Stock exhaust upgrade!

[casey_lamm]

Title says it all. I don't know much about the bikes as im just coming back into this and just got my 400ex.

Its a 07.

So it has a factory exhaust!

My 1st ? is what DB level is on the factory exhaust.

2nd is will exhaust increase the hp of this machine?

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If it requires welding, I dont think I will be able to put this one myself. So what do you think I should do. I could pay someone to put it on, but if it something I can do for myself, I will.



So slip on vs full system pros and cons.


I want more horsepower and louder...but not insanely loud, just want it to sound like a race bike.


Thanks for your advice.

When you post info to help me assume I know nothing...cause thats probably close to the truth. I am trying to do some homework b4 making my decision.

[TYayo420]

a full system is much better, more free flowing. certain pipes add more HP and top speed, and low end torque. You dont not have to weld a pipe on just unbolt old one bolt in new one, but you have to re jet the carb to whatever pipe you get.

[casey_lamm]

Ok, well that doesnt sound too bad, however can you explain what "jetting" is and how it would be done, tools required, etc...

Is it something I can do? Or would you recommend paying a shop to do it.



Originally posted by TYayo420
a full system is much better, more free flowing. certain pipes add more HP and top speed, and low end torque. You dont not have to weld a pipe on just unbolt old one bolt in new one, but you have to re jet the carb to whatever pipe you get.

[casey_lamm]

still need some advice on the above ?

but also im thinking the hmf slipon is within budget. Does it still need rejetting? And also need to know what rejetting is :)

Will I get some faster pickup with the slipon? Please let me know if I chose the HMF slipon what I can expect...





Originally posted by casey_lamm
Ok, well that doesnt sound too bad, however can you explain what "jetting" is and how it would be done, tools required, etc...

Is it something I can do? Or would you recommend paying a shop to do it.

[flauge]

Hmf's are good pipes.. A lot of people say they are good for bottom end. The carbureator does need to be rejetted tho but thats not too hard;)

[flauge]

http://www.exriders.com/vbb/showthread.php?s=&threadid=221872

This might help explainn a lil about the jetting.;)

[raptor88]

i just bought a HMF slip on for my wifes new bike and it came with a 165 main jet and it actually worked perfect for my bike. but jetting isnt to hard theres a bolt on the bottom of the carb that you take off and the main jet is right up inside and its a 6mm and you just take it out and screw your new one in. pretty simple PM me if you have any questions

[GPracer2500]

Full vs. slip-on for mostly stock 400EX's has been discussed here before. My thoughts on this never seem especially popular, but anyway.....

A full system is not necessarily "much better" on a mostly stock 400EX. Some full systems might even perform worse over-all than a slip-on for a mostly stock 400EX. The evidence I've seen shows the stock headpipes perform well when mated to a quality slip-on. And even for full systems that might perform better than a good slip-on (again, on a mostly stock 400EX), the additional performance isn't likely to correspond well with the additional cost. In otherwords, if performance per dollar is important--->400EX slip-ons are tough to beat. I'd much rather have a slip-on and use the savings to have the carb tuned on a dyno. Or buy an appropriate camshaft to replace the dreadfully mild stocker.

Any decent slip-on will perform significantly better than the stock silencer. Unless you plan on modding the engine further (a larger bore for example), my suggestion is to stay with a slip-on and using the money saved for other things. Although, if the nice looks of a full system are a priority, that could be a reason to replace the headers (which can be a perfectly valid reason--shiny headpipes look nice!).

When it comes to headpipes (and carbs and cams and other things), bigger does not always mean better. Sometimes it does; sometimes it doesn't. Finding the best performance is about matching go-fast parts to the needs of the engine, NOT just bolting up the every aftermarket part available because it exists. I've personally seen aftermarket cams cost power and I've seen aftermaket headers rob torque because the parts weren't properly matched to the engine's state of tune.

$0.02

[casey_lamm]

so is the jet that comes with the hmf slipon likely to be the right one?


Originally posted by GPracer2500
Full vs. slip-on for mostly stock 400EX's has been discussed here before. My thoughts on this never seem especially popular, but anyway.....

A full system is not necessarily "much better" on a mostly stock 400EX. Some full systems might even perform worse over-all than a slip-on for a mostly stock 400EX. The evidence I've seen shows the stock headpipes perform well when mated to a quality slip-on. And even for full systems that might perform better than a good slip-on (again, on a mostly stock 400EX), the additional performance isn't likely to correspond well with the additional cost. In otherwords, if performance per dollar is important--->400EX slip-ons are tough to beat. I'd much rather have a slip-on and use the savings to have the carb tuned on a dyno. Or buy an appropriate camshaft to replace the dreadfully mild stocker.

Any decent slip-on will perform significantly better than the stock silencer. Unless you plan on modding the engine further (a larger bore for example), my suggestion is to stay with a slip-on and using the money saved for other things. Although, if the nice looks of a full system are a priority, that could be a reason to replace the headers (which can be a perfectly valid reason--shiny headpipes look nice!).

When it comes to headpipes (and carbs and cams and other things), bigger does not always mean better. Sometimes it does; sometimes it doesn't. Finding the best performance is about matching go-fast parts to the needs of the engine, NOT just bolting up the every aftermarket part available because it exists. I've personally seen aftermarket cams cost power and I've seen aftermaket headers rob torque because the parts weren't properly matched to the engine's state of tune.

$0.02

go here... jets r us (http://www.jetsrus.com/main_page.htm) and then click on the link for the faq on jets and jetting...that should help you understand that aspect a lot more

[2004exrider]

The jet HMF sends should be the right one for you but if its just a little rich you can always go to your local dealer and get individual ones until you find the right one. Most dealers should let you return the ones you dont need.

Jimmy

[GPracer2500]

Originally posted by casey_lamm
so is the jet that comes with the hmf slipon likely to be the right one?

I'm not sure I'd say likely. There are tons of factors that determine which carburetor jets are the right size. In my experience most manufactures that offer jets or "jet kits" recommend sizes that are usually too rich for most situations. Running too rich will cost power but it isn't going to permenantly damage anything. Running too lean for too long could damage an engine.

My advice is to get several sizes of main jet. 3 is a start; 5 would be better. When it comes to jetting it helps to understand that it is a process. There are too many factors that are specific to YOU and YOUR ATV for there to be a "bolt on solution" to jetting. The jetting process doesn't have to be too complicated or terribly time consuming. But setting aside a couple hours to experiment with different sizes is well worth it IMO. Not only will you get the chance to choose the best size jet (among the ones you have) but you'll learn alot about what being rich and lean is all about. Tuning a carb to get its best performance is a skill best learned through experience. You can read a lot about it (which is good) but for example, knowing how rich sounds differently from lean is hard to know without experiencing it. Once you're armed with some basic knowledge about how your carb works (specifically: 1) what does rich and lean mean? 2) what factors create rich and lean? 3) which throttle openings correspond to which jets?) go out and experiment.

Changing the main jet on a 400EX carb takes about 2 minutes (with practice). If it's taking you much more than 5 minutes than you're not using the right technique or you don't have the right tools. Changing the other two jetting circuits takes a bit more time--but there are tricks for figuring out if you need to go richer/leaner that helps cut down on the number of times those circuits need to be messed with.

If none of that has any appeal and you just want it to be right without having to mess with it---->Then you can either 1) find someone with experience and ask them to help. 2) Pay someone (find an ATV tuning shop! Most dealers are terrible at jetting in my experience). Or 3) take someones advice on what's likely to be close to the right size and just run that. Among those, #1 would be the best option. #2 can be good but your trusting the shop to know what they're doing and take the time to do it right. It's easy for them to take shorcuts since you wouldn't know the difference. #3 leaves you wondering if you're leaving performance on the table and you'll learn nothing about your machine.

[casey_lamm]

got it, thanks for that.

I have experience with lean and rich from aircraft engines...so I have an idea what to look for.


Ok here is what I decided on.

Dynojet Stage 1 kit with K&N air filter
HMF slip on exhaust


Thats it for now...


Were to buys these guys...

Any recommended place that has all this stuff in stock thats reasonable?


Originally posted by GPracer2500
I'm not sure I'd say likely. There are tons of factors that determine which carburetor jets are the right size. In my experience most manufactures that offer jets or "jet kits" recommend sizes that are usually too rich for most situations. Running too rich will cost power but it isn't going to permenantly damage anything. Running too lean for too long could damage an engine.

My advice is to get several sizes of main jet. 3 is a start; 5 would be better. When it comes to jetting it helps to understand that it is a process. There are too many factors that are specific to YOU and YOUR ATV for there to be a "bolt on solution" to jetting. The jetting process doesn't have to be too complicated or terribly time consuming. But setting aside a couple hours to experiment with different sizes is well worth it IMO. Not only will you get the chance to choose the best size jet (among the ones you have) but you'll learn alot about what being rich and lean is all about. Tuning a carb to get its best performance is a skill best learned through experience. You can read a lot about it (which is good) but for example, knowing how rich sounds differently from lean is hard to know without experiencing it. Once you're armed with some basic knowledge about how your carb works (specifically: 1) what does rich and lean mean? 2) what factors create rich and lean? 3) which throttle openings correspond to which jets?) go out and experiment.

Changing the main jet on a 400EX carb takes about 2 minutes (with practice). If it's taking you much more than 5 minutes than you're not using the right technique or you don't have the right tools. Changing the other two jetting circuits takes a bit more time--but there are tricks for figuring out if you need to go richer/leaner that helps cut down on the number of times those circuits need to be messed with.

If none of that has any appeal and you just want it to be right without having to mess with it---->Then you can either 1) find someone with experience and ask them to help. 2) Pay someone (find an ATV tuning shop! Most dealers are terrible at jetting in my experience). Or 3) take someones advice on what's likely to be close to the right size and just run that. Among those, #1 would be the best option. #2 can be good but your trusting the shop to know what they're doing and take the time to do it right. It's easy for them to take shorcuts since you wouldn't know the difference. #3 leaves you wondering if you're leaving performance on the table and you'll learn nothing about your machine.

[casey_lamm]

ordered!

Again my 1st mods are:

K&N quad power kit (filter, jet kit, etc...)
New slip on exhaust.


Cant wait to try these guys.
Originally posted by casey_lamm
got it, thanks for that.

I have experience with lean and rich from aircraft engines...so I have an idea what to look for.


Ok here is what I decided on.

Dynojet Stage 1 kit with K&N air filter
HMF slip on exhaust


Thats it for now...


Were to buys these guys...

Any recommended place that has all this stuff in stock thats reasonable?

[GPracer2500]

Originally posted by casey_lamm
....I have experience with lean and rich from aircraft engines...

Nice. I've got 190+ hours myself in 152s/172s. :)

[casey_lamm]

wow, very nice. I haven't been able to afford instructions. I had a friend instructor and we were planning on doing it this summer, but I took a different job and move out of that state. I wish I could get up. I tune alot of remote control airplane engines, but they are 2 stroke, at least mine...so they aren't bad at all.

4 strokes are touchy so I never owned one...

As for aircraft engines, I didn't mean to give you that impression. im big into aviation, but I wouldn't touch any engines. I watched friends do it, I stick with the models where human life isn't at risk...well at least as much :)



Originally posted by GPracer2500
Nice. I've got 190+ hours myself in 152s/172s. :)

[GPracer2500]

Gotcha. It's all good... :cool: