If you are running a decompression plate on stock pistons, I'd stop right there.

The Decompression plate screws with the squish/quench area of the combustion chamber/pistion. So 258 is about as good as you're going to get. If you tune for more power, you'll probably run into detonation, and then either need to pull back the timing (loose power) or dump extra fuel (loose power).

Until you get those new pistions in, leave it be. It's the tuning setup you have now that's limiting the power, but you can't really modify that with the setup you've got.

You could TRY to go for colder plugs, but they will fowl under normal driving, but provide you with probably 300 WHP on the dyno under load. Under any other conditions than full load, they will run too cold and fowl.

Just leave it be, and get it retuned once you have those new pistons installed and the decomp plate removed.

 

thanks random.
tha explanation makes sense.

 

To give you an idea. Jaws021 just put down in the neighborhood of 240 WHP on 10 PSI.

Stock everything (cams, TB, IM, Head, etc...) ....but he had forged low-comp pistons.

Get them pistons installed and you'll be able to run over 300 WHP at that same PSI just by bumping out the ignition timing and leaning out the fuel ratios.