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View Full Version : 400ex build



spent21
01-16-2007, 06:13 PM
i'm about to tear my 400 down. i only ride trails (hard and fast) and i may try my hand at XC this season depending on if i have my bike set up by then.

i have an HMF full system with no lid on the airbox. as far as i know, the bike is on the STD bore.

i've had a stage 2 hotcam for about 2 years on the shelf that i'm going to try out. i've been putting it off until i got a pipe, but now i want to do a little more.

does anyone know what the stock compression ratio is for this bike?

i'd like to have the head ported/polished and bump up the compression but still run 93. i'm not keen on removing the base gasket because of cam timing issues associated with it unless there is an adjustable cam sproket available.

my biggest question is who have you guys had do your head work, and what kind of questions did they ask? will they work with me as far as my riding style goes? what kind of service/turn around time did you get? what was the price tag?

i'm not interested in big bore kits, however, a 450r carb may benifit this set up. what must be done to the 450 carb to work with the 400? there seem to be a few little electrical gizmos on the 450r carb. do you leave those unplugged or what?

i'm thinking the increase in compression will counter the bottom end i may lose by using the stage 2 cam instead of the stage 1 as was discussed on another thread, that i can't find now.

Thanks in advance!

ride_red666
01-16-2007, 07:06 PM
stock is 10:5:1 i believe, 11:1 is the highest you can go on pump gas.

QuadRacer18
01-17-2007, 07:43 AM
stock is not 10.5:1, its 9.5:1 if i remember corectly, but 11:1 is the highest with pump gas

ryandu
01-26-2007, 04:15 AM
you are correct in not big bore on your bike. I've had 400's stock bore that swallow 440's. Its all about tuning your setup from intake through exhaust.

450R carb will surprise you for sure. 6hp, and its noticable.

Do your own port work, first time I did it was not a problem. Air drill with routing metal bits, just open the holes up and sharpen the splits.

spent21
01-26-2007, 10:53 AM
i am an accomplished mechanic, but i leave the port work to folks who have flow benches and know how to squeeze horsepower out of a head. i don't believe in spending a dollar to save a dime.

zrpilot
01-26-2007, 03:25 PM
Originally posted by spent21
i am an accomplished mechanic, but i leave the port work to folks who have flow benches and know how to squeeze horsepower out of a head. i don't believe in spending a dollar to save a dime.

I had mine done at GT Thunder, but if I did it again, I'd probably use Colby at C&D.