Crap dyno numbers-car won't hold boost
 

I've got a problem that I hope someone can help with. I just finished doing all the power mods I wanted to do and I was stoked to get on the dyno at Cobb Tuning. You can see the mods I've got in my signature. I thought I'd make pretty good power in the area of 335+. After the cams went in I went to Cobb and the car made... 269 whp! {thumbdwn} WTF!? It's a mustang dyno, so they said it could be as much as 315 or so on another dyno but damn! That just sucks! 269! So I asked what the problem is and the tuner said that my car's not holding boost. He tuned it to 22 psi and it hits that boost level, but then it tapers down to 17 psi after 4500 rpm. They don't know why it won't hold boost. Cobb says that the dyno printout looks like the power would continue to about 315 whp if the boost didn't drop. They said it could be a problem with the MBC (but it's brand new, so that's probably not it), plus the shop that installed the cams said they tested for boost leaks and didn't find any. So what the crap is wrong with my car? I just dropped $1600 for the cams, install and tune and I got 269 whp? Anyone know why I might be losing boost? Any help would be greatly appreciated.

Boost Leak. Could be an issue with the boost controller as well. ECU controlled boost really holds boost much better

I asked about that. Cobb said that if it was a boost leak, the boost wouldn't hit 22 psi in the first place and it does. It hits 22 psi, but then drops steadily after 4500 rpm. I guess it's possible, but the Solid Auto Works that did the cams tested for leaks before the tune and they said they didn't find any.

Mustang dynos do read really low, but i would take it somewhere else for a second opinion about a posible boost leak.

yeah, guess I should. I'm not far from Vegas. I'm sure they've got some people there pretty experienced with evos. I thought the guys at Cobb would know what's wrong since the specialize in this stuff, but they were stumped.

Cobb told you that? HUH? You could definately still hit your target boost and still have a major leak. Do you have a datalog of the dyno pulls?

idk if i'm right but if you have a boost leak won't it still go to 22psi but the turbo just has to work a lot harder to get it to 22psi?

I've got the graph and you can see the line representing boost drops right after 4500 rpm. It drops to 17 psi or so. That's where the hp line drops too. Well, it power actually continues to climb, but at a much slower rate.

Oh sure. This will be easily seen in a log as the car will hit pretty high load cells

yeah, i'm guessing you're right about the leak, but it makes me wonder why Cobb wouldn't say that because it seems so obvious. They seemed to think that it had to be something else.

Your car is down a good 40-50 whp even more maybe from where it should be.

Ok so let me School you on Boost leaks. Your car will still hit the target number with a boost leak that is not that bad. But once the car are reached the boost level the car will drop slow or fast depending on the leak. this will cause a spike in the power and Tq but then after that a drop. The turbo will keep trying to push the air and you will start see knock or other tuning problems. Before you get mad about the numbers the car put down do a boost leak down test its really easy. If you need more info on how to do it pm me. I'm sure after you do this the car will hold boost like a champ.

Dustin

Do you have a Evoscan or Mitsulogger? If so go do a third gear pull and post it up for us.

I don't, but it seems pretty clear from the posts that I need to check for leaks. I'll pm the guy above to see how to do it.

ditch the mbc and go ecu based boost control! Also I'd use a 3-port boost control solenoid, helps out holding more boost.