In short, you will not need a tach to realize you've gained RPM on top, I think personally it idles even lower, though that may just be because mine is broken in even more now. I have run the APC 13x4 on my .52 very easily, I never did write down at what RPM. I don't know the exact differences in degrees or duration each valve is open with this cam, but comparing the two by looking at them, the car cam opens and closes the valves quicker and they are open longer, the more their open, the more fuel/air charge it'll bring in. I haven't seen one side-effect like can be seen in real V8's with big cams.

The FS-40 is rated at 0.65 hp, the car version FS-40s-c is/was rated at 0.90 horsepower, the two biggest reasons for this are the cam and carb. That's an increase of .25 hp, roughly 39%!

The .52 is rated at 0.90 hp stock, the cam change will put that into the 1.0 to 1.1 hp range and a huge value for the return at a little more than what we pay for a gallon of good fuel. For my airboat, I have LOTS of room to use the carb off the car version as well, because of the straight intake manifold, you need more room behind the engine. In my 20 years in this wonderful hobby, it's the best carb I've ever used, and makes everything I've put it on run better and super reliable. With both cam and carb 1.15+ should be cake, that's in the range of the FS-70! The only downside is more money than the cam. For some reason I'm fascinated with this FS-52 and getting the most out of it, even though there is better power plants out there. Cam, carb, lighten the piston........on and on! I've got this setup in an airboat, which benefits from a low idle cause they don't have brakes! And when I need to get outta trouble, I can crank the rudder and blip the throttle, no hiccups!

Remove the valve cover, carb, cylinder head, then pushrods and pushrod tubes, finally the cam followers. Rotate your engine to piston at top dead center, there should be a mark on your drive washer lining up with the casting of the crancase, remove the cam cover off the side, both cams are marked with a dot, that timing mark should be pointed up and just a slight bit towards the rear of the engine. With the cam followers out of the way, you can pull the cam out and put the new one in, with the mark in the same spot and piston at top dead center, put her all back together and ENJOY ! More torque, mine pulls a bolly 12x8 carbon like nobodys business, and the 13x4 as well without being too high in rpm, some day I'll dust off the tach and see what it reads. Throttle response is much improved, remember, cars and buggys require that in copius amounts!

The best prop I could recommend on a stock .52 would be the 12x6 carbon fiber bolly, desert aircraft carries them, pricey, but worth it!