Honda 400EX Engine and Exhaust Upgrades: How To Make A 400EX TRX450R Fast

Honda 400EX Engine and Exhaust Upgrades, How To Make A 400EX TRX450R Fast. CT Racing Engine's Allen Knowles explains what it takes to make the torquey and fun Honda 400EX engine as fast as a piped TRX450R.

Ideal for those in need of an engine rebuild, this engine included a CT Racing Exhaust, porting, 5-angle valve job, 13:1 high compression JE piston, 2004-2005 TRX450R carburetor, Uni air filter, and more.

Learn more about CT Racing's 400EX engine packages here.

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Honda 400EX Motocross Racer Quad Builder Project Part 1
Honda 400EX Motocross Racer Quad Builder Project Part 2
Honda 400EX Motocross Racer Quad Builder Project Part 3 The Test

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[DirtObseXXion]

I wouldn't kick her outta bed! Sick build! LOVE THE GRAPHICS! 🤩👍

[theviking]

This was an old video right? I feel like I’ve watched this a long time ago. Still good though, I miss the 400’s sad no one makes them anymore

[ATCREVOLUTION]

I love the CT exhaust, would love to have that setup on my 350x! I had a 05 400ex I bought new that I built with the parts available at that time and it was faster then a piped 450 off the start as long as my 460EX was hooking and getting good traction by a decent amount, I could stay in front until we both got into 5th gear and then the 450 would slowly creep up to me and eventually take the lead absolutely topped out. The 450's where just a hair quicker top speed wise because of the modern liquid cooled engines revving out more then the old 400ex. Other then that I could hurt some ones feelings with my 400ex against their 450 in a drag race, I could come out in front as long as we weren't racing on a 2 mile stretch of road because of the top speed being so close. In a longer drag the 450 would have time to slowly overtake my 460ex stroker on the very top end. On a Motocross track my 460ex could hang no problem if not outright beat the 450's, and the dang thing had reverse lol. I put in the required cylinder sleeve to run a hotrods stroker crank and CP custom piston designed for the stroker crank kit to get to 460ex, also got a stage 3 cam kit for it from Hotcams with new valves and heavy duty springs. The compression ratio was just low enough to get away with running premium pump gas rather then requiring race fuel. The head was also fully ported on a flow bench with a 5 angle valve job. I also installed a performance CDI that raised the rev limit a bit with a more aggressive power curve, full trinity racing exhaust system, no air box lid, k&n air filter, and the carb rejetted to perfection. I'm sure there's more I'm forgetting at the moment but back in 05-06' it was definitely a hell of a motor! I just ran OEM gearing with 20" tires on the back mostly as I did a ton of woods riding on it, I did have 18" rear tires on wheels that I swapped on for a track scenario. I was literally building that 400ex for the sole purpose of making it TRX450R fast and it pretty much worked out. Awesome video for sure! That set up has to me much much more reliable then my stroker engine but it served its purpose until I traded it for my first 350x lol. I always had the feeling that it was a ticking time bomb but it held together for me for a couple years no problem. I had to drive 2 hours one way to pick up the 350x and drop off the 460ex but oddly enough 5 years or so later I ended up seeing my old quad out at a local riding spot that was 30 seconds away from my house! A guy bought it that lived 20 miles away from me so it ended up coming back to my area. He let me take it for a ride and the thing still ran just as good as when I got rid of it, the new owner told me he had it for awhile before I ran into him and it gave him zero issues! I was shocked that that thing was still running on the same engine build that I had done when it was mine 6-7 years before I happened to see it again out on the trails by my house. Have not seen it again since 11 years ago so who knows what ended happening to it. I use to always watch for it to pop up for sale but it never happened and I bought 2 brand new 450's after trading for the 350x and had plenty of things to play with and race. Awesome video man, this brought me back to 05 when I was trying to achieve the same exact goal!!

[doc_teamwaxoffroad]

Really hard to beat an ol 400... 👍👍
#savesportquads
#makeatcsgreatagain

[nicholaskarapetian]

These guys are awesome, love both these companies. Awesome content🔥💪🏻

[GrowYourOwnFun]

Awesome information, I have a 400ex and thinking of doing some upgrades for power. It already has a Yoshimura exhaust and Elka front suspension. If on a budget do you recommend this option?

[evanpetersen]

My old built 400ex was alot of fun but it always ran ridiculously hot after I put the kit in. It was an overstroked 427cc kit. Always worried me how hot it was, so I sold it.

[BackwoodBassHunter]

Thanks. awesome tips man! I needed that info. I didn't think the TRX450 carb would fit. That's killer my bike already has a full pipe system by white bros. But Ill add the UNI air filter and the 450 carb. I think that carb is really gunna wake her up. I liked and subbed.

[straightupstreetracing]

How much does this build cost and where are you located

[Davido]

Not bad for a Honda! Won't beat my YFZ450R tho..not close.

[richarddevaottien]

I always hate the modern advertising graphics plastered on race quads. These people seem more like Mexican gangsters than regular Americans, so I couldn't watch, ATVOD