bob27s

My Feedback: (19)

Nelson built a handful (10-12? ) of special design, purpose built, big block .61 10cc engines for r/c speed trials and control line class C speed use. Rear exhaust engines, big inlet venturi, used an OS .65 crankcase to start with. Amazing engines, internals not unlike the Nelson/BVM .72 size fan engines. Those would be the only .61 engines I know of capable of that power. But I seem to recall most were flown with smaller diameter, higher pitch along the lines of 7x12 or 8x10 (carbon props only) and would turn those over 20,000 on the ground. So 4.5 or 5.0 hp was probably about accurate. I would imagine that 18K on an 11x7 would be easy enough to achieve with a different pipe setup.

For reference, the Jett 90LX engine (similar in size, shape to most 10cc engines) in RE configuration with a properly selected pipe is capable of turning a 10x10 prop or 11x7 prop in excess of 16,000 peak ground rpm.

I would imagine if 100% reliability and throttle were not necessary, with a big venturi, a serious marine pipe, and a few porting tweeks - it would be possible to get another 500-1000 rpm out of the setup and push an 11x7 near 17K. Maybe more. It would be possible to get a 10cc version to perform in a similar fashion - just pushing the limits of things.

Usually the ultimate limits of an engine like this is the front intake design - fuel throughput is somewhat limited (limits on how much you can bore/cut the crankshaft).

Reference application shown here http://www.rcuniverse.com/forum/fb.asp?m=4672159

DarZeelon

Brian,


That is basic engineering...

If a two-stroke engine in 'base' form is running at a VE of 80% and some kind of 'super duper' pipe increases the VE to 120%, the increase is 50%, as is approximately the increase in torque.

But this engine will now be running at a VE of 120%; not 150%, even though it is making 50% more torque than the engine made initially. Pipe boost made by the most efficient tuned pipe is about this much.

If the engine was initially burdened by a very restrictive muffler, a good tuned-pipe can double the torque at the RPM pf peak HP.
But the ultimate VE will not be 200%; only 120, or maybe 125%.

...I don't even pluck chickens, certainly not numbers.

Sport_Pilot

Bob,
I suspect that more than a little nitro could push it into those numbers. They have used 70%+ nitro in speed in the past. Though I don't think that is legal anymore.

bob27s

My Feedback: (19)

For the FAI C/L speed classes (and I think the r/c speed cup events) the engines run on FAI fuel (0% nitro). Running more nitro is always an option - ask the marine guys But that does require de-compressing the engines and a variety of other considerations.

Flyboy Dave

My Feedback: (21)

The question was....a 'sport" engine. This engine might come close with a MAS, but maybe not 18K.

FBD.

shakeelsid

I would repeat my message and refer readers to earlier posts

no matter how you crunch your numbers and argue on technical correctness, if a 40 could produce even 2.81 hp, a 60 should be able to deliver 4.21 hp. If we accept that the Bolly pipe results are accurate (hard to swallow for me), our 61 could (hypothetically) produce around 4.71 hp -

Volumetric effeciency is not an abstract concept, it is an engineering aspect, and has little to do with this debate - At the end of the day Fuel is the energy source and an Otto cycle internal combustion engine is the converter - it converts thermal energy into mechanical, and it is very inefficeint at that. At the moment it is around 34% in best of the engines and thus I would estimate that 15% increase in thermal extraction efficiency at the same swept volume of a glow engine would double the power output. It is magic until you connect it to the mechanism. The trick could be very simple, and could well be applicable on a sport engine - would the engine last a prolonged run - I dont know, but I think it is possible.

I may have opinions about everything but I dont know it all, I think it is possible, and thats why I asked the original poster to tell us all about it.

Flyer95

My Feedback: (1)

I can tell you a story[8D]
A very experienced speed R/C flyer gave me an Carbonfiber prop. to try on my piped engine. My engine would usually turn APC 10x10@17600rpm on a quiet pipe before one prop-blade came loose and got 4" under the ground[:@]. On his CF-prop my engine only turned 15600rpm[].
His highly modified 91-sized competition engine with a very short unmuffled pipe turned this CF-prop. @19000rpm[X(].
You can imagine what it would do to the APC 10x10. Yes it would destroy it imidiately, but before that my guess is that the tach would hit +20000-21000rpm.

DarZeelon

Sid,


VE has everything to do with this debate!

It is a measure of how efficiently the engine circulates its air...

Getting a certain output from an engine is possible at a certain RPM.
Let's take the example of 4.71 HP at 25,900 RPM...


To get the same output at 18,000 RPM, or at 69.5% of the RPM, you would need the torque to be 43.9% higher and torque is a direct function of VE.

Marcol

A 40 FSR wouldn't do that with an 8x6 let alone a 10x6

Whatever it is you're taking or smoking, you need to stop !!!

NM2K

My Feedback: (14)

----------------------


Pardon me for paraphrasing, but that is a great signature line, in case anyone missed it. Wish I had said that.


Ed Cregger


***My apology to you shakeelsid

shakeelsid

duplicate message: deleted

shakeelsid

Hi Ed,
Would your correct your source please - It was I who claimed to have opinions about everything and knowledge of so few -

[&o][&o]
36 years in schools of all sorts, and I am still there - I must be the biggest ignoramus ever - and each year if I learn anything is that I know so little.

downunder

I'll give you one thing Dar, you're a master at discombobulation .
You pluck a figure out of the air for a base VE then manipulate the figures so the end result will appear to match what you say. So what if the piped VE is 120%? What matters is how much it increases it from the best the engine can do as open faced (which means it's running 100% the best it can ever do). Taking your 80% base figure at face value, then a final figure of 120% does mean it's made the engine 50% more efficient. This 50% is in regard to its bmep (torque) and not HP. The HP increase is far more than the torque increase. Actually, as I mentioned earlier, the real increase in torque with the Bolly pipe was 57.3% and the HP increase was 227.5%.

MrMotor

To get a big boost from a tuned pipe, you must have a long duration of exhaust timing on the cylinder. The most I have ever run accross was 195 degrees of exhaust on a Rossi 15 speed engine. If the engine has more than 156 degrees of timing it will run better with some exhaust pressure than open exhaust. I have a pair of old Supertiger 15 speed engines from the 70s. One is pipe timed and the other is not. On the same prop and fuel open exhaust the pipe timed turns 19,200 without pipe and the milder timed engine turns 25,000. Adding the header to the pipe timed engine allowes it to turn 22,500 and adding the full pipe allowes it to turn 25,700.
When you compare the increase with a pipe timed engine without the pipe it will show a much larger gain when you add the pipe. The same engine with milder timing will turn higher to start with, but not gain much with a pipe and may even lose RPM adding any exhaust over open exhaust.

MyWay

In addition, adding a header with the correct length will add rpm to the non piped engine.

DarZeelon

Brian,


I believe you chose the wrong word here: 'a feeling of embarrassment that leaves you confused' is the meaning of 'discombobulation'.

-----------------------------------

VE is an absolute term, reflecting the percentage of an engine's cubic displacement, which is actually filled in each complete cycle.

There was no increase in VE of 227.5%!!! Show me where you think there is such a humongous VE gain?

This was the relative HP between the open exhaust number (100%) and the Bolly pipe number (227.5%).

HP gain is a combination of gain in RPM and the gain in torque at the same RPM. Gain is a relative term, since it relates to the previously recorded condition.

The gain in HP with that engine going from open exhaust to the Bolly pipe, was just 127.5%.


The RPM increase was 31.1%... Divide the 2.275 by 1.311 and you get 1.735... a 73.5% gain in the peak HP RPM torque value... Not in VE, but very possibly in relative VE, like going from 79.5% to 125%.

Where on earth did you 'pluck' (ouch!) that 57.3% number from???

The increase in VE is very close to the increase in torque, or 73.5%; certainly neither 227.5%, nor your last 'plucked' value of 57.3%.


You gotta start thinking straight, Brian[>:] and not to believe everything you read, just like that...

DarZeelon

Actually, Paul, the more significant term that determines the power gain from installing a tuned pipe, is the 'blow-down' period.

It is defined as the timing in degrees between the closing of the intake bypasses; and the closing of the exhaust port by the rising piston. It is during that time that the reflected wave crams fresh mixture ingested into the header, back into the cylinder.

This is the supercharging effect of the tuned exhaust.

downunder

When you do a google Dar, don't just look at the first link provided. The 4th one down would have been a better one to see so you could understand that word as I used it.

DarZeelon

Brian,


I did not Google!

I only took the results that you publicized in several of your previous posts.

I got my numbers from calculations made on those same results.
Not even once did I state in my calculations a numerical value for the maximum torque.

I only stated the percentage of Δ torque.


Looking at the results you just publicized now, in post #43, they cannot be right. At least one is a bit off, since they don't correlate properly.

The Bolly pipe gave a horsepower value of 3.14, or 11.74% higher than the OS pipe's 2.81 HP.
The RPM at which the OS pipe was achieved was 9.77% higher than Bolly's pipe.

The maximum torque numbers for both pipes are given at the RPM of maximum HP, so calculation of Δ torque can be made from Δ HP and Δ RPM. If the OS pipe really was 95 oz. in., the Bolly is 116.5 oz. in.; not 118 as is publicized.

The open exhaust number is given at a lower RPM and I calculated the Δ torque from the HP number at the peak HP RPM.
The open exhaust torque has already declined somewhat, as RPM increased from 17,417 to 19,756 peak HP RPM, hence my result for Δ torque from the Bolly pipe was a higher 73.5%.


Let's see which of the two piped numbers is correct.

If torque is expressed in lbs. ft. then HP / RPM * 5,252.1 = torque.
For torque in oz. in. we must multiply the result by 192 (16 oz. in lb. x 12 in. in ft.).

3.14 HP @ 25,900 RPM is a torque of .... 122.25 oz.in..
2.81 HP @ 28,430 RPM is a torque of .... 99.67 oz.in..

Neither number is right!!!
I already told you not to believe everything that you read...

I cannot calculate the number for the open exhaust, since the maximum torque and HP are given at different RPM values.


Elementary, my dear Brian, elementary.

...And you still owe me an answer on where you found the 227.5% increase in VE...

MrMotor

The simple answer is NO

Sport_Pilot

Dar,
I don't think I have ever found a manufactures HP/torque figure I believe. It's rare that they put all these numbers up that don't calculate. I suspect most of the time they simply inflate there numbers by X percent.

As I stated before I don't think you can hit 18,000 with an 11-7, unless you tip the can.

Flyboy Dave

My Feedback: (21)

.....MrMotor....I think your are correct....

....keep in mind, a Jett .90L turns an 11-8 at 15,000.

FBD.

jaka

Hi!
Neither do I ..But we have a fellow over here that claims that his HP.61 turns a 11x7 prop at 18000rpm with a tuned pipe (modified engine).
I really doubt this ...but who knows???

shakeelsid

Hi Jan,
Some of the radishes are getting very testy here, could you please ask your friend to substantiate his claims - I used to have a couple of HP 61s SE years ago - they were good engines, but not that good. I would assume my 61s were only as good as my 60FSR, about.
Which HP engine, may be there are versions I am not familiar with - and what modifications and fuel- even if his claims are not 100% accurate, we could learn something here.
cheers
sid

Sport_Pilot

I think maybe he misread the tach. I have one that will do almost 14,000 with a Semco muffler. I doubt it would do over 16,000 with a pipe, probably less.