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MVVS 91 setup

Old 03-23-2008, 01:47 PM
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Default MVVS 91 setup

Using this motor on pattern model and want to mount tank on CG, should I use Perry pump or Cline fuel regulator.(using 13x10 prop and MVVS pipe) Has anyone tried this setup or similar. Dave
Old 03-23-2008, 04:32 PM
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Default RE: MVVS 91 setup


Most who bought such engines that I sold, use an APC 14x8 props, with the original MVVS #3250 pipe, with a sizable extension (in rear-exhaust configuration).

Initial RPM with the engine new, was ~9,700, and it grew to ~10,200 after about 6-10 hours were accumulated.
Using the #3219Q carburettor added ~200 on top of that.

With the tank on C/G some kind of pump is imperative.
I believe one of the Walbro regulator diaphragm devices (Cline/Iron-Bay) would run better than a Perry.
Old 03-31-2008, 06:35 PM
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Default RE: MVVS 91 setup

DarZeelon, Thanks for the info. Got Cline regulator, will let you know how I get on. Dave
Old 01-24-2012, 01:55 PM
Don Kabirnov
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Default RE: MVVS 91 setup


I am digging up this old thread because I got myself a .91 MVVS and want to ask some questions.

The intention is to install the engine into a 1.80 m pattern plane that I built. The plane with the engine (no fuel) and electronics weights 3900g. The engine was bought broken, with no carb, broken big bearing, broken cylinder (ingested a ball from the bearing). I bought a new piston - cylinder assembly from Pe in Holland and changed the bearings with new SKF explorer series. I adapted a 9300 Perry carb (after all, the MVVS is a late 80's HB Grand Prix design) and turned the exhaust to the rear. I have a lite Bolly CF tuned pipe intended for the mid 10K's on the .61 engines.

I don't want high revs on this engine but as it has a stroke 1 mm longer than the OS .91 I want to use a 15x10 APC and dreaming of 8700 - 8900 rpm , or 9800 - 9900 rpm on a 15x8 APC. My usual fuel is Tornado 5% (from year 2010 has 14% P2000 synthetic oil 2.5% castor) in which I add another 3% high quality castor oil.

1. Can the engine turn a 15x10 prop ? I mean will it detonate / bend the conrod / damage itself ?

2. Can the engine get to the power band (top of the torque curve) with the 15x10 prop , or it will just stay below in the fast idle at 6 - 7k ?

3. What glow plug should I use to prevent detonation ? (I have acces to OS and Rossi plugs)

Thank you very much !
Old 02-02-2012, 08:15 AM
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Default RE: MVVS 91 setup

The MVVS 15cc engine can swing (like all other engines of the same size) rather big props. I've used both 15x4W, 15x6 and 16x4W APC props with good results. By trail and error I have found out that my own 15cc engine in my You-Can-Do .60 3D plane like a 16x4W APC best. I have tried 14x4W, 14x5N, 14x6, 15x4, 15x6 and finnaly 16x4W.

Weather or not a 15x10 APC prop will work, I dont know. A 15x10 prop will put much load on the engine but with a long tuned pipe or MVVS short pipe I think it will work. But I don't think it would be the best prop size for what ever model you have intended to use. -But try one! I guess the rpm with a 15x10 APC would around 8000-9000rpm on 5% nitro fuel and using a tuned pipe.

Standard glow plug for the MVVS 15cc is a Nova -Rossi 6 plug but Nova -Rossi 4 or 5 works good too, as well as OS 8 and Enya 3.
Provided you use 5% nitro!
I run all my engines on 15% Motul Micro all synthetic oil and 5% nitro.

But be ware! Some MVVS 15cc engines cannot tolerate even such low nitro contents as 5%. But if soo, just add another 0,1mm head gasket.

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Old 02-05-2012, 01:39 AM
Don Kabirnov
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Default RE: MVVS 91 setup

Hello Jan, and thanks for the reply !

I will remember to have a 0.1mm head gasket at hand when I will do the testing. I will also take OS #8 and A5 plugs to retard ignition.

The plane is an F3A pattern so it will need to have a 1:1 traction/weight ratio at flying speed, so from the calculus a 15x9 propeller would be ideal. Since there are no 15x9 APC's or G-Sonic's on the market, I will have to use the 15x10 prop and make the engine go for 9k rpm.

After some more modding with the engine I manage to attach a HB Perry pump to the backplate. I also did something risky: enlarged the exhaust port to open 7° sooner to create a larger blowdown interval. The original timings, as precisely as I could measure them are:
- front intake opens 41° after BDC and closes 44° after TDC , total = 183°
- exhaust: 70° before BDC
- transfer: 57° before BDC - crankcase ventilation: 57 - 41 = 16°
- boost: 54° before BDC - blowdown: 70 - 57 = 13°

On the other hand, the famous OS Hanno Special which operates best at 9750 rpm has those timings:
- exhaust: 76° before BDC
- transfer: 58° before BDC
- boost: 53° before BDC - blowdown: 18°

I wanted to enlarge the blowdown period by 5° to allow a better reaction from the tuned pipe, but I actually did it by 7° so now the exhaust opens 77° bBDC and the blowdown increased to 20°.

From what I read, for tuned pipe operation a 16° / 10k rpm blowdown should be ideal. Lower rpm -> smaller blowdown. By factory it seems that the MVVS was timed to have the highest torque output around 8000 rpm.

Right now the engine weights 555g including glowplug and the header + tuned pipe + silicon coupler 225g so total weight is 780g. My ST G-90 weights 611g bare so the MVVS is quite light.

All that I need is that the engine will spin the 15x10 prop at 8950 - 9000 rpm (equivalent to a 2.4 HP power output). I will start the runing in as soon as the weather gets better, hopefully in about 3 weeks.

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