This is Part 6 of a series written by guest writer Ricky Nietubicz on his experience on the Formula SAE team at the University of Delaware. FSAE is a competition where students design, build, and compete with small formula-style racing cars. Ricky was President of his FSAE club, and his team went to the Nationals in Detroit during the 2006-2007 season.

As I alluded to in the previous article, selecting an engine is a massive decision in and of itself, and should not be taken lightly. The rules are pretty open as to what engine you can run, as long as it displaces 600 or less cubic centimeters, is a four-cycle piston engine and burns the specified fuel (93 octane this year) and breathes through a 20mm restrictor. The rest is up to you.

There are more engines that meet this criteria than I care to count. 600cc sportbike engines, and all manner of single-cylinder dirtbike and ATV engines. We went round and round with engine selection when I was president, so I’ll gloss over those arguments. There is a domination of the series by high-revving sportbike engines, particularly the Yamaha R6. However, there is a movement away from these engines toward large single-cylinder thumpers by a few teams, particularly the Yamaha 450.

4-cylinder engines rev high. Really high. Like 14,500 rpm or so high. Thus, they make crazy amounts of horsepower. Single-cylinder thumpers are smaller, lighter and torquier. But you take a hit in horsepower, at least in theory.

One thing to bear in mind is that you have to make sure you’re comparing apples to apples. In stock form, these engines run without restrictors, and with carburetors. On your car, they will clearly be run with restrictors, and more than likely with fuel injection. This means that you’ll be able to tune things out, so lots of engine figuring is based on conjecture and anticipated ability to tune.

The 4-cylinder engine is bulky. Hard to package, big and heavy. You have to fabricate exhaust and intake for it, wire it, tune it, everything. The single cylinder means you only have to have one intake runner and one exhaust tube off the engine. You only have to run one spark plug and one injector. The thumper is much easier to package, and saves you a great deal of weight.

A major argument in favor of the thumper is the fact that the FSAE courses tend to be tight and narrow, not the sort of place that is terribly conducive to a high-revving, wind it out type of motor, but definitely favors the torque monster (relatively) that can pull almost from idle, while the 4-cylinder is having trouble producing enough power to get out of its own way. The 4-cylinder has trouble pulling enough air through the restrictor to reach redline, no matter how well the restrictor is designed. In stock form, the R6 motors we used were set up to breathe through quad 36mm (if I remember correctly) carbs, whereas the 450 only breathes through a single 39mm carb. This means that the impact of the restrictor is inherently less on the 450.

I have spoken a lot about the thumper and almost universally referred to it as a “450” because the 450 Yamaha on the newest YFZ450 ATV is a fantastic little motor. Five titanium valves, dual overhead camshafts, 11.4:1 compression and a 5-speed transmission. Not bad for a little bugger like that, pretty advanced.

The single-cylinder, being torquier, is also inherently easier to drive. Caught in the wrong gear coming out of a turn? No problem. Not a fantastic driver? Leave it in second or third and get going. I’d bet acceleration times will drop as well, as you can gear up the car more and shift less.

If FSAE ran cars on actual race tracks, whether Watkins Glen or Laguna Seca, I’d be advising the exact opposite, as for high-speed running, it would be very, very hard to beat a nice, high-revving 4-cylinder sportbike engine. But on a tight autocross course, torque and lightweight are more important than ultimate horsepower. And don’t forget the engineering competition part of it- it all comes back to engineering- packaging impacts the frame design, and if you spin it right, can really bolster your design report and presentation.