MASS moto exhaust custom made,thoughts?

[GuzziMoto]

16 hours ago, gstallons said:

Are you sure you don't mean H-pipe ? These were on factory dual exhaust cars in the 60s and had some kind of affect on the performance .

An H pipe is a different layout than an X pipe, an H pipe fails under the category of simply trying to share the exhaust between the two sides. It is more about making the exhaust quieter than it is about making power.

[68C]

Still very confused how a V11 crossover works.  The two down pipes are different lengths, the four stroke 90' V twin exhaust timing is not even.  I understand how a parallel 360' crank can have even length down pipes and by merging at the correct point can make use of the scavenge effect from the other cylinder, albeit probably really effective at one throttle opening and one rpm.  But how all that uneven scavenging would help a V twin I cannot work out.  In my confusion I did once draw out the V twin exhaust timing as a graph, did not help, perhaps if one cylinder had a much longer down pipe.  Looking at the HD 45' V twin layout made even less sense, yet loads of clever exhaust systems on the market.  Then throw in that other thread with the dented down pipes.......

[Anders]

Here is a picture of the xover connecting part:

It looks like a very narrow area at the crossing point.I don't know what that will do to the preformance.

My explanation to the people at MASS moto wasn't that great,so this part and the silencers + pipes are going back and they will do some changes,and put a hole in for the Lambda sensor.I'm not bothered because I'm waiting for the neck surgery to heal anyway.

 

[GuzziMoto]

1 hour ago, Anders said:

Here is a picture of the xover connecting part:

It looks like a very narrow area at the crossing point.I don't know what that will do to the preformance.

My explanation to the people at MASS moto wasn't that great,so this part and the silencers + pipes are going back and they will do some changes,and put a hole in for the Lambda sensor.I'm not bothered because I'm waiting for the neck surgery to heal anyway.

 

Well, a name is just a name. But I would call that an X Pipe. And generally X pipes work well. The stock Guzzi piece is a lower cost version that does not work as well. The stock Guzzi piece is just welded up out of stamped steel. That one has far more effort into it and should work better.

The X pipe is supposed to be that narrow at the crossover. It should be the same diameter as the rest of the pipe. A sudden larger cross section in the exhaust results in the exhaust gases slowing down. When they slow down the loose energy. That should keep velocity up, which keeps energy up. I think it is a reasonably nice looking system

An even more extreme exhaust style is a merge collector. For those they go to great lengths to keep cross section even and velocity up. But they take up too much room and you probably could not fit one on a Guzzi easily.

[Anders]

2 hours ago, GuzziMoto said:

Well, a name is just a name. But I would call that an X Pipe. And generally X pipes work well. The stock Guzzi piece is a lower cost version that does not work as well. The stock Guzzi piece is just welded up out of stamped steel. That one has far more effort into it and should work better.

The X pipe is supposed to be that narrow at the crossover. It should be the same diameter as the rest of the pipe. A sudden larger cross section in the exhaust results in the exhaust gases slowing down. When they slow down the loose energy. That should keep velocity up, which keeps energy up. I think it is a reasonably nice looking system

An even more extreme exhaust style is a merge collector. For those they go to great lengths to keep cross section even and velocity up. But they take up too much room and you probably could not fit one on a Guzzi easily.

Good to know the x pipe is supposed to look like that.I had only seen it on cars but had no idea what the design did for preformance.I thought that there would have to be room for some of the gases to go straight forward and some to be able to use the other pipe back and forth.And for that there was a need for some bigger area where they came together.But I guess not then.Perfect!

When  I ordered the exhaust system I asked for the same ID (42mm) all the way from cylinder to end of silencers with as big hole joining the pipes as possible.

The aim was to keep the exhaust gases from not slowing down.To hopefully help torque on low revs.

This looks very different from that Stainune exhaust that was the inspiration but it should work in quite the same way then.Great!

[po18guy]

5 hours ago, Anders said:

Here is a picture of the xover connecting part:

It looks like a very narrow area at the crossing point.I don't know what that will do to the preformance.

My explanation to the people at MASS moto wasn't that great,so this part and the silencers + pipes are going back and they will do some changes,and put a hole in for the Lambda sensor.I'm not bothered because I'm waiting for the neck surgery to heal anyway.

 

Remember that the exhaust pulses are timed and do not pass through that narrow section simultaneously. The design seems to allow each cylinder to utilize both mufflers to some extent, so may actually boost mid-range and even top-end sightly.  

[68C]

Sorry po18guy, I really do not follow your logic.  How are the pulses timed?  They cannot be even due to it being a 90' V twin.  Why do you think it will improve mid range and top end?

[Lucky Phil]

19 minutes ago, 68C said:

Sorry po18guy, I really do not follow your logic.  How are the pulses timed?  They cannot be even due to it being a 90' V twin.  Why do you think it will improve mid range and top end?

The process is that as the positive exhaust gas pressure wave travels down the primary pipe and comes to a large cross sectional change( the collector/crossover) that change creates a change in positive pulse pressure which results in a negative pressure wave back along that cylinders primary pipe to assist in evacuating the cylindes on the exhaust stroke and on the overlap to help with cylinder filling. In The case of a twin with uneven firing cylinders is difficult to get the cylinders to cross talk like a multi with a complex collector system however Ducati went some way towards that with their famous Spaghetti collector in the 80's and 90's on the 888 race bikes. The crossover in the image isn't narrow in the least. where the two headers come together there is a dramatic increase in the cross sectional ID at that point which creates the pulse.

Ciao     

[68C]

And how is that pulse timed to help the extraction.  I can believe it will help on one cylinder but, unless you quickly change the pipe lengths, how does it help the cylinder?

Edit,  should say 'other cylinder'

 

[Lucky Phil]

1 minute ago, 68C said:

And how is that pulse timed to help the extraction.  I can believe it will help on one cylinder but, unless you quickly change the pipe lengths, how does it help the cylinder?

 

The other cylinder? it cant really to any great extent.

Ciao

[Lucky Phil]

Here's an image I have of a Ducati 888 Corse spaghetti exhaust cross over collector and the complexity of trying to get the length and pulse timing right and a little cross talk between the cylinders. I used these images to make make my own system. Whats hidden in this image is another small diameter cross pipe behind the one in the image which connects the rear header back to the front header at another point. You can see its retaining spring at the bottom.As you can see the primary reason for the smaller cross link pipes is for negative pulse generation not to redirect exhaust gases. You're not going to get exhaust gases to turn at nearly 90 deg but it will generate a negative pulse due to the sudden change in pipe cross section. Where you locate the cross sectional change in relation to the distance from the valve is whats critical in what you want from the torque curve and any cross talk to other cylinders if possible.

 

Ciao

[po18guy]

6 hours ago, 68C said:

Sorry po18guy, I really do not follow your logic.  How are the pulses timed?  They cannot be even due to it being a 90' V twin.  Why do you think it will improve mid range and top end?

Interval should be the word. Firing interval = exhaust pulse interval. 360º parallel twins are perfect examples of one cylinder helping to scavenge the other, but other designs (exception below) cannot achieve that. I have a 180º twin. The left cylinder helps to scavenge the right, which fires 180º later, but the left cylinder does not really benefit from the exhaust pulse of the right cylinder, which arrives 540º later. Guzzi's, Ducs etc. have one cylinder which has help scavenging the exhaust, but the other cylinder has to deal with an exhaust pulse which comes, not 270º later, but 450º later - thus far less scavenging effect. For that reason, the pipe engineers have the headaches and the tangle of snakes pipe designs. Inline 4s can achieve this by pairing the two inner cylinders and the two outer cylinders (2 and 3 firing 360º apart and 1-4 firing that same 360º apart), but factory exhausts are only rarely done that way. Cool, curvy 4 into 1s look far better on the sales floor. Honda Civics, with hidden exhausts, often use the tri-y setup in aftermarket headers, pairing cylinders which fire 360º apart. They have the room to do that, but space (and looks) is at a premium in bikes.   

[68C]

That is exactly how I see it. 

Our OEM pipes were probably designed to tuck the system away neatly under the bike, perhaps for cornering clearance but most likely cosmetic.  There may be a weight saving in having two smaller shared silencers. All this discussion about Stucchi, Mistral et al is really about which system is least bad, none of them probably enhance power over the Tonti H system.  Two seperate pipes may even work best for peak power. Hence that system that looked like a crossover but had no hole between them.

But, as I said  I do find the V twin exhaust system confusing.

[Anders]

There is alot of knowledge and experience on this forum.It's all good read for someone like me who has no technical education,only a big interrest.Great!

[MartyNZ]

On 6/26/2020 at 9:03 AM, Anders said:

When  I ordered the exhaust system I asked for the same ID (42mm) all the way from cylinder to end of silencers with as big hole joining the pipes as possible. The aim was to keep the exhaust gases from not slowing down. To hopefully help torque on low revs.

It looks like a great system, I'm looking forward to pictures of it installed. 

A comment on pipe size: as exhaust gasses travel out, three changes happen.

1.The pulses smooth out slightly as they expand into a larger volume.

2. The gasses cool down due to both expansion and heat loss radiating out of the system.

3. In a constant diameter pipe, the gas flow speed slows due to effects 1 & 2.

This explains why motorcycles with two headers leading into one muffler (eg Griso) do not suffer any power loss caused by exhaust system restriction.

Bigger pipes are less restrictive to gas flow, however, with all other things being equal, gas flow in a big pipe is slower than in a small pipe, so the negative pressure pulses, or extractor effect, can be reduced.

Your aim of 42mm dia pipe all through could be a great idea, or it may just add weight. It will be great to hear how it works out.