Dyno results but weird knock problem?

[Quigs]

Hitech Motor Sports had its grand opening last Sat. and they had free food and $25 dyno pulls so I figured I'll see what my car can do before I put my TE-44 and front mount on it.

During the pull everything was going well until it started picking up a few counts of knock then it took out alot of timing around 8-9 degrees and ran pig rich 9.x Air/Fuel. I was told that it could be because of bad motor mounts because the downpipe started tapping on the chassis.

What else could it be?

My car is a 87 GN. I rebuilt the engine just because I was pulling the car apart for paint.

Stock rebuilt rotating assembly
poston 107T cam
30lb hr. injectors
I think a 255 walbro fuel pump w/hotwire kit
and a 2 1/2 in hooker cat back.

 

[Roc87]

What kind of chip are you running? While on the dyno, my A/F stayed rock solid with an extender chip. Running that rich, could it be "rich" knock? What type of fuel (octane) and boost were you running? First thing to determine if it's false knock is to throw some high octane race gas in it, to see if it still shows knock, if it does, then you can be sure it's chassis related.

 

[Quigs]

93 oct. Stock chip, 15psi of boost but dropped to 12-13psi when it pulled out timing.

 

[Roc87]

The stock chip is burned for 28# injectors, and "iffy" for any performance on a completely stock car. If you're running 30# injectors, that alone would cause it to run rich. It seems like the boost is dropping off because of how rich it's running. Get ahold of Eric at Turbotweak for a new chip, they are pretty reasonable. My GN had a bunch of KR with the stock chip at 14# of boost.

 

[Quigs]

What do these cars put down stock