In this fifth part of our series on building an IMCA stock car, we move to the engine department. We will locate and mount the engine, transmission, and radiator. Also, we’ll be using a unique tranny/torque converter setup. The radiator is a narrow, one-row, down-flow type. Unusual, but logical.
Transmission and Converter
This car will use a torque converter and a Powerglide transmission from Mike’s Transmissions. This is the result of several discussions with Mike Stewart about trannies and converters.
The IMCA stock car is a nose-heavy animal. In the building process, one should make every effort to keep weight off the front. One problem with not having enough rear-weight percentage is wheelspin off the corner. A good driver can compensate somewhat by rolling into the throttle instead of slapping it wide open.
That said, the right torque converter might help with this situation. And Stewart has come up with the right one. He had an 8-inch converter, and this isn’t a drag-race unit, either. It has been specifically built for circle track racing.
“This converter has the lowest stall speed possible for its size and for the size of its components. Its slip percentages are close to a stock unit,” Stewart says.
He has done quite a bit of machine work on the inside to achieve these results. The unit bolts directly to a Chevy flexplate.
It weighs only 22 pounds, which gives up some weight to a coupler that weighs 6 to 8 pounds. However, a stock converter weighs about twice that much. Be aware that converters are usually measured by the turbine inside. This is an 8-inch converter inside, but its outside diameter is 10.1 inches.
I think there are several advantages to using a converter such as this one. Harsh throttle inputs are softened, which helps keep the tires hooked up, then torque is multiplied for acceleration. On restarts, the brake can be held with the throttle slightly open. This builds power in anticipation of the green. Another is the driver’s ability to keep the engine going in a traffic tangle. This could mean several places up on a restart.
The downside is a loss of inertia in on-again, off-again situations on the straights. This happens sometimes, but you drive off a corner twice each lap. I think the traction off the corner may be more important.
The converter is installed in front of one of Mike’s modified Powerglide units. The company makes a lot of Powerglides for direct couplers with internal valving to match. However, this one is set up for a converter. It can be driven just like a street machine—put it in gear, hold the brake, and drive off when you are ready. This tranny still has the good, strong racing parts, input shaft, clutches, and so on, just like the ones for couplers. All in all, it’s a reliable unit.
Stewart cautions against using a coupler with a Powerglide, which will race in low gear rather than high. “When using the low-gear clutches to move from standstill and also to pull under power, even the best clutch life is short, maybe six or eight races,” he says. “A converter will solve this problem.” This might be a good reason for choosing a 9-inch Ford rear, where gears as low as 6.50:1 can be found.
The downside is a loss of inertia in on-again, off-again situations on the straights. This happens sometimes, but you drive off a corner twice each lap. I think the traction off the corner may be more important.
The converter is installed in front of one of Mike’s modified Powerglide units. The company makes a lot of Powerglides for direct couplers with internal valving to match. However, this one is set up for a converter. It can be driven just like a street machine—put it in gear, hold the brake, and drive off when you are ready. This tranny still has the good, strong racing parts, input shaft, clutches, and so on, just like the ones for couplers. All in all, it’s a reliable unit.
Stewart cautions against using a coupler with a Powerglide, which will race in low gear rather than high. “When using the low-gear clutches to move from standstill and also to pull under power, even the best clutch life is short, maybe six or eight races,” he says. “A converter will solve this problem.” This might be a good reason for choosing a 9-inch Ford rear, where gears as low as 6.50:1 can be found.
The fuel pump is the limiting factor to rear-engine placement. In this case, you are not trying to get the engine low in the chassis. Lower it only enough for the air cleaner to clear the hood. IMCA doesn’t allow any holes in the hood. I like to leave a minimum of 1/8-inch clearance between the fuel pump and the crossmember; more is better, though. Check distributor-cap clearance with the firewall. Also make sure the left header can be removed after the engine is bolted in.
The next step is to make the part of the engine mount that welds to the frame. Weld a ½-inch nut in the end of a piece of 1-inch tubing about 6 inches long. Two pieces will be needed—one for each side. When the engine is placed to your satisfaction, these will be cut accordingly and welded to the frame. The steel mounts on the block will rest on top of these tubes and bolt in. Tack-weld everything until you are sure of the final placement. It may also be necessary to relocate the mounting holes in the rear crossmember.
The Radiator
Chris Paulsen at C&R Racing built the down-flow radiator for this car. Its outside measurements are 20x 27 inches, and guess what? It has only one tube, but that tube is almost 1½ inches wide. Chris was an Indy race-team chief mechanic before he started this business. Fabrication is topnotch. Unlike some, there is no epoxy in the tube-to-tank joints in his radiators. Chris’ are aluminum tubes to aluminum tanks. This type of construction can survive more tweaking around under impact and cools better, too. This radiator weighs just 10 pounds.
This installation is unusual because the radiator stands on end to become a down flow. The narrow dimension allows the radiator to be placed more to the rear. It fits between the steering box and the frame on the other side. Keep at least a ½-inch clearance between the radiator and the fan. Remember that we are trying to reduce front weight.
To gain hood clearance, tilt the radiator slightly forward at the bottom. Check fan clearance again. A short water pump is necessary.
Using 1½x.095-inch tubing, fabricate a wide U-shape piece. This will form the bottom radiator mount and connect the frame horns together. Make it 34 inches wide (outside) and 7½ inches tall. Trim to fit. You should have the same ground clearance as the front crossmember. The mounting plate for the radiator welds near the bottom, parallel to the ground. Brace the tubing mount with a 2-inch triangle on each side. Locate the radiator so it barely clears the hood.
The upper mount consists of 1-inch tubing in a U shape from the top of the grasshopper bar on one side to the other. A short piece of 1-inch pipe, facing forward, forms a socket for the mounting bar. One-inch-wide tubing fits into 1-inch pipe, which has a 11/8-inch inside diameter. These tubing sockets are welded to the top of the grasshopper bars. Now the radiator can be removed to service the engine without disturbing the shroud. Engine removal is easier, too. A smaller radiator also holds less water. Thus the light and efficient C&R unit takes some weight off the front end. Moving it back will give more protection when the driver becomes aggressive.
Since these cars run on gasoline, not alcohol, a good fan shroud is always desirable. But it becomes imperative when using a small, light radiator. I have built many shrouds from .024-inch aluminum. It is sometimes available at hardware stores, but only in 50-foot rolls. Ask someone in the home-siding business or a race shop to give you some scraps.
Fit the shroud to the fan with about 3/8-inch clearance all around. Make it fit tightly to the radiator. Fewer air leaks mean more air through the radiator. Some snips and pop rivets are all you need. A hint: Make a mock-up with cardboard and tape, then transfer everything to metal.
With these parts fitted and welded in place, it is time to take a break for this issue. I’m going to paint the interior of the car and the underhood area before any final installations. Next month, we will spend our time on the engine package.
Update
I have two updates to last month’s story on the cockpit. I spoke with Virgil Brown of M&R Products. He told me not to worry about the Y-type shoulder belt stretching. It is rated for 9,000 pounds. He said that in the past, some racers disliked Y-belts because they were sewn together at the crotch joint. No longer true, Virgil says. All his Y-belts are double-looped and can’t come apart. He still likes double belts and says you can’t get too much safety. My preference for double belts comes from having a Y-belt mounted too close to the driver. The Y would chafe the back of the driver’s neck.
Roger Mealey of QA1 says his company makes the same shocks described in the January issue, with stock mounting ends. These are rebuildable and revalvable and about $75 each, $25 cheaper than the rod-end mounts.
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