Carb modification for blower use

Quick Fuel uses roller bearings on the throttle shafts to prevent binding, (billet baseplates also) that and making the power valve boost referenced is the other. I imagine you can find some bleed numbers online to get a place to start.

Generally you want larger needles & seats, and your jetting will probably need to go up several sizes, 20% is not uncommon. boost referenced power valves and boost referenced fuel pressure and timing are also good ideas. Conservative timing and a limit on total timing as well. You will love the throttle response it's addictive.

Power valves account for a big portion of your total fuel flow, if you choose to use power valve plugs then you will need to make big jetting changes to compensate for the lost fuel or your engine will go lean as a cutting torch. You might take a few minutes and call the Holley Tech line and give them your engine specs, they have out of the box blower calibrated carbs,they can give you those as a baseline starting point and they are usually very close. Edelbrock offers the same service too, and their carbs with blower calibration work well too.

http://www.motorsportsvillage.com/modifycarb.html

Back in the day most guys myself included ran Holley's without boost referenced power valves with no problems on 6/71's.

PS: The other two ways I have seen them modified is a port in the main body or a port in the base plate.

http://www.quickfueltechnology.com.au/content/Quick%20Fuel%20Carb%20Size%20with%20details-AUST.pdf

Check out page 3. I believe the Q650-B2 is the dual quad blower version and it shows the spec's.

i had a holley hp 950 blower carb. boost ref. only doing about 5 lb on a holley 174 roots blower. I pullyed down and got about 11 psi and ping like hell with a 93/116 mix. so I decided to send it off for an E85 conversion. mark sullens is doing the conversion. after a long talk he said trust him on no boost ref power valves. so I don't know what kind of voodoo magic hes doing with the carb. guess well see how it turns out. I told him I really need an emphasis on driveability. that 950 out of the box was awesome once the engine warmed up. not that it was bad cold. just no choke..