When you do the modification, take the vehicle back to
the same dyno and test it again.
It was pointed out to me that if you do two back to back runs of the same car on
the same dyno the graph of the results will be different.
Same day runs of the same car on
the same dyno should be the same or very nearly the same (keeping in mind that a cold, a warm and a heat soaked car will all make different horsepower).
You want as close as you can get and using
the same dyno is about the only way to do it.
Not exact matches
You can look at the
dyno graphs for a naturally aspirated and turbocharged engine (on the
same bore, stroke, cam) and they will peak and drop around the
same area.
However, Lieberman takes issue with this quoted figure, citing a
dyno test which reported the M5, which is powered by the
same engine, as pumping out a whopping 660hp.
Porsche claim the
same 381 hp (284 kW) power output as the standard GT3 but Porsche's control
dyno showed a jump to nearly 400 hp (298 kW) The RS also has progressive springs rather than linear.
We've seen engines explode on tuned sports cars running on
dynos before, but how about a DT466 diesel engine... yes the
same kind used in tractorpulling competitions, exploding and flying through the air?