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Old 04-21-2005, 08:59 PM   #1
darksands
Scooby Specialist
 
Member#: 75122
Join Date: Nov 2004
Chapter/Region: SCIC
Location: Im in a glass case of emotion
Vehicle:
2005 Impreza WRX
Crystal Gray

Default How would you tune the VF39?

Just curious. I was looking at the Base map for the Stage2.5 COBB with the VF34. Im planning to get a 39 and modify the 34 map with the StreetTuner. Now, I know that there is more lag with the 39 but it does push more CFM's later. Just curious on how you would tune the vf39. Im not asking for super specifics, just curious on different theories. Understanding the characteristics of the VF39, how much boost would you run? Timing advance? Fuel ratio's and also theories. Im not looking for the ultimate tune or anything and I dont want this thread to turn into a "this theory is better than that one." Just looking to learn a bit more on different tuning methods. If you feel that your tuning secrets are too valuable to share then thats fine as well, just dont say, "my tune is better but Im not gonna tell you how its better."

Thanks a bunch

Peter

Here are the mods im working with.
VF39
STi "Pink" injectors
Walbro Fuel Pump
Perrin Light weight Pulley (Stock Size)
Up-pipe
Helix CATTED Downpipe (3")
Stock Intermediate Pipe (2.5")
Stock USDM STi Axleback (2.5")
IC Hoses
California Piss pump 91 octane
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Old 04-21-2005, 10:39 PM   #2
crazymikie
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Member#: 56321
Join Date: Mar 2004
Chapter/Region: NESIC
Location: Hopkinton, MA
Vehicle:
2006 Honda El Camino
Green

Default

Here's my $.02- I'm no pro by any means. I'm not responsible for anything

So here's what I would do- I'd start with the 2.5 map. It's already got turbo dynamics for the vf34 and the fueling should be close. Since the vf39 is going to run slightly less volume than the vf34, I'm guessing you are just going to run rich if anything.

From there, I'd work on getting boost right. Playing with the turbo dynamics has consumed much of my time, but maybe you'll have more luck. Try doing pulls in different gears to make sure that you aren't overboosting or spiking. Start with a conservative boost level and get things in good shape. Then start adding boost until you don't feel any benefit (eventually, the turbo is going to get out of it's effeciency range and you'll be blowing hot air, taking away power). If you have a road dyno, it would be helpful here. Make sure to keep an eye on IDCs, EGTs and KC/IT. You don't want your injectors to go static, your EGTs to go too high and you want to watch for the ECU pulling timing.

Next, I'd work on AFRs. I'd start by slowly pulling out fuel to see if it yields more power. You'll need to keep an eye on EGTs too. If you generally don't do pulls in higher gears, you can probably run the car a little leaner. EGTs won't have a chance to climb as much during pulls in lower gears, whereas the extended periods you'll see high loads in higher gears will cause them to climb, making you susceptible to det.

Then, I'd add in timing in places where it yields more power. After a certain point, you will not see additional power from additional timing (once you are past minimum best timing). If you continue to advance past that, you'll det. Again keep an eye on EGTS. Also, you might need to correct your boost a little bit since higher heat means higher velocity of exhaust gasses, which means your boost might increase a bit.

Yeah....and of course this all seems a lot simpler in theory than it is in practice. I think the biggest suggestion I can offer is to make small changes and make sure things are progressing the way you intend them to. Sometimes changes have effects that you may not have thought of.

Again, I could be 100% wrong, so anyone feel free to correct me. I'm just trying to share I'm actually pretty curious to see how the vf39 does on a 2.0L engine.

Also, I believe the stock maps are made for real 93 gas, so you might want to pull a few degrees of timing off to give yourself some headroom. Seems like the ECU will protect the car to some degree- as long as the changes are small. If you go and set your timing to 40 degrees across the board, then there's not much it can do.

Mike

Last edited by crazymikie; 04-21-2005 at 10:41 PM. Reason: Stupid CA Gas
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