Yes, they are..stock.
Let me explain whats been done a bit for those who may happen upon this thread.
The zenoah g62 was an engine designed to be used in, well, everything. Chainsaws, weed eaters, hedge trimmers, etc..RC was just a happenstance when zenoah found out people were pulling the engine from the above stuff and modifying it for use in rc planes. But Zenoah didn't go too far with making hobby engines out of the G62..mainly just designing bolt on parts to the base engine. As far as tuning the timing..they didn't change a thing.
The zenoah was produced on a point to point assembly line, no detirmination made on the engine's final use until near the end of assembly, be it a chainsaw or a 60 cc gas P51. So specific tunes for specific uses was never done. The tuning zenoah did to the engine was basic, at best, to get it to run reliably on cheap gas without backfire or kickback and be easy to start. It even had, at one time, near the top of the cylinder, a compression release valve to make it even easier..its the flat spot at the rear of the cylinder. The magneto/coil had no mechanical advance, or electrical for that matter..what you saw, was what you got.
You, sir, are correct, A stock Zenoah loves to rev, and it loves it even more with a cdi conversion.
What I had done goes beyond that and actually addresses the basic tune for all G62's done by zenoah. Performance unlimited took my engine, took it apart, upgraded the bearings, replaced all the seals, then converted it to cdi and changed the timing.
As a point of reference only, prior to the timing change, the compression at point of spark from the plug was 9:1..the piston was further down in the cylinder when the fuel was ignited than it needed to be.
After the timing change, the compression is 15:1 at the point of spark,
translated, the zenoah timing was 9 degrees before tdc stock.
Tuned its 15 degrees before tdc..the piston being closer to tdc at point of spark and ignition..It now uses more of its stroke to make power..vs wasted rotation. Its more efficient.
The result of that change alone did the following during Performance's bench test of my engine.
Base line: A stock zenoah engine can spin a 22x10 apc prop at 7200 rpm, according to zenoah.
My engine, tuned spins that same prop at 8000 rpm with throttle left. They did not take it any higher.
They then switched to a 23x8 apc..and it hit 7400 rpm at WOT.
I gave them a goal. that goal was to make the engine powerful enough to turn a 4 blade 23.6 inch Ramoser Varioprop (ground adjustable, variable pitch) at 6300 rpm..prop max rpm is 6400
That goal was given in error..of sorts..6400 is the max rpm unloaded..in flight.
This means rpm on the ground from 5200 to 5500 rpm. I'm going to have to crank up the pitch to drag the motor down enough to keep the prop whole.
The cdi conversion, also means lighter flywheel-4 oz lighter.
The loss of the magneto/coil-6 to 8 oz
They also machined off the tail shaft 1/4 inch past the rear seal-5 oz
Not just savings in weight, but savings in rotating mass as well, the engine won't use as much power to rotate 4 oz of aluminum and 5 oz of steel..that translates to more power at the prop as well.
Its come back almost a pound lighter and turning a 1 inch diameter bigger prop at 200 rpm more than the zenoah base..
That is the Performance Unlimited "ProMod" G62
Then we went further yet. The one funky thing thats always plagued the zenoa was the position of the carburetor, stock its kind of clocked forward, the throttle and choke levers requiring some funky gymnastics from the servos to work. Add in, that we wanted to further bolster the engine's power in the mid range...a problem with the walbro carb is the point of transition between low side and high side (the needles) in that transition walbro's tend to go slightly rich..we hear it as kind of a burble.
To address those three things took a lot of research searching for the right solution. It was difficult as the G62 is no longer produced by Zenoah. They've gone on to other engines. So supplies for parts either stock or aftermarket are also drying up. But I lucked out.
Volgelsang Aeroscale still had a few of their 90 degree turn intakes in stock, along with the thermal blocks and gaskets. It addresses two of the three above, and may also help with the third.
1. It moves the carb to the rear corner of the cylinder, facing the firewall, and it clocks the carb so the throttle levers are level..
2. Its a longer intake runner, longer intake runners translate to a slight bump in the mid range, but with a down side, they also slow throttle response a bit.
3. the longer run might let the carb transition without causing the engine to go rich in the mid range.
Its a G62, basically, by casting and name, but its not the same in regards to performance, weight, and reliability any more..It won't run happy on cheap gas, Its going to require mid grade or premium to keep from detonation. Its also going to be more prone to kick backs..so I will be getting an RCS to start it with. I like my fingers where they are..thank you.
Last edited by Txmustangflyer; 12-26-2021 at 12:29 PM.