Any engine builder will tell you that the key to making gobs of power is using the correct combination of components. In other words, using a .700-inch lift cam in an 8.5:1 compression small-block with GM 1.94-inch, 1.50-inch iron heads just doesn't make sense. Nevertheless, some builders think more cam means more power. We're here to tell you that even without tons of cubes you can make great power if you use the correct parts for your application.
As a quick refresher course, we left you folks at the machine shop where our Huffer powerplant received freshly machined surfaces, a full engine balancing, and all the necessary details in preparation for assembly.
Project "Huffer" as we've come to call it was designed off of a very common short-block, the 427 Chevrolet; an engine that GM made for many years and is very accessible in the used marketplace. As any avid 427 enthusiast will tell you, the 427 loves rpm which we found was one of the keys to making horsepower with less displacement.
When we began our huffer overhaul we started with a blank piece of paper and asked ourselves what we hoped to accomplish on the dyno. We determined that 700 hp on pump gas and 800 hp on race gas sounded like respectable numbers from 427 inches. At that point we were left with the details of how to make the magic happen with off-the-shelf parts. Since we already had the 427 crank, block, and Merlin heads, we thought that a 7.9:1 compression ratio was perfectly attainable with flat-top pistons and 120cc combustion chambers. The cam choice no doubt left us with the biggest questions. Since most supercharged engines move the powerband down slightly on the rpm table we chose a cam that ordinarily would have been large for a 427, but we figured that 11-13 pounds of boost would be just right. Our Lunati solid roller (50231 LUN), while listed as a drag race cam, had the perfect specs for our blown 427. Valve lift was .680 inches on the intake side and .700 inches on the exhaust, while duration at .050 inches was 258 degrees on intake and 268 degrees on exhaust. Our choice was actually made much easier by the Lunati guide specs provided by their online catalogue. If you're not quite sure what cam specs are best for your engine, it's best to give the tech support a call, they'll probably have the answer you're looking for.
Knowing that boost retard technology was available, we chose to retire the old Vertex magneto in lieu of an MSD 6BTM electronic ignition combined with an electronic boost retard module. While the magneto is great in race applications, the ability to retard timing in situations where detonation may be present is invaluable.
Carburetion is yet one more example where less is more. We often find over carburetion in blown applications. While unsure whether the difference would be significant, we brought our Holley Dominator 1050s as well as a set of HP950 blower carbs with us on dyno day. As we suspected, the smaller carburetors actually produced 12 hp more than the dominators! We have only two words to say, POWER VALVE!
As a general rule when a big-block is going to spend time above 7,000 rpm, it's wise to take a few precautions. So when it came to valvetrain, we opted for a rocker stud girdle to keep things in place. We also used ARP fasteners as opposed to the fasteners traditionally found in an OEM assembly.
When our Huffer was finally assembled, we were off to Vrbancic Brothers Racing and their accurate DTS dyno to see if our combination of speed parts was indeed a winning combination. Unfortunately we found some slight leakage from the water passages on both cylinder heads. So, without a single dyno pull for the day we were back to the drawing board for a little exploratory surgery.
After tearing the Huffer apart, we drained the motor of its fluids and got back on the phone with the motor experts at Jim Grubbs Motorsports for some advice. It was at this point where we swapped the stainless O-rings for copper O-rings and ditched the copper head gaskets for a set of composition gaskets. As many people are guilty of, we too were over engineering our 427. While the common thought is to run copper head gaskets in blown applications, it's not a steadfast rule. If you're planning on keeping boost below 15 pounds, you probably don't need anything more than composition gaskets.
One week later we were back on the dyno to see if all our hard work would prevail. The plan was to create two different engines with the same parts. One combination used a pulley setup that was 10-percent underdriven on pump gas. The other combination used a pulley combo that was 18-percent overdriven on 100-octane low lead with just a splash of Marvel Mystery Oil.
After locking out the distributor and setting total timing to 34 degrees advance, we produced 745 hp at 7,200 rpm on 91-octane pump gas while underdriving the blower. With the same timing, we upped the octane to 100 and switched the pulley setup to 18-percent over and produced 815 hp at 7,000 rpm. Just to see if a little more octane would make a difference we made one more switch to C-12 race fuel, but to our surprise we found no change in power.
While the huffer motor isn't an example of the hottest combo on the face of the earth, it certainly shows value for the dollar. While a 500-plus cubic inch motor is great, it's not your only choice for supercharged horsepower on a fixed budget. Our huffer provided great numbers with off the-the-shelf parts on pump gas. What more could we ask for?