Originally Posted by Andy.F

Any car using an airflow meter such as the Subaru (especially if it has an induction kit fitted) will run totally different on the rollers to how it will on the road.
Why do you think the AFR changes when out on the road ? it's because the primary load reference value has changed. When this changes so does the ignition timing, so you can fine tune all you want on the rollers to get your desired bhp numbers............just be sure to go out on the road and do it properly afterwards ;)

Andy