IMCA Stock Car: March 2001: Installing the Engine

No stock car is complete without an engine, and this car has one from JR Motorsports. The new 383-cid Chevy arrived by truck at my workshop. Before you buy a crate motor, make sure you have a way to unload it.

Most trucks don’t have lift tailgates. My old engine hoist has a tall enough reach. It snatched the engine away and hustled it inside for a quick inspection.

At the beginning of the engine parts selection for this project, I talked with several people at JR Motorsports. I didn’t tell them I wanted certain things in the engine. Rather, I said, “From your experience, you see what works. You tell me what I need.” We then discussed the special needs of this class with the mandated Holley 350 carb. Port size, cam specs, compression, expected rpm, and the carb itself were included. I felt I was in good hands.

Powering Up

The genesis of this motor is a 350 four-bolt block, which was cleaned and inspected before other work began. The main caps were carefully checked for fit. They should be snug in the block without bolts. Obviously, there should not be any cracks nor should the cylinder walls be too thin to stand a .060-inch overbore.

From cleaning and inspection at JR Motorsports, the block went to the machine shop, where Kevin Stoa walked me through the process. The first step was to align-hone the main-bearing bores. This ensures a straight set of holes in which the crankshaft will run. More importantly, bearing crush or clamping pressure on the bearing halves is corrected. JRM fits this to the middle of the General Motors tolerance—not too loose, not too tight, just right.

Next, the block was set up on a Storm-Vulcan machine to lightly machine the decks. This procedure provides a flat surface for the cylinder heads to make contact. The distance from the deck to the centerline of the crank will now be the same on all cylinders: 9.005 inches. This helps to equalize compression in them.

All of JRM’s boring operations are carried out on a Berco boring machine. Once the block is properly aligned, all cylinder bores will be square with the crank centerline. The pistons and bearings will run straighter and have less friction. Old blocks release their stresses over time, and metal moves around. After removing the heavy cuts in the Berco, our cylinder bores were finished on a Sunnen CK-10 hone. Kevin used a 400-grit stone for the final finish. He says the moly rings seat just fine with this finish. JRM’s Hines Balance machine worked the kinks out of all the bottom-end parts.

With the block ready for assembly, Dick Boyer, head of JRM’s engine department, laid out all of the parts. A new, 400 Scat crank settled into Clevite 77 bearings. The main caps were installed with ARP bolts and torqued (oiled threads) 70 pounds. The endplay of the crank measured at .008 inch.

Then 4130 Scat rods were installed in Federal Mogul/Speed Pro hypereutetic pistons. According to Boyer, these rods, which are slightly lighter than stock, are stronger and come balanced within 2 grams. The 4.060-inch-diameter pistons have a .200-inch dome. Moly rings were fitted to these pistons. As the name implies, the rings have a moly insert for sealing, wear, and friction management.

At this point, the block was upended, and the piston/rod combo was installed. Boyer was careful to cover the rod bolts with plastic tubes to preclude the rod-bolt threads that mark the crank. After all the rod caps had been torqued to 45 pounds, the rod slide clearance was sufficient at .022 inch. An 8-quart Kevko stock car pan covers a new stock oil pump with a high-pressure spring. This pan has three gates and an oil scraper to keep oil in place.

With the bottom end buttoned up, it was time to install the cam. The cam bearings had already been installed. Still, Boyer checked the alignment of the oiling holes before proceeding.

A JRM No. 106 cam was chosen. It has a .050-inch duration of 252 intake and 255 exhaust degrees. Lift is .544-inch intake and .553-inch exhaust. Lobe separation is 102 degrees. After giving the cam a liberal coat of cam lube, it was inserted with care, so as not to scar the bearings with the edge of a lobe.

In the context of cam installation comes one of the important parts of making power. You studied the specs and bought a cam just right for your application. If you don’t degree it during installation, all your effort went out the window. Most of the time, timing gears and chains go together, but you won’t know unless you degree the cam.

Boyer carefully degreed the cam in our motor. He selected two different positions in the multi-keyed sprocket, then the cam was exactly at its recommended four-degree advance.

All the lifters were dropped in place and a retainer plate installed. If a rocker or pushrod breaks, the plate keeps a lifter from jumping out of its hole, drastically reducing oil pressure. This plate is a thin steel sheet with holes for the pushrods. It’s installed in the valley between cylinder banks, where spring strips hold it in place. It’s cheap insurance With the block finished, attention shifted to the heads. JRM decided on a set of Dart Iron Eagle heads. Due to the small carb requirement in this class, Boyer chose a 180cc port runner. A larger port, such as 215 cc, would slow the flow. When this happens, fuel and air separation may occur, causing poor low-speed performance.

Boyer asked Stoa to mill the heads to a point where the combustion chambers would be 60cc volume. With the decked block, .200-inch dome pistons, and a steel-shim head gasket, Dick figured the compression to be a respectable 13:1. The heads were assembled with PRC 2.02-inch intake and 1.6-inch exhaust stainless valves. Dual springs were used, which gave 125 pounds of seat pressure with 305 pounds open.

The heads were installed with ARP bolts. Squeezing a .018-inch steel shim gasket picks up compression by about half a point over a composite type. A word of caution: Without a true deck and head surface, as on this engine, sealing problems may occur. Again, using oiled threads, Dick torqued the heads to 65 pounds.

JRM used a two-barrel manifold for this application. Remember, this is with IMCA’s newly mandated small 350 Holley carb. Kirk Niehouse of IMCA tells me the engines are losing about 50 hp with this carb versus the modified Rochester. JRM also removes the divider under the carb and shapes the openings between the two manifold planes.

Dyno Day

Dyno day arrived. The “little engine that could” was hoisted onto JRM’s engine dynamometer. Headers were installed with exhaust gas-temp probes on each pipe. Testing began with the cheaper of the two 350 Holleys allowed by IMCA. The engine was run for a few minutes then shut down. Valve clearances were rechecked and set to .016 inch at the 1.5:1 stock-type long-slot rocker arms. No oil leaks were found, so our engine was started again, and the power search was on. Thirty-six degrees of ignition advance seemed to be the magic number with Performance Distributor’s DUI unit.

There are two Holley 350 carbs allowed by IMCA—a street model and a race model. There is about a $100 difference between them. Out of the box, Dick found the street (cheaper) one to be 4hp ahead. However, with a bit of adjusting, tweaking, and jetting, the race model proved to be superior by some 15 horses. The final power numbers showed 341hp at a peak of 5,000 rpm. Horsepower numbers stayed above 321 from 4,500 to 6,000. Above 6,000, the small carb really begins to choke down the power. Torque peak is 3,500 rpm. Torque numbers begin to build rapidly from 2,800.

Dyno’d and run in, the engine was bolted to a stand and boxed for its trip to Texas. Before it arrived, Steve Bort at JRM called and told me about some new cranks that have been coming through without a dowel pin at the flywheel flange. He said to be careful when installing the flywheel and to align the holes where the pin was supposed to be. This is necessary with the 400 counterbalanced flywheel. Fortunately, mine had the pin in place. Now I could proceed with the installation.

Installation Time

When the engine arrived, we all set to work getting it in the car. A purchased set of flexplate bolts was too long and touching the block when tightened. Be sure to check the distance the bolt extends through the crank flange.

With the right fasteners, the flexplate was installed. Next, the tiny 8-inch torque converter from Mike’s Transmission was bolted in. The 22-pound unit has close to stock stall speeds. It should be right on for the dyno numbers this engine produced. Mike’s Powerglide easily fitted up to the block. Yes, the engine/trans unit was assembled before installation in the chassis. This is one of the advantages of not having welded-in bars in front of the engine.

The mini-starter, provided by Dave Poske Performance, snuggled right in between the pan and the block. I spoke at length about header selection with Doug Schoenfeld of Schoenfeld Headers. His A/R headers (No. 184) were deemed proper for this application. They tucked in nicely so the engine could be positioned to the left. These headers have 15/8-inch tubes for the first 6 inches from the exhaust port. Then a 1¾-inch tube continues to the 3-inch collector. This step in sizes slows the reversion of gas flow back through the open exhaust valve.

A DUI ignition unit was installed after the engine was put in place. No more broken caps for me. I spoke with Steve Davis at Performance Distributors about the ignition needs of this installation. He built an HEI-based unit with his components. A module with a cap, coil, and rotor were assembled on a cleaned and checked core. Its nylon screws keep the rotor secure. Eliminating the metal screws makes it tougher for the super-sized spark to jump to ground.

Steve built in an advance curve, which is fully advanced at 2,600 rpm. That should be enough for the torque converter and the dyno numbers. I also used Performance Distributors’ Live Wires. Good wires are necessary to get the spark to the plug, not somewhere else. The Live Wires offer a further degree of protection with an outer Kevlar sleeve. This allows the harried racer to let the wire fall across a hot header for a few races and still have a good wire.

Once we had the engine in the car and everything in place, it was time to build a fan shroud. The beautiful, single-core, down flow, C&R radiator was tightened in its mounts with rubber bike-tube sections. I made a cardboard mock-up, then transferred everything to .025-inch aluminum. Pop rivets hold it together, and nylon tie-wraps hold it to the radiator. The ties go between the radiator tubes.

I ran a 3/8-inch copper fuel line from the 8-gallon ATL fuel cell to the stock fuel pump. The pump can easily feed this engine. Just get a new one, and don’t run trash through it (i.e. use a good filter). I ran the fuel line under the body inside the right-side framerail. If you put it inside the car, IMCA officials suggest encasing it in pipe or conduit.

Now, the engine is in and running; the carburetor is carbureting, the cam is camming, the rockers are rocking, and the pistons are working, too.

Next month, we’ll tie up all the loose ends. We’ll get the body panels in place and install the Performance Bodies nosepiece. That will finish the car.

Sleepy can be reached via e-mail at sleepy.gomez@worldnet.att.net.

Click Here to Return to the Building an IMCA Stock Car home page