Anyone interestes in 4-2 Factory exhaust?

[fredintoon]

I was with you until you started talking about the dual passages in the cross over. I just put a stock exhaust on and its just a tube between the two.

Hi Ivan,
I just hacksawed my rusted through stock mufflers off so I got a brief look at their innards.
Not that I took much notice as they were going in the bin anyway.
And yes, there's a single tube going across but that tube connects two chambers inside the mufflers that are fed not directly from the exhaust pipe itself but from somewhere further down inside the muffler.
So there's definitely something complicated going on in there because it ain't just a simple H-connection.

[Rasputin]

Hey Fred, any chance you have any pics or can take any of what you are seeing? I for one would like to know more. If the bin has not been picked up maybe you could get a few shots.

[hightec_redneck]

Hey everyone. This thread is working out great. I am n finished yet, but here are a couple of pictures of the crossover and the separate ports.





I will need to take a better picture of the crossover section so you can see the separate ports and internal baffle better. Please keep in mind this is off my 78 standard parts bike, and I am not an expert on all the models as to how many different exhaust systems were made. Maybe one of the more experienced members could help out with that info. I have also seen that my explanation yesterday has a mistake in the flow of the second passage, as I was trying to explain it from memory. But the 2 pieces of th cross over section are joined by a single common port. So the reflected energy that passes into the second port and through the baffle, is then released into the other half of the crossover. From here it can either enter the main port or the second port on the other side of the exhaust. I agree with others that this is the engineering behind the scavenging portion of the exhaust system. And it is also designed to increase the velocity of the exhaust gases. All of these contribute to a better, more powerful, motor. But up to this point, I had heard rumors that drilling out the end of the baffled plate will reduce back pressure and give more power. Now I understand that it is much more complicated than that, and I would not think of doing it. IMHO. One other thing that I did not like was the idea of smashing a relief in the new muffler, around the real axle. But from the measurements I took last night, I was able to layout the new system under the real axle so it could be removed, and was still higher off the ground than Cly. 2-3 headers. More to come.
Thanks, Larry

[fredintoon]

Hey Fred, any chance you have any pics or can take any of what you are seeing? I for one would like to know more. If the bin has not been picked up maybe you could get a few shots.

Hi Rasputin,
sorry, the bin men came a week ago.
If you check Hightec's latest photos you can see that his Standard system is way different than the one on a Special.
Perhaps someone with a rusted out Special exhaust that they haven't yet discarded could cut it open and take photos?

[hightec_redneck]

OK, here is a couple pictures of the finished exhaust.






The high temp black paint was to keep the welds and cross over from rusting, and unless you look close, you can not see it on the bike. The exhaust was a complete success for me as I got the bike together and fired it up this weekend. It sounds incredible, deep and powerful, yet not loud.
I will be writting up this modification with pictures and post in the modifications section, for those interested. Thanks to everyone who joined in the thread.
Larry

[crazy steve]

I was with you until you started talking about the dual passages in the cross over. I just put a stock exhaust on and its just a tube between the two.

I think he's talking about the '78-79 standard exhaust here; these have two large 'boxes' sticking out of the muffler, joined by a tube in the middle. The specials (and maybe later standards?) just have a plain pipe. These boxes do have baffling inside them, so that may be what he's referring to.

'78E original owner

[crazy steve]

... HighTech posted pics while I was working on my post.... there you are...

'78E original owner

[Guy_b_g]

I used to ride a MotoGuzzi Centauro, which was a 1000cc 90 degree 4 valve V-twin with 50mm (dual intake) Webber Marrelli open loop fuel injection and dual exhaust.

The powertrain and suspension was designed by Dr. John Wittner (who also made the Superbike National Champion "Guzzis during the 80's).

A lot of thought went into both the intake and exhaust systems as well as the fuel injection mapping.

Dr John had a hell of a time with a "midrange hole" and tried everything from no crossover to various "H" and "X" type crossovers in the system, as well as different capacity air boxes and velocity stack lengths within the air boxes.

What he finally came up with was a crossover with a fairly large capacity tuned frequency chamber which worked well in the exhaust, as well as 5" plastic velocity stacks in the air box. This seems to me a very familiar solution, much like what the XS11 standard has (except the chamber in the "Guzzi" exhaust was a lot bigger and everyone hated it, thus it got the nickname "colostomy bag")

The bike made 80hp at the rear wheel stock.

Right away people started taking off the "colostomy bag" and the air box to gain performance and make the bike look better.

Except that this caused a huge hole in the midrange.

Then Mistral started making an "x" crossover to replace the "colostomy bag" and people started putting on the plastic velocity stacks from their air boxes, (or after market machined aluminum ones) and things got a bit better.

The final piece of the puzzle was when the "Dan Hodges" of the Guzzi world (Will Creedon) started developing after market chips for the ECU.

With one of his chips installed there was no longer a mid range hole, and in an afternoon of removing stock parts and bolting on after market ones at a cost of less than $1000, your 'Guzzi now made an honest 96 hp at the rear wheel, and ran well at all rpms.

The moral of this story is that the motorcycle companies have to make a lot of compromises in several interrelated areas for rideability as well as performance, cost, and noise. Given enough time and patience either as a group or individually almost every bike will gain performance with after market parts that are well designed, and carefully tuned to work together.

I think that if you have not done something to the bike that simply cannot be overcome, you can tune the bike to a somewhat higher performance level, as well as retain the rideability of the stock bike. In my view the most difficult part of tuning these bikes is getting the carbs tuned properly, since it is the most complex of all the variables, and anything performance oriented you do to the intake or exhaust will affect carb tuning.

[Guy_b_g]

A pic of the infamous 'Guzzi "colostomy bag"