Compression

[thebig450es]

Right now my 400 runs great but im looking for more power. Could i get a new piston in the stock bore....so i can just take my piston out and install the new one without any machine work? Could i run about 12.5:1 stock piston with a very thin gasket and run a stage 2 cam. I heard of a gasket smaller than the xr400 that someone ran on here but forget the part number. I already have been running E85 for acouple years now but now hopefully i can use the increased octane benifit. i know i'll probably only get 5 more horses out of it. Thanks for the help in advance

[CJM]

12:5 will not be a good idea unless you want to run race gas (100+ octane). Stage 2 cam is really for a more built, bored out engine.

Boring out the cylinder is cheap, add another 50-100 bucks to the cost of everything, when its that cheap why not do it?

About the only other issue your gonna have with a higher compression is the headstuds dont like to stay put, you need to have the GT Thunder HD studs installed, thats another 100 (to buy and have them install it). Could be like me and they charge 75 to bore and have them do everything.

If you want to build Id suggest a 416cc bore (87mm piston), stage 1 or 2 cam (stage 1 is more low to mid power and stage 2 has more mid to highend with a small loss on the low), a good exhaust and your good to go.

[bigbad400]

yea you can do that but most people for the price and since your in there anyhow put a good cam chain in. and with 12:1 you will need race gas. are you ready to spend 6.00 a gallon when you want to go riding. bore cost 10 bucks at my local shops here. its machine work but its cheap. id do an 11:1 426. much more reliable and makes more power than stock bore hi comp. less heat. less stress on valves.


there is no replacement for displacement. less compression will keep it running longer and bigger bore will still give the power you want without sacrificing reliability. also dont ever build a 400 without gt thunder studs and a hd cam chain. simple stuff and there again keeps you reliable. i have built many a 400ex. one thing these dont like is over reving. the valves float. stock valve springs are low quality. dont buy a cdi that gives you 1000 rpm over stock, the 400 quits making power long befor the stock rev limiter anyhow. the monster coils are a great way to get the stronger spark, faster starting and better throttle response without getting over revved.

[thebig450es]

I was thinking with the E85 its 105 octane i should be able to get away with true 12.5. I've been looking a CP pistons. I was also thinking of doing the GT thunder HD head studs. You right CJM if i send it to them have them do all the work and have it done right. I know if the do the 416 i can always go bigger. I like the power i have now with my 13t front spocket but would like to go to a 15 or 16 to have the speed but need more power to pull it lol

[thebig450es]

Ive never delt with gtthunder but there prices look pretty good. What benfits would i have with going to +1mm valves i see on ebay. But then should i send gtthunder my head to get a P&P since i have a full exhaust.

[bigbad400]

bigger valves = more air in and out. more power. you dont need p&p it with an exhaust but it sure compliment it well

[bigbad400]

with as quick as you changed from just a piston to a real build.... you know a 460 stroker is faster and more powerful than my piped chipped ltr 450:D

or if you really want more power there is a guy that put a turbo on his 400ex and it would eat up modded ds 650s and 700 raptors:eek2:

[CJM]

If your gonna go all out:
416 or 426
Heavy duty head studs GT thunder
Cam
02 CRF 450 timing chain
New chain guides and auto tensioner trust me put new ones on while your in there. That tensioner fails bent valves ahoy!
Good exhaust
Right sprockets
Really want to make it sweet, find a 450R carb and get tuned in.

Your good to go.

To compare you can see my specs in my sig. I have enough power to keep up with the 450's easy, they beat me on topend due to displacement but I give them a very good run for the money. Awhile back my buddy was riding his stocker at 3/4 throttle racing along, I came up from behind him and punched it and left him in the dust with ease.

[thebig450es]

I have a problem with add ons lol ,when i try to keep a project small it gets blown out of the water lol. I have about $1000 buget to work with so no stroker or turbo or nos.....this year. Could you guys give me a part list that would work well in this buget? Thanks

[CJM]

Ok..

-Wiseco or JE 87mm piston, 416 or 426 $100 or so. Less you bore slightly less power-but more you bore if you should want to bore it again you cant go much farther, 440 is the limit unless you wanna spend big bucks.

-Heavy duty head studs $100
-Bore job (if you get GT Thunder to do it at same time as studs) $75
-Good exhaust, HMF is nice, there are others $300
-Good shocks, 450r front take offs $100-250
-02 CRF450 timing chain $50
-New timing chain guides, and new tensioner $100-150 approx.

Thats about what ya want, forgive me if I forgot anything but Im quite tired but cant sleep atm.

[slightlybent47]

This should be within your budget. I’ve had this set up for a long time now and it was worth every penny. Assuming you have a good suspension already in place, if not I would start there before doing motor work.

416 with 12.5 to 1 or 11.5 to 1
Stage 2 cam with hd timing chain
P&P
HD head studs optional
450 carb and a good slip on with stock head pipe