Dear Pro Mod Wad,

I'm running a 331 small block Chevy with forged pistons, Pink rods, Dart sportsman cast iron heads, 4-71 Roots supercharger at 12-percent overdrive = 10 lbs. boost with a modified 850 double pump carb MSD ignition.

I've added a 125 hp NOS plate system with a Jacobs Mastermind NOS control. My question is, what carb jetting should I start? At present I have not tried the NOS system. I plan to test it on a dyno. The jets I have in it are 72 front and 80 rear.

What setting to start with the retard setting on the Jacobs control? Your input would be very helpful.

Thanks
Keith Schultz

Hi Keith:

Thanks for the letter. My advice to you would be that if your basic program runs well and you are not experiencing any detonation now at 10-lbs of boost, do not touch the carb jetting.

I would advise that you set the fuel pressure on the nitrous system at 7 psi flowing and definitely use a separate fuel regulator on the system. The timing should be pulled back 4 degrees at the 125 HP level and that should give you satisfactory starting points.

If you can do a plug reading after a hard run and click off, this will help you to fine tune the fuel pressure and timing retard for more power. Because the blower makes heat at boost and the nitrous is a cooling agent, you may see another 2-lbs or so of blower boost due to the colder, denser charge of air/fuel passing through the blower, so be aware of that.

Let me know how you are doing or if I can help more.