I'm curious, other than tuned pipes, plugs and all the obvious external stuff. what can be done to-lets say a BGX or big Moki to increase performance or who is good at it? Like different pistons etc. Seems like a logical question here. Thanks

I also wander what else could be done, it any thing else is even possible ? I have BGX-1 and I got better static RPM (not flying yet) when I took away
the brass-insertion in the carb, added Perry-pump and trow away the exhaust pipe completely(in one of our airfileds that noise is permited).
Please comment on those things too.
Regards,
Nick

No one here has enough knowledge of two stroke engines to do the kind of modifications you are seeking. A two stroke engine is very simple in construction but very complex in internal operation.

If increased performance is desired, one can 'port' the engine, to increase the intake and the exhaust duration.
Cleaning up the bypasses and the crankshaft gas passage, would increase the gas flow.

Increasing the blow-down period would make a tuned exhaust system more effective.

Dropping the head would increase the compression ratio and minimize the squish clearance.

As you can see, the sky is the limit and then there are carburettors and tuned pipes and... and...

I was reading up on that a bit. Who would be the pros on that around here? Clarence Lee maybe? I know he fixes things real good. As far as lowering the head. What about the sleeve?

OR------Can more be done to improver performance ona 35 cc gasser to save on weight from getting a larger like in the 40-50cc?

Ever since my son got into RC cars I've been reading the engine section and there seems to be one magic ingredient for hopping up their engines which always works. Imagination! They'll slice a couple of grooves through the crank counterweight (!), polish the crankshaft then say they've gained another 10,000 revs .

Personally I don't think there's a great deal that can be done to get any worthwhile improvements without radically changing the way the engine is supposed to be run. The only reversible mod (and the easiest to begin with) is to optimise the compression for whatever fuel you want to use.

Woops, I just had a thought, there's one mod that can help. The carbies are very inefficient below the barrel (venturi). Ideally they should taper back out to match the opening in the casting as far as possible at the crankshaft inlet port. The better they do this then the closer they come to returning the pressure drop back to atmospheric (or at least whatever pressure is above the barrel). The top of the carb should have a smooth bellmouth with radiused edges to keep down turbulence and get the greatest airflow into the carb. Then below the barrel it should expand at no more than a 14 degree included angle to avoid flow seperation and turbulence with a final cross section area as large as possible. This is where it tries to regain the original pressure. Most carbs or venturis are about 60% efficient (below the venturi) but a very well designed one can be up around 90% efficient. Higher pressure means it'll flow more easily into the crankshaft port and more air means more power.

Blending in the end of the hole through the crankshaft below the carb with epoxy to give a smooth radius for the incoming air to make a nearly right angle turn will also help.

The Evo 35GT looks like converted 2 stroke glow to me. Anyone know how it stacks up against the BGX or the Moki 2.10?

TM,


The Evo 35GT is actually the MVVS 35 cc IFS engine, manufactured by MVVS for Horizon Hobbies and sold under the Evolution name-tag. It is available from MVVS in both glow and gas versions.

Converting a gas engine to run on glow fuel will add some power, but it is not a pure 'hot-rod'.

The MVVS 35 cc engine is in the same class as the OS BGX (35 cc) and the Moki 2.10 (34 cc).

If you have the nerve and a steady hand, you can do some work on the sleeve, case, and crank, and clean up the sharp edges...it will help the efficiency but you're not going to get a ton of perf. increase...maybe a few hundered r.p.m. I've done it many times, and have a routine that works for me...but it took practice and botching a few emgines in my early attempts. I can see gains of perhaps 500 r.p.m. without loosing tractability.

The above mods will be more effective if you have a good exhaust system...and a carb that will let the engine breathe well, without being too big.

The thing is...you don't get something for nothing...if you want substantially more power that means working so the engine puts out more power at high r.p.m. usually meaning you loose a little tractability at lower r.p.m. and perhaps the transition through the mid range if you really "have at it"...so...what it all boils down to is, what do you want/need the engine to do for you?

If you want to learn, get a few old engines that aren't of any great collectable value, and try it yourself..."experience is the best teacher" as they say...don't be afraid...just try it and see what happens. If you try something and it works, great! If it doesn't work...don't do that again

Maybe find an old Magnum .40 or a K&B .40 or .61 or something along those lines, and experiment.

Some relatively simple things you can do are to put a radius on the lower edge of the I. ports in the sleeve...if you have any questions as to which ones they are, just look at the sleeve of a typical .46 two stroke for example...the I. "boost" port is directly across from the exhaust port. The ports to clean up are the ones that are 90 degrees to the boost and exh. ports and are directly behind the carb, and right above the backplate. Just radius the lower edge or chamfer them similar to the lower edge of the boost port. Do not get carried away, and do not go into the inside of the sleeve...

You can do a little blending on the crank, by putting a radius on the rear inside edge of the induction window, and a radius at the rear of the intake passage where it opens into the case. (don't nick the crank-pin ...put a piece of brass tubing over it to protect it )

Some engines are nice and clean inside...the castings are well finished, and the port passages match the port openings in the sleeve. Some are rather crude though, and you can port match the case to the sleeve. The exh. manifold or muffler flange to the case can be matched if necessary...the area under the carb can be worked a little if necessary, etc. etc. etc.

You will need several (different shaped ) Tungsten Carbide cutting "burrs" (1/8" shank ) like a straight, and a flame shaped, and a ball end will work for starters, and a variable speed Dremel...eye protection of course...gloves, a good light source...good eyes and a steady hand, and the testicular fortitude to allow you to start cutting / removing metal on a perfectly good engine!

Some will tell you to just get a bigger engine...that's the easy way...(maybe a bigger/heavier engine is out of the question though? )
I like to fiddle with stuff...and if I can make an engine run stronger...(and I can ) then to me, that's just another aspect of our hobby.

Another thing I should mention...
If you do decide to try it...make sure you clean all the parts several times.
Wash them with a strong grease cutter (brake parts cleaner spray, lacquer thinner, acetone, carb cleaner, etc.) first, before cutting/grinding, so the filings don't stick and clutter up and obscure your view of the work piece. Then, when you're done w/ the Dremel, again clean the grindings/filings off with your strong cleaner, and lots of Q tips and paper towels...then lube asap so rust doesn't start. You can't be too clean when doing this...and when it comes to re-assembly.

Hi Guys,

Thanks for the advices but still one thing has been avoided to comment on, or I am imagining that it could
help eventually: - Do you think and did you see or tried yourself to provide higher pressure on the comming
into the carburator air, i.e. kind of "compressing" the incoming air, either by conic expansion of the top
of the carb(diffuseur) or even by adding small air-turbine driven either by crank of the BGX or by small
high-rpm electric motor, as it was done on the early version of the Mazda-car with 70,000 rpm small
el.turbine prior the turbo-charging came into car-production?

Regards,
Nick

Nick,


A real turbocharger will not work with a two-stroke engine, like those used in models.
If you want more power, just get a bigger engine.

If you want more power from a limited displacement, get a tuned exhaust system.

A mechanically, or belt-driven super-charger will work, but there is no such solution that will have a cost, less than that of 20 new identical engines... So, what gives?


Cost effectiveness is everything, so any more elaborate supercharging apparatus will not pass.

Modifying glow engines seem to be very effective on RC car engines. They give extra RPM but I notice that on track its on the high end only and not low end power. Standard planes with engines that run in the 13K-15K range do not seem to get much benefit from all that mods. Its better to get a tuned pipe or a better/bigger engine. They did come out with a super charge system for RC cars of .21 size and I think maybe .12 also. Its expensive. I think a YS is cheaper and more effective.

What do RC cars do (my terminology is far from accurate):

polishing the crank shaft
opening the ports
smoothening the ports, removing the 90 degree edge on the port
adding a turbo scoop on the crank
opening the crank shaft
adding a dollop of epoxy in the crank opening to smoothen the fuel flow
cutting some dracula teeth like shapes beside the ports

An idea can be found here:

http://murnanmodified.com/#more

One thing ... don't argue with Dar about engines ... he know TOO MUCH! Hahahahaha ... how you been Dar?

I have spent some time with a BGX. You did not mention your intended rpm range so internal mods may net very little power. A tuned pipe is an absolute must if you want power. The BGX cylinder port timing and compression are ideal for use with a tuned pipe at 8000rpm with moderate nitro(10%). Its compression is very low so even more nitro can be used with a standard muffler for extra power and wider needle valve range. The BGX does have very short rotor valve timing at 173 degrees open, industry standard is closer to 190. Opening the rotor valve doesn't do much until rpm increases over 8000 though.

Great, Wilson!


Today is a bit sad; National Memorial Day, but tomorrow is our 59th Independence Day.

Thank you for your words.

Dar - this year is Malaysia's 50th ... they will have a big bash ... anyways I love your new hairstyle ... looks great on you! LMAO!!!

Wilson,


Do you mean my 'No Hair Style', or that of the avatar 'thinking chimpanzee'???

That's me holding a typical, "non-MVVS engine" that I picked from my lemon tree...<GGGGG>

Or supercharge an engine like this: http://www.geocities.com/ramair1968/...rgedsaito.html

Thanks a lot for the comments and suggestions !

I would prefer using the BGX-1 at the highest RPM it can take,
i.e. couple specific questions:

- What is the max rpm one has driven BGX and with what Propeller ?

- What are the RMP for max-Torque and as well the RPM max-Power ?

- What tuned system you would reccomend, maker, dealer, prices, etc ?

Regards,
Nick

Tianic had a good post there.... well worth noting....

There are a number of things you can do to an engine, such as minor polishing and minor porting cleanup that can help you gain 200-400 rpm here or there.

If you goal is high rpm, and throttle or midrange is not much of a concern, then you can do a number of things with port sizes, port placement, inlet - exhaust - crank timing.

If you have a speed engine, where you are running wide open..... sure, modify away, and hope it holds together.

The notible thing here, is that there is no free lunch. It tends to be a trade for reliability vs performance. A well designed engine has a balance, edging toward the more reliable size.

Car engines are VERY different than aircraft engines.

By in large, they produce little torque - they rely on gearing. They see little in the way of crankshaft loads - aircraft both tortional, longintudinal and bending loads (yes, even supported in bearings). If you try to open up the through port on an aircraft engine something similar to a car engine ..... it will fracture at the inlet port window in little time.

Rear rotor is one way around this issue - the BGX has this configuration, but I do not think altering its existing geometry will help much.

Car engines rely on a very basic premis of 2c engines - RPM is power. And they use the gearing to an advantage here. While at that extremetly high rpm, it is possible to use a larger carb. In aircraft, this is the concept behind the QM40 and FAI engines, and ducted fan - small props, high rpm, high power output - lower frontal drag - but...... the plane must be able to function with the tiny prop. Again... a balance between engine and applicaition.

Car engines rarely run at 100% power and max rpm for more than a handful of seconds - maybe a minute.

Adding "equipment" to an aircraft system costs weight. Often this is not a good trade. Sometimes it is. Adding a tuned pipe is usually worth while.

Keep in mind too..... with something like the BGX ---- a 200-250 rpm gain, with a usable prop (say 18") - is a BIG gain in total HP. May look small, but when you work up the numbers, it is pretty impressive.

Tuned pipes such as those available from MACS are useful. Jett offers the Turbo-Jett in the 30cc size for engines like the BGX. Either can bolt on to give you a 15-20% instant HP increase without working anything within the engine.

Did you check out the prices of that modified cars stuff!? [X(] Good grief! (greif? I before E, except after C...grief...yeah, that's it!)

Not so there are lots of us working on extracting more power.

Simply by dismantling the engine, possibly ubgrading the bearings, reassembling the bottom end very carefully ensuring minimum drag.

Then smoothing out any burrs or lips in the induction tract with a Dremel and a fine grindstone.

Finally and most importantly optimising the compression ratio with head shims and selecting the optimum plug heat range for the engine with the engine running at the airborne RPM.

Get it right and the engine will last longer, run cooler and produce more power, a win, win ,win result.

I have turned near 10,000rpm with an APC16-10 prop with open exhaust. The stock muffler will choke the power equaling a 160FX around 9000rpm. I cut the rotor valve to 184 degrees open without loosing idle quality. I found best performance with 17"-18" props turning just under 9000 with open exhaust. I did not use a tuned pipe on this particular engine but have seen them used on other BGXs and they do work.

This sounds good. Bob , I'm sure Dub has run tests on this combo, what rpms numbers did he come up with?

A surprise for me is that I found the Carburator on BGX-1 to be the almost same with the Carburator of ducted fan OS.65 and OS.91.
How comes ? - surely OS saved from development cost, but those engines, especially .65 is nearly 1/3 of the displacements of BGX-1.
Is it only the position of the carb behind the engine in those ducted fun engines requiring such wide size of the barel ? I.e. seems
the Pressure of the incoming air here plays some critical role, or there is another reason(s) ?