Okay I've been flying about three and a half years now and my main competition plane is an impact with a s.t. 51 from tower hobbies (stock). I was wondering is there a difference in power or performance between same size engines? For example what's the difference between a s.t. 51, a ro-jett 51 and a p.a.51 since they're all 51 sized engines?

The reason i ask is mainly because when i find some thing that intrests me i want to learn every thing about it or i go crazzzzyyyy!lol

all replies appreciated
              thanks
                      Steve

Hi Steve,

Since I have run both a ST G51 and the PA 51 in competition for several years, I can say that the PA 51 has more "stunt grunt".  The ST G51 is an outstanding engine, but the PA shows a good bit more when flying.  I have not dug into the "whys and wherefores", but it's stronger.  No Experience with a Ro-Jett 51, but in the other "sizes", the PA and Ro Jett put out more power than a comparable baffle piston engine.

I know it has to do with the things Robert wrote about.  Timing, head shape, etc., but I just put all that in the same category as the old auto engines.  Back in the early '60s you could get "several" versions of the Chevy 327 engine.  All  with a single four barrel carb that ranged from about 225 HP to 375 HP.  Heads, valves, intakes, carb, cam, etc., were progressively changed.  Power went up, fuel milage went down.  Now, smaller engines can put out the same or more HP with even better designs in the parts.  Same "size", way different power, and better milage...................

Bill <><

I don't have or run either of these engines, but I think part of the power increase comes from the way they are run. Higher RPM and less pitch. One thing I have noticed is the difference in sound between the old baffled engines and the newer ones without baffles. The newer ones without baffles running high RPM do not sound any faster or as fast as the old baffle jobs running less RPM. At least to my ears.

Hi Jim,

I would tend to agree on the rpm thingy, but there isn't a lot of difference in launch rpm between the two as I have run them.. and prop pitch has been within 1/2" pitch.  My ST G51 (T&L) in my USA-1 ran a 3 blade 11-3/4 X 4 1/2 prop and the PA in my Geo Juno usually runs a 12.2 X 4.2 2 blade.  Both in about the same weight airframe.  The ST ran the good old 4-2 while the PA runs almost dead 4 cycle.   I will be building a new USA-1 to use the PA 51 in with a header muffler.

They are just different animals.

Bill <><