If you followed Horsepower Wars LS vs. Coyote 2: Supercharged Showdown, you probably remember how the competition ended… The LS was a clear winner, but not without some controversy. You see, the way the rules had been written, the teams were free to choose any blower they wanted, provided it was running a serpentine belt system. That led to the LME team choosing a big-boy ProCharger F-1X supercharger for their 427 cubic-inch combination, while the MPR Racing Engines team chose the smaller, but better-suited-to-the-Coyote, F-1A-94 supercharger.
Originally, the plan was to swap the F-1A-94 on the LS engine after the competition so that we would have an apples-to-apples comparison (see, we aren’t as dumb as the commenters think we are). However, when the OEM head studs (which were a budget-saving measure) let go after making 1,784 horsepower, the LS was done for the dyno session.
We weren’t content with only running the F-1X on the LS engine. We wanted to see the engine’s performance with the F-1A-94 supercharger. However, that necessitated some TLC from the LME team. With no budget restrictions this time, we could improve some aspects of the engine that didn’t get as much love as we would normally have liked.
The Original Configuration
First, let’s recap LME’s build of the LS engine for the competition. Right off the bat, Neelen knew that with a 427-cubic-inch combination, they would be able to make big power. Additionally, with a factory 4.00-inch crankshaft readily available in the form of an OEM LS7 crankshaft, there would be significant budget savings by using the OEM crank, with no perceived disadvantages.
Stuffing that LS7 crank into a Chevrolet Performance LSX iron engine block, the team at LME finished the bore at 4.125 inches and added a set of forged MAHLE flat-top pistons and Saenz billet I-beam connecting rods. They topped off the combination with a set of Brodix BR7 cylinder heads, prepared by LME.
This is where some more significant cost-cutting measures were enacted. Since the LSX block has two extra cylinder-head bolt-holes per cylinder, the team at LME opted to go with OEM fasteners — the total cost of which is less than what lunch for the LME crew costs at McDonald’s. LME knew it was a risk, but between the Cometic head gaskets and the six-bolts-per-cylinder, felt there was a good chance it would hold.
In addition to the factory head bolts, factory LS7 hydraulic roller lifters and rocker arms were used, with 3/8-inch Manley pushrods, all riding on an LME-spec custom hydraulic roller camshaft ground by COMP Cams. Topping off the combo was one of LME’s billet LS7 intake manifolds, which is as pretty as it is functional.
The ProCharger F-1X originally equipped on the combination is an accomplished race blower. It’s physically larger than the rest of the F-1 lineup and has a reputation for being the supercharger to beat on the racetrack. So it’s really no surprise that it made such a big number on the dyno. While not surprising, it was a genuinely impressive feat.
The Damage Done
After the initial “pop” on the dyno, it appeared that the head bolts simply stretched, allowing the head to lift and combustion pressure to blow out the head gasket. However, as soon as the driver’s-side cylinder head was pulled off, it was apparent that it wasn’t just the head gasket that was damaged.
The first and most recognizable portion of the damage was the flame-cutting in the combustion chamber caused by the combustion leaking past. Some of that damage carried into the cylinder, damaging the piston and cylinder wall. Obviously, some machine work would be needed, as well as some replacement parts.
Upon more thorough inspection, the driver’s-side BR7 head was deemed irreparable. Fortunately, the BR7 castings are available individually, and LME’s CNC machining program means that the new head is 100-percent identical to the destroyed cylinder head. As they performed exceptionally in the original test, a set of identical Cometic MLX 5-layer head gaskets were used, with the same .052-inch compressed thickness and 4.150-inch gasket bore were used.
The damage to cylinder number one wasn’t confined to just the cylinder head. The wall of the cylinder was scored enough that a simple hone wouldn’t clean it up enough to be usable. However, it was able to be cleaned up with a very slight .005-inch overbore. That slight change in dimension was pushed to each cylinder, resulting in a scant 1.04 cubic-inch displacement increase.
While the minor increase in the LS’ displacement was inconsequential to performance, it did demand a new set of pistons from MAHLE. Luckily, it was well within MAHLE’s capabilities to recreate the exact same piston as was previously used, albeit in a 4.130-inch final diameter instead of the previous 4.125 inches.
Additionally, while undamaged, the OEM LS7 crankshaft was replaced with one of Dart’s billet fully-center-counterweighted 4.00-inch stroke units. It’s a direct drop-in piece and should work quite well in this engine’s future endeavors, beyond just the dyno test. The Saenz billet I-beam rods were undamaged and reused as well.
Probably the most needed upgrade was ditching the OEM head bolts, and switching to a set of ARP head studs. The OEM head bolts were never designed to hold almost 1,800 horsepower, and the fact that they did for several runs is astonishing. However, even with the smaller blower, the OEM head bolts are not the right choice, and the ARP studs will eliminate any questions as to whether or not the heads will stay in place.
Moving to the valvetrain, a number of durability upgrades were made. While the same camshaft was used, the OEM LS7 lifters were swapped for a set of Johnson Slow Leak Down hydraulic roller lifters. They are a tie-bar style lifter, with .093 inch of total plunger travel and a calibrated oil metering system.
COMP supplied a new set of 3/8-inch-diameter pushrods as well as a set of its LS7 Max Lift BSR shaft rockers. While the items these pieces replace performed admirably, these upgrades provide a tremendous increase in engine reliability — as well as peace-of-mind — over the previous, overtaxed, OEM pieces.
The Crown Jewel
Obviously, the biggest change for this particular engine is going from the big-boy F-1X supercharger, with its 10.5-inch volute diameter and 4.20-inch inducer diameter, down to the F-1A-94 supercharger, with a 9.0-inch volute diameter and 3.70-inch inducer diameter.
ProCharger rates the F-1A-94 at 1,300 horsepower, and if the F-1X’s performance over its rated power level is any indication of what we’re in for, the graph should be an interesting one. The same ProCharger 10-rib serpentine drive assembly was retained. So really, the only performance changes to the engine — other than the solitary cubic inch of additional displacement — is the smaller supercharger. Once LME had the LS back together, it was off to the dyno.
After a quick SuperFlow break-in program run on the dyno, some validation pulls were made with the engine without the supercharger on it, which looked promising. Then the supercharger was bolted on, and the test sweep set for 5,500 to 7,000 rpm.
Putting Power to the Pump
LME made a few full-boogie pulls, netting 1,488 horsepower and 1,134 lb-ft of torque, before swapping to a smaller blower pulley and adding a degree of timing to the tuneup. Those changes resulted in some serious numbers on the dyno screen. When all was said and done, the dyno read 1,548.2 horsepower and 1,211.1 lb-ft of torque. That’s quite a bit above the rated 1,300 horsepower, and looking at the graph, will continue to pull past the 7,000rpm the test stopped at. The combination should make an incredible powerplant for its eventual home.