Power Differences Among Stock Zenoah Engines

[Terry Heddin]

How much real world difference (seat of the pants, not specs, so to speak) is there between the G260, G300, and G320 engines in stock form? I have searched the internet, and cannot find any real comparison.

 

[David Ashcroft]

Not much ,but I have seen 260 engines run faster than a 320 engines and vice versa.
Depends on the application .

 

[john v]

I would guess that the 32 will have more torque than the 26
From what I heard, the 32 is heavier and uses different mounts than a 26
In stock form you will probably see more 26s than other displacements

 

[Mark Anderson]

If somebody wanted to send me stock 30&32 motors for a couple of days, I could dyno them and compare to 26 with real numbers.

 

[LohringMiller]

We dynoed a lot of 26 cc engines. The only difference we found in stock 26 cc engines was due to break in. Design differences like using the same outside dimensions with larger bores and longer strokes with the same connecting rod length will cause some power loss in higher displacement engines. Otherwise the there was no difference detectable within the precision of our dyno. The mass production methods Zenoah uses make the different engine parts very close to identical.

This was not true for Quickdraw engines during that time period. We always ran carefully selected Quickdraws. (Thanks Mitch) Even the cylinder hone pattern could make a difference.

Lohring Miller

 

[Steve Smith]

We dynoed a lot of 26 cc engines. The only difference we found in stock 26 cc engines was due to break in....

Lohring Miller

Hi Lohring,

Can you elaborate? Did you find that engines with more run time (more broken in) made more power, or were you seeing differences because of 'how' an engine was broken in?

 

[Terry Keeley]

If somebody wanted to send me stock 30&32 motors for a couple of days, I could dyno them and compare to 26 with real numbers.

Last you posted on the dyno was you were getting rid of the freewheel, it sounds like it's working for you now? Are you getting any weird "upswings" in your curves?

Care to put a little update (maybe some pics or video?) in the dyno thread?

https://www.intlwaters.com/threads/run-in-stand-dyno-build.78248/page-40
I'm going to do some testing soon now that I've cut the wheel down a bit more.

 

[LohringMiller]

Not a stock engine, but this series of tests shows the power gain after an afternoon of dyno runs on an M&D engine. This engine had zero drag seals so they weren't part of the break in. I don't find such a direct comparison with a stock engine, but similar power gain still happens.

Lohring Miller

 

[JoePeters]

How much real world difference (seat of the pants, not specs, so to speak) is there between the G260, G300, and G320 engines in stock form? I have searched the internet, and cannot find any real comparison.

Terry I would start with a g300/28.5 cylinder platform. The bottom ends will use standard mounts and should be very simple to set up and will accept a lot of hop up parts when its time. The g320 is a torque monster but its size and weight should be considered.

 

[David Ashcroft]

Terry ,,, John Finch on Jims runs a large Gas hydro similar to yours using a 260 size engine and he is getting speeds of 70+
A 260 will eat a Big block if you prop it well use a good pipe and set your hull up correctly. A 260 can run with and beat the Bigblocks .

 

[DON MAHER]

The same can be said for the big blocks!

 

[bermudadude]

i ran a stock 320 for a few mins [just because] i wanted to see the issue of people not seeing a difference. long story short just like the 26 vs 30 argument ---if ur gonna carb/pipe/prop it the same then just run the 26. the 320 is a kind of beast [none of these really impress me,last i stood up was when i saw a 35sg pull wheelies in a pig of a 59inch mono]
320 needs a 35cc carb and a "35cc" ,i hate saying it like that but i mean a decent volume pipe

 

[Dave Gilles]

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.

 

[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.

yes 26 and 29 pistons need lightening. every tuner/website offers lightened pistons for them. however the 320 is designed a bit lighter- i dont see any lightened pistons for it. also having run 1 its dynamic balance is totally different. the engine rpms really easy and spools up quick. the 28/29/30.5 just make the stroke/rod/counterweight ratios more and more wrong [stroke gets longer but rod same length-it was too short from the jump]
kinda nice engine if ur stuck in the piston port world u should give 1 a try ,only a few bucks more than the others.
of course theres the obvious GLARING things wrong that u wonder how did even a failed engineering student miss but yea thats the zen world .
i mean,,if ur making a cylinder from scratch how hard is it to just cast the teacup handle ports in? instead its cast without a port wall then have to face the area and drill and thread it to "bolt on" port walls ,talkin bout "adjustable ports" uug! then the first gen had the ring locator pin in the wrong place so u cant widen the exhaust....WHAT? ive "heard" they changed it idk if its true.
if J&g had stayed around and made a cylinder for it i think i would have had fun with 1

 

[Dave Gilles]

yes 26 and 29 pistons need lightening. every tuner/website offers lightened pistons for them. however the 320 is designed a bit lighter- i dont see any lightened pistons for it. also having run 1 its dynamic balance is totally different. the engine rpms really easy and spools up quick. the 28/29/30.5 just make the stroke/rod/counterweight ratios more and more wrong [stroke gets longer but rod same length-it was too short from the jump]
kinda nice engine if ur stuck in the piston port world u should give 1 a try ,only a few bucks more than the others.
of course theres the obvious GLARING things wrong that u wonder how did even a failed engineering student miss but yea thats the zen world .
i mean,,if ur making a cylinder from scratch how hard is it to just cast the teacup handle ports in? instead its cast without a port wall then have to face the area and drill and thread it to "bolt on" port walls ,talkin bout "adjustable ports" uug! then the first gen had the ring locator pin in the wrong place so u cant widen the exhaust....WHAT? ive "heard" they changed it idk if its true.
if J&g had stayed around and made a cylinder for it i think i would have had fun with 1

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?

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.

 

[LohringMiller]

The normal Zenoah head clearance can tolerate a 1 mm stroke increase without modifications. Otherwise you may need a spacer or thick gasket. If you use a long rod you need to use a spacer under the cylinder. The stock piston only clears the exhaust port with longer strokes. This doesn't seem to matter for the small opening.

Lohring Miller

 

[Dave Gilles]

The normal Zenoah head clearance can tolerate a 1 mm stroke increase without modifications. Otherwise you may need a spacer or thick gasket. If you use a long rod you need to use a spacer under the cylinder. The stock piston only clears the exhaust port with longer strokes. This doesn't seem to matter for the small opening.

Lohring Miller

I should've said with a +1 crank there is only .020" or so. that's what I mean anyway.

 

[dr gary turner]

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.

 

[Don Ferrette]

Tiger King was working on a Zimmermann gas motor that I was following closely. All the initial results on testing seemed really promising but they stopped for some reason and opted for the new reed valve GP engine instead.

 

[dr gary turner]

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

Did anyone in the US test it?