The Bogwan Talks Tech-Anatomy of a Supermodified Push Start

Let’s go back to the early 60’s to the birth of supermodifieds. At the time, stock cars ruled most tracks in the northeast US. Being stock meant they were right off the street but modified for racing. However, they still maintained the clutch, transmission and electric starter of their stock street versions.

But in the Midwest and Canada, a revolution was taking place. Car builders were hungry for speed and knew that excess weight was not conducive to speed. But instead of just chopping up a stock car to make it lighter, they constructed purpose built race cars that were light weight by eliminating “frivolous” things such as starters, batteries, clutches and transmissions.

What was used back in the day was called a “dog clutch”. The term “clutch” is a misnomer because it contained no clutch in the traditional sense of friction discs and pressure plates, etc. It was a direct drive coupling that used a sliding, splined coupling that was actuated by an external lever in reach of the driver. When engaged, the splined coupling connected the output of the engine directly to the drive shaft. When disengaged, the splined coupling was slide away from the engine output shaft, allowing the engine to “free wheel” without propelling the car. This mechanism was contained in an enclosure that was smaller than a manual transmission. In most cases, the rear of the engine (where the bell housing would normally be attached) was attached to a flat torque plate that provided a means to mount the engine to the frame and provide a flat surface and mounting holes for the dog clutch. Smaller size, less weight and very little rotating mass made a supermodified with a dog clutch one quick race car.

A super with this configuration may be fast but how do you start it? With a stock car and a clutch, one can take the car out of gear and use the electric starter motor to crank the engine. Once started, the clutch is engaged to propel the car. You can’t do that with a direct drive car. Even if one were able to start a super while sitting still, you cannot engage a dog clutch while the engine is spinning and the drive train is sitting still. People have tried. It results in metal shavings and cuss words! Plus, with no transmission, there is no reverse gear. So, what does one do? Push start!

These Days-

So, let’s return back to the 21st century and explain the anatomy of a push start supermodified from start to finish.  Since the vast majority of my experience is at Oswego, I’ll explain the process from that point if view.

Ok, you’re in your pit stall, strapped in and ready to race. In order to go on the track, most tracks will have a designated push-off area that you must get to before you can fire up. While the car is out if gear, your crew will push you backwards out onto pit road. Normally, if a push truck driver sees this, they will pull out of their designated area and pull up behind the race car. It is a good idea for the crew to point the car as close to the direction of travel as possible so the driver doesn’t have to crank on the wheel too much (remember, the car is hasn’t fired yet, so there is no power steering. Cranking a steering wheel in a tight cockpit under these conditions is tough!) Plus, we don’t want a large angle between the push truck and the race car so the rear wing does no get damaged.

At this point, the crew’s duty is complete and it is between the driver and the push truck. The pit steward will direct traffic and tell you what lane he wants you in and where to stop. Once the car/push truck is in the proper position, you are queued up to go out on the track. For me, this is probably the most exciting time I can imagine!

However, there is still more prep work to do before we actually conjure up 800 horsepower. Up to this point, we have been “out of gear” so we can easily push the car into position. It is now time to couple the engine to the drive train. With a modern supermodified, the “dog clutch” action is located in the rear end if the car. It is still a sliding splined coupling but it is located in the housing of the rear end. Therefore, there is nothing between the crank flange if the engine and the drive shaft. The drive shaft goes directly from the engine to the rear end. This is a very lightweight, yet reliable method of engaging the engine to the driveline. On a side note, since the coupling takes place in the rear end, when the car is running, yet is out of gear, the driveshaft is spinning. This is a dangerous situation and the driver and crew must remember this.

A small lever arm (about 4” long) is mounted to the rear end housing and this lever is used to move the splined coupling. A cable is attached to this lever arm with the other end of the cable located in the cockpit with a “Tee” handle or some sort if lever mechanism which is within easy reach of the driver.  Actuating the cockpit lever will move the splined coupler into position and couple the engine to the driveline. Sometimes, the splines will not align and the coupler will not slide into gear. In this case, you can have someone gently rock the car (it doesn’t take much) to align the splines and engage the car.

Ok, we are in line, the car is in gear and we’re about to go on the ride of our lives! But first, two things must be confirmed: 1) the fuel must be shut off and 2) the kill switch must be in the “OFF” position. This allows us to control the start-up sequence.

The pit steward points to us and gives us the signal to go! The push truck will start pushing but will have a hard time getting going. You see, in order to produce 800 hp with alcohol, a supermodified engine has a high compression ratio, sometimes up to 14:1. Initially, the rear wheels of the super won’t even turn while the push truck is struggling to overcome the compression of the still lifeless engine. However, after a few feet, the motor will start to rotate. The driver generally can’t see the rear wheels to observe whether they are turning or not. For the first few feet, the car shakes like the space shuttle lifting off, but once the rear wheels turn, the shaking stops. During this time, I am observing the oil pressure gauge. When the reading snaps to 60 psi, I will turn the fuel on. We’re almost there! Now count: one-thousand-one, one-thousand-two, pull the kill switch and blast-off!

If all is well, I will raise a hand above the roll cage to tell the push truck driver that I am under my own power. Keep in mind that the above process takes only a few seconds while the car and push truck are going around a corner. You really have to be alert. But with practice, it becomes second nature.

The one thing that surprises me every time I start a super is that it idles at 60 miles an hour! If you’re firing the car up in the pits, you’ve got your foot on the brake trying to rein in 800 hp. But when you are on the track, the throttle response is so crisp, your eyes pop out of your head.

In-n-Out:It’s not just a hamburger joint-

We’re not done yet because we still have to come into the pits and park the car in our stall. After leaving the track and entering the pit area, a crew member will stand at your pit stall and point at you to make you aware of were you have to go. Believe me, when you’re strapped in and pumped full of adrenalin after doing laps at Oswego, coming into the pits can be very disorienting and I have actually missed my pit stall! Anyways, just before you are at your stall, you’ll give the throttle a quick pop while pulling on the gear lever. That little pop on the pedal will rev the engine just enough to allow the splined coupler to disengage easily. But just before you do that though, you want to make sure you are carrying enough speed to coast to your pit stall when you take the car out of gear. If not, the car will be sitting in the middle of the pits, in the way of all the other cars and your crew is pissed off because they have to come and get you. It’s reasons like this that I always have a full cooler of PBRs (wink, wink!) after the races to pacify my crew.

Now that we are in the pits, the engine is still running, but idling out of gear. If something needs to done while the engine is running, like ignition timing or checking for leaks, now is the time to do it. When it’s time to power down, we’ll shut off the fuel. This starves the engine and shuts it off with no raw fuel in the system to drip into the cylinders. Liquid fuel in the cylinders is bad news. Since a liquid cannot be compressed, if raw methanol is in the cylinder and you try to start the engine, it can’t compress the liquid but it sure will bend the piston rods! This is called “hydro-static lock” and is fatal to an engine. So do us all a favor and shut the fuel off to kill the engine!

If the driver uses the kill switch and not the fuel shut off to stop the engine, it is advisable that the crew “back off” the engine the next time the car will be fired up. This entails putting the car in gear while it is in the pit stall and having as many people as you can push the car backwards (remember, we are trying to overcome the high compression ratio of the engine. It takes a lot of man power to do this). This rotates the engine backwards and clears the cylinders of any raw fuel. One can actually see raw fuel spraying out of the injectors. After a couple of backwards rotations of the engine, the driver will take the car out of gear and the process of starting the engine begins anew.

Under severe hydro-static lock, the rear tires won’t even turn and you might need a push truck to push the car backwards while in gear to clear the raw fuel out of the cylinders.

If there is just a bit of raw fuel in the cylinders, the car can be push started but it may take some time for the raw fuel to makes it way out if the cylinders and allow the atomized fuel to fire the engine. This is one reason why it can take several tries to fire a super.

As far as a good push truck driver, I want the guy behind the wheel to be relatively gentle. I’ve had rear bumpers bent because the push truck driver slams into the back when he pulls up behind me. Please, be gentle (and call me in the morning). Beyond that, I want the “guy in back” to be aware of the rear sheet metal, especially on the left rear corner. So, when we are making that left hand turn exiting the pits at Oswego, slide to the right just a bit so when my car turns to the left, my expensive rear wing is not cruched on your left front fender.

I am not aware of any specific instructions for the push truck drivers other than what I generally just said. I do believe they have a meeting before the Classic because cautions count and a push truck now becomes an integral part of a pit stop and the initial push-off. However, they are not in radio contact with anyone. The pit stewards just use hand signals and that seems to work out fine. I suppose if radio communications were ever needed, they can listen in on a scanner to race control like the drivers do but they can’t receive instructions while the track is under green because the radio is silent except under caution.

Good question, Ben! Don’t forget to send in your supermodified questions of technical nature HERE