Monkey Spanker

Adding TBS 250 blower with 4779 750 holleys, boost referenced with power valves in front only, no chiller. Can anyone suggest a starting point for jetting? Previous owner had 86/97 jets on a 540 with brodix heads, seems really fat.

fastlane40

I would think 78's or 80's.When i would set up small blowers i bought a air/fuel autometer gauge.Fitted the O2 sensor in the exhaust,reversed down the ramp,put it in foward and read the meter.It's an easy way to get close if your not dynoing.Only trouble is you have to fit the sensor in the exhaust.

GS42fun

I dyno'd and set mine up at Tyler Crocketts. I am running 454's with 250 blowers, and dual 650 holley's. My jetting is 70 on the primary side, and 76 on the secondary side. I am also running 2.5 power valves. I am very happy with the set up. It runs and idles great.

I hope this helps you out and gets you closer.

pachanga

I don't know how a 250 compares to a procharger. I have a 9LB system on a 454 blowing through a 650. I think we are at 78's in the front and 102's in the back. Gonna scale back the fronts a little this summer because it is too much for prolonged idling. Seems fine at WOT...course it might do more but don't wanna take the chance on leaning down too much. Definately is not overly rich.

Monkey Spanker

Thanks for the info so far, I searched the forums every way I could and was stunned at the lack of information. With the amount of people running blower motors you would think you could find the jetting for just about every combo there is. Alot of people talk about Nickerson, but in talking to him he just gave the cold shoulder, blew a bunch of snow about his 35 years of doing this, and said he would work his magic for $525 PER CARB!!!! It might be time to start a thread on this. If every one with a blower combo would post their setup including the jetting in their carbs, I think it would provide a much needed source of information(and save alot of burnt pistons) If you know someone with a blower setup, ask them to post it here, Thanks.

mrhorsepower1

No need to spend that kind of money on re-working the carbs. If your going to spend that much I would get you right into a set of BG Mighty Demon Marine carbs at a great price. On your jetting , How much boost are you going to run? If you around 3-5 PSI , I would jet the primaries @ 72 with a 5.5 power valve and the sec. @ 78 with no power valve to start. Should be really close.

34Mach1

I too am trying to figure out which jets to use. I have holley 250 powerchargers on a stock 502 Mag, but am only running a single 850 Holley carb. It is my understanding Mercury uses .95 on the SC525, so that is what I plan on starting with. I am going to remove the power valve and run 4 .95's. Suggestions anyone?