i know obviosly the 46 is bigger than the 40, but why arent they physically bigger.

Ask the maker of the engine

A .46 is basically a .40 size engine or case thats been bored out for larger piston. When it comes to Airplanes, weight is everything. So it makes sense to try and get as much power out of a particular size engine without having to create much additional weight! For example: If you set a O.S .40 sf next to a O.S .46 sf, the physical appearance and size are the same. Its whats inside that makes them different. Same goes for the GMS .40 and GMS .46 etc. etc. etc. etc.

lots of engines are like this. saito .82/.72, the .82 is nothing but a bored out .72, and is very slightly LIGHTER as a result.

When an engine manufacturer offers both a .40 and .46 engine, many components between the 2 sizes are the same. A .46 will typically use the same stroke as the .40 - hence the crankshafts are the same. The crankcase casting and backplate would also be identical. The larger .46 gets it's increased displacement via a larger bore size. Usually (almost always) this is achieved by using a thinner liner than the .40 engine. The piston, liner and cylinder heads (and wrist pin) are usually the only difference. In an ABC engine, the liner is brass which has been chrome plated. Other manufactures use nickel instead of chrome. Since brass is relatively heavy, the larger .46 engine will be slightly more powerful than a .46 from the same manufacturer.

The OS LA .40 and .46 are excellent examples of this commonality.

For those of us who fly control line aerobatics, the slight change in displacement is significant. The C/L rules specify a minimum line diameter of .015" for engines up to .40 cubic inches. A .46 or larger engine must use .018" lines. The difference in weight and thickness (drag) of the larger lines is very noticeable.

The '40 class' two stroke engines typically include the following displacements, and possibly others: .40 .42 .45 .46 .47 .49 .50 .51 .52
Often, but not always, engines in this class fit the same engine mount and are very similar in physical size and weight. The different displacements are accomplished by changing the bore size and stroke within the same basic case.

Automobile makers did the same thing. The 'small block' Chevrolet V8 engine was introduced in 1955 with 265 cubic inch displacement. In the mid 1970s the engine had 400 cubic inch displacement but was exactly the same size externally as the original 265. There were lots of internal differences but not much externally that the average person would notice.

alright thanks i understand now

I see you have a car engine up there :-P

A .26 is a bored out .21 ... (Why are the .26s less powerful than the .21s I don't know.) :-(

kind of weird right. lol. i know some .12 that stay at the pace of a .15 1.2 hp. its the same specs,

You are correct. Some engines are just designed for more power than others even when placed beside an engine with a larger displacement. For example if you take a O.S .40 sf up against a O.S .46 LA or a Thunder Tiger GP 42, the O.S .40sf is going to out perform the other larger engines due to its design (porting, carberator, stroke,exaust,etc.). I am no fan of the Tower Hobbies (GMS) engines, but the Tower .46pro has a 1.75 hp rating. This kind of rating is as high as what you may find in some .60 size engines. What I am trying to say is that bigger engine displacement does not always translate to more power. There are different grades of engines, and each has a purpose behind its design. Some good engines are designed for affordabillity. Some are desined around longevity, some are designed around reliabillity, and some are designed around power. Some are designed with several of these quallities, and some are designed with none of these quallities!

ok got ya

it is NOT true that all 46's have bigger bores & thinner liners. take a look at some 45/ 46's vs the smaller 40. you'll see the head raised on the 46 because the piston and or conrod is taller & longer stroke and liner is longer. all parts are not interchangable.also when measured, SOME of these engines do not coincide exactly with the stated box displacement.