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Old 05-18-2008, 12:43 PM   #1
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Default Best Injectors for Low Boost Miata

Hi folks,

I have a 91 Miata turbo running a IHI VJ-11 turbo with a Vortech 8:1 FMU and Bipes unit running around 9psi. I am currently using the injectors from the 99 Miata (the long red ones).

Is there any different in flow capacity, max boost levels, flow patterns between these injectors, the 94-97 Miata brown ones and the 01-05 Miata long silver ones. Which has the highest cc rating and max hp potential out of these three?


I have the opportunity to get some of the above at a good price and am wondering if it makes sense to switch.

Please advise.
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Old 05-18-2008, 12:50 PM   #2
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I don't think that there is a large enough difference between those choices to warrant spending money. Check the DIY FAQs here and you'll find a huge list of injectors that fit the Miata.
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Old 05-18-2008, 12:53 PM   #3
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the ones you have are best for the FMU. They were designed to run at a higher pressure than the rest of the miatas and the spray pattern lets them atomize the fuel better. If it works now, dont go "fixing" things
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Old 05-19-2008, 09:02 AM   #4
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What about the 305cc Supra injectors, those are also easy to come by.
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Old 05-21-2008, 02:09 PM   #5
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fwiw I think you are in the medium boost range. 9-12 is above what many run (5-6). Still, my recommendation would be that if you're going to spend some dough on injectors, get some with some headroom. 302's for example if you don't have the engine management the control larger than that. Without doing the math, those at least should be able to supply fuel if you decide to bump to 10 or 11 psi.
-Ryan
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Old 05-21-2008, 03:47 PM   #6
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FWIW I was able to run up to 7psi with the stock '99 injectors without a FMU albeit they were at 100% duty cycle. But I would think you can do more than 7 psi easily with the FMU, and that the smaller injectors would be preferable for idle and for better atomization as Brain mentioned.

You might want to send them out for servicing/testing to be sure they are in good shape if you have not done so already.
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Old 05-21-2008, 04:15 PM   #7
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Quote:
Originally Posted by mazdaaz3 View Post
What about the 305cc Supra injectors, those are also easy to come by.
Unnecessary. Way more fuel then he would need, plus the 305s really are not "compatible" with just a AFPR/FMU. Yes, the stock ECU can idle them, but at the 5k "fuel dump" it will send your AFPRs dangerously rich.
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Old 09-05-2008, 07:05 AM   #8
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Quote:
Originally quoted by Newbsauce
Unnecessary. Way more fuel then he would need, plus the 305s really are not "compatible" with just a AFPR/FMU. Yes, the stock ECU can idle them, but at the 5k "fuel dump" it will send your AFPRs dangerously rich.
So what would you be suggesting he run to get 12psi in a 'compatible' ish way-without going ms??

Keen to know any ideas, as I am on a similar path with fuel stuff :-)
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Old 09-05-2008, 07:29 AM   #9
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Quote:
Originally Posted by ogwazza View Post
So what would you be suggesting he run to get 12psi in a 'compatible' ish way-without going ms??

Keen to know any ideas, as I am on a similar path with fuel stuff :-)
I wanna see picts of the wagon.
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Old 09-05-2008, 07:36 AM   #10
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Haha you're keen are you!!!

Got a couple here
https://www.miataturbo.net/forum/showthread.php?t=24700
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Old 09-05-2008, 12:33 PM   #11
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^Did you just say "keen"?

In any case, I had great success at w/305's and the BEGi 2025 AFPR and Walbro190HP. Newb is right that you get a rich spike in the upper RPM's, but you just need to tune your fuel pressure/rate of rise/02clamp to keep it "less" rich.

https://www.miataturbo.net/forum/showthread.php?t=6576

With some better boost management and a clutch, I would have been in the 190whp range that day. To make 200whp on 305's, you need about 100-110psi of fuel pressure. If you're gonna run that much, you need to replace all the stock rubber fuel lines in the sytem. There are 2 at the tank, 2 at the filter, and the ones actually in the engine bay. Fuel line is cheap.
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Old 09-05-2008, 11:50 PM   #12
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Haha Yes I did say 'keen' - get yourself down with the kiwi (NZ) lingo!!

Im def. a newb at his stuff....starting to realize why my engine runs like dogs *****! It idles good but thats about it!! 305's and no afpr!

Although I did install a fuel pressure reg off a turbo 323 - so I'm not a total ****!

Cheers Sam
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