Guess I need better boost control...

[Diomedes]

So yesterday I finally have some time to get my car to the dyno since I added my mods. I have a full TBE w/ HFC, K&N Drop-in, Wally 255, and Jestr e-flash. Since I was still using the stock BCS I figured I wouldn't make as much since my boost wasn't spiking that high (19psi) and tapered like no other (15psi at redline). Just to preface, I made 255/255 stock on this dyno in 56 degree weather. So we make our first pull in 4th gear...and I ask Ryan (guy making the pull) what I made since I was busy looking at the logs. "260" he said.....ok so I gained a total of 5whp from all of those mods...SWEET. So I look at the log first, and notice no knock what so ever. I then figure that I'm somehow on the stock map or maybe I've got bad gas and I'm not on the high octane map so I disconnect the battery and wait a bit. Meanwhile, I press the playback on my boost gauge and notice that I spiked at around 19 and tapered off quickly to 15psi. Try again and I hit 273...somethings wrong. After trouble shooting, we came to the conclusion that I need a MBC to keep the boost up, so I'm buying a Hallman Pro RX. Anywho, here's a plot of my boost vs. a/f (bit leaner than actual since the sensor was in the muffler, my Innovate never got above 11.5.

[Warrtalon]

Even with the boost being the same as stock, you should have gained 40whp from the tune + TBE. Then, you'd get another 30whp from going to 22-23psi or so. It will still taper, but not as soon and not as quickly.

You're sure your wideband never read above 11.5? I don't think I've ever seen a tailpipe sniffer read THAT much higher. I've seen as high as half a point, but if you never saw above 11.5, then that means this one is over .7 off, which is not normal at all.

[Evolvd]

AFR should not change dependent on O2 location unless you have an exhaust leak. There is no more or less air exiting your exhaust than what is coming out of the engine. Thermal expansion/reduction does not affect the reading that much. As stated it's possible that one of the two AFR readings was off.

A manual boost controller will help quite a bit in letting you achieve a higher intial boost. I'm a big believer in Electronic controllers as the solenoid will control your boost a whole lot better than a ball/spring combo. I use the Greddy Profec B Spec II and it's one of the most user friendly EBC's. I've seen them used on stock turbo'd IX's and it usually holds 23 psi falling to 21 over the RPM range. Obviously this is due to turbo design and cams in the OEM setup so with a bigger turbo/cam setup you can see solid boost all the way to redline.

[Warrtalon]

It is very common for AFRs to differ at the tailpipe as opposed to upstream near the turbo. In fact, it's very UNCOMMON for it NOT to be different between those two points.

[Evolvd]

With the same wideband and proper sensor calibration they wouldnt vary at all but different widebands read differently. We know that, and different tailpipe sniffers gather the exhaust differently. Some are more effective than others. It seems as if this is a hardware issue not a sampling issue.

[Diomedes]

Well one thing could be the fact that my a/f gauge reads before the cat, and the one in the tailpipe was reading post-cat...

[Evolvd]

Ahh...information we did not have at hand. If you want to go by what the dyno says make sure you install the dyno's O2 sensor prior to the cat converter to get the most accurate readings.

[Diomedes]

So do you guys think I should change my tune if, say, I put my MBC on and set it to 21psi?

[Evolvd]

You're top end timing and AFR will need some adjusting. Your AFR will lean out some due to the increase in air.