[rockSTAR_SS]

Hey folks. I own an 07 trx400ex. Stock, this is a really fun bike, but after 3 years of riding stock I want something that will get me ahead of the rest of my riding buddies. I mainly trail ride, but a few times a year my friends and I pack up and spend a weekend at the local sand dunes atv park.

I've done a little research and I've decided that I want to do a 426 big bore kit, stage 1 hot cam, HMF full exhaust, Uni air filter and appropriate jets/tuning.

The only 426 kits that I have been able to find fits up to a 2006 model. Why wouldn't this kit fit in my engine? It's the same engine, right!

That's my main concern. If I can confirm that it will fit then this build will be on!

 

[Helmut]

Welcome to the forums.

 

[rockSTAR_SS]

Thanks. I've been lurking around for a month or two. Finally made an account today. An intro thread slipped my mind!

 

[Helmut]

The only 426 kits that I have been able to find fits up to a 2006 model. Why wouldn't this kit fit in my engine? It's the same engine, right!

I looked over the repair manual for the 2005-2009 400EX and it doesn't say anything about the cylinder or head on any of those years being different. I would say they're the same, but just in case, it might be a good idea to call or send an email to the place where you plan on purchasing the BBK and ask them.

 

[rockSTAR_SS]

My thoughts exactly! Perhaps it's just a shop preference or something. I will give that a try.

 

[TRX2fiveO]

Welcome to the forums be sure to post the progress pics.

 

[Redracer]

Welcome to the family!!! Good luck on your build

 

[rockSTAR_SS]

Thanks everyone. I am in touch with a shop in phoenix, Arizona that has agreed to install the 426 big bore kit and possibly the head assembly with a stage 2 hot cam as well. If they can then that would be great! I would much rather let a reliable shop do it instead of me attempting it.

I'm interested in a different sprocket as well. Does anybody have a recommendation? I have read that a front sprocket with one less tooth is goof to have.

 

[dr. feelgood]

Going down a tooth on the front sprocket will give you more low end power and less top end speed. Going up a tooth is just the opposite

Rob

 

[rockSTAR_SS]

Thanks for that information. I think I need more low end power when climbing dunes and trail riding instead of top speed. I have had a bad encounter with top speed, so I'm not too excited about the bike going any faster up top. Its plenty fast enough.

I'm leery about buying a cdi box off of ebay and not from a reputable company. I don't want to get into changing valve springs and such(not yet anyways ha ha), so I'm thinking a stage 1 cdi box will be plenty enough for me. Has anybody bought those cdi boxes off of ebay?

 

[Helmut]

I'm leery about buying a cdi box off of ebay and not from a reputable company. I don't want to get into changing valve springs and such(not yet anyways ha ha), so I'm thinking a stage 1 cdi box will be plenty enough for me. Has anybody bought those cdi boxes off of ebay?

I don't know if you would be interested in this or not, but click on the link below and go all the way to the bottom of the page and read the "ignition hop up trick". According to this website, most aftermarket CDI boxes sold for the 400EX are actually stock Honda XR250R boxes.

POWROLL PRODUCTS FOR THE TRX400EX

 

[tomgodd]

Welcome to the Family!

 

[SlammedRanger]

Welcome to the forums. Going down one tooth on the front gives you more low end but you will be shifting every second if your doing a big bore with a cam. Just something to think about.

 

[rockSTAR_SS]

I'm leery about buying a cdi box off of ebay and not from a reputable company. I don't want to get into changing valve springs and such(not yet anyways ha ha), so I'm thinking a stage 1 cdi box will be plenty enough for me. Has anybody bought those cdi boxes off of ebay?

I don't know if you would be interested in this or not, but click on the link below and go all the way to the bottom of the page and read the "ignition hop up trick". According to this website, most aftermarket CDI boxes sold for the 400EX are actually stock Honda XR250R boxes.

POWROLL PRODUCTS FOR THE TRX400EX

Yeah I've read that. I forgot all about that! I can go down to the Honda shop and order that part.

Welcome to the Family!

Thank you! Glad to be here!

Welcome to the forums. Going down one tooth on the front gives you more low end but you will be shifting every second if your doing a big bore with a cam. Just something to think about.

I will try out the built motor first. If I don't like it, then I will get into sprocket changes. Thanks for the info.

Here's the official parts list from the shop I'm talking to:
426 BBK, either 11:1 or 13:1 (requires race gas) compression includes piston & gasket kit with valve seals, $275
Stage 2 camshaft, $189 - ok with stock valve springs but need new rocker arms
OEM Rocker arm set, $38.58 * 4 = $154.32
NGK spark plug DPR8Z, $3.50
Oil filter HF113, $4.95
Shop supplies, $12.95
Parts = $639.72

Big bore cylinder, $75
R&R Top-End, $325
Disassemble, inspect seats, valves, & springs, port, polish, clean & reassemble head with new valve seals, $350
Labor = $750

This is with me sending the engine to PCP Offroad in Phoenix.

I really wasn't wanting to run race gas so I'm going to go with an 11:1 compression. Not much race gas out here in the woods!