Before attempting our baseline pull on the motor, we added 7 quarts of Lucas 10W30 to our deep-sump Milodon oil pan and pre-oiled the rotating pieces. Up top, an out-of-the-box 750-cfm Holley HP series carb went on top of the Dart single-plane manifold. After a few minutes of warm-up and a quick run of the valves, we made a baseline pull of 569 lb-ft of torque at 5,200 rpm and 631 hp at 6,200 rpm.
Once the naturally aspirated baseline numbers were steady, Bob Vrbancic from The Carb Shop out of Ontario, California, came down with one of the shop's modified 750-cfm boost-calibrated HP-series Holley carburetors. He first connected it to our homemade aluminum tubing and added a few gallons of 114-octane race fuel, giving us a safety margin until we knew exactly the type of boost we were going to generate and to adjust both the fuel and timing curves. For the first pull, we again proceeded with a quick warm-up and dipped into the throttle, only to shut it right back down-it's hard to describe, but the noise we heard didn't sound good.
Entering the dyno cell, we checked the fuel pressure, and it was where we had left it at 7 psi, the timing was locked out at 34 degrees (see MSD sidebar), and plenty of fresh air was entering from the fans above. Everything appeared to be OK, so we headed back into the control room and fired the engine back to life, again. This time around, we decided to stay in the throttle just long enough to record a quick data shot at 3,500 rpm to see what was going on. Suffice to say, the F2-packing big-block wasn't happy, bucking and kicking like an angry horse. What data we did gather revealed roughly 855 lb-ft of torque at 3,500 rpm; however, it was ridiculously lean. The problem: fuel starvation-and we traced the leaks to the boost-referenced fuel regulators.
For the third round, we ran into a different situation; the engine lurched forward, out of control, toward us, making us shut it down again. So the motor was down before we'd recorded any data, but we definitely fixed that fuel problem. Strange as it may be, how do you fix a walking dyno? Simple, with two car-style trailer hold-down straps. In all our years of testing, this was a new one for us. We strapped one end to the engine cart and locked the other into the concrete floor anchors.
Once again, we checked the engine's vitals and fired it back to life. Ready as ever, the plan was to have a short pull from 4,000 rpm to 5,500 rpm to see what we had to work with. With our ears plugged and fingers crossed, we recorded an unbelievable 1,100 hp at 5,400 rpm and 1,066 lb-ft of torque at 18 pounds of boost. Even more impressive is that the powerband looked more like a nitrous curve, shooting the power straight up.
Before boosting our 496ci...
Before boosting our 496ci to the moon, we wanted to see how much power our mill made naturally aspirated. At 5,200 rpm, it made 631 hp. Boosted with no intercooler, the power level increased to 1,100 hp. That's a 57 percent increase with minimal tuning.
This is no ordinary 750-cfm...
This is no ordinary 750-cfm HP Holley; actually, it was built specifically for blower duty by The Carb Shop. Quite frankly, with the Vrbancic brothers' years of experience, it was only a matter of playing with the idle mixture screws and we never touched the carb again. The real key to the carb is that all the circuitry in the carburetor is completely different and features a special down-feed 0.152-inch needle and seat, and for street duty, it utilizes a balance line between the float boats to promote drivability at lower throttle plate positions.
A beautiful feature is that...
A beautiful feature is that there's no oil feed line required to lubricate the F2; instead, it's self contained and the oil comes supplied with the system. Features include a 10.5-inch volute diameter, flow capacity of up to 2,700 cfm with a max boost of 38 psi, and a max impeller speed of 65,000 rpm; that means with the proper bottom end, it has the potential to generate 1,600 hp.