Go to www.nitrohouse.com and you will see that the hyper 21 and the hyper 28 share most of the parts. Be aware that most 28's are based on 21 size crank cases, with just a bigger bore may and maybe a slight stroke increase. I forgot, they show a Picco P3 as a hyper 28. I had to call them to get a rod for a hyper 28 and it was the same rod the 21 uses.