Jetting with a Blower
 

I'm new to having Blowers! I'm in the proces of rebuilding carbs. The motor's are 468ci, Dart heads, Stainless Marine GENIII's, dry pipes, with 420 Mega Blowers. Each motor has dual 850 Holley's. The plugs were black! I'm thinking that they were set up way "Fat", 88s primaries with 6.5 PV and 96s with 8.5PV secondaries. Frankly I was surprised to find the big differences in jets between the primary and secondaries given that there were powervalves in each? Looking for some knowledgable feedback.

Unless the plugs were brand new, run at wot and then the motors shut off I wouldn't change anything without running with an air/fuel ratio meter. Too many variables that can contribute to black plugs. Could be way fat at idle but lean on the top end, just didn't run there long enough to clean off or burn up the plugs or pistons.

i think because of the power valves in the secondary,s you are rich.your engines sound a lot like mild thunder,s so hopefully he will see this thread and chime in.

You gotta lose the secondary PV and jet down. A power valve is close to 10 jet sizes worth of fuel. Its like having 106 jets in there. Way too much fuel.
Originally the geniuses that set up my boat put close to the same set up in my 540`s including the secondary power valves and my AFR meter was showing 9.0AFR.
Cylinders were probably getting a good wash down.
Get a AFR meter it`ll make things a lot faster and easier to figure out where you need to be jet wise, I`d say 84/92

dyno dyno dyno,no other accurate solution

AFR meter in real world conditions seems pretty accurate to me. Dyno to get you started.

danialson,you are a fast lerner.

I have good teacher, wax on wax off. I even have my own tackle box of jets and carb parts just like Mr. Miyagi :D

I agree. I was just trying to get an idea from someone with a similar setup if the 8.5 PV on the secondaries with such a large jet sounds unusual? My experience has me of the school of thought that if you have 2 power valves that the jetting is usually close in all four corners.

Are the carbs boost referenced? It does sound like way too much jet, but who knows. The motors are out right? $500 on the dyno could be money well spent. If you want to run out of fairhaven in the spring and do some plug readings let me know