AMA Pro Hillclimb racing brings about an intense combination of Nitromethane-burning horsepower and precise riding skill. We got a chance to speak with the Koesters, a father and son duo that build and race these unique machines.
Nature is full of examples of extreme adaptation, from microscopic organisms that thrive in the boiling-hot water that surrounds geothermal vents in the lightless, miles-deep abyss at the bottom of the sea, to the Venus Flytrap, the odd carnivorous plant native not to the deep jungle of the Amazon or a little shop of horrors, but the wetlands of North Carolina.
The same adaptations that make these creatures so well-suited for their strange environments often make them appear unsettling, or even terrifying, to our eyes accustomed to the ‘normal’ world. That fear is completely natural, so you need not be ashamed of having that reaction the first time you see a nitro hillclimb bike. While perfectly adapted to its environment, it simply looks wrong, and makes the kind of sound the primal core of our brains associates with imminent, serious danger.
Even when the rational, refinance-your-home-loan part of your brain kicks in, there’s still the fact that riding one of these 300-horsepower bikes is like cliff diving - when everything goes right, there’s nothing more exciting, but one wrong move means your immediate future is sky/ground/sky/ground and “oh, here comes my bike to land on top of me at the bottom of the hill…”
To get a glimpse into the mindset required to wrestle an Unlimited-class motorcycle up the face of a cliff, we talked to Gordon and John Koester, a father and son duo with a long track record in AMA Pro Hillclimb competition. John captured the 2017 Xtreme class championship (bikes limited to 700cc) and finished the season third in points in the Unlimited class, where the sky's the limit for engine size (as you might have guessed from the name.)
From The Sidelines To The Starting Line
“I’m the dad and John is the racer,” Gordon explains. “He started in 2010 full-time professionally. Up until that point he raced motocross, and was snowmobile racing a little bit. He would have been 16 at that time.” The Koester family’s involvement in hillclimb competition was a natural evolution, driven by their environment. Per Gordon, “We have one of the toughest hills in the country just 15 miles from the house in Dansville at Poags Hole. A friend of mine in his 70’s was a hill climber back in the day, and I worked with him on the hill, just basically clearing bikes off the hill after they crashed. John, when he was about 12, came along with me and started working on the hill. We had a friend who hill climbed with a 450, and John rode his bike a couple of times, and decided he wanted to do that, so that was the beginning.”
It says a lot about John that his experience helping crashed riders and moving wrecked bikes off the hill led to a desire to challenge hills himself, but there’s actually a robust system in place to get new riders into the sport. “In the classes for the amateurs, they even have classes down to 65 and 85 (cc) all the way up through the unlimited bikes, which are street bike motors put into a [hill climb] frame,” Gordon explains. While amateur competitors typically start with factory motocross bikes modified with bolt-on swingarm extensions, the pro classes feature hybrid beasts built from a mix of off-road parts, custom swingarms the size of extension ladders, and inline four cylinder sport bike engines modified to run on exotic fuels.
Powering The Ascent
“Our bikes’ motors start out as Honda CBR600s,” Gordon says. “Unlimited bikes start out as CBR900s, and some guys in the unlimited class are racing 1000 or 1100cc because you can go as big as you want, but most are going with 900cc or 1000.” Back in the day, hillclimb competition was dominated by motorcycles running Yamaha power; either the XS650, a twin-cylinder inline air-cooled design that benefited from a long development history in AMA pro dirt track racing, or XS750 air-cooled triples sourced from Yamaha’s street bike line. But just like motorcycle road racing, eventually inline fours came to the forefront.
“Back about 15 years ago, the inline four cylinder motors were whipping everything, so today a lot of guys are building them and they seem to be the hot ticket,” Gordon explains. There’s a tradeoff between power and rideability, with the edge in handling going to a narrower frame allowed by a twin or triple, but ultimately the extra oomph delivered by the wider I4 proved to be the decisive factor for most competitors. “It’s rider preference - a narrower engine gives you more room for the footpegs, but with our bikes with the inline fours, we’ve put extensions on the footpegs because the engine is wider, probably like three inches to give the rider more room.”
A stock CBR600RR street bike engine delivers something in the neighborhood of 118 horsepower running on pump gas, with the CBR9XXRR family developing between 111 and 154 horsepower at the crank, depending on model year and displacement. In order to produce enough power and torque to stay competitive in the Xtreme and Unlimited categories, those figures will need to more than double, and with natural aspiration required by the rules, switching to nitromethane is the only way to achieve it. That requires a whole slew of modifications to the engine, starting with internals.
"The first thing we’ve done is that we run a stronger connecting rod - they are the same kinds of rods NHRA drag cars use. It’s just because of the horsepower and the RPM that the motors turn,” Gordon explains. “The pistons, we pretty much run stock compression because the nitro doesn’t want high compression.” Wiseco Pistons’ Dave Sulecki elaborates, saying, “For any boosted or power-adder situation (such as turbo, supercharging, or nitrous), dropping compression is a common tactic to help protect the piston. Since nitromethane contains oxygen and burns slowly, you don’t always need a dished piston crown. It really would depend on how much nitro is mixed as to what compression is going to be needed. For example, for a mix of 28% nitro, a compression ratio of 14:1 is acceptable, where a mix of 85% nitro requires a drop to 8:1 compression ratio. At 8:1 compression for a CBR600 engine, this is for sure a dish, as compared to a dome for 14:1.”
Fire in the Hole
The high energy content of nitromethane, compared to gasoline or methanol, means that some concessions must be made in order to keep the piston alive - not an easy task in a modern sport bike engine, where the factory slugs are as short and light as they can be while still maintaining reliability. Double the power output of the engine with nitro, and suddenly you are in uncharted territory.
“In general terms, one way to protect the compression ring is to move it down away from combustion. This will increase crevice volume, but it’s a fair tradeoff when the top ring needs protection in order to be able to seal combustion,” Sulecki explains. “An alloy steel ring is required to handle the added heat and violence of running the engine at a near-detonation state, where a conventional cast iron moly-filled ring is not up to the task. Not only does the top ring land location need to move down for protecting the ring, but many times the second ring land (between the top ring and second ring) will need to increase as well. Due to the added load forcing the top ring down against the second ring land, the added strength from more thickness in the land will prevent the second ring land from pinching the second ring groove closed.”
Per Sulecki, “With modern engines and piston architecture, the piston is now being made shorter and shorter to accommodate a smaller engine envelope, all in the interest of lowering the overall vehicle height and also compacting the total package for weight. We see this with the change to over-square engine designs, where the cylinder bore is larger than the crankshaft stroke, both shortening the engine and also increasing the engine’s RPM range. Because of this type of engine design, the piston had become equally shorter, and there is sometimes little room to move things like piston rings down away from combustion. This presents a real challenge to a design engineer trying to protect a piston in an engine being tuned for more extreme horsepower demands. If the engine builder is bolting on a turbo, or planning to add extreme fuel to the mix, the piston needs to change its architecture, sometimes so much that the design demands exceed the design envelope of rod length, block height, and planned compression ratio.”
In days gone by, with aircooled engines that had cylinders cast independently of the crankcase, a spacer between the two could offer better options in terms of overall height for piston designers, but the unitary construction of modern sport bike powerplants makes this a non-option, so there’s scant room from crown to skirt to play with. Fortunately, both modern material science and the inherent properties of nitromethane offer some alternatives.
“One way to protect both the piston and ring groove from potential damage due to detonation or high heat in these situations is applying Wiseco ArmorPlating coating to the piston crown and ring groove,” Sulecki offers. “Our proprietary coating not only prevents piston damage from erosion and damage from detonation, but the coating will actually harden under the heat of combustion, adding further protection.”
Another inherent property of nitromethane, normally seen as a negative, also plays a role in piston design. Per Sulecki, “Alcohol and nitro fuels do cause ‘wash down’ of the cylinder wall, where the lubricating oil from the lower end is simply not able to stay on the cylinder wall. In many of these extreme engines, the need to control oil on the cylinder wall using a conventional oil ring becomes moot. In this very dry cylinder environment, such as engines used for hill climbing or speedway motorcycles, the oil ring can be removed from the piston design.” Because of the short duration of these racing events, between-rounds oil changes to remove the nitro-contaminated lube are the norm.
The Fuel Makes the Rules
Beyond piston design, running nitromethane dictates every aspect of engine modification, from the hardware to the fuel injection and even ignition timing. Gordon adds, “In the head, you have stronger valves and valve springs, and most of the time the motors have stock cams because the nitro is just so volatile you don’t need a lot of modification to increase the horsepower other than [ignition] timing. A normal CBR runs 5-10 degrees before top dead center, and we’re running like 58 degrees. It’s firing way before the piston gets to the top.”
Because nitromethane brings some of its own oxygen to the party, despite having a lower specific energy than gasoline, it can produce more than twice the power when combined with the same amount of air. Fuel formulation isn’t regulated in the Xtreme and Unlimited classes, so competitors run it nearly uncut. “It’s straight nitromethane with another chemical called propylene oxide that helps it start, because the nitro doesn’t burn real fast for startup and we’re using so much advanced timing that the propylene oxide just gives it that little extra flare to start,” Gordon explains. “We’re putting like eight ounces to the gallon, so when we check it with the hydrometer, it brings the actual measurement down to 95 or 96 percent nitromethane. From there to 100 percent isn’t much as far as horsepower is concerned.”
The end result is an engine that’s about as gentle as using a hand grenade as a night light. Per Gordon, “These bikes, they’re about impossible to dyno because of the quick revving of the nitro characteristics, but estimated horsepower on the little bikes is under 300, and the big Unlimited bikes probably a little over 300.” That explosive power, channeled through a swingarm that stretches more than twice the stock length to a tire shod in chain links for traction, needs to be precisely applied to the surface of the hill if the rider wants to make it to the top, let alone set fast time for the class.
“When we got the Unlimited bike, which was a 950, John rode it and didn’t ride it as well as the 600, which is actually bored out to 637cc, and it just had too much power,” Gordon admits. “A lot of guys were finding that out. We actually detuned it to an 800cc and it runs way better because it’s more controllable. There’s quite a few guys that, after we did that, are doing the same thing. You just can’t ride that much horsepower.”
A Test Of Skill
Having a bike with (as Rolls Royce would put it) sufficient horsepower and a properly set-up chassis just gets you into the running, though. Success actually depends on the talent and skill between the bars and the pegs, and it’s not a form of motorsports where you get a lot of opportunities to hone the finer points of your riding technique. Gordon says, “We get no practice - it’s so expensive, and the bikes are too risky to just run them all the time. So when we go to a hill, and especially this coming year when we will have a couple of new hills where nobody really knows anything about them like gearing or whatnot, it’s all a matter of paying attention to what is going on with the hill’s layout, our suspension, and really doing your homework on every little thing. That’s what really pays off.”
The race format consists of two or three sessions, depending on the number of entries in the class, with each rider’s position determined at random. “They draw numbers for your running order, so it’s the luck of the draw,” Gordon explains. “If you get a low number, you don’t get a chance to see how the hill reacts to anybody. It evens out though. I think that sometimes it’s an advantage to go a little later because you can see what other guys do, but by the same token, these bikes really tear the hill up, so if you go too much later and a lot of guys have gone ahead of you, you’re not running on a very smooth surface and it gets really gnarly.”
If nobody breaks the beams at the top of the hill, the winner is determined by whoever makes it highest before taking a spill, but typically hillclimbs are decided by elapsed time from bottom to top. A rider who’s satisfied with their first attempt need not make a second or third pass, but the knife-fight-in-a-phone-booth level of competition means that the quickest guy in round one will almost always have to defend that position.
"There are several hills [on the event schedule] that get really tore up, and if you get late in the order it’s a problem,” Gordon explains. “We run two rounds - run the first round in two classes, then take a break, and by the time you get to the second round there is a lot of strategy in looking the hill over and trying to find a line over a particular jump or through a certain area, and John is really good at finding a line. That’s good when it’s late in the day and the hill is really shot.”
You Had To Be There...
When power and skill come together on the hill, there’s nothing quite like motorcycle hillclimb. Gordon’s enthusiasm for the sport is contagious; “When they’re sitting on the line at idle, then drop the clutch and go, it’s like a Funny Car, just blasting off the line. That explosiveness, that’s what gets you going.” And like watching fuel cars go down the dragstrip, it’s something best experienced in person.
"The bikes are just so loud and so powerful that videos just don’t do it justice,” Gordon claims. “Like most racing, when you’re there it’s a whole different experience. John has taken a whole lot of videos with a GoPro on his helmet, and when you’re watching it almost looks like he’s going down a flat trail because you’re not seeing the whole depth of it. When you see a shot from the back of the hill a ways away it’s a totally different perspective. We’ve had so many people go with us for the first time, and once they’ve seen it in person they say, ‘We’re never going to miss this again!’”