How does an increase in GPS relate to power output?

[Matthew Harding]

At 12:31 PM 4/16/98 -0600, you wrote:
>
>     Guys:
>     
>     Quick question for you all....
>     
>     Before we make it back to a dyno, is there any way to calculate an 
>     increase in power from an increase in MAF readings (GPS)? Here is why 
>     I ask. A buddy of mine (Brian) just did a head/cam swap and showed a 
>     pretty decent increase in airflow from his previous runs. He went from 
>     252 GPS to 294 GPS (if I remember this correctly) from Diacom readings 
>     (could be off since he has a 96...which Diacom has a bit of trouble 
>     working with). When we made the earlier reading, he was at the dyno 
>     where he made 255 RWHP. Now, if I do a simple percent of increase in 
>     airflow and multiply by his old HP...I get 298 RWHP. Does this work, 
>     or are there other factors I need to take into account? The air 
>     pressure now was higher, but the air temperature was lower than when 
>     he made his dyno run.
>     
>     Now...the monkey wrench. On the SAME day he was at the dyno, I was as 
>     well. I made 278 RWHP with only 264 GPS airflow readings. So, if I do 
>     an interpolation using these numbers, I end up with nearly 400 RWHP he 
>     will be making. Now, the 298hp above seems a bit light, but the 400 
>     seems high (would be nice if it is correct though). So, first of all, 
>     does anyone have a formula that predicts power output based on airflow 
>     in GPS? Second, I assume it isn't a linear relationship based on the 
>     above....but should it be?
>     
>     Any feedback would be appreciated!
>     
>     Larry Kurek
>     
>     BTW..please copy my Lkurek at anl.gov address so I can get your response 
>     ASAP.

The difference in the relative GPS/RWHP ratio of yours and your friends car
is due to the efficiency of the two engines at burning the air/feul
mixture, this results from factors such as copression ratio , combustion
chamber shape/size etc, etc.

if you had the figures for the RPM at which the peak HP and GPS were
reached, then you could possibly make an estimation of the new HP reading.

eg. if the first peak reading was obtained at for example 5000 rpm then you
would need the new GPS reading for that rpm...

if the rpm at which the new reading was obtained has varied dramatically,
then it would be back to the dyno....

ask your dyno guy to print you a graph of GPS vs RPM, and RPM vs HP, then
next time you'll be able to estimate better no matter what RPM the new GPS
figure appears at.