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Message: <blockquote data-quote="Booboo" data-source="post: 1567673" data-attributes="member: 29137">I have been struggling with this problem for a long time and need to get it figured out.  Hoping someone here will have an idea.I have a 1997 NPI short block that I put PI heads on out of a 2001 Mustang. I had a local machine shop rebuilt he heads with +1mm stainless valves, new seals, bronze guides, new OEM lash adjusters, new ford performance followers, BTR springs and XE262AH cams. When we were tuning it, it was down on power, the tuner estimated it was making about 160hp at 3000 rpm, buy the amount of airflow. I have done the following since, sent the heads to another machine shop to check them out, installed a new MAF and computer, checked fuel pressure, double check the degree of the cams, swapped out the injectors, put a test light on each injector and spark plug to make sure they were firing. Put in a known good x-pipe and disconnected the mufflers (to make sure there wasn't a clogged exhaust). Installed a set of stock PI cams and removed the XE262AH cams. Compression tests have been good.We put a tune in it from a similar car with a similar setup so it should be close but it is running 30%+ rich. Its like the air is going into the engine but not making power.  It's like the air is bleeding off somewhere. Possibly out the exhaust? Is it possible to have two machine shops mess up the heads?  Could they have the valves installed wrong or possible the wrong valves (too long, or short)???  Any ideas?</blockquote>