Perhaps you could spend some time into high speed remote starter techniques? Makes warm up seem a bit unsympathetic i bet but with that range, who cares about 8000rpm?
No8 Wire Extraordinaire
Perhaps you could spend some time into high speed remote starter techniques? Makes warm up seem a bit unsympathetic i bet but with that range, who cares about 8000rpm?
Don't you look at my accountant.
He's the only one I've got.
No8 Wire Extraordinaire
Hey Roger.Originally Posted by lodgernz
If still had dyno I'd be hooking timing light up and seeing what happens at 12000rpm under load. Bet its not pretty and I'd also put a meter on the power supply to see if it browns out.
Don't you look at my accountant.
He's the only one I've got.
Pristine Knee Sliders
Thanks Dave, I wish you still had the dyno.
There's no power supply: The HPI ignition is a magneto with CDI. It was working fine with my last cylinder and pipe, revving out to 15000 when required. That was a very short pipe at 678mm LT.
I'll check the timing again though.
Forum whore
Ken , redo the calc for the 50cc we were discussing.
( 50/125 )* 53.3 * ( 18500/13500 ) = 29.2 crank Hp less 12.5 % to rear wheel on a Dynojet = 25.5 RWHp.
The 35cc reed engine ( converted from piston port ) making it similar technology as the TM , with the same proceedure
would be
( 35/125 ) * 53.3 * ( 23000/13500 ) = 25.4 Crank Hp.
24M/s piston speed is nothing unfamiliar now days , and 14 bar bmep is for sure not "easy " but again nothing unfamiliar or off the planet high.
I really am missing something here as no 35cc RC engine makes even 1/2 that on unleaded.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Scooter boy
Is it just the fact that these engines are used as direct drives and require a flatter/broader power curve?
If they cannot have enough power down low they may not gain enough rev's to get onto the pipe?
Weekend cruiser
Working now on Nico Claasen 50cc twin
On the left hand the Sim 17.3 hp and the right hand dyno
We find every 2 weeks 0.5 hp this moment we have 14 pk 25 cc
Fair weather rider
it's HP at the wheel. but nevertheless far off what could be done/seems possible, however currently within my capabilities
Let's see if I can figure out a better pipe...anyone reg carb size vs reed cage inlet size vs projected area?
Hardcore Biker
The ultimate limit to power is timearea.
A 125 ccm can be modelled into a 25 ccm by making all dimensions smaller by a factor of cuberoot of five(125 divided by 25) that is 1.71.
The port areas will be linear scalefactor (here 1.71) squared ie 2.92 times smaller.
A 25 ccm model of Aprillia 125 that gave 55 horseplower will thus make 55 divided by 2.92 equal to 18.8 hosepower, if you are as capable as mr Thiel and there was no extra thermal loses due to the changed relation between volume that do the work and surface that puts heat in and out of working medium at the wrong time.
A V twin 50 cubic giving 35 horsepower will be quite interesting
Hardcore Biker
As I've posted before, we only got a little under 12 hp from our 35 cc engine. It was rpm limited by mechanical issues as well. I would hope that you could seriously improve this with a modern design. I wouldn't think that reed valves be much of an improvement over a piston port for a boat engine. We need peak power over a narrow rpm range. We run all races at wide open throttle after the start. Disk valves should be better, though BZM makes a reed engine that some people feel is good. I would like to see a dyno comparison with a similar, piston ported Quickdraw. Quickdraw does post dyno results and their brake dyno results were very similar to our inertial dyno results on the same engine. Both engines are a more modern design, but could be improved.
The factor that people miss is the overwhelming importance of friction as engines get smaller. Ringless pistons have been tried, but failed in the 35 cc CMB engine. They do work in 15 cc engines. Again, I think a more careful design and manufacturing process might succeed. After all, we seized a ringed piston in a sleeve that was out of round just above the exhaust port. We seized all the stock ringless piston and liner combinations we tried despite high castor lubes and a careful break in procedure. You need to match the expansion of the hot piston to a cooler cylinder. The cylinder needs to taper from a huge clearance at BDC to no clearance at TDC. One builder compared his fit to a glass stopper in a flask. That is the piston taper matched the cylinder with no clearance at TDC. Our 35 cc ringless piston and liner sets were nothing like this good.
Lohring Miller
Hardcore Biker
Further to limit of power thinking.
A gentleman showed some very nice pictures of a worldbeating 2.5ccm model areo engine and claimed 2.5 horsepower dyno.
An eqvivalent 6.5 state of art gives 5.
He got angry and removed all his writings and pictures but I did the same area,cube thing calculation.
https://www.model-engineer.co.uk/for...?th=165845&p=1
Hardcore Biker
Well, there are numbers given by Frits as to how much time-area is needed in any application, I think the blow-down is 8,72mm2 x cc x rpm to be rsa equivalent (I or someone else has the correct furmulas if needed) Just looking, 192*, even for 50cc isn't much, and possibly 500* is a too high estimaton.
Hardcore Biker
it is interesting for me at least to make a simple ultimate two stroke power as function of cylindersize.
First assumption:
54 dyno crank horsepower from a 125 ccm is very close to limit found by lots of trial and error.
Second assumption:
Ultimate power depends on Blow Down Time area.
The formula will then be:
Power from a 50ccm cylinder can max be 54 *(50/125)**0.66666= 29.3 shp.
for a 35ccm likewise: 54*(35/125)**0.66666=23.1 shp
for a 6.5 54*(6.5/125)**.66666= 7.5
and a 2.5 ccm 54*(2.5/125)**.66666=3.9 horsepower
When cylinder gets smaller mr Lohring tells us that unwanted heat losses and friction grow.
This can explain that state of art aircraft model engines of 2.5 ccm can reach 2.5 shp and for a 6.5 ccm engine it is 5 shp.
The 2.5ccm engine only give 2.5 of 3.9 according to the Thiel /Frits law or a minus of 36%.
The 6.5ccm is give 5 of 7.5 predicted by the law or a minus of say33%.
An estimate of a 25ccm cylinder is
According to Thiel/Frits 54*(25/125)**.6666= 18.5shp that shal be reduced with something between 36 and 0% due to extra friction and thermic losses.
Let me asume 20% for a 25ccm cylinder and we can reasonably realistic expext ca 15shp from a Thiel/Frits equal 25ccm cylinder.
Forum whore
Several points to answer.
BrettS - you are right about having enough mid power to even get the boat up on the plane.
I did simulations of piston port and RV , and against the reed version they made way less mid power , when configured to achieve identical peak and overev power.
So having the reed conversion , then allows me to tune other elements alot more radically , and still have more power than previously using the piston port.
Dutch - purely by my eye dyno the cylinder Exhaust duct exit looks very big. And if its a T port , it should be oval like a Honda, and if a 3 port it should have Aux eye ducts down the side, like an Aprilia.
Re the relationship of carb size to reed block port area. I have found both on the dyno and in the sim , that having the block port area slightly smaller is compensated for by the reed petals staying open longer.
The smaller block always seems to have better mid , and looses nothing up top.
Best example I have would be the 400cc Banshee based CPI cylinder that was designed for a CR250 reed block.
When up at 100 RWHp using a CR125 block ( VeeForce ) it makes more power everywhere , than the original much bigger CR250.
Part of this is also due to the fact that to fit the CR250 block in place meant that the petal exits were off bore center by 6mm - the CR125 is 6mm narrower , so it can be put back on center with an adapter plate
then a stuffer plate fitted down one side.
So one lesson I learned is that asymetric intake regimes loose power - be it an offset block or even worse sideways angled manifolds.
Edit - you would think that the 30mm carb in the TM connected to a huge reed block would be the weakest link in making serious power. But once again the devil is in the detail.
By having a 28mm venturi inside the block as part of the stuffer makes about 0.5 Hp to 0.75 Hp , I believe by increasing the velocity of the flow within the block , thus opening the petals quicker and further.
And yes I agree completely about the friction in small engines when up at 20,000 rpm + , but this factor simply cant explain why the theoretical numbers , using well established benchmarks , is hugely higher
than what is actually being achieved currently.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
No8 Wire Extraordinaire
Charge coil might now be breaking down? Muffler hasn't partially collapsed? Needle doesn't obstruct at WO? Remove main and it must bog when blipped to wide open, maybe without pj it can't?
Try scribe timing lines and see timing light isn't breaking up or going silly. Better with load but needs must.
Don't you look at my accountant.
He's the only one I've got.
Hardcore Biker
I can easily have a huge increase of power in my MB Profi 6.65cc engines, simply by changing from glow to spark ignition and a decent ignition curve, in the sim.
Unfortunately not so easy in real life, there aren't even spark plugs that work... that I'm aware of.
Not to mention ignition systems coping with 30+krpm and 20%castor oil that are small and light enough to fit onboard a plane.
-Yes, fuel is stipulated by the rule book, 80% methanol, 20% castor oil.
Re. the small model SI engines, Id guess they are simply not very developed. Im sure you can improve a lot on those.
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