not sure to post this here or forced induction board. sorry. i have a new sbc350 and plan on getting a weiand 142 real soon. i was running n/a on the motor that is getting pulled with a demon 750 fitted to it. when i dyno'ed the old motor i was running lean in the rear banks. they told me to jet up just the secondaries two sizes.

i was also told by other people that it's poper to jet pri's and sec's together. also to always jet two sizes at a time. is this al correct??

main question is due to running lean on n/a, what should i expect when jetting for the weiand 142?? two on both? three on both or just sec's?? thanks guys

 

What model number Demon do you have now? What is the jetting in it now?

A good starting point for a four barrel carb on a 142 Blower is to increase the primary jetting 2 to 4 jet sizes up and increase the secondary jetting up 4 to 6 jet sizes up from factory stock.
This will be a good initial starting point for a motor with a blower like this.
This will insure that you do not operate the motor lean at WOT. A supercharged motor that operates lean under power will soon self destruct, so starting out a little rich provides a safety margin.
Once you get a chance to track tune or chassis dyno tune the motor you may end up with smaller/ leaner jetting to achieve max performance but start here.

A supercharged motor makes more power and requires a fuel system that can keep up at WOT. If the fuel system is not up to snuff no amount of extra jetting will help.

The mph achieved at the end of a 1/4 mile is a good indication of power changes.

 

thanks for the help, f-bird. the stock jets in the sp 750 are #76 pri's and #83 sec's. so do you think jetting to 80 and 87 would be a good start. when looking at the dyno sheet it looks like under 3000rpm the air fuel seems to be rich, but thats better than running lean. i emailed barry grant tech and they said that i may have a part throttle drivebility issue (hiccup?) also keep the jet sizes 6-10 within eachother. sounds pretty good to me. let me know guys.

oops. i already got a holley fuel pump to flow more for the blower and plan on running -6 fuel line