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Old 10-11-2010, 10:01 AM   #1
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Default Any benefits to 460s over 550s?

I can't see myself hitting the horsepower ceiling on the 460s given my goals on my Shanghai 2854. So why even use 550s? I've hoarded a set of each to choose from. I plan on initially going Shanghai turbo, cheapo BEGi-S d/p, DIYPNP, eBAY FMIC, stock exhaust & cat, stock clutch. I'm guessing that might be good for 180 RWHP.

Eventually I will upgrade the exhaust & cat and clutch, where the car will be left alone for its next 30,000 miles/2-4 years. After that possibly pulling the engine but then that's a whole new game and I'll be looking bigger than 550s. So considering that I don't see my setup even hitting 230 RWHP (probably more like 210), in my situation are there any benefits other than a little more headroom to running the 550s? Any benefits to running the 460s?
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Old 10-11-2010, 10:06 AM   #2
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460s have enough capacity to support 230-250rwhp or so depending on rail pressure, BSFC, and AFRs.

550s have enough capacity to support 275-300rwhp or so depending on rail pressure, BSFC, and AFRs.
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Old 10-11-2010, 10:50 AM   #3
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Advantage of 460 over 550: Price.
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Old 10-11-2010, 10:53 AM   #4
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Quote:
Originally Posted by r808 View Post
...are there any benefits other than a little more headroom to running the 550s?
90cc.

Seriously, if you have both just put the bigger ones in. The benefit is that you won't have to swap them later when you do turn up the boost.

Go ahead, tell us you won't.
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Old 10-11-2010, 11:58 AM   #5
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You'll find it easier to find and maintain a stoich idle with 460's over 550's.

Less of an issue with modern injectors with awesome response times and fab spray patterns, but RX7 injectors are distinctly low tech in comparison.

IMO fit the 460's.
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Old 10-11-2010, 12:01 PM   #6
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Quote:
Originally Posted by richyvrlimited View Post
You'll find it easier to find and maintain a stoich idle with 460's over 550's.
This.

All else being equal, you should run the smallest injectors available which satisfy your power needs and give you a little bit of headroom. The larger the injector, the shorter the pulsewidth required to deliver the small amounts of fuel needed at idle and light cruise, and the more difficult it becomes to control accurately.
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Old 10-11-2010, 03:09 PM   #7
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Note that an NB uses a fuel pressure regulator in the tank, which has a higher base pressure than an NA but is not proportional to manifold pressure. At 15 psi of boost you've got a lower fuel pressure than an NA, so the injectors won't support as much power as they will on an NA.

I'm hitting close to the max bandwidth of my 550s at 268 rwhp on my 99.

--Ian
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Old 10-11-2010, 04:42 PM   #8
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^^ +1, if you are still running the returnless system go with the big ones.
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Old 10-12-2010, 12:10 AM   #9
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Good info. Thanks guys.
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Old 10-12-2010, 12:26 AM   #10
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As well, RX-8 injectors flow about 420-440cc from the factory, and are plug in sets. At least on my NB. They will offer smoother idle. Much much newer technology, strays away from the old pintle style injectors. Find some on ebay, they are yellow and/or red, but get a set of either or.

I ran these, 315cc's, and RC550's, and by far the best idle is offered by the RX-8 or OEM MSM injectors vs the older style injectors. Just a much better spray pattern and thus atomization, is my theory.
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Old 10-12-2010, 12:54 AM   #11
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The newer style injectors seem to deal with E85 a little better, too.

..but then again, if you are looking at ethanol fuels you'd probably be looking at the bigger injectors anyway.
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Old 10-12-2010, 01:49 AM   #12
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probably? lol

on e85 he'd be looking at about 8-10 psi max before they'd be maxed out lol
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