Boost psi peak with Cobb AP?

-H- · Oct 4, 2009, 02:02 PM

I'm using a stage 2 Cobb map that runs and feels smooth but I'm slightly worried about over boosting. I have been using the baro minus absolute pressure to measure the boost with the AP. I'm not sure how accurate a method it is but I occasionally get a 27.5 psi peak. The ECU isn't throwing any codes but I was wondering if this is unsafe. Most of the time it's hitting at 25.5 psi but there is an occasional spike.

What is an acceptable peak boost with the mods I have listed. I have the boost pill removed as well.

Thanks!

1FastT2 · Oct 5, 2009, 06:30 AM

You need to download the newish firmware for you AP. That way you wont have to do any of that math you are using to find out your boost pressure. Just monitor relative pressure.

I have been having the same issue with my AP. Im running the AEM S2 map on 93 oct and hit spikes of up to 28-29 psi. Cobb needs to come out with a map that raises the wastegate duty cycles to help the people that are over boosting. I think this is a pretty common occurrence and with the weather getting cooler in my area the condition has been getting worse.

ScottSpeed21 · Oct 5, 2009, 03:49 PM

You want lower wastegate duty cycles if you want less boost. You can also drop the Boost Control Offset value down a bit and that will lower your overall peak boost targets.

WickedWhite2008 · Oct 7, 2009, 03:16 PM

Quote:

Originally Posted by -H-

I'm using a stage 2 Cobb map that runs and feels smooth but I'm slightly worried about over boosting. I have been using the baro minus absolute pressure to measure the boost with the AP. I'm not sure how accurate a method it is but I occasionally get a 27.5 psi peak. The ECU isn't throwing any codes but I was wondering if this is unsafe. Most of the time it's hitting at 25.5 psi but there is an occasional spike.

What is an acceptable peak boost with the mods I have listed. I have the boost pill removed as well.

Thanks!

I hit 27 PSI everyday that I drive my car and once in awhile 30 PSI. Other than a little knock if it's a hot day vs cold day I havn't had any trouble. I am using 91 oct and I am still working on my timing and my knock counts with this DD version of my 93 oct map (I am only having it between 6,000 and 7,000 RPM at WOT). I have heard the EVO X's engine can handle a lot more load and a little bit of knock and you don't need to worry about building up the the engine until you get over 30 PSI. Correct me if I am wrong. Anyone?

-H- · Oct 7, 2009, 06:23 PM

Perhaps it is the colder weather. I hadn't taken that into consideration. If I wanted to bring the peak boost down a hair would you guys recommend tweaking the waste gate duty cycle or the Boost Control offset value?

I really don't mind how the car is performing at all. It's really smooth all the way around and the power is great. My concern was whether the occasional spike was dangerous.

Thanks for the replies!

WickedWhite2008 · Oct 7, 2009, 07:01 PM

Quote:

Originally Posted by -H-

Perhaps it is the colder weather. I hadn't taken that into consideration. If I wanted to bring the peak boost down a hair would you guys recommend tweaking the waste gate duty cycle or the Boost Control offset value?

I really don't mind how the car is performing at all. It's really smooth all the way around and the power is great. My concern was whether the occasional spike was dangerous.

Thanks for the replies!

I would say to log and see what your overal PSI is to redline and what rpm you hit your peak PSI at (3,000 to 4,000) and slightly lower your wastegate duty for just that range if all else is good. If your hitting too high boost outside of that range you might want to look at lowering the offset for winter.

ScottSpeed21 · Oct 8, 2009, 01:56 PM

The good thing about occasional boost spikes is that they are quick and harmless. If you were peaking 29psi and holding it to 5500 before the taper, then I'd say you should lower the Boost Control Offset. If it's a quick spike that drops to around 26psi right away, I wouldn't even worry about it, especially if there isn't any knock. You can lower the duty cycles right in the area of the spike if it'll give you some peace of mind.

WickedWhite2008 · Oct 8, 2009, 08:34 PM

Quote:

Originally Posted by ScottSpeed21

The good thing about occasional boost spikes is that they are quick and harmless. If you were peaking 29psi and holding it to 5500 before the taper, then I'd say you should lower the Boost Control Offset. If it's a quick spike that drops to around 26psi right away, I wouldn't even worry about it, especially if there isn't any knock. You can lower the duty cycles right in the area of the spike if it'll give you some peace of mind.

+1