Power Differences Among Stock Zenoah Engines

[Don Ferrette]

Don, I remember TK as you
pointed out had a Zim gas motor.

Did anyone in the US test it?

I reached out and offered to but was told they had testing covered and that initial results were really good. Disappointing that they stopped short of making them a production piece.

 

[bermudadude]

I might. DDM actually sells 320 cases and cylinders way cheaper than 34/36 stuff. I guess due to low demand. The cases use regular engine mounts?

i was thinking of a project a while back and considered most all the parts,,, easier just get engine whole. BH has em i THINK gizmo got em ,,a little cheaper. without carb. use cmb or allot of people seem to be having success with the "veitnam" carb -havnt tried it. 1"header. pipe from ebay[performance somebody or something -its 2.75 or so diameter some have unwelded adjustable stinger or https://performanceunlimitedproducts.com in the usa -also havnt tried . he also sells the engine tho i think just modded

little confused about rod length comment. if you lengthened the rod to get tigther squish the piston will free port. At TDC there is only about .020" of skirt below the exhaust port base.

o no. not just 1 change my friend rod/crank changes require complete re-configure of ur engine . because the rod length will alter dwell at top and bottom dead center it will change everything . even with the same compression ratio u will get more trapped compression and the heat ranges will change the case pressure will change ,u will need carb changes or pop-off change or more bore [def more bore] then u might not like ur old favorite timings . then the biggest issue ,with gas folk, u might not like the "switch" type power curve or that u probably wont get a creepy crawl mill
so that .020 freeport is the least of ur worry. fun fact --some decades ago a mercury outboard guy had told me if u work with it u can actually use the freeporting . said it would take up to .04 freeport. i had an engine i could care less about at the time and extra pistons so i did it on purpose .actually had 1mm or more.. i ran the crap out of it . was reliable as hell,with canister muffler. i think that was the key- more like outboard exhaus. tnot the fastest. it was appache 50 . and. i got about 50mph. i never tried the pipe

 

[bermudadude]

in my experience, which is limited as I've ported maybe 6 engines now, big blocks have the same if not lower RPM due to piston weight. So the only thing they can do is make more torque. And the torque they make is going to be a fairly marginal increase. For me so far the best running engine has been a 26.

yea the bigger o.g zens are a trip cause the smaller port area. since ur doing ur own probably all the same try 1 thing that if it doesnt work u can just put it right back to how u had it --- cut the exhaust side of the piston down about half the way to the ring the total width of exhaust port. file back towards the center ,kinda judge by eye make it neat kinda triangle likefile less and less as u get close to middle. not right there but u can see what i mean if u start doing it .increases timing ,lightens piston,changes balance.

 

[bermudadude]

I am completely inexperienced in gas, but I do race a gas mono.
I am probably completely off base in my thinking but it seems like everyone is trying to obviously get better performance out of a weed eater motor, but not addressing the primary limitation which is the fuel induction methodology.
IE piston porting VS Zimmerman valve or drum rotor.
Is there any attempts at doing some thing different than piston porting in a similar motor of the Zenoah?
BZM has Reeds which have issues.
CMB has a Zimmerman valve. I have yet to observe a good running CMB gas motor. Is it the motor or the individual running the motor, and/or I was just not at the right race to see one perform.

Anyway just some musings.

its the owners lol
for real everybody does the same thing ,even quickdraw guys -1048 or similar and teeny tiny pipe. then say it runs the same as a zen that only cost $200
o and the same 3 props ,that the funniest

 

[Buckshot]

BZM has Reeds which have issues.

Care to expand on this?
I’ve been running BZM reed engines for many years now in both monos and hydros with many gallons of fuel through them.
Only problem I’ve ever had was I had a set of G10 reeds come apart while running, it did not hurt the engine.
IMO most engine issues are operator error.

 

[dr gary turner]

What is the rpm limitations on reeds?
Type of material I am sure is critical.
In my go kart days we had reeds. They were metal and often broke and went through the motor. It was a flat plate design.

Then a new design came out that was shape like a pyramid and seemed to do better. Soon there after drum inducted motors came available.

It seems to me we are behind in the gas RC world with the style of motors we have readily available, a weed eater motor.

 

[Dave Gilles]

I happened to be looking at NAMBA 2 lap records and thought of this thread. The times in every class are no faster for modded engines over stock. Is there something Im missing? some have stock small blocks as the fastest.

 

[LohringMiller]

Two lap records are about driver skill more than power. SAW records with IC engines are about prop pitch and rpm. Modified Zenoahs run out of significant power at about 19 to 20,000 rpm. Quickdraws can make 25,000+ rpm with some power. For years this limited G1 speeds to the high 90 mph area while we went 110 mph with a Quickdraw using 2170 propellers.

When Mike bontoft set the first G1 record over 100 mph he used a propeller with the pitch increased by cutting the blade at the hub. After this was recognized, Zenoahs have been able to increase the SAW speeds. Today Zenoahs hold most of the SAW records also. However Mike's G1 Sport Hydro record set with a Quickdraw still stands.

Lohring Miller

 

[Mike Hughes]

I happened to be looking at NAMBA 2 lap records and thought of this thread. The times in every class are no faster for modded engines over stock. Is there something Im missing? some have stock small blocks as the fastest.

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None of these classes you have posted are stock. All of them have modded motors. The stock ones should be listed as G - LTD. All G and GX classes allow modification to the motors.
G = GAS
X = open to all motor manufactures
if no X = ZENOAH ONLY motor
1 = 26
2 = every size
LTD = stock out of the box
Mike

 

[Buckshot]

What is the rpm limitations on reeds?
Type of material I am sure is critical.
In my go kart days we had reeds. They were metal and often broke and went through the motor. It was a flat plate design.

Then a new design came out that was shape like a pyramid and seemed to do better. Soon there after drum inducted motors came available.

It seems to me we are behind in the gas RC world with the style of motors we have readily available, a weed eater motor.

The current reeds are in a pyramid block and are either G-10 or Carbon. I have had one set of G-10 reeds let go, no engine damage happened. I took the cylinder off, flush entire engine and cylinder with brake cleaner and reassembled with new reeds and won the next round heat race.
Not as many RPM’s as the piston port engines. But the power is significantly more than a piston port of the same displacement.
For example the 26cc BZM engine in my slingshot outrigger pulls more prop than my 30.5 Full Mod Zen.
To each their own.

 

[Dave Gilles]

None of these classes you have posted are stock. All of them have modded motors. The stock ones should be listed as G - LTD. All G and GX classes allow modification to the motors.
G = GAS
X = open to all motor manufactures
if no X = ZENOAH ONLY motor
1 = 26
2 = every size
LTD = stock out of the box
Mike

Ahh I need to read the dang manual again. Thanks Mike

 

[dr gary turner]

The current reeds are in a pyramid block and are either G-10 or Carbon. I have had one set of G-10 reeds let go, no engine damage happened. I took the cylinder off, flush entire engine and cylinder with brake cleaner and reassembled with new reeds and won the next round heat race.
Not as many RPM’s as the piston port engines. But the power is significantly more than a piston port of the same displacement.
For example the 26cc BZM engine in my slingshot outrigger pulls more prop than my 30.5 Full Mod Zen.
To each their own.

 

[dr gary turner]

What do you think is limiting the rpm’s in the BZM?

 

[LohringMiller]

Reeds are for widely varying speeds and loads as in road vehicles. Disk valves breathe better than reeds but are considerably more expensive. Tuners have learned to tune intakes and pipes along with reed thickness to approach disk valve performance.

A piston port engine with a tuned pipe can be set up for power over a narrow range of rpm. Increased intake timing is responsible for a lot of the power gain over stock Zenoah timing. Rpm drop in the turn limits how far you can go. It is possible to run 360 degree open time on a piston port engine. It needs a retractable reed assembly for starting and idle.

Lohring Miller

 

[Mike Bontoft]

All I have left from the disc valve project are these pictures. I've looked many times but the engine is still lost in my maze. It ran quite well and I think we could definitely have improved it with some work on the dyno. The crank had a hex ground on it and a machine front crankcase and disc cover. Disc was spring steel. To do over a long rod would have been better.

 

[dr gary turner]

All I have left from the disc valve project are these pictures. I've looked many times but the engine is still lost in my maze. It ran quite well and I think we could definitely have improved it with some work on the dyno. The crank had a hex ground on it and a machine front crankcase and disc cover. Disc was spring steel. To do over a long rod would have been better.

The work is awesome.

 

[dr gary turner]

Mike, what you have done is what I think needs to be done to really advance gas.

 

[Eric Canto]

None of these classes you have posted are stock. All of them have modded motors. The stock ones should be listed as G - LTD. All G and GX classes allow modification to the motors.
G = GAS
X = open to all motor manufactures
if no X = ZENOAH ONLY motor
1 = 26
2 = every size
LTD = stock out of the box
Mike

This is a VERY good explanation of the NAMBA gas classes!

 

[DON MAHER]

This thread has really gotten off track from the original question!

In my experience with the stock 26 & 29.5 after break in, the 29.5 has more torque to allow a larger prop to be used!
That’s about all!