mitchedout

My car is behaving normally if I do a pull @2500 rmps up to redline on the Cobb OTS Stage two map 91 oct. The boost curve behaves perfectly and no problems and no knock. The mods on the car are a short dp, test pipe and catback and upper intercooler pipe. Before the install of the intercooler pipe the car did the same thing with the stocker pipe so I know its not the install of the pipe. However, if I am in 3rd gear at 4k-5k and then go WOT the car will get a spike of 25-27psi then settle back down and behave normally. This happens in both 2nd and 4th gear as well. I have the race tuner software and have made huge adjustments to both the course and fine waste gate tables to try to tune it out. I still continually get a spike then it will go down to 16psi immediately . So I know the changes that I have made have effected the boost curve and lowered the psi but I can't affect the spike. I have the stock intake and boost control and no other mods. I am out of ideas on how to fix the spike. On the logs I have taken the spike doesn't cause any knock but i don't think in 2nd gear at 4k then going WOT hitting 26psi and over shooting the boost targets by 3-4psi is a good thing. Any advice would be helpful. Has any one else experienced this? I have done a fair amount of searching on this forum and evox and have found nothing that speaks to this.

Thanks

Thegame

iTrader: (26)

I wish I could help, but I leave the tuning aspects to the pros. It does sound though that it's something simple to fix. It probably just has to do with the dual BCS's. If it concerns you that much, I would put on a mbc and set it conservatively until you get the answers you need on the stock bcs.

bwagner31

iTrader: (3)

i experienced a similiar problem last night. I have intake, test pipe, exhaust. No tune or anything yet. My car usually hits 24 psi but last night i spiked 26 for a split second. This happened in 2nd, 3rd gear when starting at 3k or so. It happened a couple weeks ago too and both nights were a little cooler so it might be the colder air causing it.

I think the test pipe is causing me to spool quicker and thus the boostcontrol can't keep up and it spikes for a split second. Im just worried about this winter. If 60 degrees causes me to spike, what is 0 degrees gonna do. Im getting a wastegate dump downpipe and i don't know if this will help or worsen the problem. I will be getting tuned in three weeks at DG Motors.

Don't know if they can tune out this spike or what can be done. But its got me a little worried spiking 26psi untuned. I just don't wanna spike any higher once it gets cold out.

LaXGSR

Could you post up a log of this behavior? What's your load look like when this happens? A log with psi, load, timing, active wgdc, passive wgdc, wideband o2, would be helpful. Also, what are the values for WOT in your boost target engine load table?

mitchedout

I will when I get home tonight . The load is 270 or around there. The map is set for 242

mitchedout

Ok here are some logs all 3rd gear. The boost load targets for the map are 242@ 4000 rpms -6k and then down to 240 by 8k. I have not messed with these values as they are standard in the Cobb map. As I have stated in the first post I have drastically reduced the course and fine WGDC and the spike still exists then the psi will go to 16 or so with the huge changes that I have done. As you can see the car is behaving normal at a 2.5k pull and not so at 4k and then WOT

LaXGSR

Honestly, it's really tough to get much out of those Cobb logs because the logging rate is so slow. However, I would try to lower the fine/coarse WGDC at least 500 rpm's prior to where you see the spike happening. See if that helps make a difference. Even a stock car can spike, and if your boost target load is really 242, then the ECU's boost error correction should also be kicking in to lower your primary (reactive) WGDC.

COBB Tuning

I will forward this thread on to one of our tuners but on stage 2 the boost you are hittingare not too terribly high. On our shop/test cars we were running upwards of 27 lbs of boost, however, on 91 octane you really only want to be seeing around 25psi. Also note that these cars do not nessecarily care what WGDC is, they only really care about calculated load. Boost is a byproduct of airflow/calculated load. Are you hitting any sort of fuel or boost cut? Does the car not behave properly or are you just freaked out by all the boost?

To lower your boost targets go into the Boost Control Offset table and decrease that value by 20 points. Then lower your WGDC fine and course adjustments by ten percent or until you hit your targets.

Travis
COBB Tuning

mitchedout

Travis,

thanks for the info.. I will give that a try. Where I live in New Mexico the car doesn't spike over 25.5. However, I am visiting my parents out in Oregon and getting some high spikes. More freaked out as the car is a DD and I don't want to run the mess out of it..


Thanks

mitchedout

Travis,

Sorry for another post but when I got to the boost offset table when I hit the minus it goes 80 to 16. I am not hitting shift minus. How do i type in a value that I want?