Homegrown Horsepower: 446 Cubic Inch Mopar Built Out Of Necessity

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An awful experience with a local engine builder who took him for $3,000 and then declared bankruptcy almost forced Ohio native Michael Clanton out of the sport he loves. But the story actually starts a few years earlier, when a divorce and subsequent need to “stay out of the bars”, in his words, pushed him into playing with cars to occupy his time.

The retired Lakewood (Ohio) Public Works employee needed a way to blow off some steam and have fun doing it.

Michael Clanton and his mean Mopar.

Michael Clanton and his mean Mopar.

“I got my 1969 Plymouth in 1988. I put in a stock 318 to get the car running but soon wanted more, so I went to the local community college in Cuyahoga County, Ohio, to take the Advanced Auto Technology program. I learned over a three year period to build an engine on my own,” says Clanton.

While paying child support for his daughter, funds were limited, so he planned out a build and planned his budget to match the build.

“I gradually got out to the track running 12.30s at a race weight of 3,900 pounds, and went through many parts additions,” he explains.

And then the budget was busted to purchase what he calls his “dream part”, a Blower Shop 8-71 roots-style supercharger. This necessitated a complete revamp of the program to upgrade the engine to match the newfound power.

Bottom and top end views of Michael's engine.

Currently, the big-block Mopar beast relies on a Koleno Performance 4.800-inch bore space iron block with a 10.725-inch deck height, siamesed cylinders, and cross-bolted mains secured with ARP main studs. The 4340 forged 440Source crankshaft is internally balanced and uses a 3.750-inch stroke. Combined with 6.760-inch Eagle forged steel H-beam connecting rods and Wiseco pistons, the engine now displaces 446 cubic inches.

Machine work was performed by Koffel’s Place in Huron, Ohio, and assembled by Clanton himself.

Listen to this blown big-block Mopar howl on the dyno!

Of course, the big boost from the supercharger required an upgrade in the induction department. Edelbrock Victor standard-port aluminum cylinder heads that have been hand-ported by Koffel’s Place to flow 355/235 at .650-inch lift. Stainless steel valves measure 2.190-inch on the intake and 1.810-inch for the exhaust. SCE‘s copper gaskets seal the heads to the block.

The Edelbrock cylinder heads have been ported by Scott Koffel of Koffel's Place in Ohio.

The Edelbrock cylinder heads have been ported by Scott Koffel of Koffel’s Place in Ohio.

Air in and out of the cylinders is handled by a custom Comp Cams camshaft with lift figures of .646-inch on the intake side and .631-inch on the exhaust side, with duration measuring 260 degrees intake and 269 degrees on the exhaust at .050-inch lift. The rest of the valvetrain consists of Manton 3/8-inch pushrods and Harland Sharp 1.5:1 roller rockers.

Checking rocker tip adjustment of the Harland Sharp roller rockers.

Checking rocker tip adjustment of the Harland Sharp roller rockers.

The Blower Shop 8-71 is set up to deliver 14 pounds of boost currently through a 63-tooth crankshaft pulley and 59-tooth supercharger pulley. Ignition is handled by an MSD 7AL-2 that sparks NGK R5671-A plugs through a set of Firecore50 8mm plug wires from longtime friend Rick Gorski.

Fueling comes from a pair of 1250cfm Holley Dominator carburetors featuring three-circuit operation.

One of the things that caught our eye when looking at the combination is the Blower Shop air-to-water intercooler that’s situated underneath the supercharger – an item rarely seen on automobiles, as they are much more suited to marine applications that have an unlimited water supply.

Clanton tells us that in the last ten years, he’s only seen one or two other vehicles using this setup.

Here you can see the intercooler underneath the supercharger. The water feed line is at left.

Here you can see the intercooler underneath the supercharger. The water feed line is at left.

dyno

“The intercooler helps to stabilize and control any heat variance that builds up in between rounds,” he says. “It’s more consistent with this setup.”

The car does fall off a little bit if he’s forced to round-robin it during an event, but he feels that the dropoff is much less than if there was no intercooler at all.

Tuning a blown and intercooled engine isn’t as difficult at it might seem.

“I approached a local old-timer here in the area and asked him what I needed to do with the carburetors. He recommended to square jet it and block off the power valve and it should be steady, and that’s been my basis for tuning all this time. I barely even touch the carburetors since I’ve gotten them dialed in,” explains Clanton.

The end result of Clanton’s assembly skills coupled with Koffel’s machine work is 1,152 horsepower at 7,000 rpm and 932 pound-feet of torque at 5,100 rpm.

As an aside, a chance meeting years ago with Scott Koffel of Koffel’s Place blossomed into more than a business relationship between machinist and customer – it turned into a friendship that had Koffel invite Clanton to be an integral part of the team that services Koffel’s ‘Lake Erie Monster’ Top Dragster at bracket races all over the Midwest, which he’s done for the last decade.

“I’ve built a few engines for myself, and a few for friends; I assemble, tune and race my own stuff,” says Clanton. “I’ve also assembled the engine for the Lake Erie Monster twice now under Scott Koffel’s supervision.”

Thanks for sharing your engine with us, Michael!

If you’re interested in submitting your garage-built engine to Homegrown Horsepower, send a few quality photos and the details to [email protected].

About the author

Jason Reiss

Jason draws on over 15 years of experience in the automotive publishing industry, and collaborates with many of the industry's movers and shakers to create compelling technical articles and high-quality race coverage.
Read My Articles

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