CAN ANYONE TELL ME WHICH IS BETTER ENGINE. OS .21 RG-MX, 0S .32 MX, MECOA .46 MARINE. I'M PLANNING TO BUY ONE, BUT ON A LIMITED BUDGET SO I MIGHT USE THE ENGINE ON DIFFERENT BOATS BETWEEN 24" - 40".. THANKS FOR ANY INPUTS..

.46

does anyone use this engine - K&B .18 marine? is it a good engine? what engine can you recommend for .15 - .32? it must be good and long lasting. thanks!!

That all depends on what you plan on using it for ? Play ? Race ? Cruiser ? A speed boat ?
or ????
Also , what are you gonna put it in ( hull type and weight of hull , if possible )? This also makes a big difference .

i'm actually planning to put it on a scale boat, put some clutch on it.. but i also put it on a boat 24-36" long, maybe a jet boat

Got a lot of "ifs" there ...
First . a jet boat would need more umph ( power ) in most cases to keep up with a prop driven boat ( most of the time , not always ) . soooooo , in that case , the bigger motor .
Next , 24 verses 36 inch hull is a BIG difference like when you run an 18 . Your best bet I think , seeing as to how you are undecided , would be around a 40 ( but not if you plan on getting a 24 inch hull [] The 24 inch hull , the 25 up to 30's would be good and not over powered or under .
Basically , its like a real boat . Gotta have an idea as to what you want and then go from there .
Best is check out hulls first . Then when you are decided , then figure out what kind of drive system you want . Then , last but not least , match the motor to the power requirements needed for hull and drive system .
One more thing to note . When dealing with nitros , they came in many different levels of max R's and BHP ( braking horse power ) The higher the BHP , the stronger the motor is ( meaning that is can move a heavier boat that one with lesser BHP )
And since 99 per cent of the boats are direct drive , the higher the R's ( RPM's ) the faster the boat will go ( as long as you have the proper sized prop , if thats the way you plan on going ) , but here comes the BHP again . You can have ( to a degree ) a lesser BHP motor that drives higher R's and still have the boat go fast . ( confusing ? Yep ! You betcha ! )
Now , here is where the prop pitch and size comes in ( and that is a WHOLE nother ball of wax )
Now , did I confuse you ? Hopefully not . Basically , go with these basic sizes - 40 motor for 36 inch and 20 up to 30 for around a 24/28
( LOL ... the style of hull also matters ALOT ... meaning deep vee , shallow vee, rigger , hydro , cat ... cracker .. so on and so forth . The numbers I gave you above basically are for a mono hull )

terbobob thanks a lot!!i've decided now i'm bulding a 30in runabout. i like it to have a good speed, but not too much like a racing boat. do you think a .18 k&b will do? or is it better if i put a .21 os.? i am planning to put a clutch on it for added scale and safety.
thanks!