I've been considering getting a larger engine lately, something that could haul a 700" sq. plane with a weight around 65oz (no, I don't have one that weighs that much, but I want to make sure that the engine could ahndle it if needed). Something along the lines of a ST.61 or one of the Stuka Magnum .53XL engines. In doing some research, I been looking closely at the Stalker-Modusa and Double Star lines of engines. Of the two, I think that Stalker-Modusa may be the better bet for me as it is a little cheaper.
My main concern, though, is on their website, they suggest all synthetic fuel, no castor. Is this right? Wouldn't that end up damageing the engine if you had a lean run? Also, are all threads on the engine metric - i.e. glow plug, head bolts, prop shaft, etc.? Lastly, of these two brands of engines, which typically runs good on a tuned pipe, as I am also considering giving that a try, though probably not for a while. I'd like the engine I get to run good on normal mufflers as well as pipes.
Also, how well do these engines run. They're heavily touted on the website and in their ads, but I want some real-life testimonials that are not payed for or sponsored.
Thanks in advance to all who help.
Tight lines to all, 
Steve Berry
AMA 628018
-------------------------------------
Texas - The "Heart" of Modern Stunt!!