PDA

View Full Version : tuning your 2.5l turbo boxer



whitevette
04-09-2005, 02:29 PM
does anyone know if you can adjust boost right out of the box on these engines? lookin for a little more go.
please reply

mrz28M6
04-09-2005, 05:39 PM
yea all you need is a boost controller, you can probably locate a cheap one on ebay.

fireguyrick
04-09-2005, 08:19 PM
If you are refering to the STi engine...BOOST CONTROLLERS ARE A BAD BAD THING! The problem is related to open/closed loop boost programming. Even setting a boost controller at 15psi can result in messing up your engine. If you have ANY questions about Subaru engines feel free to PM or Email me them. I had a fairly decently modified WRX, I NOW have a HEAVILY modified STi (400awhp+), and a modified Forester XT. I will do the best I can to answer any questiongs you have, but Boost Controllers are a BIG NO NO with Subaru Engines.

Rick

turbogarrett
04-10-2005, 10:23 AM
Just add a catless, full 3" exhaust and your boost will creep like a mofo and shoot monster fireballs out the tailpipe.

Fireguy, do you have dynosheets that show 400+? Where can I find some info on the gt35r kit?

fireguyrick
04-10-2005, 12:32 PM
For info on my setup you can check out www.ultimate-racing.com.

I have the Stage 3 STi kit with FMIC. I am running between 19-20 psi also on pump gas.

I have a dyno sheet somewhere in my file cabinet, I will dig it up (mind you it is on a Dynojet which a Stock STi will put 240-250awhp down).

Yea, with a 3" TBE your boost will DEF. creep like a MOFO...unless you have your wastegate ported (easy to do, and if you do not want to someone will for a few bucks).

Honestly, though, how much more power are you looking to make...and how much are you wanting to spend?

Rick

Oh yeah to clarify the boost controller issue here is a good write up on what is going on...


Manual or electronic, both can cause serious problems. With the stock boost control system, the car only gives you full boost at full throttle (which is over like 76% or something... ish). With an aftermarket boost controller, you'll get full boost whenever the turbo is capable of it, which includes partial throttle times from like 15% throttle on up. You do a lot of daily driving and highway driving in this range. The problem is with the ECU once again. At partial throttle the car usually sees 7 to 10 psi, or about wastegate pressure. It injects only enough fuel for 7-10 psi. When you pop a boost controller on there it just assumes you're still getting 7-10 psi, but you're getting full boost, which is probably 14.5 to 16.5 depending on where you set it. So you've got the fuel for 7-10 psi but 14.5-16.5 psi of boost! This causes an extremely lean condition because of all that extra air without any extra fuel, EGT's (exhaust gas temperatures) shoot through the roof, and soon a piston melts.

There are a couple ways around this problem. One is to drive your car at under 10% throttle or at full throttle all the time and never drive anywhere in-between. There are plenty of people who do this, but that seems like a huge and annoying sacrifice. You could get a Vishnu EMI adapter (or similar product), which tricks the ECU and makes it safe to run full boost at partial throttle, but it makes the car a bit choppy as the transition between closed and open loop operation is not well defined. Or you could get a very fancy and expensive electronic boost controller that has throttle position input. Basically you tell it not to step in unless your throttle position is over 80% or whatever number you choose. However, these are like $600+++

Now here's the kicker. For under $400 you can have your ECU reflashed. This not only raises boost SAFELY but it changes your ignition timing and fuel curves to fully take advantage of it. Less money, total safety, and more HP because of the additional tuning. Boost isn't everything. Tuning for that boost will truly make your car fly. If you need solid proof: my friend dyno'd his car with identical mods to mine, except he had a boost controller set at 16.5 psi on high setting and I have Cobb Stage 2 tuning. He put down 219 whp on the dyno, and I put down 237. I made 18 more hp at the wheels with slightly less boost and I'm not going to melt a piston like he did after about 5 months of running the boost controller. And his had two settings... 90% of the time he was running it at 14.5 psi, which is stock boost. You don't have to crank it to melt a piston. On top of that, my curves were smoother and my A/F ratio was much, much better controlled.

That was written for a EJ20 (WRX) engine, however it applies to the EJ25 (STi) engine, since both have the same open/closed loop boost programming.

Syclone0044
04-10-2005, 02:22 PM
Just out of curiosity (and you'll have to pardon my WRX-ignorance), it seems really weird what you just posted about the WRX stock fuel management - how can it NOT add fuel under boost at part throttle? I am not sure if those cars are mass air or speed density but both my cars are speed density (and I beleive boosted cars lend themself to speed density) and there are tables that compare the Manifold Pressure versus the RPM to decide the fuel, at the corner of the table it even has a spot for full boost at 400 RPM (which obviously would never be hit, but it nonetheless exists). I have used manual boost controllers on both my 1990 and 1991 GM Turbo vehicles and the increase in low RPM torque was astonishing on both, compared to the factory closed loop electronic boost control.

I am sure what you posted about the WRX is true (that it can melt a piston if you raise the boost without an ECU tune) but I was just hoping for some clarification because it boggles my mind when I read the line that the ECU will only give 7-10 PSI worth of fuel at part throttle even if you are actually producing 14-16 PSI. I dont know how that can be?? I guess I just assumed a year 2000+ OBDII ECU would be far more advanced than a crude late 80's OBDI? :confused

fireguyrick
04-10-2005, 02:44 PM
I may very well have my Open and Closed loop fueling crossed....but I believe this is the best explaination.

All current Turbocharged Subaru engines use a MAF sensor. The ECU is programmed to be in Open loop fueling under partial throttle. The ECU will ONLY add a specific amount of fuel, based on how much air is suppose to be injected into the engine at the given throttle and RPM. In Closed Loop fueling the ECU monitors the Air Flow entering the engine, and adjusts to maintaina specific AFR. Closed Loop fueling only happens under Near Full throttle and Full throttle acceleration.

There is a SPECIFIC amount of boost being produced during Open loop fueling, so altering that amount will lean the car out. The reason is that the ECU will NOT know that there is MORE air entering the engine, since it is going off of a preset number.

This is also why Intakes (Short Ram or CA) are not good ideas for Subaru Turbocharged vehicles (untill you get tuned for it specifically). Not to mention that the MAF sensor is VERY VERY picky, and many times it does not read the air moving past it correctly (with aftermarket Intakes).

Sort of follow?

I can probally find a much better write up on it, but do not have the time to do that right now.

Rick

On a side note, when it comes to fuel with an STi....the STOCK fuel system is NEAR maxed out stock. It is NOT uncommon to see IDC's around 85%+ on a stock STi.

jbiscuit
04-11-2005, 12:23 PM
well said Rick. I have to agree that a manual boost controller is a bad idea on subaru motors....I actually had one for about 3 months knowing full well that I would have to adjust my driving style around the part throttle-full boost problem. When running the stock turbo (it should also be noted) full boost under say 50% throttle happens VERY quickly. Rick's copy and paste explaination is correct....what happens is the car looks to throttle position to determine the required fuel to deliver....it ASSUMES that at part throttle (say 50%) the wastegate will maintain about 7psi of boost....so the ECU in turn knows to deliver X amount of fuel to that amount of boost.... (Open Loop) pending ambient air temp etc etc....there are a thousand parameters that are also referenced as well Josh, don't get us wrong here....basically the manual boost controller will OVERRIDE the ecu's setting of limiting boost to say 7psi at part throttle....the manual boost controller will allow the turbo to produce X-amount of boost until the set level is reached. The MAIN issue is that no modification has been done to the ECU resulting in an ECU that think things are STOCK and will not add any additional fuel for the added boost levels.

The part throttle-full boost issue is just one issue associated with the the manual boost controller. A second issue on a stock WRX/STi is the precat before the turbo. This is a retarded cat in mo opinion and has a terrible placement in the exhaust system....PRIOR to the turbo. Many youngsters nowadays want to go fast with as little invested as possible. Everyone that DOES go fast knows that speed comes at a price. This "uppipe" as its termed should be modification #1 on a stock vehicle. Boost should not be adjusted AT ALL with this piece in place. Added boost = higher exhaust temps which in turn can make this precat fail at a faster rate....even just causing portions of the cat to get sucked in to the turbo.... Your turbo will injest it and it will be destroyed. Boost controllers on the boxer motors seems to fluctuate quite a bit also. Cold nights and I would see as much as 1psi more....

Basically, the Subaru ECU is quite smart and can learn. But one thing it seems it cannot learn is how to deliver the proper amount of fuel when a turbo makes full boost under a part throttle condition.

J

fireguyrick
04-11-2005, 12:39 PM
Just wanted to add that the STi has no preturbo cat (the uppipe is indeed catless).

Rick

jbiscuit
04-11-2005, 01:30 PM
good to know.....learned something knew about the 2.5L today :thumbsup