Check out Part 2 and Part 3 of our 426 Hemi Supercharger Install!
Editor’s Note: We wanted to step out of our comfort zone just a little, and dive into a build that we wouldn’t normally highlight for you guys. We try to keep the majority of our edit focused on the street-performance arena, so when we got a call from Rich Nedbal inquiring if we would like to cover the build of a blown, Methanol-injected race Hemi, we were more than enthusiastic.
Originally, our block was used in a 900-horsepower N/A build. It features 41⁄2-inch cylind
We’re sure you already appreciate the horsepower advantages that Chrysler has bequeathed to us. The founding father of this advantage is the second-generation 426 Hemi. Sure, the Hemi started it all back in the 1950s, and the new Hemi is a very impressive engine, but look at a Top Fuel or Top Alcohol Dragster and you’ll see a second-generation Hemi.
Several years ago, I built a normally aspirated version of this legendary engine, called the Pump Gas Hemi. With that engine in a race car, I won the 2010 NHRA ET finals in Division 7. The objectives at that time were to build a very reliable, low-maintenance Hemi in the 900-horsepower range. It performed as designed, with mid 7-second e.t.’s, and no breakage in over 300 passes. But to run in the relatively new Top Dragster class, the car needs to be running 6-second e.t.’s. The math said that we would need close to 1,500 horsepower. Was this possible without compromising reliability? 1,500 horsepower is very achievable, without going to the extremes that would be required by classes such as Pro Mod or Top Alcohol.
- Reliability. We need to keep the rpm low. That is, after all, going in a bracket-class race car.
- Use as much of the previous pump-gas engine as possible, and switch to Methanol.
- Must be built using a water block.
- Consider all the options for increasing horsepower without hurting reliability.
Nitrous Oxide - Not
Nitrous is the fastest, easiest, and least expensive way to gain 200-400 horsepower, but the Top Dragster Class is basically a high-speed bracket class that requires consistency. It’s hard to maintain consistent e.t.’s as the nitrous bottle’s pressure drops. Also, at this power level, the bottle would only last for a few passes. It’s great for heads-up racing, but dubious for e.t racing. Our next idea was forced induction. Even though centrifugal superchargers such as a Pro Charger are very impressive technically, what looks more natural in a dragster than a Roots-style blower sitting on a Hemi? So we found a used Mooneyham 10-71 that fit the bill, and the math says we’ll only need about 10 pounds of boost to get the target horsepower.
What parts can we keep from the pump-gas engine?
It’s an aluminum block from World Products, with a 41⁄2-inch bore and non-raised camshaft journal. With bushed lifter bores and enhanced oiling already integrated, nothing needs to change here. Many alcohol engines use a solid, Siamese-bore block, but since the Top Dragster Class is really a high-speed bracket class, where hot lapping is likely, we’ll stay with a water-cooled block.
The existing crankshaft is a 4340 forged piece from Crower, with a 41⁄2-inch stroke and 2.200-inch rod journals. It’s more than capable of handling the horsepower. The only change is that we need to add a second keyway slot for the blower hub. The 2.200-inch rod journals, along with the smaller big end of the steel rods, means no additional clearancing of the block is required for the larger stroke, and there are no rod-to-camshaft clearance issues.
Rods and Bearings
The connecting rods from Crower are billet steel and measure 7.100 inches. The bearings are coated pieces from Calico. If we wanted to run a lot of rpm or run the boost into the stratosphere, we’d use aluminum rods since they cushion the bearings. But at a projected peak of only 7,000 rpm, and since we’re only using 10 pounds of boost, we’d rather not have to worry about the unpredictable life span of an aluminum rod. Rod bolts are unbelievably strong AMS5834 (Aerospace Material Standards) material. We like coated bearings, and used both normal and X bearings, (which are .0005 inch thinner), to allow for the extra coating thickness. That way you can mix and match to get the proper bearing clearances.
The N/A engine had a 10.7:1 static compression ratio. This is too high for a blown gasoline-fueled engine, but it’s perfect for alcohol (Methanol). Methanol will allow us to keep the compression ratio we already have. It will run cooler (when hot lapping), and will net a nice increase in horsepower with no other changes. Sure, there as some drawbacks to Methanol, but how much of what we have heard is myth versus reality? Later we’ll explore what it really takes to run methanol.
We are using pistons from Diamond Racing, and the final compression ratio will be 10.7:1. If we were starting from scratch, we would have ordered these pistons gas ported, but we’re reusing what we had from a previous build. Blown engines like gas porting to help with the ring seal, and it helps minimize blow-by. This is more critical with Methanol, as alcohol engines have a tendency to “milk the oil.” But lateral gas ports can be added, and while we’re at it, we’ll have Angie at Mopar Engines West coat the pistons as well.
If ordering new pistons was an option, we would probably move the rings lower on the piston, and might even use thinner rings to decrease friction. But since the pistons were already cut for 1⁄16, 1⁄16, 3⁄16-inch rings, we’ll use them as is. To help with blow-by, we’ll change to a ring set from Total Seal that consists of a gapless tool-steel top ring, Napier second, and a standard tension oil ring. Because of the wristpin location and the longer rod, we have to use an oil support ring too.
Foot note: Jumping ahead to the third article in this series, after testing this engine on the dyno and making several test-and-tune passes at the track, the amount of blow-by into the puke tank is minimal (about a tablespoon per pass), and the oil shows no sign of milking.
What is exotic are the head studs. We wanted to upgrade the head studs, since this block uses stock 7⁄16-inch diameter studs. ARP doesn’t sell a 7⁄16-inch upgrade kit, but you can buy each stud individually from ARP’s special division. The studs in the original Hemi kit have a tensile strength of 190,000 psi. We upgraded to studs made from L19 material, which increases the tensile strength to 260,000 psi.
Stage-V Millennium heads are great Hemi heads, which can flow over 500 cfm after CNC porting. They typically use the 10-bolt intake pattern, which allows opening the ports to massive levels. Normally, this head design requires using a custom intake manifold. But when this engine was originally built for use with pump gas, we wanted to leave the manifold options open. So we ordered the heads with the more typical 16-bolt pattern to alleviate spending a lot of money for a custom sheetmetal intake. We also ordered Stage-V’s additional spacer plates so that almost any intake manifold can be used. This sacrifices potential maximum performance, but it was a compromise we were willing to live with. The pump gas version used an Indy 4500-series manifold with a single 4500-style throttle body. The stainless steel valves are Ferrea, the springs are Pacaloy, and the retainers and locks are from Manley. These are great parts, but nothing you would consider exotic.