Who did them for you?

When I get a chance I will check with him to see if he wants is name posted on OSO. He is a member of OSO and sometimes talking about someone without their permission on OSO gets out of hand. I will say that he owns a Skater and it is a very NICE PACKAGE!!!

I dyno'd a brand new 525 EFI last summer. It made 509 (standard correction) at the prop. If you factor in 11% drive loss (which i've confirmed many times) that works out to 570 at the flywheel. So, I'd say those numbers are right on. I believe Mercury uses the more conservative SAE correction factor whereas most independent dyno shops use the standard correction factor, hence the higher hp numbers you see.

Bob
Full Throttle Marine

I believe you are right on. There are two dyno correction factor calculation factors. Merc and the car builders reportedly use one method while most smaller engine builders use another calculation which gives about 5% more hp on the dyno. Both are SAE methods and neither is "wrong" just different.

Unless the correction factor with the atmospheric data used to calculate the correction factor is posted. These discussions are not very productive.

Post the uncorrected and corrected numbers with the atmospheric data: Barometric Pressure, Temp, Humidity etc on the day of the dyno and we can have a good discussion.

BTW the data is corrected to sea level at a temp like 65 or 70 F.

If this was dynoed in Michigan this week odds are that the correction factor should not be very large if any at all due to the weather. I had a .98 CF on one of my dyno sessions which means that the corrected hp was less than the uncorrected hp due to the cool weather and the barometric pressure.

There was a dyno sheet on another web site that used 27" Hg for the barometric pressure. Standard pressure is 29.96" Hg. So these guys tricked the correction calculation to give a 1.14 CF when the actual CF should have been 1.04 or so. Made about 60 hp difference.

27" hg is very rare at normal altitudes. Maybe in the eye of a hurricane.

I like what your doing, a baseline hp vs what your going to achieve with modifications. A word about "dyno testing standards" to clear the air on your hp numbers, OEM's-ie, auto makers. merc marine etc use j 1349 which corrects to 77 degrees , 99% of all other shops use the old "std" correctected to temp of 60 degrees which is the old "detroit" standard of 60 degrees which results in numbers 4% HIGHER than sae j1349. In you case your motor made 569hp, if you take away the extra 4% the "std" correction uses your 569 hp turns into 546.34 , not a big deal since EVERYONE else (other than oem's uses this) but it clears the air on your numbers for the people in question. All my dyno testing has always been done using the " 60 degree std" too so don't feel bad , no one is lying here it is just the way the world works, just make sure your dyno runs are all made the way the original one was for accurate comparison, Smitty