Tuned Pipe Wave Velocity

[Timbo Whalen]

Remember unless you are making your own pipe your hands are tied. 

Cretin mods to the eng will work good on most all pipes. 

I have the mind set that if you let it flow the pipe will work better. 

How hard the cone has to work to draw the case down will affect how much is loaded in it at a cretin RPM.

Intake valve timing will also affect how much you can draw in at a cretin time in the RPM range.

You can only pack back in what you suck out. 

If there is nothing to pack you get nothing.

Have bin seeing some of the affects here in some new engs I have moded .

Changing intake valves  timing will have a big effect on how much you will pack in the cylinder.

Some engs that flow very good will not be able to burn all that fuel and clear out the eng as I cal it.

To much of a good thing is a bad thing some times.

You have to add more plugs to burn it all and clear the eng out.

Yep, there ya go!... these engines of today are timed and ported pretty good- particularly the NR's.

30° blow down is an excellent figure for any displacement in a light rigger heat race app today.

Personally, I won't mess with the boost/transfer circuit... but to gain blow down, cut underside of

liner flange and juggle that with exh. port height to get the blow down and 188°-190° on the exh.

Higher blow down, more peaky power...lower, the opposite is true. Raise exh. timing, better close

the intake later.... we like 67°-69° closing.

Light weight outrigger's are the easiest for me to tune - you can run them peaky with the 'gear'

ratios we have available today.

Those NR pipe's are really nice, IMO... they have the 2 stage baffle cone that puts a bit of dwell in

the wave velocity prior to return, and the reflective reaction is very fast- run 'em short, use ceramics,

open the stinger and gear them so they spin like hell, within the porting constraints.

Thus far, it's working for me.

Thanks, everyone, for contributing.

 

[Timbo Whalen]

 All the programs work off the same old formulas. Thy all add up the same way just different input parameters is all.

Thy all just predict top power at a cretin RPM.

Did some logging of EGT with my eagle tree set up a few years ago when I was all wound up in it. also had a few pipes made different ways.

Castor oil has more effect on EGT's than the tape will ever have........

Still have the pipes and run the one on my VAC1.05 eng.

If you are deep into it and can do lots of back to back testing you will see the differences. But with out hours of testing it is all just jiber jaber.

Best to try different pipes and land on one you like. Then mod the eng for flow. 

How you drive the boat will have more of a factor on what pipe you like. One pipe will not work as good for one persons driving set up.

How it comes off the corner or how it powers threw the corners or how it tops out at the end of the strait.

I had two different pipes made with two different rear cone set ups. both where 2 stage rear cones. thy both work totally different.

One come on hard in the corners and peters out at the end of the straits and one is steady in the corner and spools up a the end of the straits.

Two different ways to drive the boat or different hulls.

monos need that punch in the corners and don't like to dive in to the corners spooled up.

Hydros like to dive in HARD and maintain in the corners then unload and launch.

So 2 different pipes.

Not all of them, Dave!...but you're correct about the predictive process.

They don't offer enough input options to do much more than SWAG it, really.

Fuel and associated thermodynamics  doesn't have a decent algorithm considered.

One of them asks fuel type, but frankly, I think that's all hype.

There's only one prog, that I'm familiar with, that utilizes faith adherence to Blair, et al.

studies... and it's a rather expensive program. The pipe designer is left to contend with

the dynamics of wave velocity, based on the environment that our fuel creates, and adjust

accordingly in manual fashion.

Let's get back on the theme of the original topic... given our supplied engine and pipe

combinations, and the simple formula for tuned length (TL), we need a baseline wave speed

to get us in the game relative to setting up initial pipe length. Basically, we alluded to what's

working for us- using Ws= 1680-1700fps...it gets us close, but thinking it can be more toward

the finite.

Thanks.

 

[Timbo Whalen]

 All the programs work off the same old formulas. Thy all add up the same way just different input parameters is all.

Thy all just predict top power at a cretin RPM.

Did some logging of EGT with my eagle tree set up a few years ago when I was all wound up in it. also had a few pipes made different ways.

Castor oil has more effect on EGT's than the tape will ever have........

Still have the pipes and run the one on my VAC1.05 eng.

If you are deep into it and can do lots of back to back testing you will see the differences. But with out hours of testing it is all just jiber jaber.

Best to try different pipes and land on one you like. Then mod the eng for flow. 

How you drive the boat will have more of a factor on what pipe you like. One pipe will not work as good for one persons driving set up.

How it comes off the corner or how it powers threw the corners or how it tops out at the end of the strait.

I had two different pipes made with two different rear cone set ups. both where 2 stage rear cones. thy both work totally different.

One come on hard in the corners and peters out at the end of the straits and one is steady in the corner and spools up a the end of the straits.

Two different ways to drive the boat or different hulls.

monos need that punch in the corners and don't like to dive in to the corners spooled up.

Hydros like to dive in HARD and maintain in the corners then unload and launch.

So 2 different pipes.

Dave, expand on that statement regarding 'castor oil vs. tape'... kind of curious where you 

want to go with that... hmmm, thinkin' we may know; perhaps with regard to heat retention.

Before you can have valid, constructive test sessions, you have to start from a basis of

intelligent hypothesis.

Thanks

 

[Timbo Whalen]

Interesting.  How much weight is added form the ceramic coating?

I've had good luck with Carbon Fiber.  Doesn't seem to absorb the heat.  Really have to watch the cooling when using the Carbon pipes though.

What do you think would happen if you added some ceramic to the resin when forming the pipe,

and/or applied ceramic coating to the inside of the finished CF pipe?... CF has a tendency to

absorb sonic wave form energy, too. So, with that said, wouldn't it seem that pipe volume would 

have to be reduced accordingly?... and then, here comes the heat!

 

[David Ashcroft]

Yep, there ya go!... these engines of today are timed and ported pretty good- particularly the NR's.

30° blow down is an excellent figure for any displacement in a light rigger heat race app today.

Personally, I won't mess with the boost/transfer circuit... but to gain blow down, cut underside of

liner flange and juggle that with exh. port height to get the blow down and 188°-190° on the exh.

Higher blow down, more peaky power...lower, the opposite is true. Raise exh. timing, better close

the intake later.... we like 67°-69° closing.

Light weight outrigger's are the easiest for me to tune - you can run them peaky with the 'gear'

ratios we have available today.

Those NR pipe's are really nice, IMO... they have the 2 stage baffle cone that puts a bit of dwell in

the wave velocity prior to return, and the reflective reaction is very fast- run 'em short, use ceramics,

open the stinger and gear them so they spin like hell, within the porting constraints.

Thus far, it's working for me.

Thanks, everyone, for contributing.

This is my nova91 numbers ,however blowdown is 27-28 alright for my mono.

exh - 188.7

trans - 136

rotor open 214

rotor close 70-- cut 4 degrees more

squish 0.013" 9.4CR

216 duration

 

[charles siler]

https://www.youtube.com/user/MPAcopy

 

[David Ashcroft]

Yep... did someone say detonation?... an ounce or two of KL-600 in a gallon of fuel will take care of that.

Will even allow a bit tighter squish (or higher CR) and a hotter plug. All good things- heat is power.

Hotter gasses expand exponentially better. Clausius' 1st Law and Boyle's Law validate.

Tim using kl600 may cover a problem ,but it's still detinating and losing power regardless,,

 

[Timbo Whalen]

This is my nova91 numbers ,however blowdown is 27-28 alright for my mono.

exh - 188.7

trans - 136

rotor open 214

rotor close 70-- cut 4 degrees more

squish 0.013" 9.4CR

216 duration

Yessir...the NR's are quite wild right out of the box... blow down looks great for a mono...

 

[Timbo Whalen]

Tim using kl600 may cover a problem ,but it's still detinating and losing power regardless,,

Dave, KL-600 was recommended by Klotz engineering... I tried it and tightened up the clearance

to .008" on the NR46, went up a step on an ABC prop and it pulled it, whereas it wouldn't with

.010" clearance on fuel with, and without KL-600. And I run the engine hot, with no cooling-

no detonation. Now, to be fair, we've only ran a 1/2 gal. of fuel through this engine and it still

is a bit tight. After the P&L wear in nice, we're going to do a DFL treatment to the piston

sidewall. Also, we're using a NR C6TGC plug, as well.

Admittedly, we got off schedule and ran out of summer so testing has to continue.

Thanks.

 

[Timbo Whalen]

Then go old school and read a book.

View attachment 97900

 

[Timbo Whalen]

And we're still looking for conversation regarding mean wave velocity and

hypothetical EGT numbers. 

 

[David Ashcroft]

Yessir...the NR's are quite wild right out of the box... blow down looks great for a mono...

That's not stock Tim, my mods

 

[Andy Brown]

EGT and therefore wave velocity changes a big amount by the micro second.

Fuel mixture/mass and load, both of which are constantly changing, have the greatest influence.

Calculations will get you on the right planet. Refinement takes lots of surveying.

Man do I have a big box of chopped up, glued, welded, soldered, and screwed together pipes. LOL

 

[LohringMiller]

This has been interesting.  As Dave points out, you need to match an empirical design from some canned program with lots of testing.  I've done that with quite a few gasoline engine pipes.  Better than empirical programs are engine simulation programs.  The one I use, EngMod2T, even has a glow engine combustion model and a large choice of fuels.  The model inputs need to be realistic and match real world dyno results.  That takes accurate measurements on a real engine.  I have not played with nitro pipes other than to run commercial ones and adjust the tuned length. 

The basic mechanical design factors are maximum diameter, baffle cone position and angle, and diffuser length and horn coefficient.  A guess at an appropriate average exhaust temperature sets the various lengths and positions.  I would start at 250 degrees Centigrade for nitro.  Then you run a dyno test to see if the rpm you were designing for is actually the peak power rpm.  If not, you guessed wrong on the temperature and it's back to the drawing board.  Below is a starting point for design that has been successful for gasoline engines.  A spread sheet is also available. By the way, Brian Buaas has built several carbon fiber pipes for small engines.  One was used on a winning boat at the NAVIGA Worlds. 

Lohring Miller

 

[Andy Brown]

This has been interesting.  As Dave points out, you need to match an empirical design from some canned program with lots of testing.  I've done that with quite a few gasoline engine pipes.  Better than empirical programs are engine simulation programs.  The one I use, EngMod2T, even has a glow engine combustion model and a large choice of fuels.  The model inputs need to be realistic and match real world dyno results.  That takes accurate measurements on a real engine.  I have not played with nitro pipes other than to run commercial ones and adjust the tuned length. 

The basic mechanical design factors are maximum diameter, baffle cone position and angle, and diffuser length and horn coefficient.  A guess at an appropriate average exhaust temperature sets the various lengths and positions.  I would start at 250 degrees Centigrade for nitro.  Then you run a dyno test to see if the rpm you were designing for is actually the peak power rpm.  If not, you guessed wrong on the temperature and it's back to the drawing board.  Below is a starting point for design that has been successful for gasoline engines.  A spread sheet is also available. By the way, Brian Buaas has built several carbon fiber pipes for small engines.  One was used on a winning boat at the NAVIGA Worlds. 

Lohring Miller

View attachment 97907

"If not, you guessed wrong on the temperature and it's back to the drawing board."

Or the guys that write pipe formulas guessed wrong about what those angles, diameters, locations and volumes actually do. LOL

 

[dwilfong]

Castor oil will reduce the EGT  more than the tape will make it rise.

Now if you relay want to talk wave length speed and ex temps add water injection in the pipe to the mix.

A few records are held using this set up on a mono.

It dose not work on all pipes. 

 

[dwilfong]

It is funny the best help I had understanding what a cone will do was when Andy explained it to me at a race one time. 

He made eng noises as he told me to imagine the wave traveling down the pipe........ WOOAAAAAaaaaa or waaaaaAAAAAAAAhhhhh

You had to be there......... ^_^

 

[Timbo Whalen]

EGT and therefore wave velocity changes a big amount by the micro second.

Fuel mixture/mass and load, both of which are constantly changing, have the greatest influence.

Calculations will get you on the right planet. Refinement takes lots of surveying.

Man do I have a big box of chopped up, glued, welded, soldered, and screwed together pipes. LOL

You bet, Andy...was just interested in mean figures... WOT, under load EGT, etc.

I'm thinking, without validation, that the EGT is ~650°- 750° under those conditions.

That would give a wave velocity of 1633 f/ps- 1705 f/ps... with those velocity figures,

exh. port duration, and approximate engine rpm one can determine tuned length from

piston face to Mean Point of Reflection in the baffle/converging cone. We just put a

mark on the case and on the pipe where those locations exist.

Thanks.

 

[Timbo Whalen]

It is funny the best help I had understanding what a cone will do was when Andy explained it to me at a race one time. 

He made eng noises as he told me to imagine the wave traveling down the pipe........ WOOAAAAAaaaaa or waaaaaAAAAAAAAhhhhh

You had to be there......... ^_^

LMAO!... one cone is pulling, the other throwing it back... sounds like a typical marriage!

All of these pipe design opinions wasn't the intent here...

The intent was to determine an approximate mean for exh. temp. and the resulting wave

velocity to establish a mean starting point for TL on an OEM's provided pipe. It's very

easy to establish MPR on the baffle cone- and then go from there.

Since we do not have a practical means of dynamically tuning the pipe on the fly, the

variables that Andy referred to are somewhat moot, yet real. Sure, in the end there's a

bunch of hit or miss tweaking going on within a given snapshot in time, and all of the

relevant variables are changing-ie- weather, loading and unloading of the engine, fuel

delivery, etc. Personally, I don't like the pipe hitting that resonance sweet spot right at

peak output, but maybe at ~ 80%-90% of peak rpm.

Thanks.

 

[Timbo Whalen]

This has been interesting.  As Dave points out, you need to match an empirical design from some canned program with lots of testing.  I've done that with quite a few gasoline engine pipes.  Better than empirical programs are engine simulation programs.  The one I use, EngMod2T, even has a glow engine combustion model and a large choice of fuels.  The model inputs need to be realistic and match real world dyno results.  That takes accurate measurements on a real engine.  I have not played with nitro pipes other than to run commercial ones and adjust the tuned length. 

The basic mechanical design factors are maximum diameter, baffle cone position and angle, and diffuser length and horn coefficient.  A guess at an appropriate average exhaust temperature sets the various lengths and positions.  I would start at 250 degrees Centigrade for nitro.  Then you run a dyno test to see if the rpm you were designing for is actually the peak power rpm.  If not, you guessed wrong on the temperature and it's back to the drawing board.  Below is a starting point for design that has been successful for gasoline engines.  A spread sheet is also available. By the way, Brian Buaas has built several carbon fiber pipes for small engines.  One was used on a winning boat at the NAVIGA Worlds. 

Lohring Miller

View attachment 97907

Thanks, Lohring... '...you guessed wrong on the temperature and it's back to the drawing board.'

LOL!, yep, really like that!

I suppose some EGT numbers are required on a dyno, or a decent acquisition telemetric in 

real world application, is needed to establish a thermal mean, thus a wave velocity average.

As far as your provided graphic above, there's a whole lot wrong with it, particularly regarding

'Lmax'- again, 'speed of sound' is greatly affected by the thermal ambient in which it is measured.

'I would start at 250 degrees Centigrade for nitro'... 482°F. is rather cool, unless it's, perhaps,

an unloaded state.

By the way, I think I sent you a message on Facebook with regard to your inertial dyno.

Thanks for your input.