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Old 05-17-2007, 04:17 AM   #1
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Hi guys!
I am thinking of doing a DIY turbo project and I'm a bit lost on injectors.

Is there any benefit to using a 550cc injector and what kind of fuel pump would make it work, and what kind of boost must i be using in order to justify a 550 injector.

Would a 440cc injector work for most turbo kits and would it, in some sense, work better than a 550cc injector?

I'm looking at the RC engineering injectors. Would these be ok to be paired with a Link ECU? How do the impedance of the injectors affect?

Thanks guys
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Old 05-17-2007, 06:49 AM   #2
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low-imp (peak'n'hold) injectors respond faster than old style high-imp (saturated) ones ... so for a given cc rating the low-imp ones will be capable of a better idle and flow more at high duty cycles due to less time spent opening and closing. They'll need a resistor pack with the Link tho.

Having said that I can idle OK at 800rpm 15.4 AFR with hi-imp 550cc rx7 injectors ... just... 1.1% duty-cycle... wahlauay!
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Old 05-17-2007, 09:35 AM   #3
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pair the injectors to the amount of power you'll be making.

no point running a 550cc injector on a 200rwhp car.

550cc @ 50psi can support around 300rwhp

440cc @ 50psi can support around 250rwhp

------

The stock fuel pump should flow around 35 Gal. /Hr. at 50psi

thats 210 Lbs. /Hr.

210 * .80 / .55 = 305BHP

So if you think you might be making more than 250rwhp, I'd suggest a new fuel pump.

the new best option...the Walbro 190 Lph flows around 45 Gal/hr. at 50psi

270 * .8 / .55 = 392BHP (325rwhp)
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Old 05-17-2007, 10:17 AM   #4
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hmm. does that mean that it'd be ideal for me to get high imperdance injectors to run with the link?

A walbro would be good.
I'm hoping to run around 16-17 psi on stock internals, a T25 turbo, FMIC, Link, 550cc RC Engg injectors and a walbro fuel pump.
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Old 05-17-2007, 10:20 AM   #5
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actually the reason i'm asking is cause the 440 and 550 Rc Engg injectors cost only like 10 bucks different.
Speaking of which, anyone can recommend a goood place to get them?
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Old 05-17-2007, 10:25 AM   #6
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how about some: 89-91 RX-7 TURBO 550cc purple tops #195500-2020
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Old 05-17-2007, 11:17 AM   #7
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Quote:
Originally Posted by Braineack View Post
how about some: 89-91 RX-7 TURBO 550cc purple tops #195500-2020
I just picked up a set of "new" ones for $120. I need to get them flowed to be sure everything is right before they go in though. www.clubrx7.com
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Old 05-17-2007, 03:13 PM   #8
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on the same subject, is it worth it to get them flowed? i mean is that gonna work better than some brake cleaner and an air compressor that i can do at my house?

if i was building a kit for 235 hp now but wanted to bump it up to 350 could i use 550cc injectors while i run the 235hp kit? don't wanna spend extra $$ and time if i don't have to.
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Old 05-17-2007, 03:17 PM   #9
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its smart to do...many times the injectors fail the before test...be it spray pattern or leak test....and most of the time when all the screens, etc. are replaced they flow 10-30cc more than they should.
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Old 05-17-2007, 03:41 PM   #10
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Quote:
Originally Posted by guitarrc6 View Post
if i was building a kit for 235 hp now but wanted to bump it up to 350 could i use 550cc injectors while i run the 235hp kit?
Yes, you can use 550cc injectors with your "235 HP kit" and they will work. It's the 234 HP kit that they have problems with.

Seriously though, with the right driver circuit you could install 1000cc injectors on a stock engine and they'd "work", you'd just have a really crappy idle. It's all a matter of degrees. The greater the ratio of injector size to actual cylinder displacement, the poorer the low-end becomes. There's a reason that Mazda put staged injectors on the RX-7 engine, and it wasn't to save money.

Quote:
don't wanna spend extra $$ and time if i don't have to.
...And yet you plan to take a Miata engine to 350 HP. :gay:
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Old 05-17-2007, 05:02 PM   #11
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OH good thing i'm going for the 235 then!! dodged that bullet! yeah well EVENTUALLY i want to make a 350hp miata engine. but the jump from whats involved for 350 hp is a lot greater than 235.

correction, i do have the time, but i can't afford my car to be down that long, and considering it takes me twice as long as the avearge person to do finish any project i'm already at a disadvantage.....actually my mom said its my super power, SLO MOTION MA-eh i'll finish the rest later.
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Old 05-18-2007, 08:12 AM   #12
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would they fit with a link ecu?
or are they like rc engg
?
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Old 05-18-2007, 09:33 AM   #13
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plug and play.
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Old 05-18-2007, 10:08 AM   #14
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buy the whole shebang from FM like they sell it RC injectors and link ecu, or you could go hydra MS PNP etc and some high impedance injectors of your choice.
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Old 05-21-2007, 10:01 PM   #15
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Will a Link Mk2 ECU for 90-93 NA6 work with a set of 2001 265cc(??) injectors?
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Old 05-21-2007, 10:08 PM   #16
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yes but why run some bigger ones instead to keep the headroom open. the link can run 600's hell.
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Old 05-22-2007, 10:53 PM   #17
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i wonder whats the drivability like. i mean if you are running relatively low compression and big injectors outside of boost, will your car even idle?
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Old 05-22-2007, 10:58 PM   #18
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in comes the magic of replacement ECUs
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Old 05-22-2007, 10:58 PM   #19
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yes it should but you need to try every car is abit different.
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Old 05-22-2007, 11:34 PM   #20
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If you aren't doing a standalone ECU (i.e. you intend to run a Bipes/AFPR/O2 clamp) do 315cc injectors and jack your fuel pressure up. If you intend to run a Megasquirt or a Link or something like that, look into the 460cc high-imp injectors from the NA S5 FC Rx7. (non-turbo, later version of the second gen rx7) I got mine off a member from the 7 club (www.rx7club.com, not clubrx7.com) for $75 shipped and got them cleaned for $70. The first mod those guys do when going for power is monster injectors so tons of guys have stockers laying around.
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