how much boost can 250ccInjectors handle? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 10-18-2007, 04:56 AM   #1
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Angry how much boost can 250ccInjectors handle?

I just pluged in the MSpnp and fixed the timing and the car isn't running so good. i'm taking my car to a dyno, i have RC 250cc injectors and my boost can't be lower then 10 psi. no electronic boost controller. i am running on that ebay 16g turbo. will these injectors be a problem?
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Old 10-18-2007, 05:40 AM   #2
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Quote:
Originally Posted by Eunos_roadsterna6ce View Post
I just pluged in the MSpnp and fixed the timing and the car isn't running so good. i'm taking my car to a dyno, i have RC 250cc injectors and my boost can't be lower then 10 psi. no electronic boost controller. i am running on that ebay 16g turbo. will these injectors be a problem?
I'd have thought that 250's would be way too small for 10 psi unless you're willing to up the fuel pressure, (I wouldn't be).

you can pick up a set of 550's for 50 (about $100) that will fullfill all your needs.

Why can't boost be lower than 10psi? just adjust the wastgate accordingly.

IMO your options are:

* Reduce the boost
* Replace your injectors

if not you'll be buying a new engine PDQ.
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Old 10-18-2007, 05:52 AM   #3
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Thanks for the tip... i have so 550cc RC but they are low impedance...i don't hear to much good things about them on miata...is it really a problem?
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Old 10-18-2007, 05:53 AM   #4
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boost can't be any lower on this wastgate i guess...i heard it was stock boost since it was made for a Mitsubishi Evo 3...i tried adjusting it but wont work
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Old 10-18-2007, 06:05 AM   #5
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Quote:
Originally Posted by Eunos_roadsterna6ce View Post
Thanks for the tip... i have so 550cc RC but they are low impedance...i don't hear to much good things about them on miata...is it really a problem?
No.
Go to the junkyard, get resistor box from a honda or something or dsm, some thing like that, and wire it in.
I hear its actually pretty easy, but i dont know from expierence.
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Old 10-18-2007, 06:13 AM   #6
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where do i wire it at? i need to do some homework...
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Old 10-18-2007, 06:13 AM   #7
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Thanks for the tip... i have so 550cc RC but they are low impedance...i don't hear to much good things about them on miata...is it really a problem?
Jerry reckons with lots of extra earths they'll work fine. If you don't want the hassle just fit a resistor pack inbetween them and the ECU
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Old 10-18-2007, 06:21 AM   #8
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alright...so plug in the 550cc and fit in a risistor box? man i don't even know what that is can you guys tell me?
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Old 10-18-2007, 09:57 AM   #9
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Quote:
Originally Posted by Eunos_roadsterna6ce View Post
will these injectors be a problem?

get a wideband and find out. fwiw, I couldn't run my 305s past 7psi (160-170rwhp)

also fwiw, the stock non-turbo 1.8L injectors are 265cc.
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Old 10-18-2007, 09:59 AM   #10
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yeah, i'm running 305's right now and am close to the edge of where i'm comfortable pushing them at 6psi. i would get some bigger injectors before you even try to run anywhere near 10.
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Old 10-19-2007, 07:21 AM   #11
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What about 330cc at stocko pressure?
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Old 10-19-2007, 09:59 AM   #12
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http://www.rceng.com/technical.aspx?

The whole page is good info on this, but you can use the calculator at the bottom of the page.
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Old 10-19-2007, 11:25 AM   #13
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I guess that site must be fairly conservative, it is saying I can only get about 165 crank horsepower from 330cc injectors.
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Old 10-19-2007, 11:35 AM   #14
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i get 181BHP, you aren't plugging in good numbers. and yes that's still conservative.
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Old 10-19-2007, 12:23 PM   #15
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i get 181BHP, you aren't plugging in good numbers. and yes that's still conservative.
I can't being conservative.

target HP - 160

No of Injectors - 4

BSFC - .65

DC - 80

Fuel Pressure - 43.5

that give the requirement of 344's. That's the ultra conservative better safe than sorry.

Personally I don't see the point of pushing harder than that, if you can get bigger injectors do so, they're cheaper than an engine.
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Old 10-19-2007, 12:28 PM   #16
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when's the last time you were driving around at 43.5 psi of fuel?! you idle at 35psi and make 50psi at no vacuum.

USE .55 BSFC and 50psi of fuel.



but reality always overrides these math equations. who would ever just plug in some numbers, buy those injectors and just assume the fuel is good, no one smart.
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Old 10-19-2007, 12:40 PM   #17
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Quote:
Originally Posted by Braineack View Post
when's the last time you were driving around at 43.5 psi of fuel?! you idle at 35psi and make 50psi at no vacuum.

USE .55 BSFC and 50psi of fuel.



but reality always overrides these math equations. who would ever just plug in some numbers, buy those injectors and just assume the fuel is good, no one smart.
fair enough, I didn't know the stock FP of the car, so just assumed that 43.5 was an industry standard or sumat.

my bad!

.55BSFC is for N/A tho, 60 - 65 for T/C according to the calculator??
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Old 10-21-2007, 10:07 PM   #18
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im putting out 200RWHP on my "330cc" injectors (which actually flow closer to 370cc for some reason.) thats at about 80%D/C @ 7200rpm
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Old 10-22-2007, 01:30 AM   #19
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i bought some 550cc rx7 injectors...i pluged it in and it was leaking a little bit... i pulled it out again and the plastic on the bottom of the injectors just cracked like glass...i am soo ****!!! does that mean my injectors are done?
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Old 10-22-2007, 01:34 AM   #20
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You can get new pintle caps from places like witchhunter cleaninjectors and possible the mazda dealer or some other denso injector supplier/servicer.
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