The Honda 400EX is less responsive to engine mods due to its valve train limitations and antiquated design. The old-style rocker arms hinder the engine's performance potential. You must also consider that the TRX400EX has an air-cooled engine. The Suzuki and Arctic Cat are liquid-cooled. You can only push an air-cooled engine so far before heating becomes an issue. I've found that the Z400 engine comes with a pretty restrictive exhaust system, and a healthy boost in power can be had by installing an aftermarket pipe. Its dual overhead cams also allow for more power potential.
Should you buy a used 400cc sport quad and save some money? It makes sense because these quads haven't changed much since they were introduced. They're all good-your choice really comes down to which manufacturer has the best dealership in your area. If you live in a rural area and your service options are limited, this becomes even more important.
With the 400EX, Z400 and DVX 400, there comes a point when it would be cheaper and easier just to upgrade to a 450cc machine instead of sinking more money into a 400's dated engine and suspension. For example, if you have grandiose ideas of saving a few thousand by buying a used 400EX, then putting the money you saved into modifications and expecting to whip up on your buddy's TRX450R, think again. Remember the engine builder's motto: "There is no replacement for displacement."
If you are sport-performance-oriented, I'd really recommend shying away from the Raptor 350. Although it's a great little quad the way it is for a cruiser, it does not respond well to mods and is still going to be heavy no matter what you do, so one of the other models would suit you better if you're an aggressive trail rider.
The Honda 300EX is still after all these years just a gem of a quad. It could be the best choice for some riders-again, as long as you are not too performance-oriented. It does everything well, has good balance and is relatively agile.
The Kymco is out of my realm; it's not a model I have done any R&D on. I don't think there's a lot of aftermarket support for many of these import models yet.-Allen Knowles, Owner, CT Racing, www.ctracing.com
Ranking300-350cc Class400cc Class
| | Kymco Mongoose 300 | Honda TRX300EX | Yamaha Raptor 350 | Honda TRX400EX | Arctic Cat DVX 400 | Suzuki QuadSport Z400 |
| Bryan Nylander | 3 | 1 | 2 | 3 | 2 | 1 |
| Brian Purtymun | 3 | 2 | 1 | 1 | 3 | 2 |
| Joe Neric | 3 | 2 | 1 | 3 | 1 | 2 |
| Pete Peterson | 3 | 2 | 1 | 2 | 1 | - |
| Overall | 3 | 2 | 1 | 3 | 2 | 1 |
Best parking brake of the mixPillowy seatGood powerBusy chassis at speedShocks clunked on landing from jumpsGood and comfy with an able engine |  | 
Brian Purtymun |
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