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Old 01-25-2007, 04:24 AM   #1
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Default how much is "safe"

I'm running 9psi with 312cc injectors and a vortech set at 7:1. I'm wondering if it's "safe" to go up in boost and how much? I have a 13psi spring for my wastegate. Is that to much? I have all the recalibration disks for the vortech so I can fine tune a little. I know I should get to a dyno to see where i'm at. But for now my A/F meter says that I'm running nice and rich. At what fuel pressure is the walbro 255hp going to poop out (130psi?)?
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Old 01-25-2007, 09:10 AM   #2
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Is your A/F meter running off a narrowband O2 sensor? If so, they you can't really use that to tune. You need a wideband at the very least. If tuned well, 13psi shouldn't be a problem. The 255 pump, at the least the regular version, isn't really intended for flow at high pressure. I think it craps out around 100psi. The high pressure versions of the Walbro pumps can flow up to ~120-130psi, as I recall.
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Old 01-25-2007, 10:03 AM   #3
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I think 312s are going to be too small to run 13psi.
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Old 01-25-2007, 10:16 AM   #4
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not really, im running 12psi on 305cc injectors. You forget that FMUs raise the fueling capacity of injectors.

If you want to run 13psi you'll most likely want to recalibrate the FMU. The calculations are in my FAQ. Right now you're looking to run 145psi...not going to fly. Especially since your FP will crap out at around 100-110psi. You're probably looking at a 4:1 disc. (4 x 13) + 55 = 107psi.

107psi into 315cc injectors will allow them to fuel to around 215-230rwhp or so. That's the thing that sucks about the Vortech, it would be nice to take a few pulls and just fiddle with needle valve to see the perfect spot.

And again like Brian said, if you are reading off a NBO2, then you aren't really seeing exactly what's going on.
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Old 01-25-2007, 10:45 AM   #5
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i run 120 psi FP but i also dont run an IC or bipes so i am abit crazy compared to some of these guys with 12 psi on 1.8 injectors.
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Old 01-25-2007, 10:47 AM   #6
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braineack: good call...
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Old 01-25-2007, 01:09 PM   #7
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Sounds like I can do it with some tuning. Does anyone know a good dyno in oregon?
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Old 01-25-2007, 01:47 PM   #8
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Quote:
Originally Posted by magnamx-5 View Post
i run 120 psi FP but i also dont run an IC or bipes so i am abit crazy compared to some of these guys with 12 psi on 1.8 injectors.
If I recall correctly aren't you in the process of rebuilding your engine? Was you engine failure related to your setup? Bleeding edge is good unless it goes boom.
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Old 01-25-2007, 04:21 PM   #9
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I ran my T25 for a month spiking to 18psi w/fuel pressure at 130psi on 1.8's and 330's using a Walbro 190hp.
In all honesty, it ran fine with the exception of boost overshoot. THAT WAS NOT A RECOMMENDATION!

No telling how long it would have lasted... thankfully I got it on a dyno and spotted it. My biggest surprise was how inaccurate my boost gauge was, reading 13psi when it was really 18psi.
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Old 01-25-2007, 04:52 PM   #10
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Quote:
Originally Posted by samnavy View Post
I ran my T25 for a month spiking to 18psi w/fuel pressure at 130psi on 1.8's and 330's using a Walbro 190hp.
In all honesty, it ran fine with the exception of boost overshoot. THAT WAS NOT A RECOMMENDATION!

No telling how long it would have lasted... thankfully I got it on a dyno and spotted it. My biggest surprise was how inaccurate my boost gauge was, reading 13psi when it was really 18psi.
Dang...any reason why its so inaccurate? b/c thats a huge difference.
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Old 01-25-2007, 05:41 PM   #11
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I think a lot of boost gauges are just not incredibly accurate. My ~$30 VDO gauge seems to be inaccurate at times, at least compared with the GM 2-bar MAP sensor voltage-to-boost table that's commonly available on the internet.
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Old 01-25-2007, 05:47 PM   #12
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My first autometer was out by about 4-5 psi (high) and my new one is about 1psi out as well. Altitude will also effect the accuracy compared to MAP sensor.
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Old 01-25-2007, 06:20 PM   #13
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man you guys are scaring me with my sunpro boost gauge...
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Old 01-25-2007, 06:32 PM   #14
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Originally Posted by jayc72 View Post
Altitude will also effect the accuracy compared to MAP sensor.
Both boost gauge and MAP sensor are tee'd off the intake manifold, so they should read similarly (i.e. the difference in readings between the two should remain consistent in different altitudes).
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Old 01-25-2007, 06:51 PM   #15
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Maybe I'm wrong but I thought the MAP sensor was absolute and was not relative to the atmosphere. Where as the boost/vac gauge is relative to the atmoshere.
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Old 01-25-2007, 07:45 PM   #16
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Well, a 2-bar MAP sensor, for example, has a range from ~0-29 PSI absolute. When connected to an intake manifold, that means the sensor is capable of giving you a reading of ~-14.7 PSI/29" of vacuum to ~+14.7 PSI/boost.

Both MAP and boost gauge are tee'd off the intake manifold, so they're reading from the same location. I've got the MAP driving an EBC that displays the boost by just subtracting one atmosphere from the MAP output.

Conversely, you could just as easily replace the 30" HG on your boost gauge with a zero and the 25 PSI with a 40 PSI, and you'd have an absolute pressure gauge. It's a matter of semantics.
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Old 01-25-2007, 09:12 PM   #17
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What area of Oregon are you in? I haven't started my build yet, just started aquiring parts. If you are in the Portland area you might check with Cork Sports. He's a well known miata shop. They offer dyno tuning and are in Vancouver WA.
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Old 01-25-2007, 10:31 PM   #18
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Yeah, corksport is in vancouver, wa. Also check unnaturalinc, I think they have a dyno, great guys too.
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Old 01-25-2007, 11:08 PM   #19
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Old 01-26-2007, 01:32 AM   #20
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I live in depoe bay on the coast but i do get to the portland area now and then. I'm planing on doing some solo events there this year maybe I can arange something. My boost guage is right on with what my wastegate springs should be so I'm pretty sure that I ok there. I ordered a fuel pressure guage a couple of days ago so I can get a better idea of where I stand.
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