How to Make a 400ex Faster.... - ATV Forum - All Terrain Vehicle discussion for Honda, Yamaha and more ATVs
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post #1 of 2 (permalink) Old 01-29-2010, 02:28 PM Thread Starter
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Location: Escondido, Ca.
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Arrow How to Make a 400ex Faster....

If you own a 400ex, you know it's power is not up to par with the new 450's. This can be changed by following these few simple steps.

Step 1:

First, you need a new piston and camshaft. Hotcams make good camshafts for the Honda 400ex. When choosing the piston be careful not to get to high of a compression or you will need to use race fuel. This will give you a huge power increase but it is not cheap or very practical if you're not racing. A good compression to bump your 400ex up to is 10:1.

Step 2:

You will then need to make your 400ex breath better. You can do this by getting an after market exhaust and an air filter. There is a very large selection of after market exhausts. From my experience you can't go wrong with White Bros. K&n makes very good filters. I would recommend a full exhaust system and that you remove your air box lid for all the possible air flow.

Step 3:

A new carburator can be very expensive(EBAY). But it's the one thing that will send your 400ex's power and speed over the top. Edlebrock makes very good carbs. Make sure you have some good back tires because your 400ex is going to rip. You won't have any trouble beating 450's and raptor 700's in drag races anymore.
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post #2 of 2 (permalink) Old 01-29-2010, 06:23 PM Thread Starter
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wisco 10:1 piston (IF YOU GO 11;1 YOU MUST USE RACE GAS WITH NO EXCEPTION). bored .80 over (416) your hot cam stage 2 would be fine. i would prefer a stage 1, it has a better mid range. the stage 2 has a better top. the cdi box i would go with a tc box
Never build one with a 440 kit(Not reliable)....the best(most reliable) 400EX engine ever built was a 416.
-One other thing i would do is cut the flywheel, this is a must on any high performance 400EX. tc can do this also. it runs around $100 + shipping.
-Edelbrock is a good carb. but it is very expensive. For reliability that is what i would go with... THE high maintenance carb. but the best carb. is a lectron, get one thru tc noted. Remember this carb. IS high maintenance and difficult to install proper. The other option i have not tested myself is the stock carb. off the 04' - 05' 450r honda, you will have to do your home work if you go this option....
TC-contact him at 814-723-3514
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