Shortening Le Mans I/II standard silencers

[Simon_London]

I'm still thinking about a more free flowing exhaust to go on to my 42mm downpipes + crossover without the cost of Lafranconis.

Any comments on shortening the silencer and fitting a less restrictive baffle?

I once had a Le Mans with 1/4" holes drilled around the exit hole of the standard silencers but they didn't sound that great and there was little noticeable performance benefit.

Simon

[oldbike54]

 Seriously doubt if shortening and debaffling the mufflers will cause any real performance gain , and doing so will make the throttle into a LOUD switch .

 Yeah , I'm channeling Pete here , someone has to while he is on sabbatical 

  Dusty

[Simon_London]

Well Lafranconis are louder and more free breathing and they develop more power, no?

[oldbike54]

Well Lafranconis are louder and more free breathing and they develop more power, no?

 Pretty sure your LM already has LaFranconis on it . They were standard fitment on Guzzi . Noise does not always equate to power .

  Dusty

[Simon_London]

Sorry Dusty, I meant Lafranconi Competiziones are louder and more free flowing. The standard ones are very quiet and I asume restrictive. I actually don't mind a quiet exhaust, just interested in making the bike quicker. I already have a tweaked carbs, a fast cam and a lightened flywheel. Bike is quick and very smooth, but........

[oldbike54]

 No need to apologize Simon , we are just kicking around ideas here  Here is the deal , the Competiziones were engineered by experts , and yes , they do sound wonderful . Cutting the ends off of regular LaFranconis , or drilling holes , will not duplicate the tuning effects of the Comps . If you have already spent money on the motor , maybe time to spend a bit more on a nice set of tuned mufflers .

  Dusty

[steven c]

 The stock mufflers are pretty restrictive, my LeMans came with Bub's and is not really loud, nice rumble. I don't like loud pipes, I had bought a Bub system once, the shorty one's for my Lemans III  I had, they really made an improvement in power but after one ride I took them off because they where so loud.

[guzzista]

My nephew, Aldo, who is also on this board, has a set of  short  reverse meggas on his hot rod SP/ LM that were sourced in the UK when he lived there. They look like the early Tonti racers exhausts. Maybe you can PM him for info/ pics

[Arizona Wayne]

I'm still thinking about a more free flowing exhaust to go on to my 42mm downpipes + crossover without the cost of Lafranconis.

Any comments on shortening the silencer and fitting a less restrictive baffle?

I once had a Le Mans with 1/4" holes drilled around the exit hole of the standard silencers but they didn't sound that great and there was little noticeable performance benefit.

Simon

I have a CX100/LM II w/original mufflers and like you drilled some holes.  I think @ midrange rpms more sound get's out.  I'd be surprised if they are Franconis because they are very light and other Franconis I've seen are not.   Bub's (NLA) I've heard are loud.  I'm happy with my originals partly because they are light and rare now and louder than newer stock mufflers.  But until you really get the revs  up they are pretty quiet.

[rodekyll]

Well Lafranconis are louder and more free breathing and they develop more power, no?

Using that logic, just bin the pipes from the crossover back and you'll have the loudest + most freeflowing = max power.  It's all in the noise math.

To answer the question -- I don't see the relationship between what you propose and your goal.

[Simon_London]

Rodekyll

My belief is a less restrictive exhaust = a faster, more responsve engine. But I want to avoid to much offensive noise. More mellow rumble than rasping decibels. The bike is running really well now, pulling strongly right from tick-over but I think a less restrictive exhaust will make it rev faster and be even more punchy.

Dusty - you make a good point about the Competiziones being designed by engineers.

One of the things I have found tuning the bike is that making a bike go faster is very much about getting the carbs right. And because there are so many carb settings to change, that also effect each other, its not easy to hit on the right combinations. My mind now turns to getting the gases out as effectively as possible.


My bike is a small valve G5 caf racer. I sold my Mk 2 Le Mans because I prefer the more flexable lower compression engine of the G5  which can still be made to go surprsingly fast. Its got 36mm carbs, ported heads, a fast road cam (HMB) and an 1100 sport flywheel.

[rodekyll]

With respect, Simon -- I think this is an area where science trumps beliefs.  Yes, in it's most oversimplified form, the equation I wrote above is true.  But your mufflers aren't your restriction until you get somewhere near WOT, and with all the other mods to the engine, changing the mufflers is going to throw any tuned balance awry.  That same system serves much larger engines with larger valves and a higher redline.  In the real world you just can't pump enough air through small valves/948cc to load up the pipes.  And if I was trying to meet a performance goal, I'd be working with a tuner to figure out the properties of the exhaust rather than gutting and chopping at random cans.

$0.02

[Simon_London]

Thanks for your input Rodekyl. The reason I posted is to get the benefit of other people's experience.

The other mods I have done made a big difference. I've also dumped a fair amount of weight. Really the mufflers are the only thing left to experiment with and I like experimenting.  I will let you know how I get on.

[Arizona Wayne]

I have found on different motors that if you lose X amount of exhaust back pressure you lose power.  All these things are interrelated.   Just because something is loud doesn't automatically make it faster.

[rodekyll]

I do the same thing, Simon.  Even with mufflers.

Here's my latest tinkering as of last June:



Having all the mufflers ever made available for my project, I went OEM.

[guzzista]

The other mods I have done made a big difference. I've also dumped a fair amount of weight. Really the mufflers are the only thing left to experiment with and I like experimenting.  I will let you know how I get on.
[/quote]  Simon, the Lafranconi may  also be the lightest mufflers IMHO

[Tom]

Simon,

Out of curiosity.....when you take off from a dead stop.  What rpm's are you launching the bike at?  and what rpm's are you shifting at? 

[Simon_London]

Tom, at  guess I woud say I tend to pull way around 3000 revs. Shifting revs vary depending on how the bike is being ridden - perhaps anywhere from 3000 to 6000.

[Tom]

With a lighten flywheel, you might want to raise it 500 ro 1000 rpm's and cruise at 4k.

[Pancake]

When I bought my bike (Spada 2, small valve engine same as yours in most respects apart from being a square head) it had shorty universal silencers on it. Anyway i bought some Lafranconi comps (like the ones on a Lemans 3) as they came up second hand at a good price. When I removed the old short ones you could look right through them like a telescope without a lens. I expected the big Lafranconis to be quieter because you couldn't see through them. Technical stuff!
Anyway the Lafranconis were slightly louder in a deep and very pleasant way (not Harley style), and the improvement in performance was stunning. The bike now would rev right to the red line whereas before it kind of died around 5000.

Well the Lafranconis have now rusted holes where the welds were and I have replaced them with Mistrals, good price at the moment from Stein Dinse with favourable Euro exchange. They do not sound as good as Lafranconis, not as deep but performance is not notably different. I still miss the throb of the Lafranconis but prefer the look of the Mistrals

[Simon_London]

Just stuck some Lafranconi Competiziones on the bike.

Compared to Keihan replica standard Le Mans I / II silencers the difference is very noticeable.

Extra 5mph on top end (125mph on the probably rather optimistic clock). Feels more powerful and faster revving everywhere else in the rev range. I really like the faster pick up and am very happy with the result.

This is on a small valve 950.

So the answer to the question will a more free flowing exhaust make a small valve 950 faster is YES !

[Groover]

The Lafranconi Conpetizion are nice pipes, sound great and are well designed - and you pay for the R&D which is fine when you get a good product like that.

In regards to the topic that's been discussed in this thread, there is a science behind exhaust designs. It's all based on the scavenging phase of the exhaust. Most off-the-shelf exhaust are give-or-take and based around the general cc of the engine, so they work. Even when we modify the factory ones with holes and such, we're still sort of close to the original exhaust design.

When you get into competition quality, that's were and why some exhaust systems, typically the more expensive ones are better (as long as you are matching them to your engine setup). Sometimes the cheap ones are great too, but it's more luck than research put behind them during the design stage if they perform well.

Here is some info on scavenging, the key to a good performing exhaust system.

https://en.wikipedia.org/wiki/Scavenging_(automotive)

[mabajada]

I am curious how loud the Lafranconi Competiziones. I have Bubs on my '78 Lemans and am curious of the difference in sound.

[fotoguzzi]

with out a dyno chart as proof I really doubt you got more than 2hp with the new mufflers.

seat of pants might tell you it's faster but could it be from a lightened wallet?

RK, glad to see your back!

[265coupe]

When I had a new 900SS bevel it came with legal (quiet) Silentium mufflers fitted and Conti (loud) in a box. The difference when changed was huge. No dyno needed. Just the feeling when twisting the throttle and the rate of change on the tacho. It really was unleashing the beast.

Of course there was a price to pay. The 40mm carbs needed tuning for the new pipes (and the K&N pods to replace the ram tubes).

You might find that your engine will continue to improve with further carb tuning.

Have fun with your experimenting.

[sdcr]

I am curious how loud the Lafranconi Competiziones. I have Bubs on my '78 Lemans and am curious of the difference in sound.
[/quote

I have the LaFranconi Competiziones on my Le Mans 3. There is a decibel difference from stock pipes, but not excessive. At least my ears don't mind the sound. As to a performance increase, I can't really detect any, so if there is, it's a very small amount.
 I find the LC's to be a good choice if you want a louder, but not obnoxious sounding motorcycle.

John

Le Mans III

[Oldrat]

For what it's worth.. Many peeps muck about with their zorsts but few are aware of this (endorsable) offence in the UK.

The Road Vehicles (Construction and Use) Regulations 1986
Silencers

54.—(1) Every vehicle propelled by an internal combustion engine shall be fitted with an exhaust system including a silencer and the exhaust gases from the engine shall not escape into the atmosphere without first passing through the silencer.

(2) Every exhaust system and silencer shall be maintained in good and efficient working order and shall not be altered so as to increase the noise made by the escape of exhaust gases.

To be honest it would probably never be an issue, not enough (knowledgeable) cops around and unless you made looney tunes it wouldn't be a priority

Anyway it's your bike, your choice. 
  Cheers
 

[Simon_London]

I suspect the power gain is nearer 5bhp and the engine is noticably more free revving. The bike pulls 5mph faster on the clock.
It really wants to rev like a big valve motor. I have an 8.1 HMB cam and Michael from HMB tells me that the cam likes a free flowing exhaust.
It also smells like its running a little rich now, so dropping the needle may improve things further.

[fotoguzzi]

got any


pics?

[mabajada]

Thanks. I thinks the Bubs are also louder than stock, but the bike came with them so I dont know what the stock would have originally sounded like, an have yet to come across another Lemans around town.
My interest in the Lafranconi's are mostly asthetic. They seem to follow the lines of the bike so nicely.

I am curious how loud the Lafranconi Competiziones. I have Bubs on my '78 Lemans and am curious of the difference in sound.
[/quote

I have the LaFranconi Competiziones on my Le Mans 3. There is a decibel difference from stock pipes, but not excessive. At least my ears don't mind the sound. As to a performance increase, I can't really detect any, so if there is, it's a very small amount.
 I find the LC's to be a good choice if you want a louder, but not obnoxious sounding motorcycle.

John

Le Mans III