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how to run 14-15 psi of boost?

Old 07-31-2003, 07:02 PM
  #1  
0.5 BAR
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Default how to run 14-15 psi of boost?

i know that the stock map sensor will only read up to about 10.5psi of boost so how can i run 1 bar of boost without standalone? i know the gm 3 bar will read up to 30psi but will this work with the stock ecu and afc hack? i have a chip burner and ghettodyne, is there anything i can do with that? if anyone has any ideas they will be greatly appreciated.
TIA
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Old 07-31-2003, 08:09 PM
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Default Re:how to run 1 bar boost?

Ok, here is the delima, outlined in easy to understand segments..

True, your stock MAP sensor can support up to ~1bar manifold pressure, but the flip side to that is, your stock ECU cannot. In fact, anything above 3.0 volts (range is 0 - 5v) which is about 1.3psi, your ECU will say, "Waht, hold the hell up.. too much pressure.", throwing your ECU into "limp mode" where your car runs like crap until you ---- off, and restart it.

Now, 1.3psi, you say? But I have heard of people running up to 12psi with thier stock ECU and MAP sensor? What gives?!

Well, that is where the AFC comes into play. It scales the voltage of your MAP sensor, so your ECU doesn't think it's seeing postive pressure. This scaling is what keeps the voltage between 0 and 3 volts, allowing your ECU to not flip out.

But, if I'm scaling my MAP sensor voltage, what happends to my fuel output since it's directly related to manifold pressure?!

Well, the scaling is measured in percents. With A'pexi's V/S-AFC you "lean out" your fuel at distinct RPM ranges to cut the amount of voltage your ECU sees from the MAP. Aaah, you say this would cause a leaning condition which will blow your motor? Yes, that is what you have to replace the stock 240cc injectors with that of a 450cc or so injector. This way, during the same pulse duration, the injector flows about 80% more fuel, thus, compensating for the leaning out of the MAP signal.

But what about a 3bar MAP sensor? Won't that eliminate this problem witht he MAP signal since it can support more boost?

No. The reason people switch to "higher bar" MAP sensors is because of the MAP sensor limitation of ~1bar boost. The problem really lies above, with the ECU. Once you have code that supports positive manifold pressure running your ECU, and there is no fear of your ECU freaking out when it see this pressure, running a larger MAP sensor will only let you exceed this ~1bar limitation.

..got it?
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Old 07-31-2003, 08:12 PM
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Default Re:how to run 14-15 psi of boost?

OK, you changed the title of your post after I posted..

Not cool..

Second, yes, with the new title, you'll need a 2bar MAP sensor, and ECU modifications to offset the limitations mentioned above.
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Old 07-31-2003, 08:15 PM
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Default Re:how to run 14-15 psi of boost?

isnt 1 bar 14.7psi?
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Old 07-31-2003, 08:16 PM
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Default Re:how to run 14-15 psi of boost?

Yes, that is why I say, "about".. Your original post said 10.5psi..

Neither here, nor there, information is still correct, plus the need for a 2bar MAP sensor.
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Old 07-31-2003, 08:19 PM
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Default Re:how to run 14-15 psi of boost?

.but i still dont understand how to mod my ecu to read higher boost with a 2 or 3 bar map sensor.
thank you very much for the help
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Old 07-31-2003, 08:24 PM
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Default Re:how to run 14-15 psi of boost?

Well, basically, I think there are two different ways on the table now for OBD0 based boost code. One being the 5/8 digital MAP sensor output scaling. This is the method currently employed by Ghettodyne 2.2.

The second version is something that Mike is beta testing, for a later version, and that I'm working on writing on my own. It's a theory that yes, since the MAP sensor can handle higher amounts of boost, and the code is what is limiting it, we hook the MAP Sensor CEL light routine, and devise a new fuel interpolation routine that will interpret the higher MAP signal. Then, based on that hook, will interpolate fuel values from a secon set of "boost" MAPs.

This is still in the beta stages, but as we're all gaining more understanding of the Honda code (essentially coding backwards from what is current written) we should have this thing cracked in just a few more months. Mike probably will have it very soon! We shall see..
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Old 07-31-2003, 08:29 PM
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Default Re:how to run 14-15 psi of boost?

didnt understand that second paragraph but i guess that is why i only use ghettodyne and not write it . well i guess ill just wait till its (new ghettodyne) all laid out in front of me, so to speak.
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Old 08-01-2003, 01:36 PM
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Default Re:how to run 14-15 psi of boost?

Tune for GM 2 bar sensor.

The honda ECU doesn't know what boost you are running, it just sees 0-5 volts returned from the MAP. YOU have to understand what to do to mesh the new MAP input with the ECU's maps. The difference in calibration between Honda 1.8 bar theoretical/1.65 bar actual MAP and GM 2 bar is very minor and would not cause any problems with Uberdata or Ghettodyne - you just have to realize all your pressure columns have just shifted a little higher + need to take that into account when tuning.

FYI, atmospheric is 14.7 psi, 1 bar = 14.5 psi. GM 2 bar is good up to 29 psia (psi absolute, meaning you start measuring from perfect vacuum as opposed to psig aka psi gauge where you start measuring from atmospheric) which results in about 14.3 psig worth of boost sensing.
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Old 08-01-2003, 03:14 PM
  #10  
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Default Re:how to run 14-15 psi of boost?

can you maybe point me in the right direction as to what to do while im in the ghettodyne program? do i have to go into both the ignition and fuel maps and change each value so its higher? thank you VERY much for the info.
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