Author Topic: What is magic about the BBTU FP-20? (Read 8040 times)

RandySmith · « **Reply #50 on:** April 15, 2012, 04:28:58 PM »

Quote from: rustler on April 15, 2012, 01:43:39 PM

I haven't read all of this because I thought it was all done and dusted.
However, reading some of it I have decided I must move my 25FP on and get a 20FP. I had assumed the two would be similar.

Hi Ian

NO they are not the same ,and do not give the same run, if you go back and read back up the this thread Brett explains the differance and how much better the quality of run is on the 20.

Randy

Chris Wilson · « **Reply #51 on:** April 15, 2012, 04:32:36 PM »

And (trying to get the thread back on track) no mention of the LA 25 in this discussion as per the original post?

Though there was a mention back there of the heat of a tuned (or acoustic based pipe being based on the speed of sound) effecting how it runs and as far as I know heat will not effect a resonance based pipe to any great extent.

Perhaps a further clue as to which mechanism the muffler works under?

Tim Wescott · « **Reply #52 on:** April 15, 2012, 04:48:51 PM »

Quote from: Chris Wilson on April 15, 2012, 04:32:36 PM

And (trying to get the thread back on track) no mention of the LA 25 in this discussion as per the original post?

I'm curious about that, too.

Quote

Though there was a mention back there of the heat of a tuned (or acoustic based pipe being based on the speed of sound) effecting how it runs and as far as I know heat will not effect a resonance based pipe to any great extent.

Perhaps a further clue as to which mechanism the muffler works under?

The speed of sound changes with temperature. So while the temperature of the pipe doesn't directly affect the run, the temperature of the gas inside the pipe does, and a hot pipe will let the gases inside retain their heat. Apparently, wrapping your exhaust in an insulating blanket is one of the easy ways to change the tuned RPM of a motorcycle exhaust.

Andrew Tinsley · « **Reply #53 on:** April 16, 2012, 09:35:40 AM »

Hello Brett,
You may not be watching this thread and I can't blame you for that! However my query is a variation on the FP20 BBTU. You have explained why the FP25 doesn't work in this set up. If you load the FP25 with a bigger prop. then maybe you can constrain it from jumping above the "pipes" rev band? Alternatively from your knowledge of the E2030, would there be a reflective surface that would work at a higher rpm?
I realise that it is all a bit academic as both the FP20 and 25 can only be had second hand. You have often said that you would not be prepared to go through the exercise with a selection of more modern engines and I can understand that! I suppose my query is related to me enjoying challenges and playing with engines. If I could get either of my suggested alternatives to work, I may be sufficiently enthused to have a look at some available engines. The above two possibilities look as though they may have some merit for a tinkerer such as myself to play with. Anything drastically wrong with the two alternatives? No point trying to reinvent the wheel and getting despondent first time off!

Regards,

Andrew.

Joseph Lijoi · « **Reply #54 on:** April 16, 2012, 10:37:59 AM »

A possible consideration could be the difference in the cylinder volume versus the port area. The ports are the same size and shape but the volume of the cylinder for the FP 25 would be quite a bit larger. Just a thought.

At any rate thanks to Brett and Randy and all those guys save me time and money through their efforts. You can get these 20 FP's at swap meets and parts are still avaialable.

Balsa Butcher · « **Reply #55 on:** April 16, 2012, 10:55:45 AM »

It has me wondering if I could make my SSR go faster by substituting its FP-25 for an FP-20 w/appropriate muffler... tuna pipe effect and all that. Well, only one way to find out.

Tim Wescott · « **Reply #56 on:** April 16, 2012, 11:13:45 AM »

Quote from: Pete Cunha on April 16, 2012, 10:55:45 AM

It has me wondering if I could make my SSR go faster by substituting its FP-25 for an FP-20 w/appropriate muffler... tuna pipe effect and all that. Well, only one way to find out.

If I'm reading Brett's comments correctly, your SSR would go a bit slower, but the engine run would be dead steady all the time.

Bill Little · « **Reply #57 on:** April 16, 2012, 08:08:13 PM »

Quote from: Pete Cunha on April 16, 2012, 10:55:45 AM

It has me wondering if I could make my SSR go faster by substituting its FP-25 for an FP-20 w/appropriate muffler... tuna pipe effect and all that. Well, only one way to find out.

The OS .20FP BBTU doesn't increase power, it regulates the run. A governor effect. You're gonna get more speed with the OS .25FP.

BIG Bear
RNMM/AMM

Chris Wilson · « **Reply #58 on:** April 16, 2012, 08:57:09 PM »

Quote from: Bill Little on April 16, 2012, 08:08:13 PM

The OS .20FP BBTU doesn't increase power .............

BIG Bear
RNMM/AMM

Hi Bill,
But the use of the run away prone OS .20FP increased it in the first place.
To me the use of any tuned system allows the use of a higher powered engine that would normally be unusable.

I think that piped stunt engines do operate at a higher power than their non tuned stunt cousins and the trick is that it is sustainable without the need to resort to power robbing devices like small exhaust outlets, higher oil contents, higher pitch, smaller venturis and filters, smaller ports etc.

Put it this way, all things being equal would a successful non tuned exhaust stunt engine have more or less power than one with a tuned system?
I am going to back the tuned system to be more powerful every time because the pipe allows the engine to operate closer to its peak power for longer.

If this wasn't so then I doubt that tuned systems would be entertained as much as they are now.

Bill Little · « **Reply #59 on:** April 16, 2012, 09:07:31 PM »

I agree, Chris. The engine does produce more power simply by being allowed to run in its happy band. But shortly after putting pipes in stunters, my understanding is that the power boost most people think of in using a tuned pipe was less important than the governor effect the pipe can produce. There is plenty of power there, so it just needs to be regulated to brake the engine when it wants to make more power then is needed, etc..

Bill

Allan Perret · « **Reply #60 on:** April 17, 2012, 06:26:36 AM »

Quote from: phil c on April 12, 2012, 03:31:08 PM

The LA 46, 1/4 in. venturi, runs very similarly, as long as you don't put too much prop on it. The muffler also seems to be tuned to 11,000 rpm or so, so a 4 pitch prop works. The FP20 is also running roughly midway between its torque peak, around 9500-10,000 rpm and the peak rpm around 13-14,000 rpm. Keeping the motor running in its sweet spot by adjusting the venturi size, prop, and if necessary the combustion chamber size is the key.

Hey Phil:
In the LA 46 setup you are talking about here, are you using the stock muffler ?
If so do you know the number of the muffler ?

Chris Wilson · « **Reply #61 on:** April 22, 2012, 07:13:36 PM »

Just a short quote from a world renown acoustic engineer and pylon racer -

http://www.f2d.dk/noise/noisefreq.htm

"Some mufflers do actually amplify the noise at the critical frequencies!
This is probably a resonance effect that will let the muffler work as a tune pipe. It will give the engine a higher power but this type of muffler will not reduce the noise."

Resonance seems to be little understood as a power enhancing device.

Author Topic: What is magic about the BBTU FP-20? (Read 8040 times)

RandySmith

Re: What is magic about the BBTU FP-20?

Chris Wilson

Re: What is magic about the BBTU FP-20?

Tim Wescott

Re: What is magic about the BBTU FP-20?

Andrew Tinsley

Re: What is magic about the BBTU FP-20?

Joseph Lijoi

Re: What is magic about the BBTU FP-20?

Balsa Butcher

Re: What is magic about the BBTU FP-20?

Tim Wescott

Re: What is magic about the BBTU FP-20?

Bill Little

Re: What is magic about the BBTU FP-20?

Chris Wilson

Re: What is magic about the BBTU FP-20?

Bill Little

Re: What is magic about the BBTU FP-20?

Allan Perret

Re: What is magic about the BBTU FP-20?

Chris Wilson

Re: What is magic about the BBTU FP-20?