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MacDizzys and other forums on two stroke performance stuff. Anyone have any good ones to mention.? Im just trying to read up on two stroke engine stuff Thanx
 

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JSYK... I do know how to dig for them, and, DIFFERING DYNO SYSTEMS "DO" produce "different results"... As well as "production tolerances" creating variables.. Ever seen the 2003 F5 that dyno'do at 93._ hp for the Old Forge Shootout? Those were 105hp (according to CAT)

Jim goes much further than AC ever would (or could) in helping folks FIND where their most useable HP is at, and, shows safety range of BFSC rates to avoid disastrous results (AGAIN, something Cat would never do), way more detailed, more specific, etc.,,,

E., You (of all folks) should know the results a comment as such results in.
 

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Alright, alright,,,

In my racing days I knew a lot of engine builders and spent some time on a Superflow flow bench as well as a Dyno cell. and I have 8 dynos at work right now. I can tell you this, you can take one motor ONE, the same one, never disconnect it from the dyno run it one day, come back a week later fire it up again when the weather is different an you'll get different numbers.

E., not knocking you but I'll give credit where credit is due. Rusty always brings up clutching when someones in a horsepower conversation, that's always a good point. All the power in the world is useless if you cant get it to the ground
 

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Tony, you are spot on about power varying on a given day vs another.. Production (castings) tolerances also affect flow rates, thereby changing power numbers between two different engines..

The differences elsewhere throughout a powerplant can easily equate to a 7-15 hp difference..
That is the whole reason I gave the 2003 F5 dyno test done by Jaws Performance for American Snowmobiler magazine.... Those APV'd engines (when the APV's are working properly) are pretty consistent in making good horsepower for a little 500...
But (as SOME fail to realize), there are BOTH, "DUD's" and their opposites, "Ringers".... And more than likey, there have been enough differences between these YAMAHA engines that are being dyno'd to show these hp variances... Which leads to next point here (which I'm SURE that YOU are aware of)...

Different dyno's (and/or facilities), due to variances in how their systems are calibrated to show consistency time and time again (and not get roller coaster graph chart results), will read differently from one DYNO to the next (using the same exact engine/exh/intake/ignition on all of them).... The BIGGEST result of a dyno (to serious sledder's anyhow), is the band of rpm's in which peak torque and peak hp are registered (stock or with each mod added along the way)....

Like you said my friend... All the HP in the world isn't jack:turd: if it cannot be put to the ground EFFICIENTLY through accurate clutching.., ;)
 

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Which leads to next point here (which I'm SURE that YOU are aware of)...

Different dyno's (and/or facilities), due to variances in how their systems are calibrated to show consistency time and time again (and not get roller coaster graph chart results), will read differently from one DYNO to the next (using the same exact engine/exh/intake/ignition on all of them).... The BIGGEST result of a dyno (to serious sledder's anyhow), is the band of rpm's in which peak torque and peak hp are registered (stock or with each mod added along the way)....

Like you said my friend... All the HP in the world isn't jack:turd: if it cannot be put to the ground EFFICIENTLY through accurate clutching.., ;)

Newbies are you all paying attention

Your in the old ZR forum so a lot of you are short on cash and can't afford everything in the catalogs. Pay attention to us two old farts here because this is the chat that will save you a lot of money. Read this again,

ALL THE HORSEPOWER IN THE WORLD MEANS NOTHING IF YOU CAN'T GET IT TO THE GROUND
 

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thumbguythumbguy

Very good advise. 2 thumbs up.
 

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Gonna pin this one.... It is an eye opener as Tony pointed out... I feel it will help a lot of folks get the FULL TRUTH when it comes to adding on aftermarket components without verifying its legitimacy first..

E., if the OEM's would publish their info on BSFC's and so on, THEN I'd tend to side with you.... However, since they don't, and a Cat cannot come clutched even remotely close to where its hp is, I stand my ground here...
 

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Everybody's got a view on the horsepower publishing game. From all my years I've seen enough to know it's a good guide but it doesn't mean everything. And if it doesn't, then take that with a grain of salt. Example; in one of our cells the barometric pressure sensor enclosure got whacked with a broomstick one day early and no-one told anyone till around 1 pm one day. Guess what that guy in that cell had to do? Pull all the engines that ran that morning and do them over because all of them went through a cell that was out of calibration. Now suppose that guy didn't say anything and one of those units made it to a magazine. Hmmm? now all of a sudden those numbers are going to be gospel.

427 L88's from GM were rated at 425/435 horsepower. People took that as gospel. When behind thew scenes GM was worried about insurance implications so they purposely published those numbers. What they didn't publish is the fact they also put out a lot more, close to 500 horsepower.

Now lets put in E.'s AND Rustys senarios of whos right and whos not. Your the OP now and you wanna add stuff and you wanna add whatever, a can a pipe a y-pipe whatever to achieve what he thinks is "X" horsepower based on what now? When were all the machines in question calibrated, if at all. Even IF they were the OEM?
Doesn't mean anything even if you knew.

Ron Hottles, the designer and builder of the infamous Sesco Chevy USAC midget motor never believed in a Dyno, hence to this day no-one really knows how much horsepower they had.
 

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And Fords single 4-bbl 427 (425ci actually) SOHC Cammer went waaaay beyond the 616hp @ 6,000 rpm's (that their dyno graph listed them as)...
Most wouldnt believe how high the dual carb engine went... (Yes, it was that high..)

Again insurance rates and company secrecy play into the game...
 

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426 hemi was published at 425 hp but we all know that wasn't true lol
 

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Well I will add to the topic. Check out....

Everything2Stroke

I will also add I personally know what happens in a dyno room from the 30 or so trips to the engine dyno I made myself. IMO Dynotech is a great place to learn a lot of things. There is some very good tech papers on that site from port angles to cylinder head design let alone a lot of other aftermarket product test. There is multiple things to look at when you are looking at a dyno sheet. BSFC, Fuel in pounds per hour, The correction factor, Etc, etc. If you have been to the dyno you will know what all those numbers mean and if someone is trying to pull BS on you with fake numbers. When you do go to a dyno you will ended up with at least 3 pulls just to see how much power you are making because of the Jetting, A/F ratio, BSFC.
 

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Thanks Al.... For once again, confirming that certain numbers mean a lot more to those who understand and can use them, than what the OEM's are willing to let out to the public..

Will have to stop by some night... Just that right now I'm down and out about my boss passing away Friday morning..... :(
 

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Discussion Starter #15
Thanx Guys!!

I have had the Gordon Jennings Book for many many years. i used to race Nitro methane two stroke s (Model airplanes U control and we did pretty good as young kids even raced and won in the states back in 1975 ) long ago. I am thinking of a computer program and would also lkike to hydroform my own pipes, Anyhow Hobbies and me usually get out of control a bit. The cat fever has hit me bad .This year bought a few and some engine bits. Anyhow thank you very much Interesting reading for sure. Mike
 

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Here is some info for the guys who want to learn what all those numbers mean on a dyno sheet. This was taking off a popular dyno web site. The dyno sheet is off a twin cylinder big bored Cat. If you read what all this means youwill have a good understanding of what goes on when dyno'ing your engine.

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 100th 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 airboxand 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.

DenAlt- “Density Altitude” in feet. This is a computed combination of barometric pressure, temperature and humidity averaged out into “feet”. This is particularly useful for tuners of carbureted sleds. With dyno power related to a particular jet size and density altitude, a Mikuni sled rule can be used with a $200 Kestrel 4500 hand held race computer to optimize jetting regardless of altitude or temp! And yes it works for racers and trail riders that run from well below sea level DA to over 7000 ft.

 

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FYI this was a EFI sled with a PCV that has both fuel and timing adjustment.
 

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Thanks for sharing Al. Very interesting for sure!
 
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