When I bought the SF901 dyno 20 years ago, stock and race sled engines were less than half the torque and HP of what we're seeing today. The Superflow 901 absorber is capable of  controlling 1000 HP engines, but the 1986 sales  literature described how the absorber could be used for engines as small as 12 HP. After Terry Paine, machinest extraordinaire Skip Saupe and I built the hydraulic chassis lift, framework and driveshaft system the first sled we had to  test the dyno was a then-new  1987 Yamaha Exciter with those notoriously troublesome original butterfly carbs.

With dyno running directly off the crankshaft at engine speed, pull-starting the Exciter was brutal. The bronze absorber impeller acted like a 20 lb flywheel added to the mass of the engine's rotating mass. Once running, the Exciter 570 was unable to break idle and increase revs at all. The engine would sit there idling, and increasing opening the throttle would not cause RPM to rise at all--the engine would remain at maybe 1000 rpm going "whaaaaa" from added intake noise with no change in engine speed. This would only create excessive heat in the rubber Lord torsional vibration dampeners we had engineered into the driveshaft to protect the engine from the granite-like load of the dyno on fragile engine components.

Working with SuperFlow engineering people it was decided that I should disassemble the dyno absorber and machine the rotor (the internal spinning part of the torque convertor-like absorber) down to a smaller outside diameter. This would reduce low RPM drag on the engines, and reduce torque capacity to maybe half.

After reassembling the dyno with the cut rotor, pull starting the Exciter was a bit easier. But that awful 570 just sat there idling, and appying light throttle would only make more intake noise and Lord coupler heat, not more revs! A day later I got a call from local Yamaha dealer Sunnyside Cycle's tech Don Frasier who knew of my frustration with the Exciter on my new dyno. Don had been fiddling with the Exciter carbs and discovered that by popping out the softplugs and enlarging one fuel passage, a light throttle lean condition was improved.

I popped out those soft plugs, drilled the second metering hole as Don suggested, and JB Welded the plugs back in place. Unbelievably, now the Exciter ripped off of idle and ran up to 5000 RPM where the automatic control of the dyno took over and finally created the load necessary to hold the engine there at full throttle. HP and torque were displayed there, steady state.  Pushing the "test" button allowed the engine to accelerate to the HP peak and beyond, and data was finally recorded. Now let's figure out what that data meant.

Since the SuperFlow dyno did not come with a manual that expained things like A/F ratio and BSFC etc I was totally clueless about info that the SuperFlow airflow and fuel flow meters would eventually provide us. All I wanted to see was torque and HP and go from there. But eventually, fuel flow numbers would be as improtant to us as HP numbers. This was a fun learningcurve.

Eventually, I would tire of pulling ropes with that 20 lb dyno flywheel adding to the load. So I acquired a huge 350 HP Cummins 12v starter, had rotation reversed, and bought a $500 german sprag clutch to alllow the starter to drive the engine to start , then idle down to zero RPM, as dyno data is recorded.

After obtaining dyno info on the Exciter, including those hard to understand airflow and fuel flow numbers, other sleds would follow. Small 340 and 440 race engines would still be difficult to test even with the cut down absorber rotor. We even resorted to blowing some N2O into the carbs to lift the race engines from idle to whatever RPM they came "on the pipes".

Reducing the dyno absorber speed with a toothed belt drive was the last modification that would allow easy testing of those low torque high RPM race engines. The belt drive would surely convert some of the engines' HP to heat before being measured by the computerized dyno. To determine that percentage I dyno tested an engine at 1/1 direct drive. Then I installed the toothed belt reduction, and dyno tested the same engine again. That lost HP was then programmed into the dyno computer, with engine speed considered since friction HP increases as the square of RPM.

I've dyno tested thousands of engines in 20 years, and up until last year my reduced speed, cut down rotor SF901 has been up to the task. But now along comes  new monster turbocharged  RX1's and Apex' with over 300hp at reduced output shaft speed, and N2O injected sleds like Glenn Hall's D&D 1200 asphalt racer and my cut-rotor dyno absorber is now on the ragged edge of not being able to control the engine RPM.

The last straw was the Honda 450 four stroke quad owned by DeNoyer Chevrolet in Albany, overbored and modified to 50 HP plus brought here to tune the Lectron-like Edelbrock carb and N2O system to max HP. On motorcycles and quads, I use driveshaft adaptors to attach the dyno drive to the transmission output shaft (never call that a "countershaft"). The primary drive ratio is multiplied by the transmission gear ratio to get us engine RPM. In this case, the 50 plus HP engine was only creating 2300 output shaft RPM at 7000 RPM crank speed and the dyno could not properly control the engine to obtain meaningfull low RPM data.

So I recently called SuperFlow and ordered a new $1200 full size relacement bronze dyno absorber rotor, and all new bearings and seals for another $400. It required 20 hours of disassembling the dyno,  pressing off old bearings, cleaning parts, reassembling and pressing new components together with my new  full size rotor to be back to 1987 square one. Now I can control 1000 HP again, so I should be in good shape to handle all the full mod sleds have to offer for the next 20 years. But if you have a vintage 340cc race sled to tune, you must go elsewhere.

305/1 Dynod a second new Hayabusa with Yosh bolton mufflers belongs to a riding pal of the one I tuned yeasterday, this one made 157.4 RWHP after tweaking the identical map but midrange HP was better than yesterdays, guessing that cam timing is different by a few degrees.

'5/3 Gene Hurin and Rob Schooping with Gene's 1000 improver and XCR1200 trail sled. PM Lynn and Jim Cooper tuning their PS1000 asphalt sled.Gene's 1000 improver made record 1000cc triple HP after dialing in each Lectron carb with EGTs. Those of you who watched Webcams know the numbers, Gene is wanting to be secretive until Haydays. His XCR1200 was good but not as good as Rob's or Denny Richards' stroker 1200 both at 300 or a touch over. After dialing in each of Gene's lectrons to get identical EGT, and rolling ignition timing back and forth we maxed out at 296. Gene was bummed that he had less than 300 (like some would be bumbed that their 11.75" thing was less than a "foot long"), but his sled will be fast. Here is one instance where tweaking a computer knob could have falsely upped Gene's 296 to 300 and made him real happy while he pealed out the bills for the tuning session. Gene and his good family have been dyno tuning here for close to 20 years, and he always got the straight scoop. But a Knob Job will not make his sled faster. Fortunately when Rob Schooping was helping us remove the 1200 from the dyno, two missing pieces of devcon were found in the belly pan, had fallen out of the upper crancase where boring bars poke through while making room for big bore stroker sylinders. This surely created a crankcase leak and Gene is surely 300 plus when that's fixed.
What if I had compassion knobbed Gene's leaking crankcase engine to 300.0? After discovering the crankcase leak, with his knobbed 300 HP dyno sheet, Gene would have surely expected 305 after re-devconing the leaks.
So this is a great example for you dyno owners/ operators who are often confonted with a need for a "compassion" dyno knob job....just don't do it. What it is is what it is.

5/8 TRX450 quad, bored to 525 and modded, has Edelbrock flatslide (crude copy of Lectron) that needs tuning, I still have a dozed Edelbrock needles belonging to Joe DiSpirito maybe I'll get to try them. The supplied needle is wrong, DanF and I tuned this to achieve 12/1 at WOT but midrange part thottle is fat as a pig. The needle set I had would not work, so I asked quad owner to leave in on the dyno until correct needles are obtained.
Meanwhile, this big 525 quad in high gear could not be held by my modified SF901 below 7000 RPM--about 3/1 gear ratio in high gear meant 33 lb/ft = 100 lb/ft but worse 7000 RPM on dyno readout is a lowly 2333 RPM absorber speed where braking is most difficult.

5/21 dyno is totally rebuilt with a full size rotor, had 15 different Edelbrock carb needles to experiment, found one with same tip  dimension and leaner mid needle dimension. Achieved good part-full throttle A/F ratio on pump gas. Then we switched to customer-supplied race gas for N2O testing. Now surmising that the race gas was dead (the clean running engine on pump gas now developed some burbles), we dyno tested the N2O and got severe misfire with 031/038 N2O/ gasoline nozzles. Dropping to 031/034 made it better but still misfired. Dropping fuel nozzle size .002 at a crack it finally ran cleanly with 028 fuel nozzles adding 20 HP to the 54 HP at the output shaft (never call that a "countershaft"). But since BSFC was .75 plus the fuel flow appeared too high, so we dropped to .026 fuel nozzle. After loading the engine at 7000 the buttom was pushed in the control room, and one second later the engine died, before I could push the "start test" button. Pulled the sparkplug at it was melted and we were done. My first four-stroke detonation damage in 20 years. I called the sled owner who told me the rqce gas was many months old, and surely the light ends were gone. So much of the fuel measured by the dyno going into the engine was blowing out the exhaust port in those lava lamp-like globules. That misfiring was surely globs hitting and shorting out the plug intermittently. It wasn't until we had it down to 028 that the compressed mixture was hot enough to vaporize just enough on the dead gas to get a clean fire. But that .75 lb/hphr if we subtract what was still blowing, unburned, out the exhaust port, was probably .40. Hence, the instant deto whan we dropped to .026.

I felt bad about not discussing the pedigree and history of the race gas they sent for testing. They had experienced misfire and poor running on that same gas with N2O. That's why they shipped the quad from Albany to my dyno, and it was probably their gas quality all along.

Race gas must be stored in refrigerated rooms or under N2 pressure (about 3-4 psi), or those light ends, so important to initialize vaporization, will disappear like the carbonation in a half full two liter bottle of Coke in the fridge after being opened over time a dozen times for quick swigs.  I harp on this often, but here's another example of stale race gas biting us in the testicles.

5/14 Mike Memery and Doug Smith with a Crankshop modded SkiDoo 800 twin watercrosser. cancelled

5/22 Pete Nixon with a Crankshop MXZ800 race engine. Very nice 191 HP at 8500. May post Pete's numbers.  PM Sunnyside Cycle dyno'd a 250 2stroke honda with PSI Big Air carb, very easy to dial in on my SuperFlow eddy current roller dyno. As shipped, the carb was too fat made 20 HP, ten quick dyno runs late (all adjustements are external) the 250 was over 40  HP at the rear wheel. Next was a modded Honda CR450 4-cycle. Same deal here, massive changes to Kehein carb jetting netted huge HP gains.  A/F ratio is measured by Innovate wide band  measure by dyno computer. There is big HP  gains to be made when leaning down from 10/1 to 12.5 or 13/1  A/F ratio.

5/23 11am CJ Motorsports of Loweville NY (had a very powerful 860 Doo twin at the SW Shootout), tuning a mod 800 SkiDoo twin asphalt racer, on his way to nearby (28miles) NYIRPfor Wed night racing. Here's a case of the dyno hook-up being as important as the dyno tune! The dyno table is topped with steel diamond plate, welded squarely with the dyno and dyno drive shaft.  When we set a sled on the table the first thing we do is align the  sled's track with the diamonds.  Then we can move the sled forward or backwards to achive perfect  90 degree alignment with dyno driveshaft before sled is strapped down, and driveshaft connected. Sometimes this is impossible, and we must jack the chassis out of square to achieve perfect engine cranksfaft to dyno driveshaft alignment. This may have been the worst--probably 3/4 inch off square from the front of the track to the rear, meaning either the engine was way out of whack with the chassis, or the skidframe was way out of whack with the chassis.
We tuned this engine and added 10 HP with proper jetting, but it looks like he needs a bunch more compression to take advantage of the spec race gas used at sanctioned pro stock asphalt (don't call that "ashphalt" please that annoys me like motorcycle "countershaft sprockets" and "NOSS").
Also CJ now knows where their HP peak is from 400 degree F center section gas temp to 800 degree. His Racepack datalogger will provide the info after each pass to ensure that he eventually matches HP peak to CS temp during the nine second runs.
But if CJ corrects their out-of-alignment chassis he will pick up huge performance, maybe even greater than what he will gain with optimum jetting for nine seconds, and being able to correlate engine revs to pipe CS temp..
Also after they left I found a set of Craftsman metric box/ open end wrenches CJ left behind.  Mark give me a call either you can pick them up on your way back from Wisconsin or I'll mail them to you.

55/30 John Wilbur and Chris Squires back again with the HTG F7/8 this time to tweak Boondocker for summer weather for asphalt racing especially for the dragraces this weekend at NYIRP.. This is absolutely necessary for winter/ summer dragracers not because the Boondocker goofs but I think the stock ECU goes into enrichment at high temps like we had today (mid 80's F). The good news is it only took two pulls to tweak the Boondocker to get max HP fuel flow in 85 degree humid air. Hot humid air is another issue, since neither the Cat ECU nor the Boondocker considers humidity, or water vapor, or more modernly "grains of water per pound of air" like NHRA dragracers measures. Water  vapor takes up space, displacing O2 and fuel must be pulled out to make up for that! After this tuning plus some additional tweaks of their own, the F8 made well over 190 HP with only 12.5/1 compression ratio and .065 squish. I'm cringing because even though engine builders argue with me if you have fresh sufficient octane race gas, my opinion is that squish needs to be tight enough to kiss the piton domes on decelleration. On this engine I'm betting .045 for racing is OK.
What's the big deal?
Tight squish has two great benefits:
1) increases turbulence in the A/F mixture in the combustion chamber, increases flame speed and decreases timing required for peak HP.
2) any A/F mixture trapped in the squish band does not contribute to HP. Most of it burns on the way out the exhaust port. Thight squish blows the A/F mixture into the center of the combustion chamber, mixture is burned immediatedly and HP is added.