sinatra

iTrader: (8)

Hey everyone,

I was at the Gruppe-s dyno day yesterday and I was talking to Preston he was saying that I am almost assuradly running lean with my setup running the COBB stage 2 map. Now, everything I have heard from COBB vendors is that the COBB maps are VERY conservative and that I have NOTHING to worry about.

I am very concerned.

Unfortunately Gruppe-s couldn't get an accurate AFR for my car so I cannot confirm or deny Preston's claim. I can say though that a wrx with equivalent mods dynoed before me and he was running a 14:1 AFR.

Does anyone have any experience running lean with the CA stage 2 AP map?

I have really started to get concerned becuase I do not want to damage my motor while all the time thinking I am running a very conservative tune.

Kevin M

iTrader: (12)

First, you have to have exactly the mods Cobb tuned the map for, no changes. Second, is it lean under boost or is it the slow open loop to closed loop changeover? I doubt you are hitting 14:1 under full boost, or your car would already be toast. And why didn't you get an AFR readout? Was their wideband broken?

sinatra

iTrader: (8)

Hmm ok so a Scooby Sports DP and Blitz cat back with stock cat is a no no on the COBB AP?

The guy right before me Preston said was running a 14:1 AFR and had equivalent mods. He said above 4k RPM at WOT the guy had knocking and detonation.

The Dyno guy at Gruppe-s said my exhaust pipe was too big. I dunno if I buy that. There were guys there with bigger exhaust pipes than mine and they were getting AFRs. I am thinking their equipment was just having problems.

What I don't get is that I am hitting target boost numbers and I am running 10whp under what COBB calls for.

It seems like I am ok.

David

jc5d5d

iTrader: (3)

You should have gotten your AFR printout or they should have refunded part of your money..I think some guy with an RS there didnt get a torque measurement and he got partial refund. Im also running Cobb Stage 2 and was told the AFR was too lean.

Kevin M

iTrader: (12)

Yeah, you need a full 3" turbobacks similar to Cobb's, and you need to be sure you're running the proper map. (cat/no cat, octane, etc.)

Unless he's running the same AP map and the same mods as you, that's irrelevant.

Mike's a good tuner, he's going to steer you in the right direction. I don't know exactly what wideband setup they're using so I can't comment on why it didn't work.

That's not the issue; back pressure, EGTs, and induced knock are what's robbing your horsepower. As I said, get back into spec of what the cobb map is tuned for and you'll be fine.

sinatra

iTrader: (8)

Ok, so lose the cat and I will probably be ok or should I be selling my DP and cat delete to get a 3" DP?

Jc5d5d, I did get a $25 refund becuase I only got half of the readout. Were you the white wrx wagon?

MO REX

iTrader: (2)

Here's Trey Cobb's explination of how he sets target A/F ratio on his maps.


Trey

Fearless Leader
Member # 3

posted 03 May, 2004 04:25 PM
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In regards to the target A/F ratios, that will depend on the engine load and RPM. I will admit we do NOT run a static A/F ratio at "X" boost levels regardless of engine load and RPM. I tune for a curve based on what the engine wants/needs and the load that's being placed on it at that given time. This methodology is similar to that of Subaru, Audi, Porsche, Toyota, Nissan, and virtually every other manufacturer that's released a turbocharged vehicle to the masses.

Depending on the engine load and RPM, I will tune the engine to act like a NA engine until the onset of boost. So, at say 2200 RPM at 0psi manifold pressure I'm typically targeting around 14:1 - 13.5:1 A/F ratio. As the engine load and RPMs increase, I will increase the ratio of fuel to air smoothly towards redline. In the midrange, and near torque peak, I will often find myself in the 11.5:1 to 11.8:1 range dependant on RPM this occurs at. With a stock turbo WRX, this normally can occur around 4000 RPM. 15psi @ 4000 RPM is in a nice sweet spot for the turbo so our air temps and exhaust backpressure are good. Of course you back off timing at your torque peak as well. After torque peak, we need to again increase our ratio of fuel now more in an effort to cool the combustion temps. We'll also need to begin increasing our ignition timing. I'll tend to target around 10.8:1 by redline on most maps.

If its of interest to anyone, you can see how even Subaru does it here:
http://www.accessecu.com/update-subaru1.html
Our FXT from the factory hits 10+ psi at 3200 RPM...the factory targets in the 12:1 A/F ratio at that point!!! My FXT has NEVER detonated on me and I have absolutely no concerns on the reliability of this setup....

I will also say there are a LOT of tuners out there that feel as though you need to run a particular A/F Ratio based solely on Boost Pressure. I don't agree with this tuning philosophy. I believe the A/F ratio should be based on RPM and ENGINE LOAD. It is normally only those that tune with this A/F == Boost method that claim my maps are too lean. Don't get me wrong, boost does play a part in Engine Load but it's not the only thing to consider. I tend to take on a "bigger picture" approach.

Finally, A/F Ratio measurements can be a tricky thing is not done properly with the right equipment. Measuring from the tailpipe substantially increases the potential for error as well as increasing the latency between what the engine is experiencing and what you are measuring. People do it because its easier...not because its more accurate. Our downpipes come with an extra sensor bung directly after the turbo. This is my far more accurate and without as much latency so you don't have to mentally shift your A/F ratio graph back to the left when tuning. Also, its easy to get a very lean reading when you first start a dyno run when reading from the tailpipe. I'd consider that more of an operator error in all reality.

Hope that helps,
Trey @ COBB Tuning


Quote taken from this thread http://www.wrxforum.com/cgi-bin/ulti...=000339#000011

sinatra

iTrader: (8)

Great info. Thank you. That puts it into perspective for me. I feel much safer now.

MO REX

iTrader: (2)

That post doesn't prove that you are not having problems but it does explain how Cobb sets their target A/F ratio. If you want to feel a little more safe invest in an egt gauge, pull your plugs and look for signs of detonation. To look for the first/beginning signs of detonation, search the white porcelain for tiny black specks or shiny specks of aluminum that have fused to the porcelain. If your car is knocking real bad the porcelain can crack and eventually break off. Here is a site that teaches you how to read your plugs http://www.roadstarclinic.com/TechTi...adingPlugs.htm. I'm sure there are better sites on the subject so you might want to do a search to find out more.

wrxout

get an external wide band and youll be good the txs tuner should work on cobb right? doesnt cobb acesport read afrs? i ****ing hate cobb they blew up my car with their weak *** ecu reflash

MO REX

iTrader: (2)

I think most people would go with an egt gauge over a wide band. What exactly do you mean by "the txs tuner should work on cobb right?", what reflash did you go with, what octane fuel were you useing and what other mods did you have when "Cobb blew up your car"?

BTW, the Accessport doesn't read A/F ratio but the street tuner does.

sinatra

iTrader: (8)

I have learned how to read plugs. Thanx for the info. Car is running great so I don't think there are any problems. I just wanted to check it out. It looks like the plugs on this car a ***** to get to anyway.

David