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So I’ve got a 2000 Honda 400ex absolutely love it!! I’ve had it for about a month, I ride with bruteforce 750’s, outlander 850’s and 1000 sxs’s and I was thinking of getting a trx450r carb and a full hmf exhaust. And probably doing the air box mod too, how much power would this give my 400? Just a little different or a big difference? Cuz if it’s not much of a different I’ll just stick with my dg slip on..... thanks!

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In terms of percentage increase not much. 450 carb could make it a little snappier but its probably not worth the expense. HMF slip on is not any better than DG, however changing the header does help. It'll run a tad harder. What airbox mod do you mean? Most folks chunk the lid and that's stupid for anything but race. the last one I had we blocked off the intake with a krylon can and poked holes in the lid. it could still breathe but got cleaner air under the seat. No increase, just preference. 

Also, any changes in intake have to be reflected in fuel increase. Larger main jet is necessary for more air flow. 

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On 6/17/2020 at 11:40 PM, MarkinAR said:

In terms of percentage increase not much. 450 carb could make it a little snappier but its probably not worth the expense. HMF slip on is not any better than DG, however changing the header does help. It'll run a tad harder. What airbox mod do you mean? Most folks chunk the lid and that's stupid for anything but race. the last one I had we blocked off the intake with a krylon can and poked holes in the lid. it could still breathe but got cleaner air under the seat. No increase, just preference. 

Also, any changes in intake have to be reflected in fuel increase. Larger main jet is necessary for more air flow. 

I am definitely going to put a aftermarket head on the wheeer, I am probably going to just keep the air box as is. And thanks for your help! If I didn’t see your reply I probably would have went out and bought a $300 450 carb and been disappointed 😂

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