I to have the 502 EFI in a 230SX stingray, Last year I spent money on an exhaust system and the vortech maxflow EFI power pack.
It's a reprogramed ECU, Flame arrester,ignition amplifier, wires, ect..
The system came to about $1200.oo and the exhaust came to about $1600.oo.
All that money and I gain about 1-2 Mph.
At the end of the season I broke down and bought the mild stage 1 procharger. It took about 3-4 hrs to put it in, and the results were amazing!!!! almost 14 MPH gain.
I went from spinning a 25" 3 blade to spinning a 31" pitch Bravo 1 4 blade.
After doing some research I found that the 502 is the best stock merc. engine Ideal for super charging. All internal components are extream duty, including J & E forged pistons.
also the 502's stock compresion is a low 8.75:1 which is better for super charging.
Just a thought you might want to think about. to know then what I know now, I wouldn't of spent the money on the exhaust and ignition parts, and went straight for the procharger.
The stock exhaust on the 502 is fine for the stage one kit.
Good luck Hope this helped a little.
[This message has been edited by Kanookstr (edited March 18, 2001).]