Dynapack vs. iphone app

[slowpoke]

in my continuing quest to know what mod's have been done to my car I did a couple of dyno pulls.  We could call these "before".  

 

Notes:

1) the body is a 1970 1600

2) the P.O. says its a replacement 2.0L w/ 9.25:1 compression (but the tested compression comes in around 145psi), and it spews blue smoke like nobodies business.

3) i thought (apparently incorrectly) that it had the original 4.10 rear diff but turns out its a 3.64

4) the car weighs in at 2200lbs (resolution 20lbs) as there's a certified scale at the driveway paver store 1/2 mile away. 3/4 tank, spare tire, not me ;-)

 

High level results are:

73 whp from Dynapack  (from what i've read this is 8-10% lower than Dynojet roller dyno)

74 whp from iphone app

 

i guess its like my buddy says: "physics doesn't care how much you paid when calculating answers..."

 

First plots are Dynapack wheel dyno near my work - $100 for three pulls fun! but ended up smelling like burnt oil the rest of the day...

 ... oh, and they entered 3.55:1 rear diff after the 4.10:1 didn't match.  i couldn't remember the 3.64 until after and they typically work on 'merican iron. hence the 3.55

 ... if you look closely i corrected for the difference between 3.55 and 3.64 in pencil on a couple of the plots.  affects rpm, which affects hp. don't think it the measured torque at the wheel...

 

 

Last plot is screen grab later in the day using the PerfExpert iphone app.  This worked much better now that i've got the right rear diff and the actual weight...

 

i guess what makes the app closer is:

i) i had a very accurate weight

ii) it was a 2nd gear pull so air drag was probably not much of a factor

iii) clearly no wheel spin

iv) because the pull took so long the signal to noise was probably better than average...

 

pretty much this was probably ideal conditions for the app, was honestly surprised at how close it was

 

 

Edited May 9, 2018 by slowpoke