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Old 05-08-2008, 02:12 PM   #1
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Default Injector sources/prices

I'm on the hunt for some injectors of the mid-400cc variety to go with the MS I just purchased. I forwarded the list from the DIY FAQ of plug and play high impedance injectors over 400cc to my friend who works at a german car repair shop, he checked his database and the only ones he can get from worldpac are the 89-91 RX-7 Turbo 550cc Denso injectors at $50 each new. Interestingly, he can also get the NA rx-7 ones for those years but they are over $100 each. I've seen sets of 4 injectors out there for sub-$100 and those plus cleaning would come in under the $200 it would cost for the new turbo ones, but should I just go for the new ones he can get me? What do you guys think? Also, those are 550's which I KNOW I won't ever need to use to their full ability. We're talking maybe max 250 hp ever. Is there any benefit or detriment to running larger injectors than needed? Was hoping to find like 420's from an rx-8....
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Old 05-08-2008, 02:14 PM   #2
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You can run 550s just fine, they'll idle fine in your NA just not as lean as a set of 440s would. If you can get 550s at $50 each brand new that isn't a bad price I suppose. I got my 550s for around $80 and had them cleaned for another $60. So you're not paying much more for brand new ones.
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Old 05-08-2008, 02:20 PM   #3
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I like my gas mileage though... I mean, regardless of weather it's a 450 or 550 injector, at WOT I've obviously got to dump enough fuel to keep the A/Fs right, but I don't know how I feel about dumping extra fuel alllll the time - like at idle and in traffic and crusing on the highway... is it not possible for the 550s to close up enough? How does that work? As of now, I've only dropped from 28-29 mpg average NA to 26 mpg average on turbo w/vortech. If anything I hoped with a good fuel tuning ability (MS) I could bump that back up assuming I were to lay off the go pedal.
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Old 05-08-2008, 02:23 PM   #4
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Scott tuned an NA to idle 550s at 14:1 or leaner I believe, you won't be using anymore fuel than with any other injector. I don't see why you think a larger injector will dump more fuel on the highway. You tune for afr and adjust the VE which changes the injector PW accordingly.
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Old 05-08-2008, 02:26 PM   #5
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Shouldn't idle be at 14:7ish?
P.S. I have no idea what VE is. PW is pulse width though right? Which I actually don't know what that means either.
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Old 05-08-2008, 02:36 PM   #6
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Volumetric Efficiency I think. I idle at 13:1 because the NB's have higher fuel pressure than NAs and MSI with hi-res code cannot idle the 550s any leaner than that smoothly.
Most miata's idle at more like 14:1 from the factory, atleast NAs I believe. Some of the guys on the board idle at more like 15:1 or even leaner with really small injectors (read: stock).
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Old 05-08-2008, 02:45 PM   #7
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The 1.6, in stock trim, idles right around stoich- all cars do, for emissions purposes. Typical AFR swing was between maybe 14.5 to 15.5.

With the 465 injectors, I found my "perfect" idle to be in the upper 13s, though I can get an "acceptable" idle in the lower to mid 14s.
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Old 05-08-2008, 04:23 PM   #8
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by a "good" idle are you guys just speaking of the smoothness of the idle?
FWIW, right now on 1.6 injectors my 'swing' as Joe put it is about 14.0-15.5 during idle. Sometimes it settles down after some driving and swings from 14.5-15.0 I thought this swing was odd, as I've seen Savington's car idling at a solid 14.something but I assume a swing is ok since Joe just mentioned it.
I'll look for some 420,440, or 450's.. if no luck, I guess I can always go with the brand new 550's.
-Ryan
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Old 05-08-2008, 09:54 PM   #9
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hey i'm selling my 460s if those would help
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Old 05-09-2008, 02:58 AM   #10
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i bought my rx7 injectors for $55 shipped i believe off an rx7 forums. seems that was the going rate for them when i was shopping for them.
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Old 05-09-2008, 05:45 AM   #11
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