Exhaust experts?

[Tuono_Tom]

Off topic? You bet...

I'm in search of exhaust tuning advice- we're talking an Aprilia two cylinder V60 996cc motorcycle...

It has unequal length headers (a 2 into 1 setup)- approx 33" for the front, and 30" for the rear, between the head and the collector.
1] Why in the world does this work?
2] There is a modification I'm about to do that adds a balancer pipe between the two pipes, before the collector. The reports are that it increases drivability, flattens out the 5k RPM 'hole' inherent in these things...

My question is, any insight on the science behind unequal length headers, and where the correct placement of the balance pipe might be?

This is the string, should be accessible for viewing without subscription:

http://www.apriliaforum.com/forums/show ... p?t=138578

I'd be interested in any input. Including "WAFO" ...

-Tuono_Tom

[manchild]

Your post reminded me on a thing about that giant Mercedes V12 engine.

Compression ratio: 7.5:1 left block, 7.3:1 right block

http://en.wikipedia.org/wiki/Daimler-Benz_DB_603

I guess it has something to do with engine configuration same as your exhaust but I can't explain why.

[Carlos]

A good book.

http://www.amazon.ca/Scientific-Design- ... 0837603099

[Tuono_Tom]

A good book.

http://www.amazon.ca/Scientific-Design- ... 0837603099

Scei... sicent... sighentif...

Whew! That might be worth browsing, however it may cause serious brain strain!

[Ciro Pabón]

Welcome, Tuono Tom. I have no experience that is worth mentioning on motorcycles, but I know that in cars, unequal length headers offer less horsepower than equal length. What I know is they are easier to install, they produce less heat and, normally, they are easier, with a good design, for reaching spark plugs and other elements. Here you have real numbers on a Mustang, Hp at RPM:

Code: Select all

Exhaust type   3000 3500 4000 4500 5000 Avg
Equal length    197  226  232  237  233 226
Unequal len.    192  214  224  231  223 217

As for balance pipes, they offer two alleged advantages:

- In a dual pipe system (for cars, with pipes from each side of the block) they offer twice the exhaust, as cylinders won't fire at the same time.
- They (duhhh...) balance the pressure among the two pipes.

I don't see any of these two advantages at work in the picture you post, but I wait to be enlightened.

The picture you link us to is certainly... amazing. I repeat I'm ignorant about it. Anyway, I wonder why the exhaust you show doesn't seem to have an expansion chamber. I'm assuming you know a lot about it, so please don't laugh at this program, for single pipes: http://www.iwt.com.au/data.htm

Perhaps DaveKillens can help you a lot more.

Wow, Manchild. What could it be for?

[Tuono_Tom]

Welcome, Tuono Tom. I have no experience that is worth mentioning on motorcycles, but I know that in cars, unequal length headers offer less horsepower than equal length. What I know is they are easier to install, they produce less heat and, normally, they are easier, with a good design, for reaching spark plugs and other elements. Here you have real numbers on a Mustang, Hp at RPM:

Code: Select all

Exhaust type   3000 3500 4000 4500 5000 Avg
Equal length    197  226  232  237  233 226
Unequal len.    192  214  224  231  223 217

Sweet... and thanks for the welcome.
And that made me giggle- the plugs are on the top, under the fuel tank, the exhaust is on the bottom, single muffler attaches to a mid-pipe after the collector.
Still tough to get to the plugs... another story in packaging there, so never mind.

As for balance pipes, they offer two alleged advantages:

- In a dual pipe system (for cars, with pipes from each side of the block) they offer twice the exhaust, as cylinders won't fire at the same time.
- They (duhhh...) balance the pressure among the two pipes.

I don't see any of these two advantages at work in the picture you post, but I wait to be enlightened.

The picture you link us to is certainly... amazing. I repeat I'm ignorant about it.

Perhaps... the balancer pipe makes up for the fact that they ARE un-equal length 'headers'??
This is my quest... to figure out why it (reportedly, no dyno-charts yet) WORKS. And how to possibly improve the concept.

Anyway, I wonder why the exhaust you show doesn't seem to have an expansion chamber.

The Aprilia v-twin, running a Rotax 1000cc 60 degree v-twin has a very open, and rather short exhaust. (Muffler? barely, but not a Harley straight pipe). Due to the fact that a body has to wrap around the thing, has limited ground clearance, etc., an expansion chamber would toast legs... there may be room as the collector is under the engine, midships, but that is a whole NEW can 'o worms, as they say.
(For reference, these normally get 125+hp and about 75+ lb/ft to the ground, 430 lbs gassed up, 10,500 redline. You do the math, but they're FUN).

I'm assuming you know a lot about it, so please don't laugh at this program, for single pipes: http://www.iwt.com.au/data.htm

Perhaps DaveKillens can help you a lot more.

Wow, Manchild. What could it be for?

I'll check that out, thanks!
EDIT- oops- that's for two stroke's... and it's just WRONG to have a air/fuel mixture in the CRANKCASE!! ha.

-T_T

[Carlos]

With the unequal length pipes, the exhaust pulse from one cylinder evacuates the second cylinder at the Y where they merge. The balancing tube, emphasizes the effect in mid-range RPM instead of the top end. Usually the crossover, as a rule of thumb, has a diameter close to the exhaust valve diameter -- I don't know why -- maybe superstition?

The book is still well worth purchasing.

[ruud.]

the rsv doesnt have an expansion chamber because it isnt a 2strroke engine , the program is made of prof Blair formula's and its for a program not a bad calculation. But expansion chambers must be tested, not calculated .

[Tuono_Tom]

the rsv doesnt have an expansion chamber because it isnt a 2strroke engine , the program is made of prof Blair formula's and its for a program not a bad calculation. But expansion chambers must be tested, not calculated .

Knew that, I just got carried away typing amd stopped thinking- I guess I mentally swapped 'expansion chamber' for 'collector'. My bad.

And your statement is true. Glad I don't have to go that route!

Getting my chip mapping, fuel/ECU trim pots and throttle body adjustments is bad enough with just my measley GasTester and my old twin-SU-balancing-trained ears~!

-T_T

[Ciro Pabón]

I actually looked for the kind of engine that your Aprilia has, but couldn't find it. Four stroke exhaust desing is easier: you tune for multiple rpm points - provide a cross section change at the runner length that is required by the wave type and timing that you want. For a 2 pipes into 1, you calculate the distance from each geometry change to 1 exhaust port and use that length in your dynamic calculations.

Here is a program that does it for you, for one speed, that is, one RPM. You can calculate at several RPM, it will give you an idea of the compromises you make: http://www.kamware.com/vtr1000f/exhaust.htm

This is a downloadable package, it does essentially the same: http://www.kamware.com/TopSpeed.exe

I have no idea if these applications use exhaust scavenging in their calculations, nor I know the equations behind them, I haven't used them in real life. As ruud says, you have to test: I would say you have to start by designing and then you can test, but suit yourself. At the dyno where I go they have the SAE paper on "Exhaust Design for a 4 cylinder engine" and a different program for exhaust tuning. They include that calculation in the dyno fee. They will charge you for the parts, also.

[Tuono_Tom]

I actually looked for the kind of engine that your Aprilia has, but couldn't find it. Four stroke exhaust desing is easier: you tune for multiple rpm points - provide a cross section change at the runner length that is required by the wave type and timing that you want. For a 2 pipes into 1, you calculate the distance from each geometry change to 1 exhaust port and use that length in your dynamic calculations.

Here is a program that does it for you, for one speed, that is, one RPM. You can calculate at several RPM, it will give you an idea of the compromises you make: http://www.kamware.com/vtr1000f/exhaust.htm

This is a downloadable package, it does essentially the same: http://www.kamware.com/TopSpeed.exe

I have no idea if these applications use exhaust scavenging in their calculations, nor I know the equations behind them, I haven't used them in real life. As ruud says, you have to test: I would say you have to start by designing and then you can test, but suit yourself. At the dyno where I go they have the SAE paper on "Exhaust Design for a 4 cylinder engine" and a different program for exhaust tuning. They include that calculation in the dyno fee. They will charge you for the parts, also.

Thanks, good information.

The Aprilia V990 is an Austrian-built BRP-Rotax.
http://www.rotax.com/en/Engine/2004/Mot ... Models.htm

Interesting company, see the listings for:
Snowmobile
Marine
ATV
Motorcycle (including the new 1125 for the Buell, nee Harley-engined bike)
Kart, and last but not least:
Aircraft.

[Carlos]

Lotus Engineering offers a freeware download for design of a 4 stroke single, never used it. Looks really complex and covers everything under heaven.It's for a single, but a V Twin is just 2 singles, with an angle between them - right?

This program might help with all that mapping, injection adjustments stuff, ect, ect. Go to downloads and freeware and thats where to download.

http://www.lesoft.co.uk/

If you use it, maybe tell us about it all. Write a tutorial?

[ruud.]

i'm not a 4stroke expert at all, im only messing around with stinky 2 strokes. A collegea of mine made a new balancing pipe for his norton, i said what is that for, on which he replied without it the engine doesnt run smoothly, and also idly its just bumping. The gas presures are beeing equiled by this pipe, on which i directly thought, if the exhaust waves of your twin have such a different strengths, the cilinder fillings must be quite different (his completely different carburation set ups shows this to). It seems to me that a modern twin like an rsv engine, both cilinders make the same power allready, so why does this presure need to be balanced? As i say im not a 4stroke expert at all, but building a balancing pipe in this case is not a good idea i think..

[Giblet]

I have a Skyhawk 80cc 2 stroke on my bicycle, and it currently gets me to about 55km/h.

Since the exhaust is just a silencer, could I expect reasonable gains with a tuned exhaust?

[Ciro Pabón]

Ruud, I'd say two stroke pipes are harder to make, thanks for you correction. I cannot help you with your doubt, wait for some real mechanical engineer here to read this thread (Flyn, Scarbs, Jersey Tom, sorry I can't remember all of them).