So, you’re diving into the exciting world of swapping an H22 engine into your 3rd generation Honda Prelude? That’s a fantastic upgrade, offering a significant boost in power and performance. Like many who’ve taken this route, you’ll quickly encounter the question of OBD1 versus OBD2. This decision is a crucial fork in the road that will influence several aspects of your swap, from wiring to engine management. Having recently completed this swap with a buddy, I can share some insights to help you navigate this choice and ensure a smoother process.
One of the first major decisions you’ll face is whether to go the OBD1 conversion route or stick with OBD2. The original poster in the forum touched upon this, and it’s a point worth expanding on. Opting for OBD1 often involves converting your H22 distributor and crank sensor setup. This path is frequently chosen for its simplicity and the readily available support within the Honda tuning community. OBD1 ECUs are generally easier to chip and tune, giving you more control over your engine management.
Alternatively, you might consider retaining OBD2. This can be done, but often involves more complexity, particularly if you’re using a EuroR H22 engine, as mentioned. The original post hints at this complexity when discussing the EuroR ECU and the need for an OBD2A to OBD2B conversion harness. If you choose to stay OBD2, you might need to address differences in sensors and wiring between your Prelude’s original system and the H22.
When it comes to the physical swap, some components are straightforward. As highlighted, swapping the timing belt mount and transmission mount is necessary for proper engine installation. The VTEC oil pressure switch is another area requiring attention. A simple solution, as mentioned, is to swap the entire USDM (United States Domestic Market) VTEC oil pressure switch assembly. This can simplify wiring and ensure compatibility with your Prelude’s harness, depending on your chosen OBD setup.
Adapter plates for mounting the engine are another aspect of the swap. While pre-made adapter plates are available, the original poster describes a DIY approach using square plates, drilling, and tapping them. This “easy as that” method demonstrates a cost-effective solution, although those seeking a more refined aesthetic might opt for professionally manufactured plates. The functionality remains the same, regardless of whether you choose a DIY or purchased route.
One critical issue brought up in the original post, and a common stumbling block in H22 swaps, is the idle air control (IAC) and throttle screw. Unlike some engines, the H22’s idle is not controlled by the throttle screw. This can lead to idle issues, as experienced by the original poster, with the engine idling “wonky” and wanting to stall. The temporary fix of tightening the throttle cable is not a proper solution. The poster correctly identifies two potential paths forward: Hondata or an OBD2 conversion harness to utilize a EuroR ECU.
Choosing Hondata, or similar engine management systems, offers precise control over the IAC and fuel/ignition maps, allowing you to properly dial in your idle and engine performance. Alternatively, exploring an OBD2 conversion harness to use a EuroR ECU is another avenue, but requires careful consideration of ECU compatibility and potentially more complex wiring adjustments. The best route depends on your tuning goals, budget, and comfort level with engine management systems.
Beyond these specifics, remember the fundamentals of any engine swap. As the original poster wisely advises, address basic maintenance items while the engine is out of the car. This includes the timing belt, water pump inspection (and replacement if needed), and the rear main seal. Tackling these preventative measures now is significantly easier than doing so once the engine is installed in the tight confines of the Prelude’s engine bay.
In conclusion, the 3g Prelude H22 swap, while fundamentally straightforward, requires careful planning, particularly around the OBD1 vs OBD2 decision. Understanding the implications of each choice for wiring, engine management, and tuning is crucial for a successful and reliable swap. By addressing key areas like mounts, VTEC, adapter plates, and especially idle control, you’ll be well on your way to enjoying the enhanced performance of an H22 in your 3rd gen Prelude. Good luck with your swap!