Topic: Honda CB750 HM341 exhaust

[kyle750]

Thanks HondaMan.  Very eye opening to learn that Honda went from an exhaust with no welded internal baffles (only a baffle tube in the end) on the earliest CB750s (Sandcast and K0) and then to 2 welded internal baffle plates in the chamber, then to 3, and Honda kept increasing the baffle plates

I will be checking both my existing and newly arrived HM341 pipes by identifying the rows of spot welds (can easily be seen on the inside of the exhaust)  to try to determine the number of internal baffles.

Based on this new-to-me information is it  possible  that high quality reproductions like those made by Yamiya are actually better (many different ways to define better) than Original HM341 Honda pipes?

Late Edit: A quick review of the later Honda production replacement HM341 pipes with extra stamped disclaimer "paragraph pipes" currently for sale on Ebay and you can see many rows of spot welding for the large number of baffle plates.

[kyle750]

Spot welds are easy to see on the inside of the pipes but hard to photograph.  I put together a quick diagram of the spot welds on the newly arrived HM341  pipes.  All 4 pipes follow a similar pattern.  I am guessing that the 6 spot welds around the mounting bracket are not related to internal baffles. I don't know how to interpret this information or how it can be used to determine the internal baffles used on this exhaust system??

[kyle750]

A quick photo of the 2 right side exhaust pipes and spot welds

[PeWe]

Yamiya has sold the early 4-4 with less restrictions.
Called Lotus Root.
Less welds but cost much more.
Deeper tone.

[kyle750]

Yamiya Lotus Root Exhaust and photo of the inward side of the pipes toward the frame. Definitely can see that there is less spot welding therefore less internal baffling and less restrictions

https://yamiya750.com/en/products/m065s-1

[PeWe]

The welded parts inside can be more seen as reinforcements than restrictors?
Here a rear view.
I can take more photos another day. The Lotus Root Pipes are not used today.

[kyle750]

The Yamiya Lotus Root look like fantastic build quality. Thanks for the photo.

Another photo of the newly arrived HM341 pipes.  The inward side of the exhausts had considerable oxidation but polished up nicely

[Stev-o]

Based on this new-to-me information is it  possible  that high quality reproductions like those made by Yamiya are actually better (many different ways to define better) than Original HM341 Honda pipes?

Would not surprise me as the manufacturing technology has come a long way in the last 50 yrs.

BTW - Honda did not make all of the exhausts for their bikes. For instance, the original 4 into 1 exhaust on my 550F was made by Sankei, one of the "sexiest" pipes out there! [IMO]

[MauiK3]

Those and the one on the 400f are beautiful. These days, exhaust has become an exercise in hiding it all, they don't really add much to most new bikes appearance.

[PeWe]

Modern bikes have huge silencers to fulfill Euro 5/6  regulations.
Bikes with full fairings have hidden ugly pipes with a slip-on in the end.

The older style fully visible exhaust system can be a nice design detail.

I like to cruise around in legal speed without a screaming loud exhaust system.
But it must be louder when twisting the throttle!

[kyle750]

I'm familiar with the high quality of Yamiya CB750 pipes as I bought a #2 No Numbers pipe to replace my rusted out #2

Unfortunately like with any restoration once you replace one part with a shiny new part then the other parts really begin to look like crap. It quickly becomes a vicious cycle

[HondaMan]

BTW - Honda did not make all of the exhausts for their bikes. For instance, the original 4 into 1 exhaust on my 550F was made by Sankei, one of the "sexiest" pipes out there! [IMO]

Boy, if THAT ain't the truth!
I put a pair of those (2 into 1) on one of the 750s I rebuilt from a rusty mess, and they REALLY made that bike pop.
When the owner came back with his daughter to pick it up, they walked in and one of them (can't remember which) said loudly, "WOW, You've made Baby beautiful again!". Turns out, the bike had a name...

[kyle750]

All of the newly arrived pipes have the standard stamping on the outside top near the seam with  HMCB750 HM341.   On the inward side all of the pipes have a stamp with a different Japanese Kanji Character on each pipe with the identical  number 6.  I don't know what this 2 digit code is for but guessing it might be a manufacturing date??

[HondaMan]

The crossover pipe's welds on that one are much cleaner and more even than on most of the ones I have. Looks like nice pipes from here!

[MauiK3]

I wonder about the effect of the crossover, does it actually add anything to the breathing?

[kyle750]

What is a crossover?

[kyle750]

What is a crossover?

Google to the rescue:

A crossover (or crossover pipe) on a Honda CB750K 4-into-4 exhaust system is a small connecting tube that links two separate exhaust pipes together, typically joining cylinders 1 and 2 on the left side and 3 and 4 on the right.

Why Crossovers are Used:

In exhaust theory, a crossover serves several functional purposes:
 
Pressure Balancing: It allows exhaust gas pressure to equalize between the joined pipes, which can smooth out engine pulses.

Exhaust Scavenging: By connecting the pipes, the high-velocity pulse from one cylinder can create a vacuum (suction) that helps "pull" exhaust gases out of the neighboring cylinder, improving overall engine efficiency.

Performance & Sound: Properly designed crossovers can boost low-to-mid-range torque and refine the exhaust note, often making it sound slightly more "mellow" or less "raspy" than four completely independent straight pipes.

I did not know any of this    Which begs the question:

My old crossover collars are still functioning but the internal rubber tubes are hard and compressed.  Should I get a set of replacement rubber connecting tubes.  Sold by Yamiya for 2500 yen for a set of 2 $15 USD.  What is the inner red layer - extra strength additional sealing??

https://yamiya750.com/en/products/m105

[PeWe]

I gave up fiddling with stock rubbers with clamps during pipes assembly. PITA.

I made my own with what I found in my garage. 1/2" oil/hot water hose + nylon zip ties.
To be added afterwards.

I cut a piece from the hose in correct lenght. Easy to trim with a sharp cutter.

I opened it lenghtwise and made it to fit as one half. The pipes  welds divide it in 2.

Cut another one for the other half.
1/2" hose will not reach around small pipes.
Fastened with one or 2 nylon zip ties.

4 cut hoses needed.
See photo of my dirty K2 with Yamiya no number pipes.
When taking pipes apart, save the hose halves. Add when pipes are back, use a new zip tie.

[kyle750]

Installing the heat shields   Decided to go with the chrome vs the early dull finish.