I've got a new 26GT2. I've completed the break in w/ 30:1 per the manual and I've run about 400ml of 40:1 fuel so far. Low end setting seems right, high end is set for max rpm per PRME instructions, and ignition is per spec.
I am only getting about 5200 rpm on a Zinger 18x12 in a pusher configuration at WOT. I know this is a little more prop than recommended. Even so, 5200 is only about 1.0 HP on the MVVS prop power calculator.

Any suggestions?

Monsieur Dupuis,


In a pusher configuration, your engine does not usually get a good cooling, unless it is in higher speed flight.

The flow is taken by the prop from all around, not necessarily from directly in front...

Add that to the very heavy prop (you need a 16x12) and what you may see is over-heating...


Let's see what Pé can add.

Nothng much to add!
At these prop loads, the engine is strangled without any cooling. 18x10 already is a heavy load, 18x8 is OK, but in a pusher cooling is an issue that needs utmost attention and constant monitoring.
What are your cylinder top temperatures in flight?

DarZeelon and Pe,

Thank you for your inputs.

I don't know what the temps are but I've got a 36" shop fan blasting the test stand on high (directly in front of the engine, co-axial with the prop and flowing in the prop direction of flow). Ambient temps have been about 68 degrees F. I'm confident heating is not the issue here.

Again, an 18x12 prop is a bit much, but this engine should be putting out 3.8 bhp at WOT no matter what prop it's turning. Yes, the larger the prop, the slower 3.8 bhp can spin it.
What I'm trying to say is that my engine, regardless of the prop, is putting out nowhere near the advertized 3.8 bhp. The MVVS prop power calculator says I'm geting just over 1.0 bhp!

Does anyone know of any power-boosting tweaks I should have done that weren't in the manual? Any common power issues with these engines I could address? Thanks for your help.

Monsieur Dupuis,


The larger prop you are using is holding your engine far below its peak torque RPM...

As such, it cannot possibly come close to its performance objectives.

You must never prop any engine to below its peak-torque (you can find this 'unhealthy' range, where using a slightly 'heavier' prop will cause a greater RPM loss... because the lead is increased AND the torque is decreased).

The rated HP can only be possible, if the engine can be spun at 9,000 RPM, with a smaller than recommended prop.


You did not state what type of silencer you are using, so please see [link=http://mvvs.cz/mvvs%2026.html]this web page[/link] for bench-mark RPM numbers.

An engine spinning at a lower RPM does not give proportional HP numbers.


If you have stick-shift car and you try driving it in top-gear, at 20 mph, it will not accelerate very well...

This is what you are doing by over-propping your engine.

...And, over-heating will result despite the fan...

Hi pilot,

your propeler is very havy for 26.

Now getting 7600 rpm on a top flight 18x6 in puller config., which calculates out to be 2.13 hp.

Any idea where max torque is on these engines? Thanks.

You must berunning a very restricting muffler. !8x6 on tuned MVVS pipe will bring about 9000 - 9200 rpm! The max torque location is very much muffler dependant.
Can you please elaborate a bit on your setup?

I'm using the Evolution EVO30943400 invert wrap around from Horizon Hobby. There is no discernable rpm gain with the silencer removed. I didn't use a tuned pipe because in pusher configuration the pipe would be exhausting forward.

Monsieur Dupuis,


Using a 10-12 mm aluminium U-tube at the end of the tuned-pipe, would again spew the exhaust gases backward.

I have my doubts about some of the exhausts offered for these MVVS engines by Horizon Hobbies.
Using the various silencers MVVS has actually designed, specifically for these engine would no-doubt be preferable.

If the setup in your model does not permit the use of any of the MVVS mufflers... Well, that is a better excuse, but do expect some reduction in performance.


A Bolly wood 18x6 prop at 9,200 RPM would equate to 3.39 HP.

Here are the real life data collected by me, some very interesting info on mufflers and special engine treating .

9100 3266 Skorepa prop, data Dick H
18x6 sko

8300 1:32 3266 tuned pipe, preivers
18x8 APC 13-4-04

7600 3266 tuned pipe
18x8 menz

8700 3266
18x8 proZinger

8200 3266 factory data
18x8 mej

8700 3266 zinger pro, data dick Hansson
18x6 zin P

6400 3270 gaines
16x11x3 mej

7100 3270 gaines
17x12 APC

8400 3270 gaines
17x8 APC

7300 3270 factory data
18x8 mej

6800 3298 factory data
18x8 mej

9200 3M mintor piston top and combustion chamber ceramic coated
17x10 biela

8850 3M mintor without piston top and combustion chamber ceramic coated
17x10 biela

7300 bisson reivers
18x8 mejz

7450 Bisson
18x6Wapc

7800 ks banana "
17x8 apc 28-5-07

8300 scorepa pipe 1 gallon through the engine, 4300ft
18x6 skor

8800 scorepa pipe 1 gallon through the engine, 4300ft
18x6 mej