Not really an "a" but the evolution logo. The 46's didn't use to have the sizes stamped on them as they were the only size made. Nothing to confuse them with. So I feel confident in saying you have an Evolution .46 trainer engine. IF you wanted to you could remove the flywheel but I believe you would need to purchase a new prop drive hub. Only major benefit IMHO would be that more spinner backplates would fit easily.