ORIGINAL: 1QwkSport2.5r
I have an SS30bb R/C personally, and I find it to be a real sweetheart. I ran mine for about 50 minutes on the bench using 5% nitro 25% castor. After the break-in, it throttled great. The stock muffler sucks, robs 3000+ rpm.
If you're willing to run straight castor fuel, the iron/steel is great. If you plan to run a synthetic/castor blended fuel, I'd suggest the ringed version. Call it a superstition, but I won't run synthetic oil in my iron/steel engines. That's just me though.
3000 rpm?!! [X(] There's something wrong there. I find it costs maybe a couple of hundred, but that's about it - which is why most of us are quite happy with the stock muffler. The same item also comes with the SS35 and the 1.2 bhp 40XZS, also with minimal performance penalty. It's also reasonably light. Is there any chance there's a wasp's nest or something in yours?
There's a very good article here
http://stunthanger.com/smf/index.php?topic=4037.0 which explains why those of us who used lots of castor weren't always doing the right thing. I still use 25% castor in things like my old OS Max-S 35s, but engines like my SS30 get 11% castor,11% synthetic and thrive on it.