Rear wheel horsepower PID - ?

[Boost]

I am using this as a reference point because A) the RWHP #s are "mostly" realistic B) the ones that have higher #s "feel" better C) it's a reference point or baseline.eads

What does the PCM look at to calculate this and how accurate is it? Because sometimes I put together a decent tune and it reads way too low, and sometimes when I jump a bump it reads 1000 hp. All in all I am now on a 220 rwhp program with my 270 hp truck that feels pretty strong and has some KR and sets P0101.

[joecar]

You mean the CALC.RWHP pid...?

The scantool calculates it using P = m.v.dv/dt... it calculates power from the rate of change of VSS;

i.e. it calculates the power left over to accelerate the vehicle after canceling out friction (aerodynamic, mechanical, road);

The pid sample rate being 10 samples/second is not sufficient to give enough resolution unless the change in VSS is almost constant.

When you jump a bump, VSS suddenly shoots up giving you a falsely high power calculation.

When you use this pid for comparative purposes, you have to control the conditions.

[Gregs]

i know this thread died out before i was around, and it seems like it left a lot of hanging... was it ever established exactly how accurate this pid is?
http://forum.efilive.com/showthread....P-and-EFI-RWTQ

[WeathermanShawn]

Guys, I routinely utilize this Pid. As Joecar mentioned consistency is the key.

A lot depends on what gear you are in. For example in 3rd gear I can average ~270-330 Net HP per 1 second. 4th gear is ~240-270 as you have increased air resistance.

My Atmospheric Correction here is ~ 1.16. 300 net HP = ~ 350 HP SAE. I dyno at ~425 SAE. So my Net HP is still about 20 % lower than a dyno.

You could probably make a Calculated Pid that would have atmospheric correction, wind resistance, etc., but the bottom line is I try to find the same flat road and hit a 50-80+ mph run to compare...

[Boost]

+1 I figured so, for baseline comparison purposes it's not bad if you control the conditions. Thanks for the info.