Tech Talk #32 – The Quest for the Combination

DavidTechArticlesBy David Reher, Reher-Morrison Racing Engines

When I first discussed writing the Speed Reading column with the staff at National DRAGSTER several years ago, we agreed that I would focus on engine technology for sportsman racers. At the risk of pushing the editorial envelope, this month I’d like to expand my assigned topic with some thoughts on how chassis and car setups affect quarter-mile performance.

The simple truth is that even the most powerful engine can’t produce winning results in a bad chassis. As an engine builder, my area of expertise is horsepower – but as a racer, I know that it’s the total combination that counts.

Drag racing can be a humbling sport – just ask Warren Johnson, Kurt Johnson, Jim Yates, Jeg Coughlin Jr., Mike Edwards, Greg Anderson or any of the other drivers who have already missed the cut this year in Pro Stock qualifying. These are experienced professional racers who spend countless hours working on and thinking about their cars – and yet on occasion they have all failed to find a combination that could produce one of the 16 quickest times in qualifying. I cite this only as an example of how difficult it can be at times even for full-time racers to find that elusive setup. For sportsman racers who have interests and obligations outside of racing, it can be even more difficult to realize the full potential of a particular car/engine combination.

It’s not just horsepower that produces quick elapsed times. As you may know, Reher-Morrison supplies engines for Pro Stock racers Mark Whisnant, George Marnell, Mike Edwards and others. There have been many events where these guys have outrun and out-qualified our own car. Bruce Allen and I bust our tails to make our Grand Am fast, but when we see a customer set track records and run quicker than us with one of our engines, that’s a clear sign that we need to work harder on our car.

That’s why I cringe when someone asks me what a particular engine will run in a given chassis. There is simply no way that I can give an accurate answer. I’ve seen customers who have bought identical Super Series engines run times that differ by nearly four tenths of a second in similar cars. I’ve looked at the dyno sheets, and I know there isn’t more than one percent difference in power – so what accounts for the huge variations in e.t.? It all comes down to chassis and setup.

There is a distinction between running fast and running consistently. With the growing popularity of Quick 8, Quick 16 and Top Sportsman-style racing, the emphasis shifts from throttle stops to all-out speed. Just a simple change of rear tires can make a big difference in performance. In the Super-type heads-up eliminators, the goal is to eliminate tire spin and hit a perfect .400 light, so the cars are often “overtired” to produce a no-spin, dead-bog launch. The downside of this approach is that you have to carry these big tires all the way down the track, and they act like huge flywheels that the engine must accelerate. That’s not a problem if you have enough power to run the number, but if your goal is to run a Quick 16 show, then the smallest tires that will hook up the horsepower are almost certain to produce quicker elapsed times.

Tires are just one element of the right combination. As the technology of racing becomes more sophisticated, racers need to be aware of weight distribution, engine location, gearing, hood scoops, fuel systems and dozens of other components. With the popularity of automatic transmissions, torque converters have become as crucial in sportsman racing as clutches are in Pro Stock. Often the parts you overlook are the ones that ones that kill performance. If the brakes are dragging or the rearend housing is crooked, a stronger engine isn’t going to make the car faster than one that isn’t wasting power to overcome chassis problems.

Some racers mistakenly believe that computer programs that predict quarter-mile performance are infallible, but my experience suggests otherwise. Back in the days BC (Before Computers) we used a power-speed calculator to predict elapsed times and speeds. This device, which resembled a cardboard slide rule, matched up horsepower and vehicle weight to project performance. Today’s software programs are more sophisticated versions of the power-speed calculator, but they suffer from the same limitations. They are based on values and observations of the software programmer, and these may not accurately reflect reality. We know from experience that the condition of the track surface and starting line temperature greatly affect performance; we know that there are practical limits to the gear ratios you can run. That’s why I’m skeptical when a racer tells me that his car’s performance doesn’t match the computer projection.

The fact is that we race cars, not laptops. We race them on good tracks and on bad tracks, we race at high noon and at 10 o’clock at night, we race on chilly January mornings and on scorching August afternoons. I know that an engine isn’t going to produce the same e.t. in Madison in summer that it will at Maple Grove in autumn, regardless of what any power-speed calculator or computer software says.

On my rare weekends at home, I occasionally watch the NASCAR races on TV. The importance of setup is obvious in oval-track racing. A driver can lead 50 laps, make a pit stop for four tires, and then go straight to the back. Even a small change in tire stagger or chassis wedge can make a car a winner or a loser. In general, I think that circle-track racers and road racers are more aware of their chassis than drag racers, who tend to be engine oriented. That’s fine with me; I’d much rather work on cylinder heads than spring rates. But the fact is that the engine, chassis and driver must all be in harmony. The combination is the thing whether you’re racing at the U.S. Nationals, the Brickyard 400 or the U.S. Grand Prix.