3/18/2023 0 Comments 871 blower circuit racerThe PDV utilizes a check ball to block the boost signal to the trans modulator when the blower is making boost. I am using a BDS pressure diversion valve (PDV) which connects the transmission modulator vacuum line to an aluminum block that has manifold vacuum and under carb vacuum references. The plugs are AC R44T’s… they foul easily. ![]() The MSD distributor was new when the BG carbs were installed in 2006. The distributor does not have a vacuum advance, it is all mechanical. I have not opened the secondary bowls so I cannot positively say the secondary jets are what came from Barry Grant when the carbs were new. The floats are set so that the fuel level in each carb is at the mid point of the sight glass. The pressure stays constant while idling and driving around. He also told me to make sure that I had no more than 7 psi fuel pressure so I set the regulator to give 7psi. I called the BG tech line because of the soot spewing and the tech guy told me about boost referencing the power valves so I did and the issue improved but is still not right. I let the car sit for several years (changed jobs, moved, etc.) and just got it rewired late this summer and got it running again. The instructions that came to me from the race shop after the install did not include information on boost referencing. I am not sure that the instructions that the race shop used/received with the new carbs showed the boost referencing. When the carbs were initially set up the primary power valves were not referenced to blower manifold vacuum. ![]() ![]() It idles at 1000 – 1200 RPM roughly, has very crisp throttle response at nearly any RPM and is relatively well behaved except it spews black soot like a freight train. The car ran great then and still runs great now. The shop that did the work then chassis dyno’ed the car and played with the timing, etc. In the summer of 2006 I had a local race shop replace the Holley carbs with BG 750 blower carbs. The car was running but needed some electrical work and some other details. I purchased a pro street car in 2005 that was roughly 85% complete. I could really use some help sorting out a few issues with a roots style blown 468 with a BDS 8-71 and two Barry Grant 750 Mighty Demon blower carbs to get it to stop spewing black smoke at idle.
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