variable exhaust pipe diameter / custom system questions

[Vitamin_B12]

custom exhaust system questions

i am looking to get a full custom exhaust made by Fresco in Italy and i was wondering if anyone has any experience or tips. i am mainly trying to cut down weight and so far all i know is that i want it in Titanium and for the routing to be as straight/simple as possible

can anyone shed some light on how these factors affect things like power? (hoping for more low/mid-range power, not looking for top end)
- number of bends
- diameter of piping
- length of piping
- 2-1 vs 2-1-2 vs 2-2 (it's for a Ducati Monster 696)
- high mount vs low mount

should i just tell them my goals and leave the design up to them?

edit: thanks murf i removed the part about the expansion chambers on 2 strokes

 

[murf]

I suggest you do some research on 2 stroke vs 4 stroke engines and exhaust design......Ill give you a hint, those pics are of a 2 stroke.

 

[invictus43]

Designing an exhaust that actually works is non-trivial. I suggest if you want something that works to buy a full system from Akrapovic or something similar. Anything you design will almost certainly make less power and probably less power than the stock system.

 

[Vitamin_B12]

the only full system i have found for the 696 is by GPR in Italy for about 1850 EUR (~$2400 CAD)

i understand that i can't just be like, "i want 56mm diameter tubing", but FF by Fresco makes ready to buy exhausts and custom ones. would it be ill advised to trust them to design a well working one?

here is their gallery of custom ones:
http://www.scarichimoto.net/le-nostre-realizzazioni/

 

[Brian P]

Re: custom exhaust system questions

can anyone shed some light on how these factors affect things like power? (hoping for more low/mid-range power, not looking for top end)
- number of bends Not very important
- diameter of piping Extremely critical
- length of piping Very important
- 2-1 vs 2-1-2 vs 2-2 (it's for a Ducati Monster 696) The length and diameter of each pipe up to the 2-1 junction is important and the length after that junction is somewhat important, but whether it splits back into two or remains as one is not that important but what IS important is the total change in cross sectional area that the flow sees
- high mount vs low mount What matters is the length and diameters of the pipe, not so much where it ends up

should i just tell them my goals and leave the design up to them?

Properly designing an exhaust system requires extensive software simulation and/or extensive cut-and-try testing. In a system that is "custom" one-off that level of engineering and/or testing is not likely to happen and if it does happen, (A) you'll be paying (a lot) for it, and (B) it's possible (actually, rather likely) that the lengths and diameters that are necessary from the engineering point of view don't align with your vision of what the system is supposed to look like.

For a late model bike that has at least some performance aspirations, you can be reasonably assured that the original manufacturer (Ducati, in this case) has put some effort into making sure the stock exhaust system has a good balance of performance, appearance, weight, and regulatory compliance (emissions, noise).

It's likely that unless some considerable R&D effort is put into the design, that a one-off will not perform as well as the stock one.

 

[Scuba Steve]

Re: custom exhaust system questions

i am looking to get a full custom exhaust made by Fresco in Italy and i was wondering if anyone has any experience or tips. i am mainly trying to cut down weight and so far all i know is that i want it in Titanium and for the routing to be as straight/simple as possible

can anyone shed some light on how these factors affect things like power? (hoping for more low/mid-range power, not looking for top end)
- number of bends
- diameter of piping
- length of piping
- 2-1 vs 2-1-2 vs 2-2 (it's for a Ducati Monster 696)
- high mount vs low mount

should i just tell them my goals and leave the design up to them?

edit: thanks murf i removed the part about the expansion chambers on 2 strokes

Trade for a Monster 1100 or streetfighter end thread

 

[Brian P]

It appears from the web-site that they have some standard designs for each bike. Assuming that they have put some R&D into the configuration of those standard designs (which may or may not be the case) I'd suggest picking one of those and not trying to differ in any way.

Most common design problem with aftermarket exhaust systems in general is making them too BIG. Everyone thinks "bigger is better" ... but it isn't. A lot of aftermarket exhausts haven't had adequate research put into their design and won't improve performance.

 

[invictus43]

It appears from the web-site that they have some standard designs for each bike. Assuming that they have put some R&D into the configuration of those standard designs (which may or may not be the case) I'd suggest picking one of those and not trying to differ in any way.

Most common design problem with aftermarket exhaust systems in general is making them too BIG. Everyone thinks "bigger is better" ... but it isn't. A lot of aftermarket exhausts haven't had adequate research put into their design and won't improve performance.

Computing (or trial and erroring..) the correct header lengths and diameters to build mid-range scavenging is probably one of the trickier parts..and if someone is looking for improved mid-range, that is probably the part that will let them down. So maybe they'll get loud and maybe better high rpm power, but they'll likely kill the mid-range with a guess-exhaust. You're completely correct.

 

[Vitamin_B12]

Properly designing an exhaust system requires extensive software simulation and/or extensive cut-and-try testing. In a system that is "custom" one-off that level of engineering and/or testing is not likely to happen and if it does happen, (A) you'll be paying (a lot) for it, and (B) it's possible (actually, rather likely) that the lengths and diameters that are necessary from the engineering point of view don't align with your vision of what the system is supposed to look like.

For a late model bike that has at least some performance aspirations, you can be reasonably assured that the original manufacturer (Ducati, in this case) has put some effort into making sure the stock exhaust system has a good balance of performance, appearance, weight, and regulatory compliance (emissions, noise).

It's likely that unless some considerable R&D effort is put into the design, that a one-off will not perform as well as the stock one.

thanks for your replies guys

Brian P, can you elaborate on the importance of the length of piping? what would a shorter overall length yield vs a longer length?

i am not really concerned with aesthetics, and mainly intended to trust their judgement in the matter. i was just wondering about how the various design inputs affect the system. thanks for answering those questions

regarding price, does it seem fair to you? i think it is but it does not hurt to have a second opinion:

tig welded full titanium system with titanium muffler 300 euros + 450 euros = 750 euros ~= $950 CAD

It appears from the web-site that they have some standard designs for each bike. Assuming that they have put some R&D into the configuration of those standard designs (which may or may not be the case) I'd suggest picking one of those and not trying to differ in any way.

Most common design problem with aftermarket exhaust systems in general is making them too BIG. Everyone thinks "bigger is better" ... but it isn't. A lot of aftermarket exhausts haven't had adequate research put into their design and won't improve performance.

from what i can gather, the goal is to have the exhaust gases exit as quickly as possible with as little back pressure as possible. is that about right? would having a more straight route reduce back pressure?

would you strongly recommend that i play it safe and stick with the stock internal diameter?

lastly, regarding the previously produced designs for each bike; they do have a completed full system for a 696 that pretty much matches what i am looking for:

the only problem is that i was hoping to change out the muffler in favour of a design off the NCR M4. would this change at the end of the system affect the performance very much?

thanks again for all of your helpful information

and @ ScubaSteve, those two are great but are way too much bike for me, among other things $$

 

[invictus43]

The silencers make almost no difference to the power. It's the shape, size and lengths of the header pipes to the collector that counts. The point is not necessarily to make the lowest possible back-pressure. That may increase peak horsepower but may make the mid-range disappear. There are scavenging effects that can speed exhaust gas removal at certain speeds caused by certain lengths of pipe. Honestly, the person manufacturing the exhaust know a lot more about it than you do. I'd either let them make it or just leave it stock and put a can on it if you want more noise. Any system you put on will not greatly increase power over stock anyway..

 

[Vitamin_B12]

thank you for your honest answer. yeah i am gonna leave it up to them

i am not looking to make more noise. as stated in the original post, i am mainly trying to cut weight. any additional power gained would be kind of a bonus. if i wanted a more powerful bike, like ScubaSteve said, i'd just upgrade to the 1100 later. the questions were more just for my information to learn

plus for the price, it would be more worth it to go this route. for a pair of slip-on cans (at least the ones i wanted originally, Mivv Suono) were about $1000 CAD anyway

 

[GreyGhost]

That second muffler looks damn loud (volume of the can helps quiet things down and they don't have much).

As far as power, IIRC my old Honda twin could make more power 2-1-2 than 2-2, my car makes more power 4-2-1 than with any other configuration, but it is vehicle and exhaust specific, one approach is not always better.

Have fun, whatever you buy should be lighter than stock (as your budget vastly exceeds that allowed by the manufacturer), hopefully the design is decent and your power won't be adversely affected. Personally, I try to keep the can size up (and therefore noise down) to minimize chats with the cops.

 

[Vitamin_B12]

it actually doesn't seem that loud. the can is on the bottom of the bike. i think i want to pretty much replicate the NCR's exhaust

[video=youtube;2ZD7QHKsVio]http://www.youtube.com/watch?v=2ZD7QHKsVio[/video]