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This week on the dyno

This week and Boss Noss tuning

This week

this dyno session ZR800 Boss Noss

Things we will be testing

The rush is on

The first official DynoTech “BlowUp”

Queenan Racing's turbocharged Hayabusa asphalt drag sled on the dyno table

“Blow Up” is a commonly used euphemism among performance sledders to describe a seized piston—stuck in the bore because it temporarily grew bigger than the hole due to lean operation or deto. That euphemism annoys me because a stuck piston is not a “blowup”—it’s very non-destructive, non terrifying like a “blowup” would imply. I have always thought that the term “blow up” should be reserved for something more serious than a crankshaft that no longer turns, with something awry, but easily fixable inside the engine that is preventing normal rotation.

When funnycar racer John Force says he “blew up”, you know something way more violent than a stuck piston occurred.

In November I had my first real, true sled “BlowUp” on the dyno.

Terry and Mike Queenan had the Queenan Brothers Racing Hayabusa powered asphalt sled here to tune. This was to be a fun session—the fellow who provides parts and tuning for the Motec EFI system for Queenans (as well as the Al Anabi drag cars and bikes) was remotely monitoring the DTR tuning session from his home office in California, making fuel/ timing tweaks after each run via internet and observing the dynocams.

Creeping up on revs and boost (I think we were only running 11 psi boost and 410 HP) this fellow noted, watching data during each dyno test, that oil pressure had dropped a bit—perhaps due to rising oil temp? We cooled the crankcase for a few minutes before the next run. But what we did not realize was that a rod bearing on the big end of one of the engine’s aftermarket connecting rods was beginning to seize on the crank journal—perhaps smearing rod bearing material into the crank oil journals preventing total loss of oil pressure. This friction would eventually create heat that would in the next six seconds of boosted operation cause the rod to try to friction- weld itself to the crankshaft, then turn blue and eventually grab and snap sending parts flying.

On dyno test 10, we ran the engine up to 11,500 RPM and a sudden, loud snap accompanied a 7’ diameter ball of fire that enveloped the expensive area of the sled all the way to the ceiling tiles in the equally expensive dyno room!

This fire was accelerated by the 80mph air from the dyno air supply ducts—making it look exactly like one of John Force’s Funny Car “blowups” where headgaskets squeeze out and spew oil onto the headers creating one of those nasty, terrifying oil fires and an out of control funnycar. But in this case it was the rod cap blowing out the front of the Hayabusa crankcase, showering the cherry red header/ turbo with engine oil and creating the first DTR fireball.

I bolted from the control console, grabbing one of the 25 year old, but previously unused Halon fire extinguishers, and ran into the dyno room and with two pounds of Halon completely extinguished the fire. Terry and Mike Queenan were duly impressed with the speed at which Jr. Fire Marshal Jim was able to run from the control console, grab the the extinguisher and reach and address their burning sled. Halon is great stuff—today banned by the greenies but still said to be available, at a premium, from suppliers who have a stash of this stuff.

But with the fire extinguished, there was still a substantial amount of oil left on the dyno table beneath the sled….what if this sled was running down the dragstrip at 180mph instead of sitting on my diamond plate steel table?

 That unburned oil, instead would surely have been spewed and drizzled in front of the smooth rubber track with instant loss of traction and directional control! It’s one thing to have an engine explode (truly “blow up”) and shut a sled down, but the prospect of dumping oil directly in front of the smooth rubber track is terrifying considering what we all know might happen should a high speed sled/ rider encounter a guardrail or concrete barrier at 180 mph plus!

Fortunately, Queenan’s sled features a high tech multi-stage dry sump oiling system which minimizes unnecessary oil volume within the crank case and the sled also has a solid pan beneath the motor which trapped some of the oil from spilling out under the chassis. Without these features, the fire on the dyno table and the potential real-world scenario could have been much, much worse.

Why not add some sort of diaper-like oil catcher like the top fuel racers use? For them,  dropping oil mostly between the two rear tires is not a huge control issue, but NHRA is mostly concerned with downtime necessitated by cleaning up the mess. But sled racers with boosted four stroke engines approaching 10 HP per cubic inch will surely occasionally “blow up” engines, inevitably dropping oil directly in front of the tracks. It would be wise to deal with the inevitable spewing oil ahead of time.

From now on, people bringing heavily boosted engines to DTR must endure a pre-test fire drill.

SuperFlow Windyne software, SFD files

SuperFlow 902 dyno terminology explained

Dyno Terminology—Fresh and Refresh

The new SuperFlow 902 software has some subtle differences in channel headings in our test data compared to our original 25 year old  SuperFlow 901 software. For long term DTR members I need to clarify the difference, and for new DTR members I need to explain the channel information in our dyno printouts, and what each channel means to us.

EngSpd RPM self-explanatory—this is RPM, and on engines with digital tachs, the readings have proven to be identical from dyno to sled. But analog sled tachometers are another story—vast differences can be seen from digital dyno RPM to analog sled tachometer readings. So it pays to have analog sled tachometers calibrated electronically (Aaen does this for a small fee) or with a digital tach like those sold by Stihl (less than $100) for tuning chainsaws. Those are perfectly accurate. But keep in mind that the peak HP RPM on our dyno tests is with pipe(s) extremely hot. And since the speed of sound increases with temperature, the HP peak in the field may be at lower RPM (trail riders on-off-on throttle) or at higher RPM (lake runners or mountain climbers who might spend minutes at WOT). Sled dragracers used to think that they achieved best acceleration by clutching to the “peak torque RPM” which often occurs 2-400 rpm lower than dyno test HP peak. But now we know that we clutch to a shifting HP peak—cool pipes on takeoff will make peak HP several hundred RPM lower than hot dyno test pipes, and finding that constantly changing peak HP RPM is critical in creating best acceleration.

STPPwr CHp horsepower, corrected to 60 degrees sea level baro 29.92 in hg.
This is derived by taking RPM x torque lb/ft divided by 5252. Complicated initially but it takes into consideration the twisting force and how quickly it can be done (RPM). HP is what we need to create acceleration and maintain top speed. Read on:

STPTrq Clb-ft this is the twisting force, or torque that the crankshaft is exerting at any given RPM, corrected to 60 degrees sea level barometer 29.92 in hg. But by itself, torque does no work—it takes speed—lots of speed—to do meaningful “work” (HP). To emphasize that, I sometimes talk about me (200 lb Jim) riding my Schwinn bicycle with 12” long pedal cranks. With my 300 lb girlfriend riding on my shoulders (facing forward of course), by grunting and lifting my butt off the bike seat I can make 500 lb/ft of torque at the pedal crank! That kind of torque should create wicked acceleration, shouldn’t it? But my spindly legs can only muster 3 RPM! So based upon the math RPM x torque lb/ft/ 5252 = HP that means that I can make about ¼ HP. Not bad for a 62 year old. But if I were instead twisting the throttle on a Honda 90cc scooter with 8 lb/ft at 5000 rpm I would be making 7.5HP—accelerating much harder—even with my 300 lb honey riding with me! No contest. It takes HP to create acceleration. We need a combo of torque and lots revs to do work—to make HP. 

FuelAB- fuel flow into the engine in pounds per hour. This is a combination of the two dyno fuel flowmeters (flowmeter A and flowmeter B), measuring fuel flow from the sleds’ EFI pump to the rail, or from the mechanical pump to the carbs. Flowmeters can be used individually to measure N2O flow separately from carbs/ EFI. But combining the two flow readings is necessary for computing BSFC.

FulA_B- fuel flow from EFI pump to rail (A) minus fuel flow from bypass regulator back to the tank (B). Can’t use a – so we must use a _ instead. Polaris uses this type of system.

BSFCAB and BSFA_B- pounds of fuel per HP per hour. 25 years ago when I bought this dyno system there was no manual to explain the significance of this number. Early adventuresome guinea pigs (including all of the current eastern US aftermarket sled modifiers) and I proceeded to just tune engines blindly to max HP and beyond until engines seized. But after our 100^th piston or so, we realized that there was a pattern to this destruction if we went too far beyond max HP.  Fuel flow is meaningful information and we finally understood that our race engines would make best power at @.55 lb/hphr and pump gas engines needed @.70 lb/hphr to be reliable. Don’t go lower than that! But today, with modern race engine configuration two stroke race engines can make best power closer to .50 lb/hphr and new stock engines can be completely reliable at .60 lb/hphr and even lower! SkiDoo ETEC EFI systems allow way less short-circuiting, and a greater percentage of fuel flow contributes to HP, and not blowing out the exhaust thus reducing BSFC to bizarrely low numbers.  New cooling system designs like those used by Arctic Cat employ modern “reverse” cooling systems like all modern automotive race engines, deliver the lowest temp coolant to the combustion chambers where it’s needed most allowing way more deto-free power! High volume “bathtub” coolant passages are passé, and smaller volume but higher velocity “shrinkwrapped” head coolant passages scour heat from combustion chambers way more efficiently! They use high velocity, turbulent coolant flow to maximize heat transfer from hot engine parts to cold heat exchangers. “Low and slow” is for smoking barbecue meat, and for smoking pistons!

Air_1s scfm- This is the airflow through the engine in Standard Cubic Ft per Minute. The dyno flowmeter is affixed to the airbox, or inserted in the insulated duct from the DTR refrigerated air system to the sleds’ air intake.

AFRAB and AFRA_B ratio- this is the mathematical ratio of air pounds per hour/ fuel based upon the weight of the air (converted from CFM based upon air density) to pounds of fuel per hour. 10/1 is rich (richer than 10/1 can result in misfire), and 17/1 is lean (leaner than 17/1 can result in misfire).

LamAF1- the SF902 uses an Innovate wide band A/F ratio meter to measure exhaust gas, and give us A/F ratio readings. The O2 sensor can be plumbed into the exhaust via a bung welded into the pipe, or with a dyno probe—with a long ¼ ID steel tube inserted colonoscopy-like into the stinger/ muffler. This reading can show leaner than the mechanical reading if oxygenated fuel is used.

LM1air- if there is no airbox and no possibility of accurate airflow readings, then approximate airflow SCFM can be determined by comparing mechanical fuel flow and the wideband A/F ratio. The math is done by the 902 computer and SCFM is shown.

ExhPrs psig- this is the average gauge pressure inside the tuned pipe(s) measured with a combination pressure transducer/ open element temperature probe in the fat part of a pipe center section. To generalize, 4.0 psi seems to be optimal in creating max HP in two stroke engines. If backpressure is lower, then power might be sacrificed. But then there is less possibility of detonation-producing active radicals being packed back into the combustion chamber by the pipe(s) return sound wave(s).

Exh_1 deg F- this measurement tells us that a pipe is at optimal temperature for best HP. Also it’s critical in telling us where peak HP occurs. The most savvy clutch tuners/ dataloggers can use this particular dyno test data to ensure that their engines run at max HP RPM from clutch engagement to the end of the track, or to the first turn.

Sunday's Dyno tuning results