Jump to content
timwhalen

Tuned Pipe Wave Velocity

Recommended Posts

Hi-

Has anyone done any research on the wave velocity (fps) and the exhaust gas temperature (EGT), or concluded such

within a reasonable hypothesis, with regard to the high nitromethane %'s we run in these engines?...

The formula for determining the tuned length (TL) of our pipes utilizes a given engine's peak rpm in the equation.

That seems to create the problem of the engine not getting 'on the pipe' in a loaded state.

It seems that using a figure of 75% of peak rpm allows the pipe to hit at approx. 3/4 throttle, and so on.

Be interesting to hear any thoughts that others have, rather than 'it just works best with the pipe set at 11.5" from

center of cylinder to where the diffuser and baffle cones intersect.'... pipes vary in design and it seems prudent

to establish the mean point of reflection within the baffle cone and measure to the piston face at the exh. port.

with regard to tuned length (TL)...

Thoughts, anyone?...

Thanks for any input-

Tim

image039.gif.4f8c745a53816a83c7b77a5d6bf0d529.gif

image042.png.4b45f54df1f166b588e91cb191301a23.png

 

Edited by timwhalen
Image Error

Share this post


Link to post
Share on other sites

Tim there is more to it than just what you are showing in the examples.

The pipe will pull a vacuum in the case all the way back to the carb if it is flowing right.

Intake timing will also effect how a pipe comes on and also port timing and design.

Some eng with the same pipe set at the same length with the same prop will be on pipe as soon as thy hit the water.  

When others will struggle to get on pipe.

So why dose this happen???????? 

Is it  the pipes fault??????

Just some thing to chew on........................................

 

Share this post


Link to post
Share on other sites

Peak rpm, fuel, exhaust temps are just a few of the points we need to consider when designing a pipe.

As much as we want to achieve peak power at a given rpm, our engines have to lug the prop off the beach, and run through the engines power band (get on the pipe) to hit peak rpm.  Hence a pipe designed for peak power at max rpm will not be the fastest pipe or even a good pipe as you need the engine to be able to accelerate from lower rpm’s to get to peak rpm, i.e. it’s all a trade off.

The vacuum David discuses is the purpose of the diverging cones of the pipe, that section of the pipe creates a low pressure to help draw the fresh air fuel charge into the cylinder.  The diverging cone or cones are what create a high pressure wave that super charges the air/fuel mixture into the cylinders bore just prior to the piston closing off the exhaust port.

As far as getting on the pipe, I think there is even more to it than the power band, the engines dynamics come into play.  I know when I raced shifter karts if I took a took a wrong which resulted in me short shifting and getting the engine out of it’s powerband it seemed to take me several revs through the powerband and shifts to get the engines dynamics back in sync.  I don’t know if that had to do with the carburation becoming out of sync, the crankcase having some extra fuel, fuel starvation, the pipe having less hot gasses or what, but I could definitely tell the process of getting an engine on the pipe has more going on than just pegging the throttle and waiting for the engine to wind out.

Also as David mentions engine mods to timing affect how the pipe works.  So the question is, do you do you match engine mods to match the pipe, or do you mod the engine and design and test handfuls of pipes to match the engine mods???  Then you throw in air temperature, humidity and pressure and add in water conditions for the day.

Share this post


Link to post
Share on other sites

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.

 

Share this post


Link to post
Share on other sites

The pipes are made of the wrong material to achieve both power and RPM.  The aluminum dissipates heat so you then need to run shorter lengths to get the RPM and thus lose low end.  This is why the wrapping of pipes has been catching on more.  

 

I don't have any scientific evidence to back my claim, just results from personal testing. So I'm concluding that under higher temps the pressure wave travels faster.

 

Share this post


Link to post
Share on other sites

Tommy tape is your friend.  

As the eng loads up at High RPM the pipe will hold more heat and shorten the tune length.

As you slow down and cool off the pipe it acts longer.

Share this post


Link to post
Share on other sites

I don't believe the loss in power is due to the shorter pipe needed for cooler exhaust gasses.  Our engines convert the heat of combustion into mechanical motion.  The more heat we can produce, through the fuel we burn and how hot we can run, the more power we make.  Big hot fire, big power.  If we over cool the engine, or if the pipe cools the exhaust gasses off, then the heat is not being used to produce power and we're wasting the mechanical energy required to pump the air and fuel through the engine.  Insulating the pipe, or running a longer or smaller diameter stinger is a means of retaining more heat in the engine and making more power.

But as with all good things, too much of a good thing is a bad thing.  If we run our engines too hot, we get detonation and we melt pistons.

Even though it is hard to visualize, the tuned pipe is effectively the same device as a turbo supercharger, but with no moving parts.  The reason turbos are placed as close as possible to the exhaust ports and the headers and turbos often wrapped in heat tape is so that the exhaust gasses running through the turbine are as hot as possible as that gives the maximum power to spin the turbine, and subsequently the compressor.

Share this post


Link to post
Share on other sites
18 minutes ago, dwilfong said:

Tommy tape is your friend.  

As the eng loads up at High RPM the pipe will hold more heat and shorten the tune length.

As you slow down and cool off the pipe it acts longer.

Yes but you can retain more heat with a different material. 

Heat sinks are made of aluminum and the purpose is to dissipate heat quickly.  We want to hold that heat and use it to our advantage so why would we want aluminum?  Most likely for cost and ease of production.

Share this post


Link to post
Share on other sites
19 minutes ago, PaulHail said:

I don't believe the loss in power is due to the shorter pipe needed for cooler exhaust gasses.  Our engines convert the heat of combustion into mechanical motion.  The more heat we can produce, through the fuel we burn and how hot we can run, the more power we make.  Big hot fire, big power.  If we over cool the engine, or if the pipe cools the exhaust gasses off, then the heat is not being used to produce power and we're wasting the mechanical energy required to pump the air and fuel through the engine.  Insulating the pipe, or running a longer or smaller diameter stinger is a means of retaining more heat in the engine and making more power.

But as with all good things, too much of a good thing is a bad thing.  If we run our engines too hot, we get detonation and we melt pistons.

Even though it is hard to visualize, the tuned pipe is effectively the same device as a turbo supercharger, but with no moving parts.  The reason turbos are placed as close as possible to the exhaust ports and the headers and turbos often wrapped in heat tape is so that the exhaust gasses running through the turbine are as hot as possible as that gives the maximum power to spin the turbine, and subsequently the compressor.

The shorter pipe is for a faster return of the pressure wave due to the heat loss from pipe.  If you hold the heat you can run a longer pipe for launch and still achieve the high RPM.

Share this post


Link to post
Share on other sites
3 hours ago, dwilfong said:

Tim there is more to it than just what you are showing in the examples.

The pipe will pull a vacuum in the case all the way back to the carb if it is flowing right.

Intake timing will also effect how a pipe comes on and also port timing and design.

Some eng with the same pipe set at the same length with the same prop will be on pipe as soon as thy hit the water.  

When others will struggle to get on pipe.

So why dose this happen???????? 

Is it  the pipes fault??????

Just some thing to chew on........................................

 

Dave, well aware of all that, and it's fine if designing a pipe from the ground up.

There must be a relatively mean constant regarding wave velocity, as also a

baseline temperature for EGT.

In today's world, the timing numbers for any given displacement are all quite similar.

Blow down duration with a tuned pipe is, perhaps, most important.

Wouldn't think it would be the pipe's fault, as it's an inanimate object.

Thanks for input, Dave.

Share this post


Link to post
Share on other sites
2 hours ago, PaulHail said:

Peak rpm, fuel, exhaust temps are just a few of the points we need to consider when designing a pipe.

As much as we want to achieve peak power at a given rpm, our engines have to lug the prop off the beach, and run through the engines power band (get on the pipe) to hit peak rpm.  Hence a pipe designed for peak power at max rpm will not be the fastest pipe or even a good pipe as you need the engine to be able to accelerate from lower rpm’s to get to peak rpm, i.e. it’s all a trade off.

The vacuum David discuses is the purpose of the diverging cones of the pipe, that section of the pipe creates a low pressure to help draw the fresh air fuel charge into the cylinder.  The diverging cone or cones are what create a high pressure wave that super charges the air/fuel mixture into the cylinders bore just prior to the piston closing off the exhaust port.

As far as getting on the pipe, I think there is even more to it than the power band, the engines dynamics come into play.  I know when I raced shifter karts if I took a took a wrong which resulted in me short shifting and getting the engine out of it’s powerband it seemed to take me several revs through the powerband and shifts to get the engines dynamics back in sync.  I don’t know if that had to do with the carburation becoming out of sync, the crankcase having some extra fuel, fuel starvation, the pipe having less hot gasses or what, but I could definitely tell the process of getting an engine on the pipe has more going on than just pegging the throttle and waiting for the engine to wind out.

Also as David mentions engine mods to timing affect how the pipe works.  So the question is, do you do you match engine mods to match the pipe, or do you mod the engine and design and test handfuls of pipes to match the engine mods???  Then you throw in air temperature, humidity and pressure and add in water conditions for the day.

Very much understood...however, the topic centered around a baseline tuned length (TL)

for an OEM pipe, as provided by the engine manufacturer.

Thanks.

Share this post


Link to post
Share on other sites
33 minutes ago, David Murany said:

The shorter pipe is for a faster return of the pressure wave due to the heat loss from pipe.  If you hold the heat you can run a longer pipe for launch and still achieve the high RPM.

Basically... at present, we're experimenting with ceramic coatings on/in pipe, header, squish/bowl area, and piston crown.

At this point, the thermal stability is much more consistent once the ideal needle is found.

We're playing with bleed resistor ID now to control inner pipe ambiance and pressure.

Share this post


Link to post
Share on other sites
42 minutes ago, David Murany said:

Yes but you can retain more heat with a different material. 

Heat sinks are made of aluminum and the purpose is to dissipate heat quickly.  We want to hold that heat and use it to our advantage so why would we want aluminum?  Most likely for cost and ease of production.

Ceramics are the key.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×