Dynamometers
Seasoned HDF Member
Joined: Aug 2008
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mr. max makes some good valid points
second, a mfg advertised performance figure is an elusive beast and means nothing. it is a generic cookie cutter number.
third, a dyno run is good for tuning and diagnostics but lacks the ability to predict real world performance, it is a starting place.
there are soooo many factors when using dyno numbers, i had mine done three times for grines and giggles when the mobile unit came to a nearby hd store. each run was diff and nothing changed.
as an example, hp number do not mean much:
aj floyt was at the track and smoking the competition with his daily runner chevy wagon, yep he drove the streets. well the losers got their panties in a bunch and file a complaint so the officials loaded a few bags of concrete in the rear of the wagon.
WELL, he smoked them even worst, they shut up and NEVER questioned him again. little did they know, the weight got his traction up and out the hole quicker.
why do some race circuits demand throttle plates???
many people forget about after peak numbers, here i would rather have my numbers carried further up the scale than fall like a rock. if i carry my power 200 rpm further than the other guy, i shift out at a higher speed and take advantage of my gearing multiplication. one reason i chose to retard my cam timing.
numbers do not win all the time, i have seen toooo many times a lesser machine walk away victorious.
second, a mfg advertised performance figure is an elusive beast and means nothing. it is a generic cookie cutter number.
third, a dyno run is good for tuning and diagnostics but lacks the ability to predict real world performance, it is a starting place.
there are soooo many factors when using dyno numbers, i had mine done three times for grines and giggles when the mobile unit came to a nearby hd store. each run was diff and nothing changed.
as an example, hp number do not mean much:
aj floyt was at the track and smoking the competition with his daily runner chevy wagon, yep he drove the streets. well the losers got their panties in a bunch and file a complaint so the officials loaded a few bags of concrete in the rear of the wagon.
WELL, he smoked them even worst, they shut up and NEVER questioned him again. little did they know, the weight got his traction up and out the hole quicker.
why do some race circuits demand throttle plates???
many people forget about after peak numbers, here i would rather have my numbers carried further up the scale than fall like a rock. if i carry my power 200 rpm further than the other guy, i shift out at a higher speed and take advantage of my gearing multiplication. one reason i chose to retard my cam timing.
numbers do not win all the time, i have seen toooo many times a lesser machine walk away victorious.
Last edited by bustert; Feb 11, 2021 at 09:32 AM.
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Then let's not forget that the dyno's used today can be cheated, for bragging rights. I've seen more tricks played to get a dynosheet to look a certain way and that's almost ruined the use of them for any meaningful information. Your spinning a drum of some amount of weight and that's all it is. When used properly its a good test bed with lots of useful information, but when used for bragging rights its bad news. You will see people posting sheets in STD because it shows and unrealistic power output, others who remove the A/C because it shows again a better set of numbers, then yet others who cool the top of the engine down keeping the lower end hot because it show better numbers. All games just for the sheet and bragging rights.
The best way to find how good or bad your engine is working is to take the bike and accelerate it while in 3rd gear on a closed coarse and accurately measure the time it takes to do it. Run the engine in the RPM range that your interested in. For a Street ridden HD that should be 1500 - 5000 for 98% of the riders on a Harley. For drag racing you would change to 4000 - 6500 RPM. Once you have a good baseline set of numbers you make your changes then repeat the testing. This way removes all the shifting and wheel spin from the picture and you get to see your true results, but no sheet of paper to sit at the bar with!
The best way to find how good or bad your engine is working is to take the bike and accelerate it while in 3rd gear on a closed coarse and accurately measure the time it takes to do it. Run the engine in the RPM range that your interested in. For a Street ridden HD that should be 1500 - 5000 for 98% of the riders on a Harley. For drag racing you would change to 4000 - 6500 RPM. Once you have a good baseline set of numbers you make your changes then repeat the testing. This way removes all the shifting and wheel spin from the picture and you get to see your true results, but no sheet of paper to sit at the bar with!
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From: Poolville
Then let's not forget that the dyno's used today can be cheated, for bragging rights. I've seen more tricks played to get a dynosheet to look a certain way and that's almost ruined the use of them for any meaningful information. Your spinning a drum of some amount of weight and that's all it is. When used properly its a good test bed with lots of useful information, but when used for bragging rights its bad news. You will see people posting sheets in STD because it shows and unrealistic power output, others who remove the A/C because it shows again a better set of numbers, then yet others who cool the top of the engine down keeping the lower end hot because it show better numbers. All games just for the sheet and bragging rights.
The best way to find how good or bad your engine is working is to take the bike and accelerate it while in 3rd gear on a closed coarse and accurately measure the time it takes to do it. Run the engine in the RPM range that your interested in. For a Street ridden HD that should be 1500 - 5000 for 98% of the riders on a Harley. For drag racing you would change to 4000 - 6500 RPM. Once you have a good baseline set of numbers you make your changes then repeat the testing. This way removes all the shifting and wheel spin from the picture and you get to see your true results, but no sheet of paper to sit at the bar with!
The best way to find how good or bad your engine is working is to take the bike and accelerate it while in 3rd gear on a closed coarse and accurately measure the time it takes to do it. Run the engine in the RPM range that your interested in. For a Street ridden HD that should be 1500 - 5000 for 98% of the riders on a Harley. For drag racing you would change to 4000 - 6500 RPM. Once you have a good baseline set of numbers you make your changes then repeat the testing. This way removes all the shifting and wheel spin from the picture and you get to see your true results, but no sheet of paper to sit at the bar with!
That's precisely why I used my Wego III on my carbed 98 Fatboy, to data log Time, AFR's and rpm's for quarter mile.... But I did that on an out of the way road (quite secluded).. However I did the runs from A dead stop which gave me a lot of wheel spin in 1st, 2nd and 3rd.. This spring I will try the 3rd gear roll on and record all that data from 2000 rpm to 6000 rpm.. Thanks Steve... Would you know what would be a respectable time? Thanks...
Last edited by 98hotrodfatboy; Feb 11, 2021 at 12:10 PM.
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All great responses, thanks guys..
That's precisely why I used my Wego III on my carbed 98 Fatboy, to data log Time, AFR's and rpm's for quarter mile.... But I did that on an out of the way road (quite secluded).. However I did the runs from A dead stop which gave me a lot of wheel spin in 1st, 2nd and 3rd.. This spring I will try the 3rd gear roll on and record all that data from 2000 rpm to 6000 rpm.. Thanks Steve... Would you know what would be a respectable time? Thanks...
That's precisely why I used my Wego III on my carbed 98 Fatboy, to data log Time, AFR's and rpm's for quarter mile.... But I did that on an out of the way road (quite secluded).. However I did the runs from A dead stop which gave me a lot of wheel spin in 1st, 2nd and 3rd.. This spring I will try the 3rd gear roll on and record all that data from 2000 rpm to 6000 rpm.. Thanks Steve... Would you know what would be a respectable time? Thanks...
Doesn't really matter if your testing your changes. What I've done for years is to get the bike up to normal operating range of temperatures then once in 3rd with the clutch out, slow the engine to below 1500 RPM and go WOT as fast as you can twist it. Most if not all street engines will never spin the tire this way yet you can see just what it's doing if your recording the data with a fast enough recording device. The problem is many device record way to slow to make it meaningful data. If your recorder is sampling at better than 30HZ there is some very meanful data in the recordings but if it only runs at 2 HZ the resolution is just too slow to look at the various ranges. At 30Hx and above you can see clutch slip in very good detail over very short RPM ranges.
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From: river
Then let's not forget that the dyno's used today can be cheated, for bragging rights. I've seen more tricks played to get a dynosheet to look a certain way and that's almost ruined the use of them for any meaningful information. Your spinning a drum of some amount of weight and that's all it is. When used properly its a good test bed with lots of useful information, but when used for bragging rights its bad news. You will see people posting sheets in STD because it shows and unrealistic power output, others who remove the A/C because it shows again a better set of numbers, then yet others who cool the top of the engine down keeping the lower end hot because it show better numbers. All games just for the sheet and bragging rights.
The best way to find how good or bad your engine is working is to take the bike and accelerate it while in 3rd gear on a closed coarse and accurately measure the time it takes to do it. Run the engine in the RPM range that your interested in. For a Street ridden HD that should be 1500 - 5000 for 98% of the riders on a Harley. For drag racing you would change to 4000 - 6500 RPM. Once you have a good baseline set of numbers you make your changes then repeat the testing. This way removes all the shifting and wheel spin from the picture and you get to see your true results, but no sheet of paper to sit at the bar with!
The best way to find how good or bad your engine is working is to take the bike and accelerate it while in 3rd gear on a closed coarse and accurately measure the time it takes to do it. Run the engine in the RPM range that your interested in. For a Street ridden HD that should be 1500 - 5000 for 98% of the riders on a Harley. For drag racing you would change to 4000 - 6500 RPM. Once you have a good baseline set of numbers you make your changes then repeat the testing. This way removes all the shifting and wheel spin from the picture and you get to see your true results, but no sheet of paper to sit at the bar with!
Not all dyno operators/tuners are cheats and number fudgers. There are some great, honest and really good dyno tuners out there. Just sayin, the dyno is a great tool in the hands of the right person.
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I agree 100%. Its just sad there are those who feel they need to cheat the results and when the honest guy comes along, the customer questions "why are your results so much lower than what the other guy gets" or "it said so on the internet"!
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hummm, why even dyno if you want to cheat, yep, they got an app for that.
not seen it on mc's but the computer in a cars can give some pretty good insights in actual operation. my software has a dyno section.
although i did the dyno thingy, i still like the tried and true butt dyno, if i am happy its all the grin factor i need. i never was into how fast from x to z, i am all about top end. i guess this is a throw back to the sixties doing the two stoke thingy. it was all about who was fastest, what do you expect from small displacement engines. in the dirt, skill out weighed power hands down.
how about a twinjet 100 doing 120mph. my suzuki b100p would do 85mph.
not seen it on mc's but the computer in a cars can give some pretty good insights in actual operation. my software has a dyno section.
although i did the dyno thingy, i still like the tried and true butt dyno, if i am happy its all the grin factor i need. i never was into how fast from x to z, i am all about top end. i guess this is a throw back to the sixties doing the two stoke thingy. it was all about who was fastest, what do you expect from small displacement engines. in the dirt, skill out weighed power hands down.
how about a twinjet 100 doing 120mph. my suzuki b100p would do 85mph.
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From: Poolville
Speed is nice also... Won't disagree there.. I once had my 98 Evo doing 137 in the HOV lane on the LIE.. I was in 5th gear and still had 6th.. I thought that was enough for that road..
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