Fabricating a 2-1 exhaust

[luhbo]

Yes, A/F logger combined with Autotune and all neccessary diagnostic tools as dashboard, based on Bluetooth and available for Win, WinPC and Android.

 

Have you read Jaap's thread where he described the pimping of his V11 with a Ghezzi&Brian kit? It's a very nice peace of work, topped with an even nicer DIY-exhaust. Search it.

 

Hubert

[GuzziMoto]

The collector itself is hard to build yourself and get right. I would suggest you buy that part.

And a two into one pipe should not need a muffler with an inner pipe/baffle much larger then a two into two pipe. They are both flowing the same amount of exhaust at any one time.

[Bjorn]

Im more concerned about the whole pipe diameter topic. I dont think I follow you on the 2-1 muffler dia should or can be identical to a 2-1-2. The headers will join in one pipe and flow towards the muffler. Doesn't that mean the amount of gases multiplies by 2 compared to the 2-1-2?

 

Looking at the stock set-up each cylinder basically has its own muffler. taking the stock collector in mind, you could even say every exhaust pulse from one cylinder can divide over the 2 mufflers, can you not?

 

To me it sounded plausible to choose a muffler with a large® volume/pipe diameter, because more gases go trough. But maybe i overlooked something here....

[68C]

With a 180 degree parallel twin four stroke engine there is one exhaust pulse per cylinder every two revolutions of the crankshaft.  If the exhausts are arranged as  2 into 1 it is possible by using equal length pipes to have these pulses  follow each other evenly, one pulse will create a drop in pressure which will help the next pulse.  This really only works well at one throttle opening and rpm, the length of the pipes determining the rpm.

 

However we have 90 degree V-twin engines, the exhaust pulses are not evenly spaced, it is not possible to have a true 'extracter' exhaust system.

 

I admire your desire to build your own system, you should be able build a lighter system.

[GuzziMoto]

Im more concerned about the whole pipe diameter topic. I dont think I follow you on the 2-1 muffler dia should or can be identical to a 2-1-2. The headers will join in one pipe and flow towards the muffler. Doesn't that mean the amount of gases multiplies by 2 compared to the 2-1-2?

 

Looking at the stock set-up each cylinder basically has its own muffler. taking the stock collector in mind, you could even say every exhaust pulse from one cylinder can divide over the 2 mufflers, can you not?

 

To me it sounded plausible to choose a muffler with a large® volume/pipe diameter, because more gases go trough. But maybe i overlooked something here....

I did not say the two into one muffler should be the same size as a two into two muffler. I said the two into one muffler does not need to be much larger than the two into two mufflers are. By that I was implying that it will be larger, just not twice as larger. Sorry, I could have been clearer.

A common mistake is to think you are flowing twice the exhaust out of a two into one muffler then you are out of a two into two muffler. That logic assumes that the exhaust gas flow is constant and even. It is not, the exhaust flows in pulses. The pulses from one cylinder are happening when the other cylinder is not exhausting. Think of it as two dotted lines that you are merging together. If the dots don't overlap each other than they can be merged into one line. In reality, the size of the collector pipe should determine the size of the muffler. The muffler should be as big as the collector pipe in inside diameter. It can be bigger (more noise) but it should not be smaller.

As two the idea that you can't make a two into one pipe act as a "true extracter (sp) exhaust system", I used to think that until a real exhaust guy showed me that it does work. I now know it can and does work if the pipe is made correctly. I have seen it with my own eyes. And there are at least two peaks of the return pressure wave helping the exhaust get out of the cylinder on a two into one system, while a two into two system may only have one. And it is not only at a specific rpm where it works but peak effect is centered at certain rpms. But the effect is more of a wave form with the peak of the wave at a certain rpm. And obviously, having two waves (as a two into one system does) allows for better coverage of the rpm range as a whole.

 

And I think 68C meant with a 360 degree crank parallel twin you get an even pulse between both cylinders and thus is easier to make any kind of exhaust extractor pipe work. A 180 degree twin does not evenly fire its cylinders. In fact, it is more offset on the firing than a 90 degree twin with a single crank pin like Ducati's or our Guzzi's.

[Bjorn]

Clear on the 2-1 muffler volume

 

As for the second part, Sounds like you know one or two things about exhaust-systems. I understand the part about the exhaust-pulses of the engine not happening at the same time. However the ''peaks & waves'' are still kind of hard to get my head round.

 

If the 2-1 set-up does not result in a loss of ride-ability or lots of power i guess im a happy camper

 

At the moment im trying to find a suitable muffler. Not as easy as you think without seeing them in real life. It stays a bit of a gamble, same story with the noise it will produce in the end. The collector I will probably build myself so it fits my needs. 

 

The first exhaust modification is already done. During the winter i removed the balance-pipe between the headers. I tried several different solutions to keep it from rattling/leaking. Nothing worked properly so i decided to remove it. Ive been riding around 300km since, no noticeable difference in performance or smoothness.

 

 

[docc]

Wow, man - nice weld!

 

And, finally, a Bjorn thread without a hammer in sight!

[68C]

And I think 68C meant with a 360 degree crank parallel twin you get an even pulse between both cylinders and thus is easier to make any kind of exhaust extractor pipe work. A 180 degree twin does not evenly fire its cylinders. In fact, it is more offset on the firing than a 90 degree twin with a single crank pin like Ducati's or our Guzzi's.

 

 

Yeah GuzziMoto, you are right in what I am saying . 

[GuzziMoto]

"Clear on the 2-1 muffler volume 

 

As for the second part, Sounds like you know one or two things about exhaust-systems. I understand the part about the exhaust-pulses of the engine not happening at the same time. However the ''peaks & waves'' are still kind of hard to get my head round.

 

If the 2-1 set-up does not result in a loss of ride-ability or lots of power i guess im a happy camper "

 

The effect from the negative pressure wave getting back to the exhaust port is not a yes or no deal. The exhaust valve opens, then closes. If the negative pressure wave arrives at anytime during that event you will see some positive effect. Heck, even if it gets there slightly early you would see a small effect. Peak effect is when the negative pressure wave arrives right when the valve is opening. But on either side of that is still an improvement in scavaging the exhaust gases out of the cylinder. So, the effect is not a yes or no sort of thing but rather a wave with the peak of the wave at the point where the timing is perfect. But there is still a positive effect even when the timing is off one side or the other a little. Plus, as mentioned, with a two into one pipe there are two pulses, two negative pressure waves that are going back up the pipe. With a true two into two system would only have one. The two into two pipes with a cross over like Guzzi's have are somewhere in between.

In my experience a properly designed and built two into one pipe will have better power, better "ride-ability" then a two into two pipe. What a two into two pipe is often best at is making maximum power at a given rev range. But less power everywhere else. So, if you are running the salt flats for maximum speed a two into two pipe would probably work the best. But for street running or roadracing a two into two pipe can work better. But a poorly designed and built pipe, whether a two into one or two into two, will not make as much power as a well designed and built pipe, regardless of type.

You can make power with a good pipe and you can loose power with a poor pipe.

My favorite collector style is a Merge collector. they are a cool design and you can buy one to use in your pipe.

I am not expert, I only know enough to be dangerous.

[Bjorn]

Good explanation! If i understand it correctly the ''under pressure'' of the negative wave would ''suck'' the new exhaust gases out of the cylinder right after the ex. valve opening. In turn creating a better flow of gases?

 

How does the negative wave travel backwards?

 

Practical part:

 

I dont know what a merge collector is exactly, but the disadvantage of the stock collectors is they have a straight inlet (and cost money ) like this example:

Because space is tight, im building it more in a ''Y'' shape. This helps with the headers coming from left and right. A bit more like this:

Anyway i found 2 or 3 suitable mufflers to use, just need to choose which one that suits best. Im free on friday, to go shopping for stainless steel mandrel bends. Cant wait to start

[68C]

Dr. Gordon Blair of Queens University Belfast with ace tuner Paul Dunstall did a lot of work in the early 70's on 2 into 1 into 2 systems for the Norton Commando, might be worth a Google search. Also I remember a 'Thruxton' tuning kit for the late 60' early 70's Triumph T120 had a system in which the header pipes had a larger diameter for about the first nine inches or so then thinner, I think the idea was to have a larger volume for the gasses to initially enter then as the gasses cooled to flow into the reduced diameter.

 

Are you going to have equal length pipes before the merge? I believe some of the Harley tuners like uneven pipe length for V-Twins.

[Admin Jaap]

.............Also I remember a 'Thruxton' tuning kit for the late 60' early 70's Triumph T120 had a system in which the header pipes had a larger diameter  for about the first nine inches or so then thinner, I think the idea was to have a larger volume for the gasses to initially enter then as the gasses cooled to flow into the reduced diameter...

 

There is an exhaust kit by German Guzzi specialist Daes Mototec which has those conical headers: http://contentmanager.brainst.com/8118/index23a1.php3?news_id=4418

[luhbo]

Do a Goggle search for Ducati superbikes, or Honda SP1/SP2. All used 2-1-2 with the most possible success on racetracks.

 

Go for 2-1 if you like the look of it, that's what counts for private road use. In another thread you mentioned that F/I and cylinder selective tuning is not your thing - in this case consider a 2-1-2. Anyway, have fun, such things always are nice projects.

 

Hubert

[Bjorn]

Its more the last part. I like the looks, and its unique for a V11. No the tuning part is not my favorite but I planned to get it dynoed anyway. There are two candidates who seem to know what they are doing

[luhbo]

Anyway, consider an Ex-Box like solution. 2 into 1 bigger expansion chamber/collector, from there into one exhaust pipe/cone/whatever. Jaap has done it, the OEMs do it, it would be my approach as well. You could build this based on a used standard V11 collector which would provide the correct connectors to the headers and also a solid basis for your further welding.

 

Hubert