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!

While it looks like just a...        read full caption While it looks like just a small-block Chevy, this potent 400ci engine is about 170 pounds lighter than a production small-block. It'll make a tad over 600 hp, run on pump gas, and be docile enough to drive to work (thanks to the F.A.S.T. EFI system).

If you're wondering why you...        read full caption If you're wondering why you would run an aluminum block, here's the reason--they're light! It weighs only 92 pounds, while a GM Bow Tie cast-iron block is 202 pounds. The aluminum block comes with doweled, four-bolt main caps and is meticulously machined for GM by Schwartz Machine.

One of the details that Kurt...        read full caption One of the details that Kurt Urban is very clear about is using a grinder to remove any casting flash or parting lines on the inside surfaces of the block. Aluminum expands at twice the rate of iron and is less rigid, so the metal in the block is experiencing a lot of forces. Any sharp points in the metal have a higher chance of being a "stress riser" or a point where a crack would begin. These stress risers are more critical here than with an iron block. He also doesn't like to have sharp edges that might cut his hand when he's building the engine!

Since the aluminum block "moves...        read full caption Since the aluminum block "moves around" and "grows" a lot as with an increase in temperature, the tolerances like those for the main bearings are tightened to reduce the amount of oil flopping off the crank. For an aluminum block, Urban sets the main bearing clearances at .0018 inch, versus .0025 inch on an iron block (this is on everything but the rear main). On the rear, he runs .0025 inch versus .0030 inch with iron. Urban told me, "Stielow, you'll shift this thing at 7,000 rpm, and I want a little oil on the thrust bearing to prevent a problem." We've brought him back problems before! Here's a tech tip: Urban always line hones and measures the mains with the oil pump bolted to the main cap. "It's amazing how much the torque of the oil pump stud will pull the main out of round," he says, "So I always bolt up a dummy oil pump before doing that machine work."

Another step in maintaining...        read full caption Another step in maintaining oil control is preventing the oil from pooling in the valve cover (which keeps it from being sucked out the breathers). To do this, Urban recommends threading the two feed holes to the lifter oil gallery and installing these .060-inch restrictors. The center hole is the feed from the oil pump. The only risk in doing this is running the valvesprings short of lubricating and cooling oil, but I'm running special valve covers from Billet Fabrication that spray a light mist of oil directly on the valvesprings, so there are no worries. These were developed in NASCAR and are used on all forms of racing machines now. By the way, I chose to not run one of these restrictors in my PHR 427 stroker--which's why it blew up at Sebring in the One Lap! I learned my lesson there....

Urban adds these additional...        read full caption Urban adds these additional oil feed holes (drilled .125 inch) on each side of the main bearing to the road race motors he builds to insure there is sufficient oil to the rod bearings. The location of the hole on these bearings needed to be lower than what he would normally put on his cast-iron bearings as the oil slot in the block didn't go as far along the side of the bearing.

Even with a lightweight crank,...        read full caption Even with a lightweight crank, the counterweights on the Scat crank hit the extra thick main webs (the aluminum has less strength than the iron, so the webbing is needed to be thicker). Urban solved this by having the crank counterweights machined by John Kominski to remove about .120 inch at the very edge of the main web-face. This created a 5-degree angle on the counterweights. Kominski then balanced the rotating assembly. To finish off the clearancing, the webs on the block were slightly reworked with the grinder. When completed, there was .060-inch clearance between the crank throw and main webs of the block.

To duplicate the stresses...        read full caption To duplicate the stresses on the block when it was initially machined and to ensure round bores, etc., a very specific torquing procedure is specified. Even the thread lubricant provided by GM must be used. Urban suggests following this exactly: "GM spends unbelievable time and money to get the most from this equipment--the least we can do is follow their instructions on torquing." Notice how Urban has written notes to himself on the block regarding the tolerances he saw on the mains during his initial mock-up of the parts in the block.

The Chapman 15-degree aluminum...        read full caption The Chapman 15-degree aluminum cylinder heads were a late choice after I spoke with the pros at Scoggin-Dickey (I was originally going to run 18-degree heads). After mocking the heads on the block with a piston/rod/crank combo in it, Urban found he needed to open the radial valve clearance .080 inch for the intake on the Arias pistons (because they were built for the 18-degree heads). Once that was done, he polished the surfaces to eliminate any of the machining marks.

Here's another quick tip:...        read full caption Here's another quick tip: Never install a part straight out of the box. Even if the part looks super clean, random pieces of packing materials and cardboard particles can clog an oil passage faster than you know. Whether they're straight out of the box or just back from the machine shop, Urban lets the solution of a solvent tank pour through the passages of parts for a long time, then scrubs everything thoroughly to make sure any trash is washed out.

I have used Arias pistons,...        read full caption I have used Arias pistons, Speed-Pro rings, and Scat rods in the past and must say they have never let me down. On the pistons, notice they are a lightweight design but the ring package doesn't need a spacer ring to support the oil control ring--a common crutch used when the wrist pin bore intrudes into the oil ring land. Not having this reduces piston weight and simplifies the ring package (which is made up of .049-inch/.049-inch/3mm rings from Speed-Pro).

Urban has spent many years...        read full caption Urban has spent many years building engines and one facet of knowledge he has gained has been on where to place the gaps of the rings on the pistons--a process known as "timing the rings." You see the Top Fuel guys doing this right before they stick a piston in a bore on TV. For this engine, Urban placed the ring gaps for the top ring and the oil expander gap facing the non-thrust side of the piston, and the second ring gap and the oil rails are clocked on the thrust side.

Urban spends a lot of time...        read full caption Urban spends a lot of time honing the cylinders to achieve a very specific diameter and surface and then washes the block thoroughly. He grinds the ends of the rings to get the piston rings gapped for each cylinder (this engine has gaps of .018 inch on the top, .022 inch on the second), installs the rods, uses a ring spreader to install the rings on the pistons, lubes the piston-thrust faces with non-detergent 30-weight motor oil and slides them in. Notice on each piston he has written the cylinder number and thrust face.

Urban is a big believer in...        read full caption Urban is a big believer in using lubricants designed for specific applications. The assembly lube is liberally poured on the bearing surfaces and wiped across the face, and ARP moly thread lube is slathered on the rod bolts. Torque readings can easily be fooled by using a different lubricant than the component manufacturer recommends so it's important to use the same lube the manufacturer uses--not doing this could lead to inaccurate torque readings and the disastrous loosening of fasteners after the engine is running.

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.

There is no other choice than...        read full caption There is no other choice than a solid roller cam for this type of engine because of the large cross-sectional runner--racing-bred intake ports get in the way of the standard pushrod location. To get the pushrods pointing straight up again, the rocker arm is offset .450 inch and the pushrod hole is offset another .180 inch in the lifter. These offsets increase the side thrust, which hydraulic lifters weren't really designed to handle.	There are many slick features...        read full caption There are many slick features on the GM aluminum block, but one of the most visible components are these threaded, anodized, and O-ringed freeze plugs located all over the block. They are tightened in place with large diameter allens and seal the engine tightly.	The Crane cam is degreed "straight...        read full caption The Crane cam is degreed "straight up," neither advanced nor retarded, and is held in place by a Crane billet roller timing chain. The cam sits in the bearings with a tight .0015-inch clearance (cold) to account for the aluminum block's expanding at twice the rate of an iron block. Compare this to the .0025-inch clearance Urban would run on a cast-iron engine to end up with the same clearance at operating temps. Because of this tolerance, I'll have to take a little time warming up the engine (to go to work!) on those cold Michigan mornings to prevent scuffing a bearing.
The aluminum block requires...        read full caption The aluminum block requires 1/4-inch-longer threads on the head studs (3/4 vs. 1/2 inch) than the cast-iron block studs to maintain the required torque rating. This is because the aluminum threads don't have the same load capability as the iron block threads. Notice all the different lengths and thread depths on the head studs alone! ARP is great in these situations as they can tell you what to use based on their experience.	The installation method Urban...        read full caption The installation method Urban is using (two box end wrenches clinching the blank portion of the stud) is neat, so I captured it for you.	This is not your everyday...        read full caption This is not your everyday small-block valvetrain, so a little massaging was required. Once mocked up on the engine, Urban discovered he needed to open up the passage with a grinder where the Crane 3/8-inch pushrods pass through the Chapman heads. Also, the Crower rocker stands and Crane spring buckets needed some grinding to allow room to tighten various head fasteners. This is a high-end valvetrain, but one that will easily handle 7,000-rpm run-ups and flow a lot of air/fuel, which is what I wanted.

Roller cams must be bushed...        read full caption Roller cams must be bushed very carefully to keep them from "walking" forward and back excessively in the block. They move around because roller lifters don't rotate around their centerline like flat-tappet lifters, which hold the cam in place. For roller-cammed engines, Urban spends considerable time choosing and machining a cam button, like these shown, to hold the cam between .012- and .020-inch clearance.	Since this head was designed...        read full caption Since this head was designed with big ports that have as few turns as possible, many components end up on top of each other--like the center head studs between the two middle cylinders. The only way to access these is to trim the valvespring seat buckets with a grinder--far away from the engine, of course! (NOTE: Every time Urban grinds or machines something, it is thoroughly cleaned before being brought back into the engine assembly area.)	The Crower shaft rockers come...        read full caption The Crower shaft rockers come with this setup system to shim the rocker stands for optimum geometry. When the "mock-up" rocker sits on the fulcrum with the valve stem tip at the top of the gap, the rocker pivot height is set properly. Unfortunately, if the valve stems are not exactly equal, a compromise must be made between the two valvestem heights--how do I know this? The Ti exhaust valve stem has a "cap" on the end of it to protect the tip from excessive wear, which threw off the heights.
Urban did his best to split...        read full caption Urban did his best to split the difference on the shaft height, and I learned an important lesson about parts selection. Notice how the offset in the lifters and rockers creates the space for the ports--slick, huh?	How would you like to reduce...        read full caption How would you like to reduce the noise from your performance exhaust by 6 dB for only 12 hp? I'd say them's good numbers! We ran the dyno with the entire Mule exhaust system, which was built by Stainless Works and will be thoroughly covered in a future story (cool stuff!), to fully replicate what the engine would experience in the car.	The intake manifold ended...        read full caption The intake manifold ended up being quite the wild, little player as it was completely ported by Flow Technologies and received electronic fuel injector bungs (in each port) and rail stands welded on by Force Fuel Injection along with many welded-on bungs to mount sensors and fluid lines. Notice how the fuel rails are both fed from the rear and have a return at the front--I think this maintains more consistent fuel flow to all the injectors versus the full loop (feed in one rail and loop around to return from other rail). I haven't run the nitrous setup--yet. I built a nitrous solenoid bracket from 2-inch angle aluminum, and we should be testing this on these pages in the near future.
To mount up to the 15-degree...        read full caption To mount up to the 15-degree heads, the mounting faces were first machined parallel to the heads by Flow Technologies.	Then, I created this 3/16-inch-thick...        read full caption Then, I created this 3/16-inch-thick aluminum spacer rail, drilled and tapped some 1/4-20 holes, and mounted the spacer pieces with countersunk Allen screws liberally dabbed with red Loctite(R).	To control the oil in the...        read full caption To control the oil in the top end of the engine, I'm using Billet Fabrication "oiler" valve covers. The covers are plumbed into the oiling system with these Earls -4 braided steel lines (left hand) to spray a light mist of oil on the valvesprings. This increases valvespring life while reducing the amount of oil in the top end of the engine. The right hand is pointing to the Y-fitting to feed both fuel rails. Notice that the MSD distributor was ordered with an electronic trigger output (small wires at top of billet housing) to give the fuel injection computer a reference of where the No. 1 cylinder is in the sequence of eight cylinders.
The Chapman 15-degree, CNC-ported...        read full caption The Chapman 15-degree, CNC-ported aluminum cylinder heads from Scoggin-Dickey are almost too nice to bolt on, but that's where they do their magic. I know the small-diameter, stemmed Ferrea titanium valves are a little overkill, but I like quick revving engines--and lightweight gear helps the engine "yacha, yacha" when you snap the throttle. The head gasket is a .041-inch Fel-Pro composite with a combustion fire ring (everyone calls them the "blue" gasket because they're blue, imagine that...).	Probably one of the more knowledgeable...        read full caption Probably one of the more knowledgeable EFI calibration tuners in the nation, Dave Henninger (left), runs the dyno at Wheel to Wheel with Kurt Urban (right). He calibrates every EFI motor that rolls through the shop (usually one a day), so his skills are flat-out scary. Just wish he was your friend! His basic attack is to first drop a "best-guess" calibration (from literally hundreds he has created) into the EFI controller (which Wheel to Wheel can email for a reasonable price). Then tune the engine based upon the O2 sensor reading of the air/fuel ratio, ignition timing, and manifold pressure at various rpm for maximum power and efficiency. The refinement of the calibration on the dyno is mainly for power production. Once the engine is in the vehicle, the "cal" is tuned for optimum driveability (startup/warmup, idle, cruise, accel/decel, etc.) with two people at the controls (one driving the car and another running the laptop computer). I have used this type of EFI on the last few cars I've built and know I couldn't go back to a carbureted vehicle--they are so nice once you get them dialed in. Carbs do make great power, however, and do so at the right price!	I used a GM factory, V-6 engine,...        read full caption I used a GM factory, V-6 engine, remote oil filter mount to relocate the oil filter to the front of the engine, and built a custom oil dipstick from 0.0.375-inch, 0.065-inch-thickness stainless tube. I'll show the dipstick creation in detail as the car comes together.

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.