Meticulous Mouse For The Mule

After building and running practically every engine known to the Bow Tie world, you might be wondering why I would build a plain-Jane-looking small-block Chevy to power the wacky conglomeration of one-off prototype parts that make up The Mule. Have you ever needed to find shaft-mount aluminum rockers for a one-off splay-valve, small-block Chevy in the middle of Missouri? No? Well, I have, and they don't exist.

Through life's painful lessons, I have learned that the oh-my-gosh, hood-raising factor of an "unobtainium" engine is a certain kind of cool, but if the car is going to be really driven, nothing beats the simplicity and power potential of a small-block Chevy. I think it brings on the thought of a subtle cool, which is what this engine represents. It might look like a regular small-block, but this engine is loaded with its share of charm.

Take the beautifully created GM Motorsports aluminum engine block, the lightweight Scat crank (only 47 pounds!) and the "fully CNC-machined everything" of the Chapman cylinder heads. These and the rest of the engine parts have benefited from years and years of refinement on the racetracks around the country and combine to produce exciting performance with minimal weight.

THE BIG DECISIONS
The engine I'm building is 400 ci to provide the maximum power potential in the small-block architecture. I have built small-blocks of larger cubic inches, but to go much bigger than 400 ci requires expensive custom parts and modifications to the block and other components, all of which I'm steering clear. That's not to say the Scat crank and rods aren't trick--they are--but they're also sitting on the shelves of many speed shops, ready to ship.

On the street, I feel having an engine that will rev quickly is just as important as making big power. For that reason, the reciprocating components have been selected to minimize weight but without getting into ridiculous territory. I really drive my cars hard, so the parts need to take serious abuse without a lot of maintenance. The crank, rods, pistons, rings, and valvetrain were combined to provide the least mass and frictional losses as possible in the system without compromising durability.

The fuel mixture will be controlled by a port-injected, throttle-body controlled EFI setup similar to systems I have used on previous project vehicles. The preciseness of fuel injection helps the engine to be crisp, powerful, and repeatable through practically any driving situation I can throw at it, which is very important to me.

I have assembled engines before, but like body and paintwork, I prefer to have a specialist do the work since they develop wisdom based on experience (which usually involves breaking parts!). In this case, I'm having Kurt Urban at Wheel to Wheel (Warren, Michigan) prep the parts and assemble the engine. Wheel to Wheel does many engine and vehicle buildups for General Motors, so I figure they are qualified to throw together my small-block. This is also the shop that built the 427 that PHR Editor Cameron Evans and I flogged on the '00 One Lap of America. Urban applied some of his knowledge about building an aluminum block engine for the street-stuff I didn't know, which made me happy to have him doing the work.

As much time as I spend building my cars, you'd think that's what I really love--but it isn't. My favorite aspect of building fun cars is driving them. While this engine is light and subtly trick, it should act a lot like a "driver." The only special treatment it will require will be on cold mornings. Urban has said it will need extended warm-up time on cold mornings to ensure the aluminum block is up to temperature (the bearing clearances are tight to take into account the expansion of the block). Other than that, I plan to drive it like a rental car!

CNC Heads, A Computer is your Friend

If you've never seen a five- or six-axis, CNC-machining center chiseling away on a cylinder head, you don't know the magic of CNC cylinder heads. As far as I'm concerned, this is some of the most awe-inspiring racing technology available--the technology will improve the performance of practically any engine. The computer numerical control (CNC) machine can be programmed to do multiple machining processes, which is what Chapman does (and used to have to do by hand, with repeatability only in the direct hands of the porter!)

The Chapman 15-degree heads start as raw GM 18-degree castings (originally designed for the top ranks of NASCAR stock car racing, before they converted to the new SB2.2 design a few years back) with the head mating surface faced to locate the head in the CNC machine. From there, the intake and exhaust ports and the combustion chambers are machined to their final shape in the CNC machine. Many of Chapman's products, like these 15-degree heads, are now available through Scoggin-Dickey. I got these heads because I feel they will make excellent power due to the fully CNC-machined ports and chambers and they can take the abuse of hard street driving.

Chapman creates the 15-degree valve angle by "rolling" the head 3 degrees before machining it in the CNC. This process raises the intake ports up about .150 inch compared to a stock head, promoting airflow both into the intake port and past the intake valve. To mate the intake and heads, a set of spacers are needed to get proper port alignment of the GM 18-degree lightweight manifold.

TOP 5 ENGINE-BUILDING "D'OHS!" (OR "DOUGH")

1. Starting without enough dough.
2. Making compromises due to slow part delivery or lack of dough.
3. Taking more time then expected (and time is dough).
4. Changing the plan midstream and spending lots of extra dough.
5. Always costing more dough than you expected.

A Little Tip
Oil Pan Red Alert! I had the wet sump Moroso road-race oil pan powdercoated, and the coater sandblasted the pan! Not good. Don't let anyone get any loose abrasive near the internal components of your engine pieces! Luckily, Urban is good enough of an engine builder that he caught this problem and spent an enormous amount of time flushing the abrasive out of the many trap doors and kickouts of the pan to prevent the engine from eating itself once running.

A DAY ON THE DYNO
Dyno time is usually sold by the day or hour, so here's a breakdown of the Mule engine's day on the dyno.

7 a.m.
Roll engine into dyno room. Connect flywheel, water, oil, electric, etc.,
8:30 a.m.
Spin engine to determine if all connections are working properly. Build fluid lines and adapt various systems to dyno to get everything working right. Load initial calibration into EFI controller.
9:30 a.m.
Fire engine to check for leaks, etc. Fix leaks. Refire. Warm up engine.
10:15 a.m.
Make initial power pull. Begin tuning calibration by stepping to rpm, holding it there, and setting air/fuel ratio and ignition timing based on O2 signal, manifold pressures, and power output.
Noon
Time for a full pull! Continue refining air/fuel ratio and ignition timing and retesting to determine max power production.
2 p.m.
Swap parts (throttle-body spacer: lost 5 hp; low dB mufflers: down 16 hp, but 6 dB less, etc.) and retest.
4 p.m.
Whew. Remove engine from dyno.