Hi,

I really want to rebuild my 03 400ex top end, (and up some hp's) and I was wondering what kit I should use if I still wanted to use pump gas.(I know it has to be the highest quality) I've heard bad things about the 440 kit, so I'm not sure what to do. How does this look? 426 cc 11:1 Big Bore Kit Honda TRX 400EX TRX400EX XR400:eBay Motors (item 270371507998 end time Aug-06-09 16:14:32 PDT)

Please give me any opinions or tips, or even links to the best kit. Thanks

 

The 440's blow head gaskets and overheat. The 426 can be tuned faster than a 440. You should be good running regular gas with 11:1 compression. If you have the cash, go for it.

 

Thanks. Regular gas as in REGULAR, or like high octane?

 

You could safely run anything from regular to premium. Any higher compression ratio, say like 13:1, you would need to run strictly 100 plus octane race gas.

 

I ran my 440ex hard as f' for atleast 2.5yrs with just regular oil changes. Never head a blown anything, never had a reliability problem period. I just used the basic IMS Kit with stage 2 cam and titanium valve springs. It was fast, probably 48-52hp. definately a banshee beater up until the banshee hit 6th gear on the flats ofcourse but hill shooting was it's specialty. gear down with 10 paddle haulers ftw

 

ok thanks for the info.

 

If you want longevity, go 416. If you want a timebomb, go 440. If you want a compromise, go 426.

If you need a rebuild you need a rebuild.....but to hop up an old school EX makes no sense in this day and age when there are so many higher performance machines out there!

 

426 would be my pick they can be tuned in real well and still be pretty reliable, ive seen a few of those that flat out hauled a$$, the 440s "can" also be good but they are prone to head gasket probs and overheating if not done right, some people have 440s that are just fine with no problems its just that they are known to run into problems sometimes with 440s.

 

I agree with recon. Do the 416. If it wears down go 426. The differences between 416 and 426 is so little that it's not worth it.

 

Are the 440s still unreliable if you go with a whole new aftermarket cylinder?