Troubleshooting low power on the dyno
08-20-2012, 06:43 PM
#21
TECH Fanatic
iTrader: (6)
Join Date: Jan 2002
Location: Springfield, IL
Posts: 1,194
Likes: 0
Received 0 Likes
on
0 Posts
We didn't get crazy with it, but he only picked up around 4rwhp with 1 more degree of timing. We quit there since that's not on par with where the gains should have been if it was happy. I'm not saying it couldn't handle more, we never saw any knock anywhere, and the knock sensors were tested and working. Perhaps that backs up the theory of the exhaust housing being too small?
08-21-2012, 10:27 AM
#22
On The Tree
Thread Starter
iTrader: (5)
Join Date: Jun 2007
Posts: 118
Likes: 0
Received 0 Likes
on
0 Posts
Had a talk with some turbo guys here at work and one of them is thinking that the wastegate spring is potentially too "soft" for the application. The wastegate opens and over compensates and then enters a cyclic pattern of over/under correction.
After that conversation, I went into the datalog from the street and I can see (upwards of) a 5kPa swing and what appears to be some cycling of pressure.
The guy I talked to earlier suggested moving to a smaller wastegate to combat the "waves" were seeing on the dyno. The frustrating part is that its unlikely that will do much for my low power issue.
After that conversation, I went into the datalog from the street and I can see (upwards of) a 5kPa swing and what appears to be some cycling of pressure.
The guy I talked to earlier suggested moving to a smaller wastegate to combat the "waves" were seeing on the dyno. The frustrating part is that its unlikely that will do much for my low power issue.
08-22-2012, 01:49 PM
#24
On The Tree
Thread Starter
iTrader: (5)
Join Date: Jun 2007
Posts: 118
Likes: 0
Received 0 Likes
on
0 Posts
Its got two springs in it from Tial that equate to 10psi, which is inline with what we see. I can tell you that it doesnt feel "soft" when putting the wastegate back together after putting the springs in.
One thing I am curious about is still the intercooler being a restriction. I am pulling the wastegate reference line post-IC. If the IC acted as a restriction it could potentially pulse air which could in turn pulse the wastegate - somewhat of a cyclic pattern.
I've been thinking about moving the wastegate reference line to pre-IC just to see how it reacts
One thing I am curious about is still the intercooler being a restriction. I am pulling the wastegate reference line post-IC. If the IC acted as a restriction it could potentially pulse air which could in turn pulse the wastegate - somewhat of a cyclic pattern.
I've been thinking about moving the wastegate reference line to pre-IC just to see how it reacts
08-22-2012, 02:48 PM
#25
TECH Regular
iTrader: (15)
Join Date: Jun 2004
Location: Shawnee KS
Posts: 498
Likes: 0
Received 0 Likes
on
0 Posts
MAP holds steady, so its not a boost issue in my eyes. The waviness does look like it wants more timing, or has a valve spring issue.. I would not recommend adding more timing on pump gas.
If you can try a different turbo, you may want to try that as well. On similar builds with a 76mm turbo, it will usually pull smooth to 58-6000 using a manifold kit like what you have. And that is using the basic LS9 HGs, LS6 style cam, but always with dual valve springs vs the single 918s. On one where the springs had some miles the power curve looked similar to what you have, changed out the worn out dual gold springs for new ones and the power jumped back up gaining over 100rwhp.
If you can try a different turbo, you may want to try that as well. On similar builds with a 76mm turbo, it will usually pull smooth to 58-6000 using a manifold kit like what you have. And that is using the basic LS9 HGs, LS6 style cam, but always with dual valve springs vs the single 918s. On one where the springs had some miles the power curve looked similar to what you have, changed out the worn out dual gold springs for new ones and the power jumped back up gaining over 100rwhp.
08-22-2012, 02:56 PM
#26
On The Tree
Thread Starter
iTrader: (5)
Join Date: Jun 2007
Posts: 118
Likes: 0
Received 0 Likes
on
0 Posts
MAP holds steady, so its not a boost issue in my eyes. The waviness does look like it wants more timing, or has a valve spring issue.. I would not recommend adding more timing on pump gas.
If you can try a different turbo, you may want to try that as well. On similar builds with a 76mm turbo, it will usually pull smooth to 58-6000 using a manifold kit like what you have. And that is using the basic LS9 HGs, LS6 style cam, but always with dual valve springs vs the single 918s. On one where the springs had some miles the power curve looked similar to what you have, changed out the worn out dual gold springs for new ones and the power jumped back up gaining over 100rwhp.
If you can try a different turbo, you may want to try that as well. On similar builds with a 76mm turbo, it will usually pull smooth to 58-6000 using a manifold kit like what you have. And that is using the basic LS9 HGs, LS6 style cam, but always with dual valve springs vs the single 918s. On one where the springs had some miles the power curve looked similar to what you have, changed out the worn out dual gold springs for new ones and the power jumped back up gaining over 100rwhp.
Additionally, I'm at a crossroads with the turbo. I'm not aware of anyone that has a "test" unit I could at least try out which means shelling out coin for a new turbo, and then deciding if I even want to go down the "chinese manufactured" route again
