The Indy Racing League is to revert to its 3.5-litre engine capacity in time for the 2007 season, this week's Autosport reports.
The IRL mandated a reduction of half a litre before the 2004 Indianapolis 500. The move was in response to concerns about high speeds on superspeedways after Tony Renna's fatal testing crash there in October 2003.
The change decreased power outputs by almost 10 per cent.
The make-up of the series has changed since then, however. Honda is now the sole engine supplier, so the series is looking to increase engine life and find more torque on the road and street courses that have joined the calendar.
Another pressing reason for the change is the switch to ethanol fuel next year, which is expected to give significantly less power than the current methanol/ethanol mix.
The first test for the increased displacement units, which are all supplied by Honda Performance development in California, should take place after the series finale next month.