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dyno question

JJDH

JJDH

Active Member
need some help here...at a bike rally i had my bike dynoed, paid 20 dollars, this was on one of those portable dynoes, it made 79.5 hp. it was a stock 96 with a heavy breather, no tuner, no exhaust on a 2010 street glide.
now i went ahead and bought a sest for compulsive purposes and had century harley tune the bike, their tuner guy has a good rep, i let him tune it. the bike made 76.5 hp, now with the d and d 2 into 1, heavy breather. of course i asked why the change, they said the portable dyno may not have been accurate, the conditions didnt matter because the humidity and temp were better the day the dealer tuned the bike... is it a true statement that the portable dyno may have been off, or that the dealers dyno was reading low because of the new program they have in the dyno? they just had a dyno shootout this weekend and a few people were upset because their built up bikes were a few hp low on the dyno? any advice or exact answers on this???:newsmile082:
 
Dyno's and their results are only as good as the operator. The operator can make the dyno "say" anything he wants it to say.
 
how though? any short explenations, on the portable he didnt do anything funny looking to get the high number... so which is accurate?
 
on a dyno they use a correction factor to smooth out the graph .. say a sae 5 gives ya a rating of 79.5hp but a 10 or a different way of smoothing will give you more HP ... you would need to search how a dyno works and the way the software and corrections are done.. its a long long read with many different answers on who is right or wrong and what way is best..

put your bike on 2 dynos next to each other with different operators and the reading wont be the same .. with the same operator they will still be different but much closer

and of course the maker of the pipes site is gonna show the most HP
 
There are several factors that can influence numbers from a dyno. One being the type of dyno used (inertia vs eddy brake).

As far as corrections factors go, there are two standards commonly used for correcting power relative to atmospheric conditions:

STD and SAE.

STD is defined as: 59 F, 29.92” Hg, 0% humidity.

SAE is defined as: 77 F, 29.23” Hg, 0% humidity.


The STD or SAE correction is not correcting for drivetrain losses or
friction. It is merely correcting atmospheric conditions.

Typically STD corrections read slightly higher than SAE due to the multiplier used.

In your case it's hard to say exactly why the reading was higher on the portable than at the dealer.

It could be operator influenced, incorrect data input, dyno out of calibration, etc.

Did you get a dyno sheet from either place? If so, if you post it here it may tell the tale.
 
the sae was 5.. tomorrow i will repost the dyno sheets. i will have the wife scan them onto the puter so i can post a nice clear image, whenever i take a pic and post it it isnt very readable. for now its off to work in the mornin so i will let you kno.. thanks
 
the sae was 5
Click to expand...

That is odd. Typically you would see something in the range of say 98.0 to maybe 1.02.

That would be the multiplier.

"5".....I don't understand?!?!

Post the sheets when you can or if you already did just link to them.
 
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