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Old 04-25-2008, 04:30 PM   #1
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Default noob question..injectors 1.8 s/c

Sorry for the noob questions but i can't figure it out from search results i've found.

Installing MS (hopefully next weekend) on my s/c 1.8. I'm assuming I can ditch the AFPR. If I do this will I need larger injectors?

My goal is 250whp with a turbo next year. If I don't need new injectors yet I'd rather wait. If I do, I want to buy something with the 250hp goal in mind.

I bought my car with the whole JR Kool-Aid package installed by the previous owner - M45, fuel pump, afpr, header, cat, and I think clutch as well......
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Old 04-25-2008, 04:37 PM   #2
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Originally Posted by soloracer View Post
Installing MS (hopefully next weekend) on my s/c 1.8. I'm assuming I can ditch the AFPR. If I do this will I need larger injectors?
Yes, and yes.

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My goal is 250whp with a turbo next year. If I don't need new injectors yet I'd rather wait. If I do, I want to buy something with the 250hp goal in mind.
If you're going to install the MS now, I somewhat advise you to do the larger injectors at the same time, so you don't have to completely generate all new fuel tables twice. Granted, you'll have to re-tune the fuel table anyway when you switch from S/C to Turbo, but it'll be more of a fine-tuning. There's no reason you can't run with a set of 550s while the S/C is still in place and making 140 HP. Remember that technically, most of us running big injectors are only making 30 - 40 HP 90% of the time.

It sounds like you've already purchased your MS. Which one did you buy?
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Old 04-25-2008, 04:40 PM   #3
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Dang. I was afraid of that. Another expense i hadn't counted on.
So what's a good (read - inexpensive) source for Hi Z injectors? How big should I go?
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Old 04-25-2008, 04:46 PM   #4
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It sounds like you've already purchased your MS. Which one did you buy?
I got one off the MT classifieds. One that Brain built but was never installed. Ver. 3 board. Made for a 1.6 so I'm gonna have to change some stuff first. I THINK I'd like to do a knock sensor and I'm contemplating a simple DIY WI setup. Don't yet know if the MS will need to be involved in that. I'll probably ditch it for an IC once I go turbo.
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Old 04-25-2008, 04:49 PM   #5
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https://www.miataturbo.net/forum/showthread.php?t=10821
post #3, figure out which injectors you want to use, and then find them whereever they may be hiding. I got my 550cc RX7 injectors from a guy out of Bellingham WA who posted in the Seattle Craigslist who a friend of mine in NC saw and emailed me about and I got them for $70 shipped. Will this happen to you, i don't know, but keep your eye out, I think a lot of people get them from RX7club.com or something...
Get creative, they will not find you. Also, check the classifieds here, sometimes they pop up.
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Old 04-25-2008, 04:54 PM   #6
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Thanks Zabac. I'm good at 'finding' stuff. What I should have asked was - what injectors are plug - n -play. i.e. what cars are good sources. But you answered that. So the RX-7s plug right in? I don't want to monkey with resistors and converting low Z to hi Z stuff if I can avoid it. I like simple....
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Old 04-25-2008, 05:03 PM   #7
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OK, I suck. I read that whole thing a month ago and forgot about it!

I'm at around 9psi right now. The search is on for 550s I guess.
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Old 04-25-2008, 05:18 PM   #8
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If you do go for RX7 injectors, make tripple sure they are the correct part number...you never know man
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Old 04-25-2008, 05:29 PM   #9
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id go with 460s. you dont need 550s for that power.
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Old 04-25-2008, 05:30 PM   #10
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he wants headroom for 250ish, yeah he does
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Old 04-25-2008, 10:16 PM   #11
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250ish
i think 460 will do it.
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Old 04-25-2008, 10:27 PM   #12
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I run at 11.5psi (about 220bhp) on 320cc no problem.
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Old 04-25-2008, 11:41 PM   #13
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Quote:
Originally Posted by Zabac View Post
If you do go for RX7 injectors, make tripple sure they are the correct part number...you never know man
and although some people on this forum disagree with me, make sure you get the high z regardless of part #. A guy at witch-hunter told me he's seen high and low z rx7 550's with the same part #.
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Old 04-26-2008, 12:42 AM   #14
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250hp on a jr m45?
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Old 04-26-2008, 12:49 AM   #15
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250hp on a jr m45?
read the op
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Old 04-27-2008, 01:03 PM   #16
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oops.
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Old 04-29-2008, 12:15 AM   #17
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www.mx6.com

a 90-92 mx-6 / 626 / ford probe turbo will get you a set of 320's for around $50 shipped. I just bought four sets of them at an average of $60 shipped a set.

-meaty
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Old 04-29-2008, 10:09 AM   #18
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I'm just afraid those won't be big enough in the long run. I'd rather not swap and pay twice when I could do it once and do it right with a little patience. I MAY have found a newly cleaned set of RX& Hi Z 550s for $150.

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www.mx6.com

a 90-92 mx-6 / 626 / ford probe turbo will get you a set of 320's for around $50 shipped. I just bought four sets of them at an average of $60 shipped a set.

-meaty
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Old 05-09-2008, 05:25 PM   #19
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Quote:
Originally Posted by Joe Perez View Post
If you're going to install the MS now, I somewhat advise you to do the larger injectors at the same time, so you don't have to completely generate all new fuel tables twice.

If you change to larger injectors after a base map has been created, you have to alter the entire fuel table?

I was thinking all you had to change was REQ FUEL since the injector size CHANGE is the constant across the whole table.

Since my wife is going out of town this weekend, I was going to finally install my larger injectors in the Miata before the turbo build really gets started... you know, one change at a time...

but does the whole fuel table need to retuned?
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Old 05-09-2008, 05:36 PM   #20
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Originally Posted by emerilnut View Post
If you change to larger injectors after a base map has been created, you have to alter the entire fuel table?
In the OP's case, the proposed change was both to add larger injectors and remove an AFPR. Because AFPRs are non-linear by design, removing one would necessitate a complete re-tuning of the VE table, rather than a simple re-scaling or Req_Fuel recalculation.
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