Topic: 1974/1978 CB550 Exhaust Compatibility?

[dylboss]

Newbie here!   Just picked up a 1978 CB550 and am planning to turn her into a cafe.  Need to replace the exhaust and am having trouble finding a stock 1978 used one without breaking the piggy bank for a new one.  I did find a 1974 exhaust that is somewhat local to me (NH) but am unsure about the fitment.  Does anyone know if the '74 will work on the '78?

Thanks.

[bryanj]

If it's aftermarket yes but you will need to make mounts if its the standard 4 into 4 not without majour mods to kickstart, rear brake pedal and welding on the frame for mounts

[dylboss]

Thanks.  No, I'm talking about '74 2-1 OEM pipes to a '78.

[OldSchool_IsCool]

Thanks.  No, I'm talking about '74 2-1 OEM pipes to a '78.

If it's a 2-into-1, then it's not from a Honda CB550 of any year.  Do you mean a 4-into-2 (2 sets of 2-into-1)?  If so, then it's not OEM, it's after market.  CB550's rolled out of the factory with either 4-into-4 (the K series) or 4-into-1 (the F or Super Sport series).

If you are cafe'n the bike, you can pretty much use whatever you want, no need to keep to OEM parts.

[dylboss]

Thanks.  Maybe i'm confusing things here.  Basically I have someone with an OEM '74 exhaust setup that I want to put on my '98.  It's not aftermarket.  The reason I want to go OEM right now is because I think I have stock jets in the carbs, but someone along the line who had the bike before me put an aftermarket exhaust on it.  Runs awful.  Needs tune-up anyway, but I want to eliminate all possbilities out of the gate, plus the current exhaust is shot.

[TwoTired]

Boy are you confused. 
The 550 was only sold in two configurations; 4 into 4 exhaust (K models), and 4 into 1 exhaust (F models).
The 78 CB550 model was only available in the 4 into 4 - K model.

If you have a 78 CB550K, it will have PD carbs which were finely tuned to the stock 4 into 4 exhaust and the stock air induction setup including paper air filter.

Pre 77 - 4 into 4 exhausts were different (less back pressure) than those found on the 77 and 78 K models.  They can be adapted to the 77-78 K models, but you will have to fabricate hangers for them at the rear of the frame.  And, they require different settings for the PD carbs internally.

If you found 4 into 2 exhaust (any brand), they were never stock for any CB550, definitely aftermarket, and almost certainly expected carb tuning as found on the pre-PD carbs.

Still in question, is if you really have a 1978 Model (it will say on the headstock tag).  Or, given the presented confusion, it may be an earlier model titled in 1978 by a government agency, rather than a parts authority or maker for your bike.

Good luck!

[Bankerdanny]

The 4x2 might not have been stock, but it is common. A large number of the 500's and 550's I see on eBay and elsewhere have the 4x2 exhaust with flared muffler ends. I have to assume this was a common replacement system for these bikes available through dealers. I know that they are available new on eBay.

I would be surprised if they required rejetting.

[TwoTired]

The 78's were tuned "lean burn" to placate the EPA.
They also ran slightly hotter than previous years without the extra fuel earlier years had to help with cooling.  The higher heat helped the engine configuration to pass the exhaust sniff test need for importation.

Losing the extra back pressure of the stock exhaust, means it needs more fuel (in ratio) for the now more available oxygen in the cylinders.

The less restrictive exhaust change on this model will allow the engine to run, of course.  But not well, and at higher temps, particularly with today's sabotaged fuel.  These factors add to the requirement to change the carb jetting.

Don't be surprised with reduced performance and early valve jobs and valve guides seal replacement, if you fail to address the carb jetting.

Cheers,

[Duanob]

Not to get off topic too much but if the 74 oem exhaust is in good shape buy if the price is right. They are worth their weight in gold. Well maybe silver anyway. If they are cheap put them back up on ebay and make some cash towards a 77-78 set. I see them often on ebay.

[bryanj]

If you can find a DECENT set of 77/78 genuine Honda exhausts they are worth a fortune as they rust out badly and have been obsoleted for some years.

the 500/550 from 71 through 76 are still made by Honda and Dave Silver sells sets of 4 for about £450 (GBP)

[OldSchool_IsCool]

If you can find a DECENT set of 77/78 genuine Honda exhausts they are worth a fortune as they rust out badly and have been obsoleted for some years.

the 500/550 from 71 through 76 are still made by Honda and Dave Silver sells sets of 4 for about £450 (GBP)

I still have these hanging in my garage.  Guna get 'em in shape for the relay!!

http://forums.sohc4.net/index.php?topic=67830.0

[dylboss]

Thanks for all the great info.  I guess I have my work cut out for me.  If I was to just pony up and buy a BCR 4-2 exhaust, what kind of jets would I need to buy for this config?

[TwoTired]

Thanks for all the great info.  I guess I have my work cut out for me.  If I was to just pony up and buy a BCR 4-2 exhaust, what kind of jets would I need to buy for this config?

Oh, that's easy.  Just find or make a chart/graph that maps the back pressure provided by the stock exhaust in relation to the RPM range.
Then compare that to the same chart/graph that maps the back pressure provided by the BCR exhaust in relation to the the RPM range.

If they are the same, you don't have to make any change to jetting.

Otherwise, install the replacement exhaust and get an exhaust sniff fuel map from the folks who operate the Dyno machine.  This will tell you what parts of the carb need to changed to restore the proper A/F ratio to the engine.

Or, install the replacement exhaust, learn to read spark plug deposits for combustion conditions, find a test track to run the engine under power, and read the plugs for signs.  Then adjust and repeat testing until all throttle ranges produce acceptable spark plug deposit patterns.

Or, take wild guesses at changing jets and adjustments to the carbs, and as long as the engine still runs, declare victory and that it runs good enough.
(you can expect poor fuel economy with this approach.  But, you might get lucky!)

The chart below will help you address the parts of the carb that that need attention/scrutiny.  What could be easier?

(In review, I believe that the provider of the exhaust ought to accurately tell you what changes are needed to the bike in order to use the replacement part properly, this includes jetting changes for your specific application.  It was the manufacturer's responsibility to make the bike run properly off the showroom floor.  It is also the manufacturer's responsibility to make replacement exhausts operate properly for their customers.  Both, manufacturers make a profit on your trust in product.)

It is your choice to pay for the cost of engineering research on your own volition.  And, you may have no other choice in the matter, depending on the manufacturer you chose or the price you are willing to pay.  IMO

Cheers,

[dylboss]

This is great info!  Thanks a lot! 

I actually just came across a set of 1976 pipes OEM, but i think this falls in the category of 1974 as well.  Anyone know if this will fit the '78?  Would rather not spend all the dough for the BCR right now if I can avoid it.  If not, i guess i'll be playing the carb jetting game.

[bryanj]

The ONLY ones that fit a 77/78 are the 77/78 ones. All earlier  models from 500f in 71 to 550 K2 in 76 (excluding the 550F) are the same and need major mods to fit