samtech

Bob,
Might take you up on that. My aluminum welding isn't the greatest. Been practicing on beer cans for some time... I burn better holes now.

bob27s

My Feedback: (19)

As long as you and your friends have to empty the cans first.... its cant be all that bad

samtech

Ok, Got it running again. I gave the pipe to one of my in-laws for some welding practice.... He's going to school for welding. We'll see...
So I bought a macs pipe and have run into another problem. Followed the directions on their web page. Got it up to 17640 took another little sliver off and it didn't change. I'm happy with 17640 rpm with a 8x9 apc.
The problem is that plugs have a very short life span. Very, very short. 30 to 45 second blast and there is no restarting without a new plug. I've read that is pretty normal but I'm not sure whats causing it. I'm running wildcat 25% with a O.S. #8 plug. To much nitro?? Too hot of a plug?? If I used a cooler plug like a #3 could I go higher on nitro? I don't really mind eating plugs like theres no tomarrow but I'm thinking it's detination that's doing it. Definatly not good. Plugs are one thing...pistons are another.
So what do the experts think????

bob27s

My Feedback: (19)

The #8 is a cool plug... An A3 is a hot plug (lower number, hotter)

You simply have the pipe too short. The engine is struggling to hit the RPM you have it dialed in for.

I would lengthen that setup about 1/2" at a minimum.

The other way is to back off on the prop size....... unload the engine... but you are already running a tiny prop, and you already have reached the internal flow limit of the engine....

The GS-40 or GS-45 should be set up so it runs just over 16,000 peak ground rpm. Maybe push 16,500 ground peak. Something like that should unload into the low 17Ks rpm in flight.

samtech

Thanks Bob,
So an #8 is about as cool as I can go... I'll try pulling the pipe out a little and see how the plugs hold up. So if I want more RPM I'll have to do some internal work... I really don't want to mess with the port timing... Do you think a little porting and polishing on the outside of the sleeve is worthwhile? Slotting the transfers and so forth, like some of the car guys are doing.

bob27s

My Feedback: (19)

there are always things you can do for port timing and such...

but with a GS-40..... there is more to i than the sleeve. Carb is designed for sport use.... crankshaft and porting are designed for sport use. I guess what Im saying....... its a sport engine.... take what you can get from it, but probably not worth tweeking it

For consideration, you can take a box stock TT-46Pro, bolt on a jett-stream muffler, and turn a 9x7 up about 17K rpm. That, with no other modifications than adding the muffler. GS-45 can do about 500 rpm less than that on average.

samtech

Well put. It is a sport engine. The carb is limited but very tuneable. That's why I had Dub make me a red one I have to give props to you guys for that one. It is the single largest improvement I've made. Night and day difference. I had him make it for a G-51 but I toasted the ring in it not long after I had ordered it so it went on the 45 instead.
I have no intention on doing any porting until it's time for a rebuild... if it's rebuildable at that point... and cheaper than a new one. I do love that fact the ST's are so cheap... Or maybe even save my pennys for one of those 50's you guys make. Mahahahahha

bob27s

My Feedback: (19)

yes, from an experimenting view point.... is not an expensive test bed

Years ago a buddy of mine and myself were able to do some magical things to Como and ST engines.... with little effort... and with little impact on reliability. But we were working with the ABC engines.

samtech

Hi Bob,
The GS-45 is an ABC or so they say. No rings. I'm not sure whats under the chrome on this one. I haven't taken it apart yet. The G-51 is a ringed job though. Got any tips or tidbits to share???

bob27s

My Feedback: (19)

Well, you have the red carb on there.... that is a big advantage getting air into the engine.

Usually we would swap out the .40 size carb with the round spraybar for the bigger Mag V carb and/or use the flat spraybar. Sometimes airfoil the spraybar a bit.

Other than that, radius the outside bottom edges of the sleeve inlet ports -- dont touch the chrome, just work the outside and smooth it a bit.

Exhaust system is important, as discussed. You can do far more with a good exhaust system and a properly matched prop than you can tweeking the inside of the engine

Use a hot plug like a Rossi 2 or 3 (or equiv).

And if you have the skills and tools, I use cut the top of the sleeve to drop the head about .010, and then raise the liner about .015 (liner shim)

I would not go much beyond that...... stay away from the crankshaft. Does help to change the intake timing a bit, but you will very likely end up with a broken crankshaft not far down the line.

Any of this for a GS-40 or one of the older S-40 engines would not be legal for racing. Sport rules almost always require a stock engine.

samtech

Bob,
Dropping the head .010 and Shimming the liner up... effectively raising the compression and jumping the timing up? Is that what your saying? I thought the compression was pretty high already but the fact of the matter is that I don't know for sure what it is. I haven't CCed the thing. Do you think I can still get away with 25%? or is it pistion melting time? Would I need to cut down to 10 or 15% Also, is it better to shave the liner deck or cut in to the head? I've had the head off and the squish band looks like it could use some improvement. It's rather high angle. Another question for you.... Is there any benefit to polishing the combustion chamer/squishband area? Heat disipasion/absorbtion...
I'm coming from a Small block V8 background so I'm not completely ignorant but two strokes are still a bit new for me...at least modding them is. Up to this point I've been fairly happy leaving well enough alone. Thanks

bob27s

My Feedback: (19)

no...

dropping the head .010 and raising the liner .015 effectively increase the piston/head distance .005 ..... lowers compression a bit.

I suppose you could machine off the head to drop it .010 too. When I did it, the proceedure used favored cutting/polishing the liner flange top.

The changes noted above help if you want to play with the 25-30% heli fuel at higher rpms.

Polishing the head does not help much. It wont stay polished for long. Im not sure about the squish angle. Very likely it is optimized to help midrange and transtion.

2-c engines are quite differnt than 4-c engines, and glow engines are even more drastically different than ignition engines... a small block chevy for example. The compression, port timing and glow plug (and a few other factors) determine the ignition timing. There is no spark. In an ignition engine, you can mess with compresison, head shape or valve timing without direct effect on ignition timing. The key to good 2-c glow design is a balance of performance, reliablity, idle, transistion..... all with fixed geometry. In some ways, it is more like designing a rocket engine that has to work all the way from sea level up through the vacuum of space..... its all about optimizing for the application, and compromising for some conditions. For extreme model engines, such as what Nelson and MB currently offer for FAI, the design is right on the edge of either running, not running, or mechanically failing.... mainly because they are designed for wide up operation, with a fixed geometry tuned pipe. Even then... its difficult. The pipe timing is set for flight rpm, not ground rpm.... so as much as setting the needle valve is all a crapshoot (well, trial and error, and a box of blown globee plugs).

Like I said earlier..... its all an experiment anyway. No guarantees here, especially since the last ST I messed with in the shop was an old Como 50. So feel free to try different things.

But remember the key to experimenting.... establish your existing performance baseline.... change one thing at a time..... get new data and compair to your baseline info. Only that way will you see what works and what does not work.

Fortuinately these days...... the Jett engines are already tweeked better than I ever could, and they are balanced for all the requirements. The 60LX is all I'd ever need from a "40" size sport engine. It is the model airplane equivalent of a 410 sprint car engine you can put in your street car

Dave McDonald

My Feedback: (19)

I've been sport flying an old Spickler Q-500 for years with a ST 45 GS. The stock muffler was replaced with a Mousse Can Pipe, otherwise the engine is factory stock. With the MCP it's been turning an APC 9x8 at 16,500 on 15% fuel for years and still runs great. Don't even worry about 16,000 on the ST 45 GS. It will handle it easy.

cncswiss1

[link=http://www.osengines.com/accys/glowplugs.html]os glow plug chart[/link]

samtech

Howdy yall,
Ok, I maidened the LR-1 yesterday.... It's silly fast, at this point I don't want to go any faster. Had a hell of a time keeping it in sight.
Total beast to take off. It slides sideways down the run way untill it lifts off...then it flys sideways for awhile. Flys good, just gets away from me fast. Landing.... I thought it landed great. I took the advise of Sir. Charles of berserk "you know how you are" and sent it way out long and low and it was great. I can't believe how slow it would really go.
Ok, As far as engine issues.... I didn't want to take two jugs of fuel with me to the field so I only brought 15% stuff. Well, I set up on the bench just to lean it out for the 15% and low and behold I picked up more rpm 17850 and the glow plug isn't getting trashed.
Bob, What happened? That wonderful ignition timing that I don't really understand? I suspected detonation before.... but... What happened? Now I'm really confused.

bob27s

My Feedback: (19)

what happened?
just an example of how sometimes more nitro does not help, unless the engine is setup or capable of using it properly.

clearly the chamber temperature was getting a bit too high. When you go up in nitro, you have to decrease the compression. When running on FAI fuel.. zero nitro.... you raise compression. Sport engines designed for sale in the US and some other markets are almost always designed for 10-15% nitro. Euro engines are frequently set up for FAI right from the factory.

Destiny-RCU

Don't mean to hi-jack. But this made me also curious, which set up in the end makes most power? High Nitro=low compression or low nitro= high compression? Or can they be mixed with the proper plug and tuning?

bob27s

My Feedback: (19)

depends on who you talk to...

consider that FAI racing uses piped engines, no nitro... and those are the most powerful model engines out there (size/power/weight wise)

Our old F-1 engines were similar...... but no pipe.... and a crap load of nitro....

Hard to say what made more power. Id say you could do better with the FAI setup. Both are extremes of performance.

Our sport engines and the current Q-500 and QM40 engines are the balance you are speaking of.

Bob