875 HP TIME BOMB?
Reading through our adventures here, it is readily apparent that our 440 is nothing more than a stock Chrysler engine, with some "old-school" high-compression SpeedPro forged pistons, basically the old TRW 440 Sixpack replacement street forgings, for those of you who can remember these from back in the day. Our goal was to explore the power potential of the blower system, and in doing this we adapted it to an existing test engine. We made close to 900 hp, with basically all stock bottom-end parts: the block, crank, main caps, and standard 440 connecting rods. We know the factory Mopar stuff is fairly robust, and making power on the blower isn't as hard on the bottom as some other forms of power enhancement, or even making significantly less power normally aspirated. That said, we knew it would work on the dyno and probably not blow up, especially since we would be extremely careful not to detonate it, or lean it out under the controlled dyno conditions. However, it was a calculated risk, and one that you, your machinist, or your engine builder might not want to make.
Would we run exactly this combination on the street, or duplicate it in detail for even a drag racing project? No way. We'd definitely look to build a dedicated blower engine with a host of durability mods. Frankly, we'd consider a partial fill on the block, with aftermarket main caps, preferably with a girdle system, or better yet an aftermarket block. We'd buy the best forged-steel crankshaft we could afford, and the same goes for the rods. We cheated with the head spacers and gasket stack to get the compression ratio down, but for a real world application like this you'd better be thinking about a nice set of custom forged dished blower pistons in the high strength alloy. We'd also be looking really hard at a set of steel rings like the Hell-Fires. Making big power with stock factory components is not the formula for a happy long-term marriage. Sure, some of these kits can work just fine at lower boost on a relatively stock engine, but longevity is a dangerous roll of the dice with anywhere near these boost or power levels.
Carb vs. Injection
We were impressed with the amount of pure horsepower out 440 Mopar made with the blow-through carb arrangement, but the reality is that it took some doing. Initially we had a dedicated "blower carb" bolted to our engine, and the fact is it didn't want to run under boost, no matter what we did at the jet. The carb simply would not provide a working fuel curve, actually delivering less fuel as the boost escalated. We had direct readings of air/fuel ratio and fuel flow, allowing us test through and identify the problems without destroying our engine. We pity the guy who bolts a problem like that on and tries to tune it in a high-powered vehicle. We solved the problem by bolting on another carb, and tuning from there. At best the mixture curve was a compromise, but it was a working one. Generally, you are going to be pig-fat down low to get enough fuel to avoid a lean condition as the boost builds.
Frankly, a carb is a velocity-sensing device, and that is the key variable upon which a carb varies the air/fuel ratio. It does a very poor job of compensation for changes in pressure. That's the plain physics of how it works, period. It will work best at lower changes in pressure, which means lower boost. Outside of that, it will be difficult or impossible to tune the carb to offer an optimal air fuel ratio over a very broad rpm range, with the accompanying broad pressure changes associated with rapidly escalating boost pressure. For a high-powered, high boost engine expected to operate efficiently over a very broad rpm range, I would highly recommend an EFI system.