1,000-Plus Horsepower Naturally Aspirated Big-Block For The Mud

Every once in awhile, we get to see an awesome engine built, which is used in a less-than-traditional manner. This particular engine, built by Motorsports Unlimited in Terra Haute, Indiana, is more reminiscent of a bracket racing engine than an almost-unlimited Mud Drag Racing engine. However, Tyler Knight had a limited budget and wanted a 1,000-horsepower big-block to be competitive in his local series.

“It’s a pretty serious deal, where there are a lot of 600-plus cubic inch engines in the class,” says Lance Stillwell, owner of Motorsports Unlimited. “We’re trying to build something competitive within a budget. We came up with a 582 combo that I think will be competitive and stay within the budget. Our main goal is to get good enough parts to make sure it will last more than one year and make enough power to be competitive.”

One way that Stillwell aimed to keep costs down was to use off-the-shelf items. The scale of economy says that shelf-stock parts will always be less expensive than custom parts. The trick is having the knowledge to utilize off-the-shelf parts to their fullest. Stillwell has a strong relationship with PBM and decided to use the PBM catalog for as many parts as possible in the build.

The World Products Merlin IV block makes for a great foundation for this build. While capable of more displacement and horsepower than the goals of this project, being a little overbuilt never hurt anyone.

Not So Short Block

With there only being a few rules in the rulebook — one of which requires an iron block — options were pretty open. Stillwell opted for a World Products Merlin IV block. With a number of deck height and bore options, he opted for the shorter 9.800-inch deck height, and a 4.595-inch rough bore, which Stillwell finished at 4.600 inches. Since one of the other rules for the class was that all engines need to be naturally aspirated.

Because of that, Stillwell opted for the nodular iron main caps. Like the billet upgrade, there are four bolts per cap, but unlike the billet upgrades, only the outer bolts on the center three mains are splayed-bolt design. The .600-inch-thick deck surface and priority-main oiling systems are both improvements over a stock block, along with the cylinder wall thickness and the built-in clearance for stroker crankshafts.

The PBM H-beam rods are made from forged 4340 steel and measure 6.535 inches center-to-center.

Into that Merlin IV block, Stillwell dropped a forged 4340 steel PBM crankshaft with a 4.375-inch stroke into the Clevite H-series main bearings. While the Merlin IV block can handle significantly more stroke, they are planning on running at a significant engine speed to achieve the customer’s horsepower goals, and wanted to keep piston speed in check. Constructed with standard 2.750-inch main journals and 2.200-inch rod journals, the PBM crankshaft will allow the use of several more off the shelf parts and equate to a total displacement of 582 cubic inches.

Hanging off the crank are a set of PBM forged 4340 steel H-beam rods, also with Clevite H-series bearings. While an off-the-shelf 6.535-inch rod length is used, they do have a unique feature in that they use .200-inch shorter rod bolts than standard. The 1.600-inch ARP2000 bolt have the same strength, but provide additional clearance and shave a small amount of weight.

While an impressive piston, with its large dome, vertical gas ports, and anti-friction skirt material, it’s an off-the-shelf piece from JE Pistons.

Attached to the rods is a set of off the shelf JE Pistons high-compression slugs. With a finished bore of 4.600 inches, there are plenty of ready-to-go options. These forged pieces feature a well-refined dome design that not only brings compression up to around 15:1, but also doesn’t interfere with flame propagation.

Additionally, the pistons feature vertical gas porting, designed to help the .043/.043/3.0mm ring package seal under high cylinder pressures, along with JE’s low-friction skirt coating. Since the short deck is being used, the compression height needed to be so short that the wrist pin encroached on the oil ring, necessitating the use of a support rail.

While checking camshaft endplay, Stillwell found it to be a little tight. To bring it up to the target .010 inch, he machined a few thousandths of an inch off the timing cover.

Speaking of oil, one of the other rules of the class is that the engine’s oiling system be of a wet-sump design. Looking for every advantage, Stillwell went with one of Moroso’s billet aluminum oil pumps. The revised inlet area reduces the chances of cavitation and the whole setup weighs a pound less than the stock pump and pickup.

One caveat to the Moroso billet oil pump setup is that it requires an 8-inch-deep sump. Fortunately, Canton offers a fabricated deep-sump drag race pan for the big-block Chevy, with an 8-inch sump depth. In addition to the drag race baffling, a louvered windage tray is used to control excess oil motion at the full seven-quart capacity.

While the Moroso billet oil pump weighs less than stock, it does require an 8-inch-deep sump. Fortunately, Canton offers that exact sump depth with drag-race baffling.

Stylin’ and Pro-Filin’

For the combination’s cylinder heads, Stillwell once again went to the PBM catalog. He chose to use a set of Pro-Filer Performance Products Sniper X 24-degree big-block Chevrolet cylinder heads. Aimed heavily at the X275 drag racing class, the headwork with standard BBC pistons and come completely CNC ported right out of the box.

The monstrous 375cc intake runner flows 460cfm as delivered, while the exhaust flows a whopping 325cfm on the exhaust side. However, Stillwell added a few of his own touches to the ports as well as the 119cc chambers, as well as Erson 2.350-inch stainless intake valves and stainless 1.850-inch exhaust valves, both with 11/32 valve stems.

The Pro-Filer Sniper X cylinder heads come completely CNC machined, out of the box. However, Stillwell wanted to put some personal porting touches on the heads himself.

Controlling those valves are triple-nested Erson valve springs with a 2.100-inch installed height, secured by Erson titanium retainers. The springs offer 350 pounds of seat pressure and an open pressure of somewhere around 1000 pounds. That is required to control the valvetrain at almost 8,000 rpm.

The camshaft is a custom-ground Erson solid-roller piece. Stillwell was reluctant to divulge all of the specs, but did mentions there was approximately 25 degrees more duration on the exhaust lobe than the intake lobe, and that valve lift is way north of .800 inches. The only other details he’d mention is that it is a 4/7 swap cam.

Riding on those large lobes are a set of Morel tie-bar solid roller lifters, paired with Erson Pro Series 7/16-inch-diameter, 0.135-inch wall-thickness pushrods, measuring 8.750 inches on the intake, and 9.350 inches on the exhaust side, thanks to the shorter deck-height block. Translating motion from the pushrods to the valves is a set of T&D Machine Products 1.70:1 ratio shaft-mounted rocker arms.

The valvetrain on this engine is quite impressive. Using triple valve springs with "about 1000 pounds" of open pressure, along with T&D 1.70:1 shaft-mount rockers.

Keeping the cam and crankshaft in time is a billet steel, double-roller, 9-way adjustable timing set, while a locked-out MSD Pro-Billet distributor keeps the ignition timed right. An electric water pump frees up some horsepower while a Moroso billet three-vane vacuum pump helps the engine seal up.

Topping off the stout combination is a Pro-Filer Sniper single-plane intake manifold. Designed for a 4500-series carburetor, the intake has a 1-inch riser cast into the design. On top of that was a Holley Ultra-Dominator 1,350cfm carburetor to provide all the Renegade Racing Fuels 112-Plus race gas this beast should need.

The Pro-Filer single-plane intake manifold is a beast, with a built-in 1-inch spacer on the Dominator flange. So it was quite surprising all around when an additional 1-inch spacer made significant gains.

With everything together, a few initial break-in runs were performed and some early data gathered. Then, just to see what would happen, since the Pro-Filer Sniper intake has a 1-inch spacer built-in, they added another one-inch open carb spacer to see what would happen and were immediately greeted with another five horsepower.

With an original goal of making 1,000 horsepower for $20,000, this engine surpassed it. Looking at the dyno sheet, it’s not some trickery to get a magic number, the curves look quite solid, with final peak numbers of 1,053 horsepower and 834 lb-ft of torque.

The team complete the tuning session with the spacer attached and ended up with final power numbers better than the customer was hoping for. 1,053 horsepower at 7,300 rpm and 834 lb-ft of torque at 5,700 rpm. 1.81 horsepower-per-cubic-inch is nothing to sneeze at, especially when you consider the whole engine came in under $20,000 and used all off-the-shelf parts.

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About the author

Greg Acosta

Greg has spent seventeen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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