Power dropping off way early?

[omj]

Would anyone like to guess why my power is dropping off abruptly? Spark, fuel and boost are where they should be. My tuner suggested possibly needing valve springs. I have a stock bottom end, stock heads/cams, psr, longtubes and vortech ti trim sc. The lower hp graph is with a 3.6 pulley. The higher hp is with a 2.8 and a wastegate set at 10psi. 1999 Cobra. Notice the nosedive at ~5500 rpms. I've attached a datalog from a street pull.

 

[nxhappy]

these aren't high rev engines. You are going to lose boost and power after 5500 rpms. you could also be getting belt slip with the smaller pulley. That would be indicated by the "squiggly" dyno chart. I don't see anything abnormal here.

 

[omj]

This is a 4v, not a 2v. It should be dropping around 6500. Boost was good. I had the wastegate set at 10.15psi and it was climbing to 10.8 when we let off.

 

[Ironmancuck]

Every time I run into a person calls themselves “a tuner “ I’m surprised by their lack of knowledge in regards to the way automobiles work.

A vacuum test can easily spot week valve springs so I’m not surprised that your tuner is just guessing and suggesting that valve the valve springs are week .

My guess would be a compression loss .


I would check for signs of belt slip or vacuum leaks . Hook up a scanner and check for codes and other data.

 

[bigjeezy04]

The lower hp pull was still clambing by 5500rpms why did u stop the pull?

The smaller pulley might be slipping and creating a lot of heat! the car might be pulling timing.

What was the IATs at? What was the timing? What octane?

 

[omj]

The first pull was stopped because I ran out of pump.
We were seeing about 20* IAT over ambient on the day of the second tuning session. I can't remember timing but it's in the log I posted. Timing wasn't being pulled. Octane is 93.