Well you can always measure the engine, or the specs are on ZDZ's website if want to double check what RCS has but I wasn't aware that their website was even still up since TBM bought 'em out.

The other thing you might consider is hitting the local Harbor Freight and look for the 6 inch (they call it a 0-150mm) digital caliper. Not suggesting I'd use it for machine work, but mines been a real time saver for model stuff. Cost's about 15 bucks or so and goes from SAE to Metric with the press of a button.....