Rich Daly (owner of DynoPort/ Bender Racing) brought his notoriously quick Pro Stock 1000 SkiDoo triple for a tuneup here. Besides being a savvy pipe designer and thrashaholic, Rich has spent a great deal of creativity including time and $ building as light an asphalt sled as possible. The greatest possible HP and the lightest possible weight = best potential for low ETs and high MPH. Rich was interested in maximizing his HP here, possibly assessing differences in pipe center section temps vs peak HP RPM.
He brought just the engine to be tested on my dyno engine plate. The plate is about a square foot of 3/8″ thick aluminum, swiss-cheese drilled to accommodate the dozens of different crankcase engine mount bolt patterns encountered over the years. The plate is supported by six cylindrical stanchions, each of which bolt solidly to the steel table. Six stock early Yamaha Phazer rubber motor mounts connect the plate to the six stanchions and allow for ample movement and absorption of engine vibration. The rubber mounted engine plate combined with the rubber-dampened drive shaft between crank and dyno brake provide a safe, smooth running environment for even the nastiest big twin or stroker multis.
But this pleasant rubber dampened operating environment is probably foreign to a vibrating triple stroker like Rich has! The engine is normally solid mounted into his ultra-light drag chassis, which probably provides a certain amount of flex and vibration absorption itself, but every chassis is a bit different. That’s why I prefer dyno testing engines exactly as they are to be used–mounted either solidly or in rubber of various stiffness. That way if the carbs are unhappy with a particular frequency of vibration they are subjected to in the sled, fuel flow problems show up immediately. The dyno fuel flowmeters show dramatically how the carbs can shut off, run dry then surge back again as revs climb. We’ve often cured those problems with larger needle and seats, higher fuel pressure, adding weight to the carbs, softer carb boots, or better yet softer motor mounts that some racers dislike. But soft mounts (if that’s what it takes) are way better than carbs whose float bowl levels rise and fall like Maine ocean tides, and fuel that gets aerated into the consistency of a vanilla milkshake. In that situation, you get at worst shutoff before the finish line and unexplainable seizures, or at best extreme difficulty maintaining maximum horsepower jetting.
That’s why I suggested to Rich that he bring the whole sled, but he indicated that the chassis was out somewhere being lightened(!). So we bolted his stroker triple to my normally forgiving dyno engine plate.
While we were setting up the engine Rich explained his engine’s unorthodox cooling system–bare combustion chamber domes with no covers, bolted to cylinders that are filled with stagnant water which is cooled between rounds. That saves the weight of a water pump, cylinder head covers, and the coolant that normally surrounds the combustion chamber domes. Plus no need for heavy radiators or heat exchangers. But this seemed like a step backwards–“free air” cylinder heads with no fins? And what about combustion chamber heat being allowed to climb with no coolant? I know from too many first hand experiences that boiling water above the combustion chamber creates steam pockets which = instant detonation. But pressurized steam is hot, fairly dense stuff, and surely must not be as bad as still air around Rich’s smooth bare combustion chamber domes!?
Rich also expressed his admiration for the CrankShop pipe stampings he was using, explaining that the shape and body length was ideal, giving him a broad HP curve, and giving credit to Larry Audette. Why recreate the wheel? Sure he could have copied them out of cones or had his own stampings made, but it’s refreshing to see that there can be honor among the few who create good things like this. That’s one of the reasons why Rich has so many pals.
He also was using huge (52mm I think) Crankshop carbs and a stock ignition which on his dyno made max HP at stock timing setting. So no need to mess with timing, just max out HP with fuel flow and assess its effect on pipe temp and subsequent HP peak RPM.
Initial dyno runs were shortened by poor fuel flow, allowing the middle carb to run lean and allow that cylinder to drop. We fitted a dyno pressure transducer to the carb fuel lines, and found that the stock SkiDoo fuel pump was defective, delivering only the pound and a half fed to it by the dyno fuel system. So Rich had a spare, hooked that up and 4 psi of fuel pressure made the engine happy. But even though fuel flow was fairly constant it remained very low at about 100 lb/hr, way too low for the 250 hp we were making at the time.
So thinking that even with the rubber mounted engine plate carb vibration might be the culprit, we decided to add some mass to the already fairly hefty CS carbs. Rich tiewrapped/ duct taped my five pound two and a half ft long nickel plated pinchbar to the three carbs. Instantly we picked up 30 lb/hr constant fuel flow from 8500 to 10,000RPM! We also picked up 15HP. Now Rich was able to begin jetting down. Even though BSFC was still high, without measuring airflow to get us an accurate A/F ratio reading we must lean out cautiously since wildly ported engines can have excessive short-circuiting of mixture, creating high BSFC at max power. Plus we had the added variable of the hot aircooled domes instead of cold liquid cooled domes.
So Rich checked plugs, jetted down a few sizes and me made 150 lb/ft and 270 plus HP with a broad powerband from 9000-9800 RPM.
Now looking for max max HP, Rich removed the air cooled combustion chambers to have a real good look at the piston domes. Nearly a one-half inch wide “wash” band was there, like you might see on a safely tuned trail engine. “Wash” in this case was the shiny residue from oil that remained on the cool piston surfaces (oil is an excellent temp indicator).
Rather than jet down some more, Rich left the carbs safely fat and installed a set of stinger restrictors to increase backpressure.
Thinking we were safely fueled, the next dyno run with tighter stingers rewarded us with misfire at 9000. Subsequent investigation revealed a DTR first–broken mag and center cylinder spark plug insulators on the top side! Fortunately, the insulators were not damaged inside the combustion chambers which could have dropped ceramic chips into the cylinders.
Could the bare combustion chamber domes, unsupported by sturdy head coolant covers, have deflected enough under the hammering of deto to break the plugs? Estimating the plug outside mass at 2 oz, and figuring it must take 30 pounds of force to snap the insulators, that equates to 240 Gs if that’s what caused the plugs to break!
So stepping back, we removed the stingers, jetted down 10 lb/hr and the HP stayed constant. We had maxed out on Rich’s race gas, with what the dyno showed as trail-safe BSFC.
Back to weight vs HP; I’m surmising that after helping dyno tune maybe a thousand full mod engines like this, if it had good cold water coolant around the combustion chambers we could make more power with less fuel! Here, with Rich’s “free-air” finless chambers, extra vaporizing fuel is needed to keep chamber temps low enough to stave off deto. That extra fuel makes no HP, just cools the compressed charge and takes up space in the combustion chamber.
So I’m guessing that if Rich added coolant to his chambers, that is cold coolant, he would make maybe 8 more HP with .10 or .15 lb/hphr lower BSFC. That might mean adding 25 lb of pump, coolant, heat exchangers etc. After Rich does the math, I’m betting that those odd bare chambers will remain. Plus now he has $5 [spark plug] deto sensors on each cylinder, so he can “jet” accordingly.