This thread was originally in the glow forum. This will explain all the responses from people other than MVVS people. -Jim, Moderator


I`ve just run 3 tanks of break in.I must say i`m not impressed with performance so far.When I ran 0% nitro it would not peak and scream, just seemed slow when I leaned it. I then miksed the fuel 50/50 with some 15% nitro fuel and it became much better. it now peaked and sang high when I leaned it, so I think it definately needs some nitro. I couldn`t tach it because it was not enough light out, but I doubt it gave more rpm than my asp 52 xls on the 12.25-3.75 prop.maybe I had to high expectations of this engine.My new harrier 46 is going to carry one of the two engines, and I`m going to pick the most powerful one even if it turns out to be the asp. I couldn`t care less if the asp will not last as long as the mvvs as long as it is powerful while it runs. A setup or a couple of bearings dont cost much.so Is there any chance that my mvvs will pass 13300 on the 12,25 prop or is that to optimistic to be expected.I have the tuned muffler(3248) and the outlet seems a bit small to me. It measures about 6.6 millimeters which is smaller than all other engines in the 50 size I`ve seen.I suspect it to be a little restrictive and I wonder if it would help to open it a bit. any thoughts???

Hi!
It might be that MVVS has altered the compression ratio on the latest 6.5-8.0cc MVVS engines.
This certainly applies to their Q-500 6.5cc engine which is made for 15% nitro (but MVVS has heads specially made for 0% nitro too).
As for the your expectaition regarding MVVS 8.0cc engine...I think it is by no means no more powerful than any other 8,0cc engine...! Simple as that.
As for the pipe outlet being to small...no... to the contrary, you can perhaps gain some rpm by decreasing it even more.
Did you have the 7mm carb? I would definitely try the 8mm carb as I have personal experiences from it on my 6.5-8.0cc MVVS engines.


Regards!
Jan K

Three tanks is not a broken in MVVS by far and If you keep playing around with the nitro Jug it will be a broken/damaged MVVS.
I am sure one of the MVVS reps will be giving you some advice shortley. BTW I have a good Magnum 52 xls that I would trade you......

he he tanks for the offer gizmo, but as mentioned above I already have an xls 52. It has also just been run 3 tanks breakin and is strong as h.ll already. About nitro I don`t think I`m going to destroy it because it supposed to run around 0-5% and I`m at 7.5% tops, maybe less because I also added some castor, it was really weak when run without nitro.will try to tach it tomorrow. will a maglite work as light from behind the propeller or does most tachometers work only in good daylight?

I forgot to mention that I do have the 8 mm carb

asmund
I suppose you want to do hovering and 3D stuff because of your prop selection?
What exhaust system do you have on your mag52?
Is it the MVVS minipipe you are using on your MVVS49? with the separate header and a black colored short pipe?
If so then you most read in the instructions at what rpms it will give you tuning benefits.
If the pipe is too short for your rpm range then it will not work and load up in the midrange (trouble).
Maybe you need to try the APC 12x4 instead to let the tuned minipipe come on.
If you want to run the 12.25x3.75 the you can add a 5cm (2") pipe beetween the header pipe and the minipipe so it will work at the lower rpms.

I also think you should try the 12X4 APC
The 12.25 X 3.75 is a much draggier prop than the 12 X 4 (draggier...is that a word? It is now... )

I tached my TT .46 Pro @ 12,500 w/ the 12.25 X 3.75 and @ 14,100 w/ the 12 X 4 on the same day, all else being equal...

For 3D, choose the prop that will be in the top rpm range of the 3248 muffler. Then you will have the best idle and midrange of any engine you ever tried.
The engine will get better and better, and needs a lot more running time than three tanks to break in. They last long, but therefor need to run in longer

edited typos

yes the engine is going into a harrier 46, so 3-d stuff is what I`m aiming for. I have on hand the 12.25-3.75 and 13-4, but will borrow a 12-4 from a friend tomorrow and give it a go. also I run the minipipe (3248) and 8 mm carb.I dont consider the engine fully broken in yet, but ready to fly. I will try to tach it tomorrow.

Still willing to trade.
I have 10 Magnums and three MVVS engines(along with an assortment of other well known brands).
YOU CAN BASE THE PERFORMANCE OF ANY ENGINE ON THREE TANKS?........He,HE.

Another thought...or two...
The 12.25 X 3.75 will have slightly better vertical pull, but the 12 X 4 APC being much lighter, and having narrower blades, will have a lot better (quicker ) throttle response.

I`m not going to trade it just yet I will try to add even more castor as adviced by mvvs support forum, and run a prop with less load. but I still think that it must have a little nitro because of the evident lack of power when running no nitro compared to when running the mentioned 7.5% blend

hi flyer95. On my xls 52 I have the stock muffler, only with the baffle removed and I also have opened up the outlet a bit. the instructions for the mvvs tuned muffler says it going to increase engine power in the 13-15000 range. I thought the 12.25-3.75 prop would be in this range, might be just a tad to heavy, so I`ll try the 12-4. I`m waiting around for the light to be sufficient to do some tachreadings today

Asmund,


The 12.25x3.75W APC is going to be spun at about 13,100, by the time the engine accumulates some time under its belt.

The 12x4 APC is going to see about 13,800.


You may want to extend the pipe a bit, to 25 mm (1" ) between the end of the header and the front of the tuned silencer (within the silicone coupler), for the engine to achieve this.

Although the #3248 is not a true tuned-pipe, it still needs the gas column inside it, to resonate at least at the base-line RPM, to get the engine on the boost.
Making the system longer will allow this Helmholz resonator to get in tune.

This C/L Stunt prop is indeed on the heavy side.

Most of my 3-D customers use this size and those who don't use the 12x4, or the Bolly 11.5x5.

great, thanks Dar. I will try to extend the lengt and run the 12-4 later today. I guess this engine and exhaust combo just needs some tinkering to get to run at optimum. I`m used to just slap on a prop and run, but I will take the time to experiment a little on this one. so Gizmo, no trading

well, I just ran tre more tanks run in prosedure( total amount of fuel trough so far is almost 1/2 gallon). used the 12-4 apc and a maglite to get the tachometer to work. I have added some more castor,so my fuel now should be around 5% nitro and minimum 20% oil. It`s a little difficult to keep track of the exact % due to all the miksing, but I should be close to a optimum fuel by now. I had a gap between the header and pipe at about 10mm and I got only 11200 rpm. I will try to slide the pipe in and out of the silicone coupler to try to find the sweet spot next time I run the 49, but I can hardly see another 2600 rpm coming from this to get up to around 13800

Asmund,


11,200 RPM compared with 13,800 is only 53% of the horsepower output....
It is completely off the pipe and seems very far from peak.

13,800 RPM on the 12x4, is achievable with only 5% nitro and the stock head setup.
I have several customers that see this every time they fly and I have too.

MVVS does not produce different high and low compression heads.
You just use the existing head shim, unaltered, for up to 5% nitro. You can add an extra head shim for 10-15% nitro.

The engine is produced using CNC, so there aren't any out-of-tolerance parts.


Just slide the pipe out, to leave 25-30 mm of 'air' within the coupling and adjust the needle.
See what RPM you are getting, with this fuel, which I now hope has at least 10% Castor oil and 20% total oil.

When you set it, make sure the engine returns to max RPM, with the application of full throttle and without having to re-tweak the needle. If you have to readjust every time, add some more length.

I understand that you are pretty far to the north, but can you not get enough sun-light to take an RPM reading?

Try removing the the glow-plug and turning the prop slowly, to feel if the piston has some pinch in the sleeve, at TDC.

I`ve just adjusted the gap between header and pipe to 30mm. I think the fuel should be about right now. The engine has pinch at tdc when I remove the plug. You are right about me living far north, about in the middle of Norway, and the daylight is not sufficient for any tach reading yet, of course the dark clouds full of rain doesn`t help either. But we are heading towards lighter days now. I must say that the maglite did the trick though.I was of the impression that the mvvs minipipe was "plug and play" but it seems it must be tuned like a full length tuned pipe after all.

Hi!
Dar ...MVVS produce a (for the Q-500 6.5cc engine ) head that is made for 0% nitro.
This is an option produced for those of us that dont like the standard Q-500 6,5cc engine that is produced with a head made to run on 15% nitro.

Regards!
Jan K

Jan,


I have a #3068 engine in stock, with that head, which will use up to 5% nitro.

This is the standard head and two head shims are included, should the user wish to use more nitro.

This is just as I explained in post #17.


Mr. Å*vajda says they only make one standard head (0-5%) per engine.
And if one wishes, he can add one head shim, for up to 15% nitro.

If one wants to use even more nitro, I guess the second shim can also be added (three in all).

Maybe at some point there were high and low compression heads produced, but it doesn't seem to be so any longer.

could my problem with low revving come from having to long header and coupler?? I`ve just been searching around for info on the 49 engine and found that some shorten the header when running the 12.25 prop. If I dont get my rpm`s up, now with the increased length between the coupler and pipe, I `ll have to break out my hacksaw and start copping some aluminum.

Asmund,


When an engine uses too long a pipe, it is said to always be on-the-pipe.

When you use a larger propeller, the engine will peak at a lower RPM, so the system must be longer to entertain this lower RPM.

The engine must be able to reach the system's base-line RPM, without the tuned-exhaust's help.
If it cannot do this, boost will not be felt...

Please read about how a tuned exhaust system works [link=http://www.prestwich.ndirect.co.uk/tunedpipetheory2.htm]here[/link].

Essentially, if the system is too short for the RPM, the reflected wave will come back with the bypasses still open.
Some of the fresh mixture will be pushed back into the crankcase and will not remain in the cylinder.

Boost will be poor.

The boost is at its optimal state, if the reflected wave comes to the exhaust port, with the exhaust port still open, but the bypasses closed, so the fresh mixture previously sucked into the header, by the previous negative wave, is now crammed back into the cylinder, just before the exhaust port is closed.

With the pipe too long, the reflected wave arrives after the exhaust has closed, but the fresh mixture sucked into the header is lost, raising the fuel consumption.


If the engine cannot reach the lowest boost RPM (base-line) on its own, no boost will occur, unless the engine is unloaded... And then a lean-run can occur.

yes I knew this from before,but maybe not as detailed. I used to have a rossi 53 with tuned pipe, also I`m into scooter tuning so I understand how a tuned exhaust works, but on this 49 engine I have done as adviced and still no power well i`ll try again tomorrow and se if the added length does the trick or not. according to your posts elsewere on rcu the engine is run in when it can hold its top rpm for a minute and that usually appeares after a relatively short somewath rich 2 stroke run in, so I dont think further run in will show significant increase in performance, so I think its all in the adjusting of the pipe from now on. strangely, reports on this engine wary wildly from realistic 13000 to unbelievable 15000+ on my beloved 12.25 prop. also I find that people say to just press the pipe and header all the way together, and now I know that doesn`t work either. Its just a little frustrating to read all about how fantastic and powerful this engine is and not be able to even get close to the same performance myself. I might add to this that I`ve been into this hobby for quite some time and also race buggys and monstertrucks so I`m used to playing around with glow engines. hopefully the added length in the coupler was the missing link

Asmund,


I did write this before.

The 15,000 claim is not even for the Jett .76L BSE engine....
It requires 2.04 HP to spin a 12.25x3.75W this fast.

Lies are not true claims...

This is not within the capability of any engine I can think of right now.


My break-in thread deals with 'when can you start using the engine normally', to signal the end of the break-in process.
MVVS engines do gain a lot of additional power; around 600 RPM within the 6-10 hours after the break-in.

Your engine seems to be too low on power, for it to be a case of needing more break-in time.

Something is out of adjustment and most likely it is the tuned exhaust.


Do try to find a way to measure RPM, in daylight, without using the torch/flashlight.
It can also be a case of an inaccurate sampling.

Did you try to tach another engine at the same time and got a more positive result?

yes I had my asp xls 52 running alongside and tached it the same way on the apc 13-4 and got a rock steady 12400.I`m starting to like the asp that seems to be a correct measure since I have tached it before in daylight on the 12.25-3.75 and got 13300 then. so I think the low numbers on my mvvs today was in fact low numbers rather than error in the taching