (DIY FAQ).

Easiest thing would be to source 265cc 94-97 or 01-05 miata injectors.
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Old 01-19-2007, 10:30 AM   #4
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Have you seen more than one set of NA 1.8 injectors flow past 235cc? Everything I've read has said that they are 235cc, I know Ben had a set that flowed 265cc, but is this the only case?

the EMB is supposed to control 50% more injector. On a 94 this would mean the ability to control nearly a 400cc injector, which seems a little on the high side.
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Old 01-19-2007, 10:35 AM   #5
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Yes 3 accounts.

Ben

FM (multiple tests, supposely)

& Here's Bruce's (Olderguy) : http://www.cruzinperformance.com/inj...=607171-607174

Even Witchhunter.com rates them at, at least 255cc:






All the math adds up as well:
265cc @ 50psi = 285cc
285 x .50 x .80 = 115BHP = 107RWHP (anything smaller would barely support the stock power.)
You're falling victim of M.net Tom-Foolery.


Magnamx-5 was idling 440cc injectors with a AFC on a 1.6, I'm sure the EMB could handle 400cc injectors on a 1.8, has anyone tried?
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Old 01-19-2007, 12:13 PM   #6
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I'm not falling for anything, I don't blindly accept what anyone says ... that's why I asked the question. I just can't see why Mazda would put in an injector with that much headroom, when it really wasn't needed.

NA car doesn't use .55, more like .45, so your math does not support this logic. [email protected] will support about 145-150hp. Or about 125whp. When I dynoed my car NA with no changes besides intake and exhaust I made about 100whp, and was running very rich.

I can't argue with the results that Ben and Bruce got though. Anyone ever flow test 1.6 injectors?
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Old 01-19-2007, 01:37 PM   #7
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search m.net for a post by Jeremy from FM. He posted flow results from all variations of 1.8 injectors. IIRC his 94-97 tan tops flowed 265. Also, IIRC mine flowed 3 x 266 and 1 x 267 cc/min @ 3 bar.

The only dude who has posted the low ratings after an actual flow test was that guy Popstoy, who claims that his flow 235 @ 4 bar. Which I showed to him was impossible, but whatever....

I think the "common knowledge" injector ratings are at idle fuel pressure. The math works out.

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Old 01-19-2007, 02:29 PM   #8
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when these things are flow tested do they have an industry standard PWM signal? Or do they just lock it open with 12V constant and hope it doesn't overheat?
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Old 01-19-2007, 05:29 PM   #9
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Quote:
Originally Posted by jayc72 View Post
NA car doesn't use .55, more like .45, so your math does not support this logic. [email protected] will support about 145-150hp. Or about 125whp. When I dynoed my car NA with no changes besides intake and exhaust I made about 100whp, and was running very rich.

Changes are in your favor, do the math, I calculated for .5 not .55 (i'm just used to writing it)

285 x .45 x .8 = 103BHP
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Old 01-19-2007, 05:39 PM   #10
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Where does that formula come from? It seems a little simple for figuring out how much 4 injectors can handle. I used the widget over at rcengin.com to figure out how much 4 205cc @ 50psi could support.

Unless I'm not following what you are trying to prove I think you missed a step in your math.
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Old 01-19-2007, 05:43 PM   #11
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For a 1.6 Injector @43.5psi
205cc=19.5 lbs/hr

19.5 X .8 / .45 = 34.67hp per injector
4 X 34.67 = 138.67hp

At 50psi it would be 159.58HP
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Old 01-19-2007, 05:45 PM   #12
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I wonder if the 235cc number came from the difference between 43.5psi and 50psi?

50/43.5 * 205 = 235.63
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Old 01-19-2007, 05:58 PM   #13
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ah, you're right I was using CC/Min. not Lbs./Min., my bad.

haha acutally I dunno what I', thinking, that's not even the correct formula.....sigh. whatever.


#edit# somehow I took a crazy diversion of this : Est. Horsepower x B.S.F.C / # of injectors x duty cycle = lb/hr per injector
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Old 01-19-2007, 06:16 PM   #14
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both of you guys are using wrong formulas. I broke most of it down here
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Old 01-19-2007, 06:49 PM   #15
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Then RC Engineering is using the wrong math.
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Old 01-19-2007, 07:00 PM   #16
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No you used an incorrect formula and put an incorrect value into it. Coincidentally, the answer you received proved some point you were trying to make. But since your work was wrong, it does not matter.

To find out how flow changes with pressure, you take
(square root (the new pressure/the old pressure)) * old flow rate
The idle pressure for an NA is 35psi.

Using my correct formula, tan tops flow ~237 cc/min at idle pressure.
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Old 01-19-2007, 07:11 PM   #17
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Yup you got me I forgot to apply the sqrt when I was using the forumla for flow difference. My calculations for 205cc @ 43.5 PSI were correct.
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Old 01-19-2007, 10:40 PM   #18
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Those flow numbers for the RB20DET injectors seem very low, Here in New Zealand we probably have the highest number of R32 skylines and the general accepted flow rates for those injectors is 265-270cc.
Most of the Australian and New Zealand tuners say that the MAX these injectors can support on the 6 cylinder RB20det is 200RWKW, so in a 4 cylinder car youd be looking at a max of around 135-140Rwkw which is about 185 RWHP.
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Old 01-19-2007, 11:01 PM   #19
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we are debating 1.8L miata injectors.
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Old 01-19-2007, 11:14 PM   #20
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do dabate, regulate ha!
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