How to make a reverse cone exhaust quieter?

12018 Views 30 Replies 9 Participants Last post by Farmer_John, Oct 3, 2020

pbergmans

Discussion Starter · Sep 22, 2020

Hi all...I recently installed a reverse cone exhaust on my 2017 Yamaha SR400. When I fired it up for the first time I immediately realized that it's too loud. I'm quite sure my neighbors are going to hate me for this mod. My question is, how can I make this exhaust more quiet? I've seen some videos of people adding baffles to their exhaust but in these examples the person had a (more or less) straight pipe and they were able to drill a hole in the pipe to secure the baffle. When I look at my reverse cone, I don't really understand how I can do that. I'd also like to add that I'm a newbie at making modifications and I don't have any fabrication skills. So, if you have a suggestion for me, it'd be best if I could buy something that's semi-easy to install. Here is an image of my exhaust...

Thanks in advance.

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TrialsRider

· #2 · Sep 22, 2020

That's a shorty pipe.
Not sure how to break this to you, but you bought the wrong exhaust system for street use. That one is perfect for the race track IF it passes the sound check.

Your bike came fitted with an oxygen sensor, does or did the bike originally have a catalytic converter? We have strict laws up here that make it illegal to tamper with the emission control equipment on a motor vehicle this new. & yes, an irate neighbour might help you discover the existence of those laws.

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TrialsRider

· #3 · Sep 22, 2020

Are those pop rivets just in front of the reverse cone or just reflections on the photo?
If they are pop rivets, drill them out and that will gain you access to what's inside there now.

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TrialsRider

· #5 · Sep 22, 2020 (Edited)

" I'll look into my state's laws requiring catalytic converters." It's a federal law and it won't state you require a cat, it will say you can't mess with your pollution and noise control equipment. It will also compel the original manufacturer to put a warranty on those parts that exceeds the warranty term on the rest of the motorcycle.

If the aftermarket exhaust you buy does not specifically say it meets the rules for street use it won't! If it says for track use only it means it's absolutely not street legal.

Woven fibreglass cloth has and can be used, but mufflers dampen sound by making the exhaust pulse reflect off things and change direction before exiting the hole, that is the baffle part. If you can't change the direction of that exhaust pulse before it reaches the opening, it's too late, we already heard you.

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TrialsRider

· #6 · Sep 22, 2020

Does anybody here buy a brand new car and immediately remove the exhaust system to fit it with loud pipes ?
Why do people think that is ok to do on a motorcycle.

Too many are living in the wrong era, the days when you would dump your oil changes down the storm drain in front of your house are gone people! We are suppose to be beyond that point and in this century the general public has been made fully aware of the problems it creates.

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TrialsRider

· #10 · Sep 22, 2020

pbergmans said:
@jcw - thanks for the useful information. Am I right in thinking that your comment "and mount with a set screw from the outside" is not easily possible since I have a cone? Or, do I disassemble my exhaust (e.g. remove rivets) and replace the core? Do baffles exist that have a different mounting mechanism other than an external screw? Or, is welding it in my only solution?

@TrialsRider - thanks for the information, I certainly learned more about exhaust from your few comments and, in a way, wished I had known this info prior to purchasing my shorty reverse cone. I guess I was just excited to get moving on my mods. But, with that said, what is one to do if they want to modify the exhaust on their motorcycle? After all, isn't that the reason why some of us have joined this forum? Heck, even the picture at the top of this page has three motorcycles with custom exhausts? Do the exhausts on these three bikes have catalytic converters.

Can anyone recommend a "cafe racer" style exhaust that meets emissions laws?

View attachment 103801

First off, those are really really old motorcycles, they never had pollution control equipment to remove.

and yes, there are a very few aftermarket companies that are making aftermarket performance exhaust systems for specific model motorcycles, and they have gone to the extreme effort of having those systems tested to meet with current environmental law. The purchase price will reflect that.

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TrialsRider

· #11 · Sep 22, 2020

A large percentage of the regulars on this site race their bikes, there are people on here that are into breaking land speed records, people that scratch build high quality frames or restore near priceless antique bikes, you can find people on here to help you make your bike into a track only bike real easy. Great place to ask a technical question about a weird bike.

Not too many here are into firestone whitewall tires and freshly stolen USD front forks grafted onto a bobber CB350, you might want to ask about those things somewhere else.

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TrialsRider

· #12 · Sep 22, 2020

By the way, how do you like the bike? Does it perform well?

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TrialsRider

· #16 · Sep 22, 2020

The pipe you have in hand is workable, I won't say it's street legal, but I bet with some rework you can make it awesome. Don't send it back take it apart imho. take pictures best you can of what you have to work with.

I think the SR is a really nice bike, always did. You chose wisely.

and hang the original on the garage wall once you get this one working right, those parts should go with the bike for the next owner. Your grand son or whatever

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TrialsRider

· #17 · Sep 22, 2020 (Edited)

You're going to need some expanded metal screen that won't rust, to go with that fibreglass cloth.
and it needs to take intense heat, but you don't need tons of it,
you need enough to make a cone, pretty darn close to the same size as the long cone, you need it to keep the glass in place.

... if you line that long cone with the sound absorbing material you will have something far less tinny for the reflecting pulse that you are going to be creating with the short reverse cone. In a perfect world :/ that pulse would arrive back at the exhaust valve at a magic calculated time, & the math required for that to happen makes my head hurt.

Have you ever watched the movie Worlds Fastest Indian
you should

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