Perfexpert

[Pfreen]

Has anyone used the app perfexpert for ios and android?  Just used it and got the attached results.  It costs 9.99.

[gideon]

I haven't used it, but it does look useful.  One aspect that I would question is the model of aerodynamic or total drag that it uses.  The Europa has very low aero drag compared to most cars, so I wonder how well the app models that.  What information can you give to the app about that? 

It occurs to me that you could get a good estimate of the total drag by doing a deceleration run,  i.e. find a flat piece of road, get the car up to, say, 60mph then put it in neutral and let it coast to a stop.  Then, if you are pedantic like me you'll do it again in the opposite direction.  The average of the two runs gives you your drag curve.

[Pfreen]

Gideon.  The inputs to the program are cda (I used .29*15.75 ft^2), curb weight with full tank of fuel, fuel level, driver weight, and cargo weight.  It also needs the speed per 1000 RPM for gears 2-4.  Also wheel dimensions.  I tested my car on a chassis dyno within the last few months.  That test was conducted in 4th gear while thistest was in 2nd gear.  The chassis dyno results were similar at 115bhp.  The peak torque was at around 5200 RPM. 

I plan on using this to evaluate engine changes on performance with this app.  I am putting a Fidanza lightweight flywheel on on I wanted to be able to measure the difference, instead of “feeling” a difference.

I would not expect the hp measurement to be dead nuts, but it should be consistent.  A 0-60 time is very much dependent on the shift points, so is not very repeatable for small engine performance changes. My hope is this app, which uses acceleration to calculate bhp is more repeatable.

Check out their website http://www.perfexpert-app.com.

[gideon]

Where did you get the 15.75 ft^2 figure from?

[Bainford]

I plan on using this to evaluate engine changes on performance with this app.  I am putting a Fidanza lightweight flywheel on on I wanted to be able to measure the difference, instead of “feeling” a difference.

I will be very interested in hearing any results from fitting a lightweight flywheel, either numbers or 'seat of the pants' feel.

[Pfreen]

The 15.75ft^2 area is the front projected area.  The cd of .29 is widely published.  I used the projected area numbers from https://www.automobile-catalog.com/make/lotus/europa/europa_1_s3/1973.html

[gideon]

Right, I knew that number was meant to be frontal area.  What I don't know is where you got the frontal area figure from.  I haven't seen it published anywhere. 

[Pfreen]

The website I attached publishesthe data I used.