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post #16 of 37 Old 10-25-2005, 11:16 AM
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Quote:
Originally Posted by ahains
Cosmo,
Thank you for sharing this information. I was intending to swap in a ball & spring MBC (and boost gauge) off of my Talon to regulate to a conservative ~13psi, with a goal of increasing 1st and 2nd gear boost.

I would greatly appreciate it if you could provide any hard numbers of what you have observed, correlating the a/f ratio with the boost & throttle position. Doesn't have to be precise, just ball park numbers that you recall. If it is somewhere south of 12.0 a/f under all TPS values for 13psi, I may still be satisfied since I will be installing my water injection system as well for some additional safety. This is assuming that WRX's do not run super aggressive timing, which I will need to research first (just started researching yesterday).

I know that replacing the first cat is highly recommended for increasing boost / power, but I would much prefer to keep my exhaust system stock at the expense of less power. I'm at a stage in life of caring more about the exhaust I'm shooting at the person behind me in traffic

Thanks much!
-Adrian
Now that I am a bit older and wiser on WRX's, I thought I'd reply back to myself.
The fact is that on 04 and 05 WRX's, the stock programming will target 14.7/1 AFR even at full boost. This is horrible horrible horrible. Not only would I NEVER but a boost controller on a stock 04 or 05, I wouldn't put up with leaving the factory programming in place.
If you know anyone in your area with an OpenPort cable from tactrix.com in your area, they can use free software to flash your stock ECU with some changes to the open loop/close loop delay and protect you from this horrible stock programming.

Once you do this, it is not nearly as risk to up the boost slightly with a boost controller. Although it is better just to use the same cable to edit your boost targets in the stock ECU to raise the pressure. Since there is not yet a published tool to do this it means busting out your hex editor, but it is not hard if you are a geek

-Adrian
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post #17 of 37 Old 11-12-2005, 07:31 PM
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doesn't the ecu sense load via the output voltage from the hot wire mass air flow meter?
the factory ecu measures the air entering the engine, not the boost pressure, the map sensor is only used for boost cut purposes, so the load axis is actually cfm not psi. the problems you mentioned occur because the airflow exceeds the maximum allowable cfm which the ecu is tuned for. (afm voltage goes out of range) and as a result the ecu can no longer calculate the engines fuel requirements, as a result it either makes it excessively rich (safety feature when excessive airflow is detected the ecu dumps massive amounts of fuel in to avoid detonation) or excessively lean (fuel system cannot flow the required fuel)depending on how far the boost is raised. The heat in the stock intercooler due to raised boost pressure can also lead to detonation.
90% of ebc related engine failures is a result of the owner setting a boost target to high (owners often creep the pressure up a little bit at a time over a few weeks or months and then they get a batch of bad fuel or a hot day and things go bang) or using inferior fuel with the raised boost pressure but not owning up to their own stupidity and using the good old excuse of "it just blew up, i didnt do anything out of the ordinary."
i have set up many ebcs on wrxs which run max pressure of 16.8psi from 3200rpm, and tell the owner they have to use BP Ultimate (98 Octane pump gas) and things run fine. The factory boost cut at 17psi is there for a good reason, the ecu only meters airflow a small amount above this.
if it was possible to setup a someones ebc and pull all the adjusting knobs off so they couldnt fiddle with things many more engines would survive.
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post #18 of 37 Old 11-18-2005, 11:58 AM
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Quote:
Originally Posted by mosc
forgive me for asking the newbie question but doesn't swapping in a new downpipe raise the boost from 13.5 to say 14.5? Isn't that raising the boost without changing the fuel system?
Does the 1.0psi increase hold true for a Helix catted DP? The cat is a high flow cat and I have noticed more torque since adding it. Note: I had an upipe installed before my dp but didn't notice any difference with it. I have another question but will leave that for a different thread.
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post #19 of 37 Old 11-19-2005, 01:20 PM
 
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Yep any DW or bellmouth DP gives about 1 psi.
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post #20 of 37 Old 11-20-2005, 04:58 PM
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Quote:
Originally Posted by stileguy
doesn't the ecu sense load via the output voltage from the hot wire mass air flow meter?
the factory ecu measures the air entering the engine, not the boost pressure, the map sensor is only used for boost cut purposes, so the load axis is actually cfm not psi.
Anyone know for a fact which is correct?

I'm from the DSM (eclipse turbo) world where this is how things work. I'm trying to understand what makes the STi ECU different. Everyone talks about needing new maps for every little change. On my eclipse as long as you had a big enough fuel pump and injectors you could throw on any size turbo, downpipe, exhaust, whatever and not have to make any tuning changes (mostly).
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post #21 of 37 Old 11-20-2005, 07:32 PM
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I am new to the WRX world but I know my turbo basics. Most of my knowledge comes from turbod MR2 and Supras in which case you can use a boost controller to raise boost past the Fuel Cut point without even thinking about the ECU. Why are these WRXs so delicate to raising boost? On an MR2 you can raise boost from a stock 12psi to 17-18 psi safely only requiring an upgraded intercooler, spark plugs, and a Fuel Cut defender and any other type of basic bolt on (downpipe, exhaust, etc) all on a stock turbo with no piggybacks or reflashing.

edit* ok i just read stileguy's response and that is exactly what I was getting at. It shouldnt matter that you raise your stock boost slightly. your MAF sensor is there to detect the amount of incoming air and adjust fuel pressure accordingly. Thats the whole reason behind fuel cut. The ecu will cut fuel and retard timing at a preset boost level (17psi i hear in wrx) as to prevent from knock. So why not use a boost controller to raise boost to 16psi or 17 with a fuel cut controller like the HKS FCD. In cold winter conditions boost tends to creep higher simply because of the cold air. The ecu knows this and adjusts fuel accordingly.

Last edited by dunham; 11-20-2005 at 07:55 PM.
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post #22 of 37 Old 11-21-2005, 08:42 PM
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most hotwire airflow meters use an output voltage from about 0-5v (0 being engine stopped and 5 being the highest airflow that sized airflow meter can maintain the hotwire temp at.) once this "wall" is reached it is time to get either a bigger airflow meter (pipe diameter) or change to a completely different meter (ie nissans use Q45 infinity meter) or go for map sensed load axis. either way you will need a retune on your ecu. it is possible to max out an airflow meter on a nissan without hitting the boost cut by using an aftermarket turbo with stock boost levels, the subaru ecu does not have af meter out of range cut, only a boost cut, when you disable the boost cut with an fcd the ecu will adjust fuelling to excessively rich to the point where the fuel system is not capable of maintaining. ie as boost is raised the stock ecu gets excessively rich to a point where the fuel system runs out of flow and results in a lean condition often ending in cracked ring lands or melted piston crowns or both. this is why the stock ecu shows little extra power when boost gets above 15-16psi on a stock turbo as it runs air fuel ratios in the low 10:1s to protect itself and looses power because of excessive rich mixtures. the subaru engineers have tuned the fueling within the confines of the factory turbocharger and factory boostcut with an excellent compromise between safety and power. if you go beyond the factory boost cut with an fcd or aftermarket boost control you can measure the life of your engine in seconds or minutes. anytime boost or airflow (via turbo replacement) exceeds the factory limits (boost cut) a full ecu retune should be done. no exceptions. So the obvious conclusion is that boost controllers dont kill engines, boost controller USERS kill engines.
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post #23 of 37 Old 11-27-2005, 09:41 AM
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This is true. There is some important info in the original post though, and that's the part about part-throttle boost.

With a boost controller you'll be able to hit full boost at part throttle (the ECU normally prevents this). Since the ECU is expecting you to be off boost at part throttle it's still aiming for a 14.7 : 1 AFR (way too lean for on boost).

I seriously doubt the 19:1 claim though, that seems impossible and I've never heard anyone else say anything about AFRs leaner than 14.7 : 1 as a result of a boost controller.
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post #24 of 37 Old 11-30-2005, 01:50 PM Thread Starter
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Quote:
Originally Posted by codemonkey
I seriously doubt the 19:1 claim though, that seems impossible and I've never heard anyone else say anything about AFRs leaner than 14.7 : 1 as a result of a boost controller.
When I get a chance, I'll show you the logs showing insanely high AFR's. Granted, they only hit them for a split second, but, as you know, sometimes it only takes a split second to do damage...
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post #25 of 37 Old 01-28-2006, 01:47 AM
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Noob question. You state that the air fuel ratio is controled by the tps sensor. Isnt there a map or maf sensor on thies cars? I would think a map sensor has more to do with air fuel ratio then the tps. Cause how is the computer supose to know how much air is going through the throtle plates when all it know is how much you have the throtle open.
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post #26 of 37 Old 01-28-2006, 04:14 PM
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Yes there is a MAF sensor in the intake tube to tell the car how much air is coming in.
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post #27 of 37 Old 01-29-2006, 03:32 AM
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So wouldnt the maf be able to compensate for the extra air?
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post #28 of 37 Old 01-29-2006, 07:45 AM
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Quote:
Originally Posted by Iroc-Z
So wouldnt the maf be able to compensate for the extra air?
Its not so much compensating for extra air as it is for a condition called PTFB (Part Throttle/Full Boost).Plus the ECU controlls the boost amount in correlation to ambient temps & barometric pressure.The MBC or some self programmed EBC's just won't allow the ECU to correct for all the conditons listed above.This could be bad fo da engine.Its allways best to let the factory ECU do as much as possible.Spend the money for some engine management and let it control the boost safely.
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post #29 of 37 Old 02-03-2006, 06:30 PM
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and if the ecu is tuned to boost 12psi and the boost controller is set to boost 18, they will fight each other the whole time causing lag and sudden power loss (the ecu doing everything it can to stop boost)

but if you still want a boost controller... haha my friend is selling his... and for a reason.

Gregory-
keep it in the dirt.
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post #30 of 37 Old 03-27-2006, 03:44 AM
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Okay i hear everyone saying theyre getting 12psi stock, my 03 stock is only pushing 6psi for reasons unknown. i just ordered a perrin MBC to up it to 12psi, would this be a bad idea considering its what stock levels are set to?
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