ESE's works engine tuner

[nitro2tfx]

do you know of any rules of thumb regarding com ratio and nitro percentage in a 2t or is it just trial and error to see what works ? theres almost no info about 2t and nitro that ive been able to find so far

Nitro makes more cylinder pressure. A turbo makes more cylinder pressure. Any engine will only take so much pressure no matter how it is built.

So for a fixed amount of maximum desired cylinder pressure, less compression ratio and more nitro % makes more power than more compression ratio and less nitro %. Much the same as less compression ratio and more boost makes more power than more compression ratio and less boost on a turbo engine.

Changing compression ratios changes peak cylinder pressure a lot but only changes power a little. The same change in peak pressure with a change in nitro %, changes power a lot.

[guyhockley]

You're right about the torque variations Niels, but I was talking about the radial bearing loads, which are almost non-existent in a boxer and far from small in a V-twin.
Vibrationwise it's the same: a V-twin can't compete with a boxer unless it has a balance shaft, adding volume, weight and complication.
The majority of light aircraft are using boxer engines for a reason. A propeller makes quite a good flywheel (low mass, high inertia), flattening the torque fluctuations.
Your V2-crankshaft (below) may not be heavier than a boxer-crank, but in principle it's a four-stroke crank. Unless you use an external blower, again adding volume, weight and complication, a two-stroke V-twin needs two separate crankcase volumes, and your crankshaft does not provide for that.
Attachment 333069

Couple of thoughts... Some boxer twins seem to end up with an extra main bearing one end, to control crank whip, maybe?
Niels crank wouldn't need too much extra if it was used in a JBB/outboard engine type configuration. Husa has posted relevant pictures, before.
Talking of outboards and referring back to the big bang idea, I've wondered whether racing outboards would be better off from the point of view of "traction" of using other configurations than the universally adopted boxer layouts.

[guyhockley]

There you are TZ, maybe a successful 2T EFI system, looks like an injector port in that throttle body.

Lot easier to do FI on an aero-engine...

[peewee]

Nitro makes more cylinder pressure. A turbo makes more cylinder pressure. Any engine will only take so much pressure no matter how it is built.

So for a fixed amount of maximum desired cylinder pressure, less compression ratio and more nitro % makes more power than more compression ratio and less nitro %. Much the same as less compression ratio and more boost makes more power than more compression ratio and less boost on a turbo engine.

Changing compression ratios changes peak cylinder pressure a lot but only changes power a little. The same change in peak pressure with a change in nitro %, changes power a lot.

makes sense and i think im going to lower the com ratio just a bit. the smaller engines might do fine with high ratios but this one has 90mm piston. mechanically i think it will be better off if its a bit lower. i keep waiting for it to pop the head studs out but luckily is still holding together. not to mention its acting strange when i try to kickstart it on a nitro mix. acts like theres alot of
static cylinder pressure, which it never did on methanol. . and plenty of times its sort of made a backfire noise and tried to make the kick lever go backwards.. couple weeks ago it broke the weld on com release tower but ive since fixed that

maybe you or adegnes has some knowledge about what water temp the nitro mix starts to run good at ? i was thinking atleast 50*C but i havent been able to get mine to that temp yet but ambient temps have gotten colder so maybe thats why. ive got a 70*C thermostat that i might have to install

[Grumph]

maybe you or adegnes has some knowledge about what water temp the nitro mix starts to run good at ? i was thinking atleast 50*C but i havent been able to get mine to that temp yet but ambient temps have gotten colder so maybe thats why. ive got a 70*C thermostat that i might have to install

I remember seeing Don Garlits quoted as saying he found nitro liked to run at around 140deg F. If I converted it right, that's about 55 deg C. But he's looking at the start sequence specifically where he didn't want to be held too long - or rushed through by his opponent. He had an on board tank which gave him enough reserve cooling to ensure he didn't overheat in staging.

I have some experience with a roadrace 4T engine on 20% nitro which ran very well indeed with a 70deg C thermostat installed.

[Flettner]

More than 10% and you can smell it.

[Grumph]

More than 10% and you can smell it.

20% and you get complaints if the field is held on the dummy grid.....makes the eyes water.

[adegnes]

makes sense and i think im going to lower the com ratio just a bit. the smaller engines might do fine with high ratios but this one has 90mm piston. mechanically i think it will be better off if its a bit lower. i keep waiting for it to pop the head studs out but luckily is still holding together. not to mention its acting strange when i try to kickstart it on a nitro mix. acts like theres alot of
static cylinder pressure, which it never did on methanol. . and plenty of times its sort of made a backfire noise and tried to make the kick lever go backwards.. couple weeks ago it broke the weld on com release tower but ive since fixed that

maybe you or adegnes has some knowledge about what water temp the nitro mix starts to run good at ? i was thinking atleast 50*C but i havent been able to get mine to that temp yet but ambient temps have gotten colder so maybe thats why. ive got a 70*C thermostat that i might have to install

I have the same experience with high static cylinder pressure and kickback. It's worst after a stall from loading up. Maybe lots of liquid fuel in the combustion chamber.

There seemed to be traces of combustion outside the combustion chamber when I pulled the head, it might be lifting it slightly.
Can't help with the water temp, just CHT ang EGT yet.

[SwePatrick]

A small aircooled twostroke(novarossi) Nitro blend engine(20%) runs best at about 90-105degree celsious.
But, you might need to run it a little bit lower in temp to still have some margins to piston meltdown

And guys!
Remember to setup engine for increases heats.
More gap on the rings, more tapered piston.
As all tempratures get´s higher the margin to when piston melts is getting closer.
And you do not want to have smeared aluminium all over the bore that increases blowby.
And thereby heats the piston even more.,,, aaaaaaand 'good night' as result.

You want more gap on the rings to have more margins to when the ring warps in the ring groove.
If it warps, it´s also 'good night' but often with nicasil pulled off the cylinder.

I recommend steelliner in cylinder with nitro.
Just because it can take some beating and still beeing able to use again.

[lohring]

The torque variations in two stroke boxer is just as big and nasty as in a single 1000 ccm engine.
A V2 will be smother than smooth and crank not very much heavier,if at all.
In Your very informative writing on big bang fallacy there are some curves showing it but I cannot find them.

https://imgur.com/9RprD0t

You can make an opposed piston alternate firing twin that should run smoothly with a 1:1 balance shaft. There is a split ring seal between the two crankcase areas. See below.

Lohring Miller

[136kg136ps]

In a motorcycle,it would seem that a boxer would require an additional gearset to change the plane of rotation to that of the wheel.Or would a 90 bevel gear work?I'm having a hard time wrapping my head around that,it seems like it would offset any weigh loss.Particularly after lugging older BMW motors as a kid.

[Frits Overmars]

Funny that you'd mention BMW. Below is their first boxer, with no additional gearsets, no bevels, no nothing. That included no cooling to speak of for the rear cylinder,
so after this first model, BMW turned the engine from longitudinal to transverse. But now that their boxers are liquid cooled, maybe we should send them an email asking them to turn it back to its original position; parking the bike in my garden shed would become a lot easier.
BMW was by no means the only brand to build fore-aft boxers; Douglas was a well-known example. And let's not forget König; they even did it with four cylinders.

[Niels Abildgaard]

You can make an opposed piston alternate firing twin that should run smoothly with a 1:1 balance shaft. There is a split ring seal between the two crankcase areas. See below.

Lohring Miller

The reaction torque variations will be the same as for an inline twin like Flettners newest gyro engine.
The V2 varies less.
The split ring is common outboard technology.
For a V2 it is not nessecary to sepparate cranks for starting engine and for an aircraft engine it is either idle or 60 to 110% power.
At the high end either tuned exhaust or turbocharger.
The reaction torque is what rattles aircraft.
Inertia of propeller is important for lowest possible rpm but not for smoothness during fligth.
Have flown Cessna 172 with both 6 cylinder and 4 cylinder engines and Yes there is a difference in comfort.

https://i.imgur.com/SOqAT4f.jpg

[Frits Overmars]

For a V2 it is not nessecary to sepparate cranks for starting engine and for an aircraft engine it is either idle or 60 to 110% power. At the high end either tuned exhaust or turbocharger.

Niels, I would love to see a measured power curve of your V-twin with a common crankcase and tuned exhausts.

[Niels Abildgaard]

Niels, I would love to see a measured power curve of your V-twin with a common crankcase and tuned exhausts.

Me too but two is to few for crowdfunding