Topic: '76 CB550F Swapping PO's Ugly Muffler

[magner]

This is my first bike, and I am learning a lot by wrenching on it, so any help for a beginner would be great! I am hoping to swap out this muffler that the PO had put on, and keep the current 4into1 exhaust tubing by cutting the upswept portion off so that it is more or less parallel to the ground (see red line in attachment). The exhaust pipe in that location is 2.25", but tapers down for the current muffler. My hope is to get a Cone Engineering Quiet-er Core, as I live in a dense family neighborhood and I'd like to keep from annoying people if possible, but also I hate the look of it and prefer a more classic aesthetic.

The PO told me it is tuned specifically for the current muffler to be run without a baffle, so I'm wondering what issues I will run into if I cut the exhaust pipe and slip on the 18" Cone Engineering Quiet-er core reverse cone muffler? As I am a beginner, and the bike is running well for now, I'd rather not get myself in over my head if its more complicated than it seems! Thanks guys.

[SOHCiro]

Hello magner!
I highly doubt a "perfect tune" was achieved by the PO with those foam pods, uniformly across all the cylinders within various speed range and wind conditions.

I know you may not like to go this path but personally I suggest that you spend the extra $$$ on a stock airbox.
I tried several types of pods, v stacks, combination of both, and finally decided to get a stock box with nicely oiled UNI.
My bike runs a pretty much open reverse cone with no baffle what so ever.
I always thought it ran great with pods, but OMG there really is no better set up than factory box for the street. Needless to say it will be healthier for the engine in the long run too, with longer travel of air from the atmosphere to the engine, providing better filtration from all the debris. I wish I had got my lazy ass on an eBay hunt for a good used airbox much earlier. It was the best $100 ever spent on my bike, with hondaman ignition being the second best.
You may already have, but look up Mark Paris aka Hondaman's articles on the airbox for a better idea of what's going on. I have his CB750 book and I treat it like a holy bible!

Anyways, I'd go for any decent reverse cone muffler, simply for the looks, since high-end mufflers really don't make a huge difference on a non-ported stock compression SOHC CB engines. Pods do not necessarily make our bikes "breathe better". They introduce unnecessary turbulence, lowering the efficiency of the intake.

With a cone, I don't think you will need to rejet it, since you're already running baffle-less.
With the stock box, you WILL need to down size on the jets, assuming the PO has put larger jets for the current pods/pipe set up. You'll notice better acceleration, idle, and cruising mpg with it though.

[robvangulik]

+1 to both of the above, and i would cut it just an inch or so further back, halfway in the bend, or your groundclearance in right corners will be quite restricted.

[magner]

Anyways, I'd go for any decent reverse cone muffler, simply for the looks, since high-end mufflers really don't make a huge difference on a non-ported stock compression SOHC CB engines. Pods do not necessarily make our bikes "breathe better". They introduce unnecessary turbulence, lowering the efficiency of the intake.

With a cone, I don't think you will need to rejet it, since you're already running baffle-less.
With the stock box, you WILL need to down size on the jets, assuming the PO has put larger jets for the current pods/pipe set up. You'll notice better acceleration, idle, and cruising mpg with it though.

Thanks for the detailed reply! The airbox was definitely something I was going to look into, but probably farther down the road. I was mainly looking at that "higher end" muffler just for its claims to be quieter and not necessarily higher performing, but are you thinking it won't make that much of a difference vs. a cheaper one?

[SOHCiro]

You're more than welcome, everybody helps each other on this forum!

I'd like to say that what makes "Higher end" mufflers expensive, are usually the types of materials used, geological location of the production/assembly, and the cost of marketing. Unless it's a big name racing brand, I doubt they do a lot of performance testing.
Sure, more expensive is better in terms of build quality, but as you know, not always better performing for our stock bikes.
It also depends on what kind of performance you are looking for.
You want quiet, so you're naturally looking at more low end torque and less top end.
High end mufflers almost always open up the exhaust, letting out more air specifically for top end, which may also slightly increase low end torque if tuned correctly. You will never gain power across all rev range simply by opening up exhaust. It has to be done with engine/carb work.
As for "really really quiet" mufflers, you may need to go down on jets, because you are restricting air flow so much so that the A/F ratio becomes way too rich resulting in poor performance, and polluting the atmosphere more.

So for your application, anything with stock or smaller outlet diameter and/or baffle should work.
Expensive or not, quieter mufflers simply restrict the flow of air or reflect/absorb sound waves within the muffler.
More expensive ones may have better exhaust tone to it though, some cheap ones can have "metallic" sound from what I've noticed, but it's also very subjective and you may like it.
You can always buy a cheap but good looking one, and glasspack it, or come up with a plate with lots of small holes which sits inside the muffler.

Despite what I wrote above regarding high/low end power, I hardly believe you will notice any difference in performance. Heck, I don't think it made any significant amount of difference in power when I ran straight pipe for a while after dropping my bike and the muffler mount failed. Running pods did though, haha. I also hear that 4-2-1 headers make the real difference in power.

If you wanna spend more money, get stainless steel or titanium for longevity as well as tiny weight reduction if you care...
You can look at places like CycleXchange or Carpy's if you want exhausts that was engineered with actual research, time, and money invested in making them specifically for SOHC CBs. They can be expensive, but will work great, although I'm not sure if they fit 550s, because there's more demand in 750s. You'd have to look into that.

Good luck! 

[BomberMann650]

Welcome fellow redditor!

[Stev-o]

Look in the Parts for Sale section, Frank has an airbox for sale for $45...

[magner]

Despite what I wrote above regarding high/low end power, I hardly believe you will notice any difference in performance. Heck, I don't think it made any significant amount of difference in power when I ran straight pipe for a while after dropping my bike and the muffler mount failed. Running pods did though, haha. I also hear that 4-2-1 headers make the real difference in power.

Apologies, I know its been dead for awhile, but I just realized I never got back to you about this amazingly detailed reply! I am trying to better understand the relationship that adding baffling/backpressure has with engine performance and noise level... I recently added the small little baffle that the PO included for the muffler to cut noise down, and while it reduced sound a bit, I notice that I have to add a lot more throttle to accelerate now than I did before, therefore running up in the revs and sounding just as obnoxious! While it does sound cool sometimes, when I am just cruising or commuting, myself and those I ride with find the overly 'race-y' and aggressive sound very annoying. Should I be looking into mods to my bike that will give me more low end torque to sound less annoying  ?? I feel like my bike sounds like I'm trying to race everyone around me when I'm just rolling through casual traffic before work...

[TwoTired]

The carburetors are stupid and won't automatically adjust mixtures for changes in exhaust back pressure or induction changes.  The fuel system is open loop, unlike modern engines with sensors and computer mixture adjustment.

You can't compare performance with a simple muffler change, unless you do a dyno run or at least check the mixtures at various throttle settings.

How can you be sure the mixtures are now different and your new throttle position isn't partially compensating for that mixture change?

Normally, back pressure reduces maximum cylinder scavenging (RPM dependent), leaving part of the old gases to mix with the new fresh charge.  Back in the 70s/80s before computer control domination, such things allowed the re-burn of some old gasses with less of a new charge for better emissions and improved fuel economy.

Point is, change exhaust system, change carb metering.

Cheers,

[BomberMann650]

Backpressure matters more for two stroke motors more than it does to a 4cycle engine.

What does matter is size, length, and positioning of the collectors.  As it relates to pulse frequency and intended operational speeds.  With this knowledge, I often muse that the motorcycles exhaust is an instrument to perform the aboriginal songs of our peoples.  I digress

4 strokes don't rely much at all on scavenging their waste exhaust gases.  Differing cams create more or less valve overlap, generating a negative pressure gap in the system.  Thats something which is to be calculated when deciding on exhaust configuration and intent of purpose.

Theres the magic word.  Intent.

An oversized large bore set of short straight drag pipes is not intended for quietly putting around urban centers.  They're hardly any good on a road corse as well.  They are good for wide open high rpm modified straight line racing.  And just enough of it to cause minimal hearing damage.

On the other end of the spectrum.  Long and respectably proportioned pipes that exit well behind the rear wheel, and under the saddlebags - those are not intended for ultra high rpm competition grand prix racing.  They are good for cruising long distances at a sustainable low to mid range rpm.  Which is why thats a standard among touring class bikes.

Our bikes, these brilliant little 8 valve 4cylinder creations.  They fall in the middle of what an engine needs from its exhaust.  In stock form, they're adequate.  Effective and predictable, and many here will appropriately scorn those who modified these machines without a noteworthy intent of purpose.  Or produce a hasty and haggard result using very little calculation.  Like your poor exhaust.

At this point, it'd be wise to disregard everything the previous owner told you - study up on the enginerding of a performance engine - and take some of the advice and direction offered here.

You don't need a stock airbox.  Does it make a difference?  Yes.  Can a bike be made to run without it?  Yes.  Will twotired help you don't have a stock airbox?  ...maybe.

Its really #$%*ing hard to tune a carbureted bike over the internet. 

Especially a modified one.

That said....an 18" reverse cone muffer will work fine with your existing header and mid pipe.  You're already in the ballpark where most of the meaningful maths are done, and of the available options, you chose well.

[magner]

Thanks that's a lot of great information! Some of it over my head for sure but I get what you're saying for the most part! Really appreciate your help with this, and it sounds like the cone quiet core is the way to go! My last dumb question is: where do I take a diameter measurement in order to know which size to order from Cone? Do I just measure the OD of my current pipe that I want it to slip over (I guess that being the ID of the muffler)? Ie: if my pipe is 2.25" OD, I just get the 2.25" cone?

[BomberMann650]

It needs to slip over.  So 2.3x-ish i.d. for pipe inlet.

A vernier caliper is your friend at times like these.