Performance Unlimited Products "pro mod" G62
 

Does anyone have one of these engines? If so, pm me. I am full of questions.

Did anyone PM you ?

Not through RCU (grin) bit after speaking with several, my engine is on its way back from performance unlimited..lets say its beyond what I had hoped when they tested it on the bench.

I'm now worried if a 23.6 inch 4 blade is gonna be big enough lol

on their bench, it spun a 22x8 apc, same as zenoah used yo benchmark at 8000 rpm with throttle left
a 23x8 apc at 7400 rpm.

I now have to make sure the beast thats coming home can be drug down to about 5500 on the ground so it doesn't spin faster than 6300 in the air with the variorop...
I was expecting a gain...but dang.

Zenoahs are happiest when allowed to rev. The G62 is bulletproof plus if converted to CD ignition becomes an even nicer runner.

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.

The upside: I didn't have the money to spend on a Kolm 70 cc engine. They state it has the same footprint as their previous 65 cc but at 2100 bucks, out of my price range.
To date, My zenoah, parts, and tuning has cost me 1200 bucks. Savings compared the the Kolm which would have had no problem spinning the varioprop at all is 900 dollars.

The downside: it still cost me 1200 dollars to get there, but the zenoah was the only engine that had the latitude (room) to tune to perfection. Most engines designed specifically for RC, Like DA, DLE, Kolm, 3w etc are already tuned to the max at the factory..they are going to do what they are going to do..there's not much you can do to improve on them. Again, what you see is what you get.

I saw an oportunity to take an engine that every so called "expert" in rc basically called a waste for modern rc planes and turn it into a powerhouse..I just had to find the right people with the knowledge to do it. Was it easy..Heck no. I was discouraged, lambasted, and ridiculed on two different forums just trying to find those right people. I was called stupid, crazy, and ignorant so much that I almost gave up on the engine, the plane, and rc all together. One thing to add, none of that happened on RCU

Its folks like you, sir, willing to answer questions, and help with the thought process that encouraged me to continue. As a result, the ultimate (in my opinion) Hanger 9 1/5th scale Mustang is going to be built....If Tower ever ships the farking plane that is.

I guess there is a further upside to this little journey. Its proof that if you put your mind to it, block out the so called "experts," and drive on, no matter how crazy your idea may seem. This hobby is about exploring and pushing the boundries of what is known, tested, and approved. Most things don't work, but thats ok, even the stuff that fails can be learned from..some things, like my little 62cc are a success and pave a path that can be followed.

Now I don't know how to derive thrust from the above numbers. I wish I did, or even how to translate that to horsepower numbers or torque numbers, if someone does, chime in. I'd be interested in knowing. I'd like to just compare it to stock Zenoah numbers and see how much different it is, or how close it is to engines of bigger displacement for that matter.

Here's the thing to know, in that underpowered stock engine lies a sleeping beast, all it takes is a cdi conversion and some timing to wake it up. I don't know the numbers to compare it to a DA or DLE now, but I think Performance Unlimited may have just left them in the dust. My worry is not having enough prop to get the engine down where I need it..I may end up having to order longer blades.

Wow, sounds like you've turned your house cat engine into a raging tiger. Thanks for sharing info on the upgrades you got done to it. Some, if not all of the things you mentioned are tunes Ralph Cunningham (Antique) used to offer with his G62 Lite engines, though I can't recall if his modded engines ever required premium grade gasoline. Still, that's a small price to pay for the much improved performance.

Some folks just don't have the mind set to try doing something new but prefer to be comfy in following in others footsteps. Best of luck with your build project and hopefully whenever you do you will stop by and tell us all about.

Happy holidays and all the best for 2022 when it rolls around.

Yes sir, its shaping up to be quite the machine.

Come along for the ride..there's a build thread I've started for it here in the warbirds forum. "Readying the Hanger 9 Mustang." I'm sure I'll get stuck from time to time..it always happens..especially with ARF's.
Input from the more knowledgeable is always good :D

Same to you. Hope you had a good Christmas, and Happy New Year..be safe.