Generally speaking, you will see higher numbers from an inertia syle dyno than you will from a dyno that puts a load on the drums/rollers.

Dynojet (inertia mode) vs Mustang dyno (loaded) can show a 5-10% or more variance in numbers. (The Superflow I use at Loynings Engine Service loads up the rollers.)

The main thing is to find a competent operator and stick with them for consistancy. There are variables that will effect the absolute numbers from dyno to dyno.

In your case, it sounds like a good operator with a Dynojet is what you're looking for.
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