Topic: Custom Exhaust

[Ellz10]

Bike is a 1977 CB750 K.

So I measured my stock exhaust tubes, well not stock - the crappy 4 into 1's that came with the bike when I bought it, and the diameter reads 1.5"

Is that the stock diameter for these bikes?

I'm going to try my hand at fabricating my own stainless exhaust, use the stock flanges and I'm curious to know if I'm able to bump up to 2"/2.5" diameter pipes?

[Tracksnblades1]

Stock 4/2/1 double walled 750F’s primary measure 1.500 inch or slightly smaller I’ll try to measure the 77/78 tomorrow.

My 76f has a Yosimura 4/1 from 1979 which is a single wall and has larger primaries. I’ll try to measure it for a comparison for you. The yoshi has a mechanical baffle.  My buddy used to have a 75k with a RC sidewinder. He used a Pringals potato chip can for a baffle for around town riding. It would self extract at 8500…😁

Actual measurements of the 77&,78,CB750F 4/2/1 primaries measure,1.373 inch OD. Both exhaust are bolted up so no inside primary ID of the dual wall pipe.

Yosimura primary OD measured 1.508. Also so bolted up so no ID measurements of the light weight single wall pipe. I’ve asked here before for some old RC pipe measurements but don’t remember any over 1.5  plus  some chrome plating.

Maybe someone on here can measure some cb900-1100 exhaust primaries for you for your 2 - 2.5 od performance inferences. I think you’ll find the 1100 will still wear the 1.5 inch primaries. My son had the new/old 2014 CB1100 its factory exhaust primaries measured around 1.450. His new Yosimura (black) measure 1.50 plus some black paint or ceramic coat.  He put a programmer on it to get it to run good. Factory wouldn’t allow full power until 3rd gear and then just for a few seconds until the top speed limiter shut it back off. Fun bike with a programmer..🤪

[Kelly E]

The CB 900F has 1.5" OD primaries. I can measure the ID of the inner tubes later today since I have one cut apart. The system on the 83' CB 1100F looks exactly the same.

[Tim2005]

I saw these on a bike last year, you can probably work out their diameter by measuring your flanges, they look about the maximum you could go.

I'm not sure what the optimum size is for ideal gas flow, no doubt it's possible to be too big and not have
 enough back pressure etc., but these looked pretty huge and made a bit too much of a statement I thought.

[Kelly E]

The ID of the inner tube is 1 3/16"

[Ellz10]

Looks like I'm going to have to go with the stock 1.5" at the ports. The widest I could insert there is 1.75", but I wouldn't know how to go about fabricating the flare at the end, nor installing the collars and gaskets.

[Ellz10]

I'm not sure how to word this, but I'm curious if anyone can tell me if there's other designs/ways to set up, the ends of the exhaust that connect into the exhaust ports of the motor.

For example, my '77 750 has the flared lip and is held in by the collars, gasket and then flange cover.

Is there another way to set this up, specifically since I'm going to fabricate my own exhaust.