my friend has a 2003 400ex. so far he has put on a yoshi full exhaust, k&n filter, pro taper bars, xcaliber extended axle, +2 hydrodynamics extended a-arms. now he has decided to install a big bore and hot cams.

Whats the best big bore on the market? he wants to spend around 250 bucks max for it.

what kind of cam should he get?

HELP US. he's only been in the sport for a few months and i dont know much about honda performance parts. im more of a suzuki person....thanks

 

I would start with a 416 and a higher compression piston. That way you have room to move up if something happens. The 400ex is also air cooled so the 416 will give you a nice power increase without having to worry about overheating much more. You don't have to bore the cylinder with the 416, just the sleeve. Hot cam stage 2, and possibly moving up from 10mm studs to 12mm depending on the compression. You will hear that you don't need to on a 416, but I would do it anyway. Extra strength never hurts. And if you decide you want a bigger bore down the road it's already done.

 

so how high is a high comp piston? and does the more compression mean more power? accel?? ect? and what is to much for a 400ex?


thanks

 

A higher compression piston runs in the $120-$160 range depending on how the compression is (unless you go to Baldwin or Sparks, then the price is about $200-$250). A Stage II cam runs about $125. You will have a noticeable addition of power with a higher compression piston, but the bigger bore will also add a considerable amount of power as well. I wouldn't go over 426 Bore unless you are planning to race it full time. The 440 kit is awesome, but it is prone to overheating and is pretty much made just to race.

 

ok so if i went with a 426, how high of comp would i wanna go? and a stage 2hotcam. would it be worth while to get a rev box? thanks again also, waht is a port and polished head? and are there shops that i can drop my quad off and ahve this all done at the same time or would i have to send the parts off and put them back on myself?

 

does he want to have reliability? or more speed 416 athena or wiseco. stage 2 hotcam. if he wants alot of power but not reliable 440kit.

 

You would be better off sending it to a local shop that specializes in ATV and Motorcycle engines. A port and polish shaves the intake and exhaust ports which allows for better flow, and most port / polish jobs inclue a 3-angle valve job which allows for better valve seating and for better flow around the valves while opening and closing. I think the largest compression piston that you can get from wiseco or je for the 426 is a 12:1 or 12.5:1, obviously other companies (Baldwin and Sparks as i suggested earlier) offer larger pistons but the price hike isn't worth it IMO. As far as I know, you have to press the old sleeve out and then press the new sleeve in, which is not difficult if you have a press, but you are better off getting someone with experience to handle it just being cautious. I recommend a port and polish if you are getting a higher compression piston and a new cam, better air flow is the best thing you can do for the rebuilt motor. I would also get a Rev Box in order to achieve a higher rev limit and you'll see slightly advanced timing curves which will also provide more power (the rev box usually increases spark too, giving you a more complete burn in the combustion chamber). I am being picky with my last thing, scrap the Yoshi exhaust and get something better. I personally hate Yoshi pipes and ran one on my bike during my break in period after the rebuild, and thought it was absolute garbage. The pipe sounded like it was bottled up and it didn't sound "good" to the ear like my HMF pipe did. Anyhow, as long as its a Full pipe (larger header pipe than stock) then it will be ok after all of the motor work. The worst thing you can do is keep a stock header pipe on a bike after doing motor work. Intake and Exhaust flow are extremely important when you start making alterations to the motor.

 

ok so if i was gonna go with a 426 should i get a 12:1 or a 12.5:1? and if i did this u recamend that i get a port and polish head also? along with a filter, pipe and jetting and new cam?

 

and the rev box**

 

If you are going to take the time to rebuild the motor, why not do it all at once? Your pricing will basically look like this on the parts:
Piston: $150
Cam: $125
Port/Polish: $250-$300
Rev Box: $175 (you can get cheaper, just less performance)
Jets: $60

That is $760 to $810 and you are done with it. Considering that a good set of shocks cost around $800, I would call that amount in the motor, a reasonable amount to spend.

**This does not include the new cylinder sleeve since I do not know how much a new sleeve cost**

Rather than wondering what power you could have had, you can get it all done at once and have it over with rather than tearing the motor down multiple times. It makes sense to get it all done while you are in there if you paying someone else to tear it apart and rebuild it as well, because you will be paying multiple labor charges if you wait to do each thing seperately (ie, a Piston one month, a new cam the next month, port and polish a month later, each time they take it apart, you are looking at roughly another $120 in labor costs).

As for the pipe, if you already have a FULL Pipe system (even if it is a Yoshi), you should stick it out for a while to see how the bike performs. You may run across a friend that will let you test another full pipe on your bike (like I did with the Yoshi), and you can test it out to see what you like best.