Honest hp numbers
- Thread starter Bbrstompit
- Start date
I have sensors for Engine RPM, Wheel RPM (2 magnets), CHT, EGT, Mass Airflow Sensor, Intake air temp and a built in weather station for ambient air temp, Humidity and Barometer. I have found that you can tune the engines on a sunny day or a rainy day and get the same dyno results with the corrective software. But they will not perform the same on the track. An engine tuned on a rainy day will be great on a rainy day but will be down on power on a sunny day. It's not a lot of difference but when 10th's of a second count it can be significant.
alvin l nunley
Site Supporter
That's good, your number matches my number in my dyno spreadsheet. The thing is, that .021 represents a change in humidity of 50 points. From 30% to 80%. Seldom are you going to see that much of a change in "actual" humanity through the day. Even then, increased humidity comes with an increase in temperature. Many times that means a drop in the barometric pressure. As far as horsepower is concerned, it may end up being a wash. More and more I believe that air density is the thing to watch.
steve baker
Moderator
Definity air density................HP is proportional to the mass air flow rate! I agree with you Al.........
We have auto test conditions with our weather station built in humidity and temperatures are huge factors on your dyno pull but we are only using ours for tuning and comparison but then again we know we can make them read 30 hp some of the guys that brag about 12 and 13 hp come to see what they have just to go home not happy !!!!!
DynoDon
Moderator
on a side note, i sent my flathead back in the day to checkered flag for a dyno test. Checkered flag did the first video on the flathead called from the box to the dyno. They did the video in steps as they made changes within the rules. After each change they would do a run on the dyno. I ask them to send me the dyno sheet back with my engine and they did. I then began tweeking my torque arm to get the same numbers they got on a day that was very similar to the correction factors they had when they dynoe’d mine. How close/accurate was their dyno you ask. Well, i would say pretty close when you consider that the 212 is extremely close on my dyno when i calibrate to that engine.
alvin l nunley
Site Supporter
I'm wondering, when James Watt came up with the formula for calculating horsepower, why didn't he include "absolute" humidity in that formula? I can't help but think; he must have known what a big part it had in an engines performance, if it does!
When, whoeve it was, came up with the correction factor formula, didn't they understand what a big affect humidity has on horsepower, if it does? Why do all the dynamometer manufacturers, to this day, ignore the effects of humidity in their calculations of HP? Is it that hard to compensate for?
People want to know!!
When, whoeve it was, came up with the correction factor formula, didn't they understand what a big affect humidity has on horsepower, if it does? Why do all the dynamometer manufacturers, to this day, ignore the effects of humidity in their calculations of HP? Is it that hard to compensate for?
People want to know!!
Pete_Muller
Moderator
Possibly because it was the late 1700s when he came up with it?
steve baker
Moderator
Possibly because steam engines didn't care about humidity!
alvin l nunley
Site Supporter
I can agree with your statement, if!! If all you want to do is compare last week's build with this week's build, it makes absolutely no difference what the actual peak torque and peak horsepower numbers are. What I have a problem with is people posting those numbers without verifying they're correct! I'm sure it's not an easy thing to do, but I think it's doable.
I once saw a HP curve of an open Briggs (clone!) Were at the absolute peak the HP curve jumped up rather steeply at the peak RPM point of the curve. When I entered the numbers in my HP spreadsheet, I found that his computer was giving him delayed numbers. Can't really explain that. After back figuring the numbers, I concluded there must be a delay between the time the torque number is recorded and the time when the RPM number is recorded. Enough of a delay that the curve was skewered. One can only wonder what that delay was doing with the rest of the curve?
Another problem could be calibration. I had a weight, its weight was precisely measured, that I would hang on my water break for calibration. How they would do that with an acceleration dyno I have no idea.
Freezeman
Site Supporter
Alvin, I think I remember that an acceleration dynos weight of the wheel that is accelerated and timed to record and measure torque is calibrated by the time it takes for it to decelerate from a given rpm back down to 0 rpm. Instuctions to do that are in the Performance tends instructions.
alvin l nunley
Site Supporter
Without a doubt, I'm sure the people who build those things know what they're doing.
Don may I ask what type clutch you use and the engagement I have used the same clutch for 20 yrs and just changed it to another just like it believe it or not it’s a max torque always start my run at 2800rpm is where it’s calculated from and stop at 6800 to 7000 but we do have some that just wants to keep on going and I’m not gonna mention the rpm it stops some say it’s bs but that’s ok to 
steve baker
Moderator
Nice picture ! 3 question..........what style load cell are you using ( looks like your brake housing is bolted down ? ) & do you use Performance Trends software & is that a Stuska water brake ?