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Best bang for your buck full exhaust systems for a 2004 400ex


Aiden R

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Hello, I am 15 years old and I recently bought a 2004 honda 400ex back in July, in terms of engine wise it is bone stock, I have put nerf bars and some new protaper handle bars and a graphics kit, I am looking to get a full exhausts system. I was looking for any suggestions that would give a good increase in power and sound/look really good. My budget is currently 400 to 500 dollars but will hopefully go up alittle after Christmas. I am also looking to get some info about what else I will have to do after getting a exhaust system, like what size jets would work best and anything else that I would need to do. I do not know everything mechanically wise, but I would say I know alittle more then average, thanks for your help.(I added a few photos if anyone wanted to see the bike)

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Nice quad, enjoy it and ride responsibly.

Just wanted to let you know that if you think bolting on an aftermarket exhaust is going to make your quad run stronger and faster, you would be wasting your money. To really get the most out of a new exhaust, you will need to spend time properly rejetting  for that exhaust, otherwise, you might actually lose HP just bolting the exhaust on.

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Ya, that's why I said that I also would want some jetting suggestions for the exhaust that anyone recommend, I have looked at a few videos on how to change the jets and I may try to do it my self but my friends dad is a very good mechanic and he works on his own atvs and dirtbikes so I may ask him for some help, but agian if you have any suggestions I would love to here them, and I was also thinking about getting a cdi rev box of some sort(I have heard that they give you alittle more rpm's and help with fuel to air mixture). Do you think one would be worth it on a 400ex? Thanks for the response.

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You might try doing a Google search for Honda EX 400 Exhaust 

I just did and there are some comparisons by different websites 

If you can find a good shootout or actual road test/dyno test it may have the jetting changes as well as the performance data 

I have used different websites in the past to get a better idea of what performance improvements that different exhaust and jetting changes would provide 

Then I could fine tune the jetting by reading the spark plug color you could probably have your friend help you with that 

Sometimes the manufacturers website offers recommended jetting for their exhaust system as a good starting point but that can vary depending on elevation and temperature 

Best wishes with your project 

I started out with a Mini Bike when I was 11 and it lead to a career as a mechanic 

Remember what other people call mistakes the mechanic calls experience 

Enjoy your project 

 

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31 minutes ago, NYoung4x4 said:

You might try doing a Google search for Honda EX 400 Exhaust 

I just did and there are some comparisons by different websites 

If you can find a good shootout or actual road test/dyno test it may have the jetting changes as well as the performance data 

I have used different websites in the past to get a better idea of what performance improvements that different exhaust and jetting changes would provide 

Then I could fine tune the jetting by reading the spark plug color you could probably have your friend help you with that 

Sometimes the manufacturers website offers recommended jetting for their exhaust system as a good starting point but that can vary depending on elevation and temperature 

Best wishes with your project 

I started out with a Mini Bike when I was 11 and it lead to a career as a mechanic 

Remember what other people call mistakes the mechanic calls experience 

Enjoy your project 

 

Thank you very much for the info and do you have any info on cdi rev boxes of any kind? I was thinking about getting one but I would like to know if they are worth it or not for a 400ex, thanks agian.

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And I am also wondering, should i get a full system exhaust? Or is it worth it on my bike, if heard that there is no point because of somthing about the size of the stock pipe, does the full system make more of a difference then a slip on?

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49 minutes ago, Aiden R said:

And I am also wondering, should i get a full system exhaust? Or is it worth it on my bike, if heard that there is no point because of somthing about the size of the stock pipe, does the full system make more of a difference then a slip on?

I have always gone with the full system as the manufacturer has designed the head pipe to work with the silencer as a matched system then with the correct jetting you will notice the most improvement in horsepower and throttle response 

Can't say about the rev box as I haven't used one 

I try to focus on midrange power and throttle response as it improves drivability it's more fun to be able to feather the throttle while riding than trying to keep the RPM's up on technical trails, but that's just my preference 

 

 

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Are you riding any sort of public trails? Here in Wisconsin, you're not allowed to be over like 80 decibels at idle, and like 92 at full rpms (don't quote me on the exact numbers). I had a 300ex that came with an aftermarket muffler and had no idea that they were illegal here, and my first ride out on the trail I ended up getting a ticket. $450 bucks just because I was making a little too much noise.

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5 minutes ago, yz j said:

Are you riding any sort of public trails? Here in Wisconsin, you're not allowed to be over like 80 decibels at idle, and like 92 at full rpms (don't quote me on the exact numbers). I had a 300ex that came with an aftermarket muffler and had no idea that they were illegal here, and my first ride out on the trail I ended up getting a ticket. $450 bucks just because I was making a little too much noise.

I'm in California and to be honest I have no idea, but I usually ride govt land in the hill and no cop car is gonna make it to wear I ride anyway so I am not looking for a "quiet" exhaust.

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8 minutes ago, NYoung4x4 said:

I have always gone with the full system as the manufacturer has designed the head pipe to work with the silencer as a matched system then with the correct jetting you will notice the most improvement in horsepower and throttle response 

Can't say about the rev box as I haven't used one 

I try to focus on midrange power and throttle response as it improves drivability it's more fun to be able to feather the throttle while riding than trying to keep the RPM's up on technical trails, but that's just my preference 

 

 

Ok thanks for the info, I have found an exhaust brand called Empire Industries exhausts that make really good looking and sounding pipes(a full system) and I am look for anyone who has heard of them and or has any info about them that I should know, thanks agian and here is a pictures of the top three designs I would get from them.

Screenshot_20211117-154237_Google.jpg

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3 hours ago, Aiden R said:

And I am also wondering, should i get a full system exhaust? Or is it worth it on my bike, if heard that there is no point because of somthing about the size of the stock pipe, does the full system make more of a difference then a slip on?

As a 15 year old here’s what you should do: scour craigslist / fb marketplace / ebay for a used aftermarket muffler, it could be anything as long as it’s a decent size (like not a super shorty streetbike muffler). An R6 muffler, a ninja muffler, a crf450, kx450, whatever. You can find something like a good condition FMF for $20-40, not kidding I’ve done it myself multiple times.

Now cut the pipe off the muffler, hold it up to your quad find where it fits and cut the muffler off the quad. Bring your new muffler and the midpipe from the quad to a local exhaust shop and have him weld them together, some will do it for free others might charge $25-50. Alternatively you could have an exhaust shop just make a custom mid pipe to connect the new muffler to the stock header and keep the stock muffler intact, that would probably run $100-150. Now just make a bracket out of a piece of sheetmetal (you can probably get a piece for free from whoever does the welding) to bolt from the mounting tabs on the frame to the mounting tabs on the muffler. Done. You now have a name brand (FMF or whatever muffler you source) exhaust for well under $100. Even if you have to buy an angle grinder to cut the pipes, and some vice grips to bend and hold the bracket, and a drill for the bracket you’ll come in around $200 and have a bunch of useful tools. 
 

Those empire exhausts use a generic chinese muffler you can find on ebay that’s worth maybe $10-20 (that’s why it bolts to the mid pipe instead of having the mid pipe welded to it, because it’s a cheap generic chinese muffler), probably a chinese-made header and mid pipe, and charge you $700. That’s a massive ripoff in my book. If you want to spend big money on tiny gains for a quad you might as well buy something legit, like FMF, and at least look and sound cool. 

Any exhaust will give you pretty much the same gains, you’ll never notice headers on a 400ex and probably would never be able to tell the difference between a Frankenstein exhaust I could weld up for $20 and a $1000 fmf full system. Don’t waste your money, especially at 15. You could put $700 in a mutual fund and when you’re 30 it will be worth more than a brand new dirt bike.


As far as jetting and a “rev box”: if you get an exhaust and higher flowing air filter start by going 1 size larger on the pilot and main, tune from there. More flow means you need more gas, can’t make more power without more fuel. The rev boxes are a total waste for a stock motor, you don’t need modified timing and you don’t need to remove the rev limiter. 

I would sell the bike and save for a raptor 660/700 waaaay before i even contemplated putting $700+ into a 400ex. 400s are great bikes but if you want power, sell it for 3.5k take that $800 mod budget, put in another couple hundred and get a raptor 660.

Or have fun modding the 400 on the cheap, that’s what I’d do. 

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10 minutes ago, OKDinosaur said:

As a 15 year old here’s what you should do: scour craigslist / fb marketplace / ebay for a used aftermarket muffler, it could be anything as long as it’s a decent size (like not a super shorty streetbike muffler). An R6 muffler, a ninja muffler, a crf450, kx450, whatever. You can find something like a good condition FMF for $20-40, not kidding I’ve done it myself multiple times.

Now cut the pipe off the muffler, hold it up to your quad find where it fits and cut the muffler off the quad. Bring your new muffler and the midpipe from the quad to a local exhaust shop and have him weld them together, some will do it for free others might charge $25-50. Alternatively you could have an exhaust shop just make a custom mid pipe to connect the new muffler to the stock header and keep the stock muffler intact, that would probably run $100-150. Now just make a bracket out of a piece of sheetmetal (you can probably get a piece for free from whoever does the welding) to bolt from the mounting tabs on the frame to the mounting tabs on the muffler. Done. You now have a name brand (FMF or whatever muffler you source) exhaust for well under $100. Even if you have to buy an angle grinder to cut the pipes, and some vice grips to bend and hold the bracket, and a drill for the bracket you’ll come in around $200 and have a bunch of useful tools. 
 

Those empire exhausts use a generic chinese muffler you can find on ebay that’s worth maybe $10-20 (that’s why it bolts to the mid pipe instead of having the mid pipe welded to it, because it’s a cheap generic chinese muffler), probably a chinese-made header and mid pipe, and charge you $700. That’s a massive ripoff in my book. If you want to spend big money on tiny gains for a quad you might as well buy something legit, like FMF, and at least look and sound cool. 

Any exhaust will give you pretty much the same gains, you’ll never notice headers on a 400ex and probably would never be able to tell the difference between a Frankenstein exhaust I could weld up for $20 and a $1000 fmf full system. Don’t waste your money, especially at 15. You could put $700 in a mutual fund and when you’re 30 it will be worth more than a brand new dirt bike.


As far as jetting and a “rev box”: if you get an exhaust and higher flowing air filter start by going 1 size larger on the pilot and main, tune from there. More flow means you need more gas, can’t make more power without more fuel. The rev boxes are a total waste for a stock motor, you don’t need modified timing and you don’t need to remove the rev limiter. 

I would sell the bike and save for a raptor 660/700 waaaay before i even contemplated putting $700+ into a 400ex. 400s are great bikes but if you want power, sell it for 3.5k take that $800 mod budget, put in another couple hundred and get a raptor 660.

Or have fun modding the 400 on the cheap, that’s what I’d do. 

I might try to do that, I am 15 so I obviously cant drive myself anywhere yet and my mom and dad are usually busy with work or my little brother so they wont be willing to drive me to get the exhaust or to go to a shop, maybe in the future. But as for the Empire Industries exhaust it isnt a Chinese exhaust, it is sold by it own chain of garages and the main one is on Phoenix Arizona, and I really love the customization you can do, Christmas is coming up so I hope that my aunts and uncles and grandparents will be generous this year, if so that I will probably get the Empire, I have been doing some research on them and they are actually a pretty good brand and are used alot for racing. But thanks for the info I wont be getting a rev box cause your right I just dont really need it. And I was also wondering what your option on cutting the front fenders smaller on the 400ex's? Thanks agian.

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12 minutes ago, Aiden R said:

I might try to do that, I am 15 so I obviously cant drive myself anywhere yet and my mom and dad are usually busy with work or my little brother so they wont be willing to drive me to get the exhaust or to go to a shop, maybe in the future. But as for the Empire Industries exhaust it isnt a Chinese exhaust, it is sold by it own chain of garages and the main one is on Phoenix Arizona, and I really love the customization you can do, Christmas is coming up so I hope that my aunts and uncles and grandparents will be generous this year, if so that I will probably get the Empire, I have been doing some research on them and they are actually a pretty good brand and are used alot for racing. But thanks for the info I wont be getting a rev box cause your right I just dont really need it. And I was also wondering what your option on cutting the front fenders smaller on the 400ex's? Thanks agian.

I'm not familiar with Empire Industries 

I would recommend going with a well known brand that has been involved with motor sports for a while as their research and development has been proven on the race track as well as in recreational use 

I personally like FMF, Pro Circuit and Yoshimura as I have used those brands with good results in the past 

It is your decision and I wish you success with whichever one you choose 

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10 minutes ago, Aiden R said:

I might try to do that, I am 15 so I obviously cant drive myself anywhere yet and my mom and dad are usually busy with work or my little brother so they wont be willing to drive me to get the exhaust or to go to a shop, maybe in the future. But as for the Empire Industries exhaust it isnt a Chinese exhaust, it is sold by it own chain of garages and the main one is on Phoenix Arizona, and I really love the customization you can do, Christmas is coming up so I hope that my aunts and uncles and grandparents will be generous this year, if so that I will probably get the Empire, I have been doing some research on them and they are actually a pretty good brand and are used alot for racing. But thanks for the info I wont be getting a rev box cause your right I just dont really need it. And I was also wondering what your option on cutting the front fenders smaller on the 400ex's? Thanks agian.

All I can say is it looks chinese to me, the end cap design is the same as the $30 pit bike exhausts on ebay which makes it look super cheap imo. Empire is definitely not well known, I’ve been around powersports for ~20 years now, rode sport quads somewhat seriously in my youth for a couple years before sport quads died off, rode track on streetbikes for a few years, and the entire time my main passion was dirt bikes. I’ve never once heard the name empire or seen a single one of their products - and I’m a gear head, I could name 15 motorcycle exhaust companies off the top of my head. 

For an out of the box ready to go solution I’d just recommend a slip on, something reputable like FMF pro circuit yoshimura etc. Half the price of a full system and you’ll never know the difference. An air filter and opening up the airbox will make way more difference than headers. 

Cut the fenders if you like the look I guess, it does hurt resale value a bit if that matters - makes it look like a dune quad or owned by a goon kid / street rider which indicates a hard life, plus it’s an irreversible free mod so intact fenders don’t turn anyone away but cut fenders might turn some away.

I live in the dirt not the sand, so I liked having fenders to keep some of the mud out of my face. You can only fit so many tear offs on your goggles in a muddy race, every bit helps. 

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14 minutes ago, OKDinosaur said:

All I can say is it looks chinese to me, the end cap design is the same as the $30 pit bike exhausts on ebay which makes it look super cheap imo. Empire is definitely not well known, I’ve been around powersports for ~20 years now, rode sport quads somewhat seriously in my youth for a couple years before sport quads died off, rode track on streetbikes for a few years, and the entire time my main passion was dirt bikes. I’ve never once heard the name empire or seen a single one of their products - and I’m a gear head, I could name 15 motorcycle exhaust companies off the top of my head. 

For an out of the box ready to go solution I’d just recommend a slip on, something reputable like FMF pro circuit yoshimura etc. Half the price of a full system and you’ll never know the difference. An air filter and opening up the airbox will make way more difference than headers. 

Cut the fenders if you like the look I guess, it does hurt resale value a bit if that matters - makes it look like a dune quad or owned by a goon kid / street rider which indicates a hard life, plus it’s an irreversible free mod so intact fenders don’t turn anyone away but cut fenders might turn some away.

I live in the dirt not the sand, so I liked having fenders to keep some of the mud out of my face. You can only fit so many tear offs on your goggles in a muddy race, every bit helps. 

I started looking at the company and when it was started and by who, this is what I found out, has anyone heard of these names in the article?(images attached)

Screenshot_20211117-201906_Chrome.jpg

Screenshot_20211117-201922_Chrome.jpg

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6 hours ago, Aiden R said:

I started looking at the company and when it was started and by who, this is what I found out, has anyone heard of these names in the article?(images attached)

Screenshot_20211117-201906_Chrome.jpg

Screenshot_20211117-201922_Chrome.jpg

Ok so they got a good write up online 

Have you ever seen any professional racers running their systems? 

It's your decision to make but again I prefer going with a company that has proven its products on the dyno and the race track 

Also a good air box and filter should be considered with the exhaust they will provide the most improvement and any changes to the air box/filter or exhaust will require rejetting 

Again it's your choice 

Best wishes for success 

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If you aren’t a pro racing “LEAVE IT QUIET” you’ll only draw attention to yourself that you don’t want. Bad attention ruins our chosen hobby. Seen but not heard is best. Tread lightly and don’t destroy someone’s land. 

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I looked at R/M. They have a bucket load of exhaust systems. You can look there and then do research on other sources that sell the same items for the best price. 90% of the time if its your money (cost) tells you what your going to buy. At 15 and your parents or whoever else is footing the bill, pick the highest performing product and give them the bill.  

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