Engine dyno sweep RPM

[maxracesoftware]

by ClassAct » Mon Sep 27, 2021 4:24 pm

I’m interested in this.
What points on the time slip would you start with? 60 to 330 feet 330 to 660 or 660 to 1320?

I’m learning from this thread and it’s interesting.

i can calculate a bunch of different ways to achieve what you are looking for ,
any combinations of Feet Time MPH ,
but your best TQ and HP estimates will come from 660 FT -to- 1320 FT interval as Engine fights against the Wind ( aka= Dyno Absorber analogy )
and in the 660 FT -to- 1320 FT interval ... no more Traction problems crop up into calculations ,
no more RPM Shift points and Gear engagement problems ,
no more Clutch or Converter excessive Slip problems to account for ,
Engine RPM/SEC Rate is more stable and progressively constant .

another problem in Simulation is in this Picture that you will discover :
..... same ET and MPH in my previous Pics in what 425 HP would run and Engine RPM/SEC data

ETA_Calcs_comparisons.jpg

[maxracesoftware]

i might add that NHRA averages 660 and 1320 Feet MPH's over a 66 Feet distance
so that the ET Slip's MPH is really "Average MPH" ... and not actual real MPH that is at those distances

and that will change RPM at those distances
change RPM/SEC Rates ... Rotational Inertia difference for each rotating component
ETC .....

[ClassAct]

How I do it.

You take 2 MPH and their time points.

You convert MPH to velocity in feet per second.

You subtract the first Velocity from the second velocity.

You subtract the first time from the second time.

You divide the results of the time difference in the results of the velocity difference.

You then divide that answer by gravity.

Stan

I’m interested in this. What points on the time slip would you start with? 60 to 330 feet 330 to 660 or 660 to 1320?

I’m learning from this thread and it’s interesting.

What I posted uses MPH / Velocity. The time slips that I have seen only have 1/8 mile and quarter mile MPH. 60 to 330 feet 330 to 660 or 660 to 1320 would be time and distance which would be a difference set of formulas.

Stan

Got it. I see where I missed it.

[ClassAct]

by ClassAct » Mon Sep 27, 2021 4:24 pm

I’m interested in this.
What points on the time slip would you start with? 60 to 330 feet 330 to 660 or 660 to 1320?

I’m learning from this thread and it’s interesting.

i can calculate a bunch of different ways to achieve what you are looking for ,
any combinations of Feet Time MPH ,
but your best TQ and HP estimates will come from 660 FT -to- 1320 FT interval as Engine fights against the Wind ( aka= Dyno Absorber analogy )
and in the 660 FT -to- 1320 FT interval ... no more Traction problems crop up into calculations ,
no more RPM Shift points and Gear engagement problems ,
no more Clutch or Converter excessive Slip problems to account for ,
Engine RPM/SEC Rate is more stable and progressively constant .

another problem in Simulation is in this Picture that you will discover :
..... same ET and MPH in my previous Pics in what 425 HP would run and Engine RPM/SEC data
ETA_Calcs_comparisons.jpg

If I get a copy of your V4.70 PipeMax I can calculate all that?

[maxracesoftware]

by ClassAct » Mon Sep 27, 2021 9:45 pm

If I get a copy of your V4.70 PipeMax I can calculate all that?

i wouldn't recommend V4.70 PipeMax just for calculating HP like that !
that HP Calculator is too "bare bones" with a lot of variables grouped together in a few Inputs ,
so that some variables have to be very accurate or you might get wrong HP .

[weedburner]

Do modern engine dynos have the ability to do 2250rpm/sec sweep rate? If so, has anyone done a sweep up vs sweep down comparison of accel/decel at the same rate?

Grant

[ClassAct]

Do modern engine dynos have the ability to do 2250rpm/sec sweep rate? If so, has anyone done a sweep up vs sweep down comparison of accel/decel at the same rate?

Grant

Good questions.

[sr4440]

Do modern engine dynos have the ability to do 2250rpm/sec sweep rate? If so, has anyone done a sweep up vs sweep down comparison of accel/decel at the same rate?

Grant

I have a SF Powermark dyno, I do a sweep up and down as part of the calibration of the dyno for each engine. Superflow has, what they call, a "inertia correction factor". What this " factor" does is corrects for the weight of rotating assembly (crank, flywheel, driveshaft) being accelerated. When the factor is correct the engine will read the same HP/TQ number at the same RPM regardless of the sweep rate or test type. Meaning a step test will read the same as a 600 RPM/sec test.
But to answer your question, " sweep up vs sweep down comparison" without correction the decell will read higher because the energy stored in the rotating assembly getting to the test rpm will have to be removed by the brake when slowing it down.

Joe