Dyno variance???

[midwest]

Gentlemen:

I've had my K-9 dyno'd and it produced satisfactory numbers. Earlier in the year I had a 107 installed on my 08 Street Glide. The engine builder said the motor produced 105hp, 116tq (scan I below, similar to BigDog S&S 117 numbers). I test drove the SG and there was a clear difference in the torque from a stock 96, yet did NOT have the torque of my K-9.

Shortly thereafter, I had a neutral HD shop dyno run the SG and showed significantly different numbers (scan II below, 92hp, 103tq).

Now, it's not my intent to chase numbers, despite how this may sound. However, the dyno sheets are showing a 13hp, 13tq difference...can anyone explain why theres such a variance?

I should note - both dyno's were 250i's, both runs were in the same gear. Conditions were very similar - dry outside, dyno run conducted indoors.

Lastly, I apologize introducing this here, should it offend anyone. I've viewed other forums and this one seems to CLEARLY offer completely objective forum members...others, not so much.

Thank you, in advance.

 

[Th3InfamousI]

Interesting...I'm not a numbers guy as long as its fun then its all good!

But, I would be surprised if a stock 107 with a 555 cam in a heavy Street Glide is making 105 hp, seems a tad high. Now if any other work was done its possible. Not saying the guy lied to ya but maybe his dyno isn't dialed in properly.

 

[midwest]

Th3InfamousI, without a doubt, the SG is fun, ESPECIALLY compared to the stock 96 inch motor...but I know it doesn't pull anything like my K-9. And I grant the SG the weight difference, on the seat of the pants dyno (which, as I mentioned above on the initial test ride), however, not being an engineer, I can't see weight being a power-robbing difference on a dyno.

Other than the 107 kit, the bike has a Bub7 2-1, SE Super Tuner Pro, stage II intake along with stock heads.

Overall I'm MOSTLY happy with it, I just don't understand why there's basically a >10% variance on the same bike from like equipment?

 

[toomanybikes]

Someone with better knowledge of the dyno charts will be able to explain this. I did notice that the first showed the numbers as STD and the second as SAE, which may explain some of the difference

 

[midwest]

TooManyBikes, ok I just reviewed the charts and see where STD and SAE were indicated in the results. Is there a correction factor involved between STD & SAE, perhaps?

 

[toomanybikes]

Found this on site talking about the differences with dyno printouts

Overview:
Most of the stated horsepower numbers are “Corrected” values. The correction standards were developed to discount the observed horsepower readings taken at different locations and weather conditions. It is obvious that an engine builder in Colorado could not produce as much horsepower as a shop at sea level. There is just less oxygen for the engine to burn at the higher altitude. What are less obvious are the other weather condition effects on the engine. So in order to compensate for this all advertised horsepower is “corrected” to several different industry standards.

SAE:
"SAE (Society of Automotive Engineers), USA. Power is corrected to reference conditions of 29.23 InHg (99 kPa) of dry air and 77 F (25°C). This SAE standard requires a correction for friction torque.

STD:
STD is Another power correction standard determined by the SAE. Power is corrected to reference conditions of 29.92 InHg (103.3 kPa) of dry air and 60 F (15.5°C). Because the reference conditions include higher pressure and cooler air than the SAE standard, these corrected power numbers will always be about 4 % higher than the SAE power numbers. Friction torque is handled in the same way as in the SAE standard."

 

[Husker-Wolf]

STD correction is "typically" 2.6% more than SAE correction, but that's not the case with these two readings. It's really tough to compare dyno readings from two different machines.

 

[midwest]

TooManyBikes & Husker-Wolf, thank you...your replies are clearing up my confusion (and cynicism, for that matter). Ah...Husker-Wolf, how has your experience been with the 120R? I priced the install of one on my 08 SG - $7700 complete from my LBS. Overall, I'm mostly pleased with the 107 build, however, if I were to do it again, I would have opted for the 120R...without hesitation.

 

[Husker-Wolf]

I would have to say that Harley got this one right. Mine dyno'ed at 132/132 and is fast as hell. I know some guys are getting 140hp out of them. I've put about 10K miles on in the first year and it's holding up well so far. I've taken some long trips, loaded down, and it still gets around 42mpg.

 

[Fibersnake]

On the first dyno, was the first run supposed to be on your stock bike mod and the second showing the high numbers on the same bike after mods? Also was the mod done by the dealer on the first or did they sell you the parts?

I am more suspicious of the first sheet than the second sheet myslef. That said that is many variable in a Dyno run and quick typical Dyno Jet on inertia roller will tend to be even more inaccurate in most shops.

There is some pass post on Dyno runs in the forum with lots of technical details that gets into specific that may help you. That said if thing are done right with calibrated equipment using proper CF and input data, all dynos will give very similar numbers under the same conditions (not exact but close). A spread like this is unusal unless something was not the same on the bike.

Here found a good post with some details that may help you understand Dyno in general.

http://www.bigdogbiker.com/forums/dyno-runs/6538-superflow-vs-dynojet-vs-other-dynos.html

 

[stlmikie]

I had my bike dynoed after some big changes and then he'd it done by a different outfit a year later and they were nearly identicle. (sp)?

 

[Fibersnake]

I had my bike dynoed after some big changes and then he'd it done by a different outfit a year later and they were nearly identicle. (sp)?

Do I read this right, same bike, basic same different dyno and pretty damn close to same results? If so that is the way should be. Did you get good numbers BTW.

Safe riding

 

[stlmikie]

Fiber. Yes , same bike two machines same numbers. I was giving a reference. My numbers were good. I think. Heck, I'm happy is what I'm trying to say. 110 hp and 125 tq. The guy that did the work thought the hp would be higher I'm a torque kind of guy anyway.

 

[Fibersnake]

Good to hear, thought that was what you were saying. Hell my eye have about had it today. Been running calcs all day for piping flows for a water pump station and well to cross reference some BS design one of the local gave me.

Sometimes we put in our contracts, requirement that a nuke station would be hard to meet and in reality it is such over kill for simple system, not much more than a step up from an old hand pump-ridiculus.

Time to quit it is getting close to midnight here.

Best to you and everyone

 

[midwest]

Fibersnake: Yea, I should have been more detailed on the first dyno sheet... The lower, 68hp base pull was on the 96" HD engine, the 105hp pull was following the engine build and tune. The tune and engine build came from an independent shop who produced the first dyno sheet (dyno I).

The second dyno sheet (dyno II) was from my local HD shop. They did not make any adjustments, just a 3-pull dyno run. The engine had no changes and the 107 then had maybe 600 miles on it.

StlMikie: like you, I was expecting similar numbers from two different machines...then again, I'm unfamiliar with with all the variables that could affect the reading from one to another...which is the reason I've been leaning on you guys today! I can see the 2.8% - 4.2% difference between SAE/STD, but over 10%??????

 

[toomanybikes]

Dyno calibrations, tire pressures, temperature and humidity are all factors that can produce differences between two similar dynos. Bottom line, are you satisfied with the butt dyno readings?

 

[john sachs]

Corey,
Something changed in the tune up, as you had a big torque dip on the 2nd sheet, which wasn't on the 1st sheet. There's a difference in temperature between all the pulls. The first dyno sheet corrected up in STD. The second, SAE, corrected down. STD WILL always read higher. Also barometric pressure is in millebars on the 2nd sheet(I don't know how that compares to the 1st sheet (in-hg)(conversion). Small changes in barometric pressure can make a big difference on the dyno sheet. The lower the pressure, the higher the power and torque readings.
Toomanybikes has some other reasons for possible differences.
John

 

[midwest]

TooManyBikes & John Sachs:

Overall, I am mostly pleased with the end product. There is a slight, and persistent, hesitation when I crack the throttle hard (<2600rpm). I spoke with the engine builder and (wish I could relay a clearer description) he mentioned...increase speed of accelerator pump??? He likely used different terminology, one that you all may be familiar with...I'm just not sure. Anyhow, it was something related to right when the throttle is opened. Off idle, the throttle seems as though it cannot be blipped open for just a quick rev as it will die. While cruising above 2600rpm the engine is responsive and (mostly) without hesitation.

The torque dip. I witnessed the pulls on the second sheet. When the tech opened the throttle, I thought the engine was going to die...and in doing so, it seemed the engine took FOREVER to accelerate through the gear. The torque dip you mentioned, John, to me seems schizophrenic. Sometimes the throttle behaves and revs like a 2-stroke, other times the hesitation is pronounced and unpredictable in the low RPMs. The day of the 2nd dyno pull was the worst 'fall on its face' display I had ever seen.

Back to your question, toomanybikes - yes, the end product I'm happy with IF COMPARING to the stock 96" HD motor. When my research and questions began about the 107 build, I was told they would be able to get S&S 117-type numbers, and I'm just not seeing or feeling that. I realize the bike is considerably heavier than my K-9, however, I just thought the 107 build for the SG would be stronger (and behave predictably in the low RPMs, for that matter).

Dyno variance? Thank you all for explaining the variables surrounding why similar dynos can produce different numbers as this was making no sense to me....

 

[stlmikie]

The flat spot or hesitation your describing does infancy sound like the accel. Pump needs adjusting. When you first crack that throttle open there isn't enough fuel for the amount of air. This is where the pump comes in. When you crack it it sprays a fan of fuel at the same time. If its not set correctly it will "fall on its face". It is fairly easy to adjust. If you do a search on here you'll find a couple how to's and you could go to S&S's website. They too have instructions. I'm assuming you have an S&S carb?

 

[midwest]

Stlmikie: My K-9 does have an S&S G carb, and that bike runs great. The K-9 has been my benchmark for all the modifications I've had to my Street Glide. Both of the dyno sheets are for my 08 Street Glide. The flat, or should I say, GAPING HOLE, on the graph of the 2nd sheet is on my SG.

I began the DYNO thread on BDB because there seems an amazing wealth of overall MOTORCYCLE knowledge here, along with no one getting fussy about this or that. The thread not only answered my dyno ambiguity questions, it's directing toward my next problem, my Street Glide...Dam Thing (sp?)

BTW, love the Avatar! Do they make the 'Major League Infidel' in a t-shirt? Gotta have one!