buildinga good reliable woods/XC motor?

[400man]

I need some advice on what I should do to make a good reliable motor for a trail/occasional XC race bike? I know I wont be able to keep up with the 450s in a straight out race in the field sections, but I should have more than enough power to keep up in the woods and tight stuff, but I want to get a little more power than what my stock motor has now. its got a full big gun exhaust system and uni filter and stock carb.

my plans are to get a 86mm JE piston, either 10:1 or 11:1, and either a stage 1 or 2 hotcam. and I plan on getting the flywheel lightened and a hotter aftermarket coil, and maybe a 450r carb. the only things on not sure of is which cam and ratio piston I want. I really dont want to do the heavy duty head studs if I can help it, which is why I want to stay away from the higher compression pistons. and on the cams, I dont know which would be better for my power needs? I'd like to get better topend and midrange power than stock.

[exracer416]

the 400 has plenty of torque so use it to your advantage i was finishing top 4 on a stock bore in the a-class. but ya gotta watch the heat you get a bigger coil its more heat you go to 11:1, more heat. after i put my piston in i had a hard time keeping the motor tegether ill never go 11:1 again went through 2 motors this year from them but the other mods look good, cam port polish cam flywheel carb, and practice your woods skills

[sameltoe]

lighter flywheels help with mx and getting a "quicker" rev...But doesn't a heavier flywheel generally help make more power and less stalling? just a thought...

[tri5ron]

with what you've got,
what you want,
and the type of riding you are targeting, ...

I personally would stay with the stock piston/compression due to your riding in the woods will most likely include quite a bit of 2nd and 3rd gear riding time, which means less airflow for cooling.
but if you feel you MUST change the piston, stay at the 416 at 10:1, or 10.5:1 compression.

add to that,... the 450r carb, stage 1 or stage 2 cam, and a Sparks +6 advance key.
Leave your flywheel alone.
You NEED the heavier flywheel for the low end torque, as well as less stalling.
Besides, the Sparks key will make it rev about the same, as if you HAD a lightened flywheel.

You should be pretty happy with it it this configuration, have a near bulletproof woods machine, putting out 32 to 35 hp, TO THE GROUND, and still be just as reliable as it was from the showroom floor.

You've basically described my exact riding style, and mods to my quad, and I am quite happy with it.

I'm getting 32.7hp, on the ground, (dyno tuned and tested), and my mods are Full Big Gun system, Uni, no lid, Sparks key, 450r carb (jetted on the dyno), and I still have the stock piston AND cam.
Here is a couple of write-up's I did, that you may be interested in...


http://www.exriders.com/vbb/showthread.php?s=&threadid=349499&highlight=sparks+advance

http://www.exriders.com/vbb/showthread.php?s=&threadid=409169


I will probably be going to a stage 2 cam soon, and when I do, I will probably change out the head gasket at the same time to the thinner XR400R head gasket.

I may, (or may not), go with the monster coil,
but to be honest with you, it really does quite fine with the stock cam and coil,...
and I'm NEVER worried about overheating.

This is including when I ride 10+ mile loops with my 8 y.o. daughter, and I rarely even get to 3rd gear! Still No Heat Issues!

XC is all about Endurance and Reliability.
That goes for BOTH You AND your Quad.

My suggestion would be to hold off on the cam and coil for now, and invest in some clean used 450r front shocks, a set of Works triple rate springs for the shocks, and a CCP Steering Stabilizer.
These will help far more, in the woods/xc riding, and have a much greater "Bang for your Buck" value,
than the cam and coil combined.

Next, add a good solid .250 swinger skid at least,
or go ahead and get the a-arm, and frame skids too. (.190 is fine for them).
btw- Nerfs are highly recommended also for Woods/XC riding.

With all that being done,
you will end up with a Very Respectable Woods/XC machine, that,...

1- has not broken the bank account,
2- will run with dang near everything out there,...
3- still runs on pump gas,...
4- is reliable beyond your expectations,..
5- and is still a BLAST to ride.

hope this helps.
Ron

[Miami_Vice454]

you should work for dirt wheels ron. your write-ups are so detailed and they get to the point. i agree totally with him btw.

[81 clark racing]

imo id do your suspension first. get your self a nice set of works or something on that line. i have works and love them. no matter how much power you have, ur not going to be faster if you cant handel it.

[400man]

I guess I forgot about suspension..............;) but ive already got that took care of. I got a set of brand new HLS front shocks off ebay for 180$ shipped. they are the regular set with the dual springs. and I got a GT thunder XC rear linkage, which I will say is my favorite bolt on I have have put on my 400 so far. I only weigh about 140lbs and it makes the stock rear shock feel kinda soft, but I have messed with the spring preload and compression and have it riding pretty nice, I got it setup where its got alot of sag and sets lower than the front end and I love how it rides, especially the way it corners. it just likes to stick to the ground and not try to tip over at all. the HLS front shocks are VERY nice for what I gave for em. they ride awesome and I love how they got plenty of sag and have a very plush ride, but still have good bottoming resistance on the occasional jumps.

and for skid plate protection I got a lonestar sprocket guard and gonna try to work out some kind of rotor guard later on after I get my 450r rear brake setup. and I got a frame skidplate on the way. also plan on getting a steering stabilizer very soon. I got 14/39 gearing right now, but Im probably gott order a new chain and sprocket kit and run 13/36 gearing, its basicaly the same as what I got now, except just smaller sprockets.

but back to the engine.......lets say I just stick with the stock piston for now, but decide to put a bigger cam in it? I'd like to get more topend and midrange power out of it without loosing too much bottom end. would I be better off with a stage 1 or stage 2 hotcam?

[tri5ron]

stage 2 for mid to top rpm performance.
stage 1 for low to mid rpm performance.

[F-16Guy]

Go with the stage 1. It has less duration than the stage 2 and allows more time for the piston to build pressure during the compression stroke, which gives you a higher dynamic compression ratio and a stronger low-to-mid powerband.

If you stay with the stock piston (which is fine), buy an XR400R head gasket. It's thinner than the EX gasket, and will give you a tighter squish band and slightly a higher compression ratio to offset any loss from the cam.

Another option with the head gasket is to buy a Cometic MLS head gasket, drill out the rivets that hold the layers together, and use just the top layer. That will tighten the squish band even more and make the combustion more efficient. The top and bottom layers are identical gaskets, while the middle layer is a shim that the gasket makers use to alter compression ratio and/or deck height, so there should be absolutely no issue using just one gasket layer.

[bigbad400]

you a engineer or something f-16guy. you have alot of scientific knowledge about that stuff. i could draw the part for you. im in CAD. so why do the gasket makers use the three layer gaskets if one makes better compression? i always wondered what the hell was up with 3 layer gaskets, it seems like more room to leak in my opinion. but hey theres one on my machine so whatever.

[F-16Guy]

Originally posted by bigbad400
you a engineer or something f-16guy. you have alot of scientific knowledge about that stuff. i could draw the part for you. im in CAD. so why do the gasket makers use the three layer gaskets if one makes better compression? i always wondered what the hell was up with 3 layer gaskets, it seems like more room to leak in my opinion. but hey theres one on my machine so whatever.
lmao. Nope, not an engineer -- I've just done a lot of work on mine and done a ton of reading about this engine and other peoples' successes and problems. The reason you can get away with one layer of the gasket on this engine is that there is an unusually large amount of clearance between the piston at TDC and the head. Using one layer cuts that clearance down, and when you tighten the gap between the edge of the piston and the head at TDC, the fuel/air mixture around the outside edge of the top of the piston gets forced to the middle for a more concentrated and powerful explosion. The XR/EX engine was never meant to be an ultra high performance engine, so details like that were probably not a big deal. This engine in it's stock form can run for decades with an occasional oil change and the right rider.

[400man]

Originally posted by F-16Guy
This engine in it's stock form can run for decades with an occasional oil change and the right rider.

now I can believe that. my bike is a 2000 model and aparently before I got it, the motor has never been took apart. I forgot to also add that a few months ago I put a fresh set of rings and hone, new valve seals, new timing chain tensioner and crf450 timing chain. when I pulled the topend off it was nasty with so much carbon buildup, I was surprised the spark plug was even firing. and behind the clutch cover it looked as clean as could be, even all the bearings are still good and tight. the head gasket trick sounds like a easy and cheap way to get extra power, but I really dont want to pull the head off just to change out the gasket.

[bigbad400]

i know i have a 99 that runs like it came off the showroom yet, all stock. but ive also blown up and ruined a couple of built motors too, im only 22 so im learning a little here and there but i have quite a bit of mechanical ability. and in my mine they did that (left room for gain) for people like me who wants to see what they can get out of one, if honda built the machine with the basics in mind why is there so many cheap upgrades for it, because honda planned that, it keeps people interested, look at the ktms they really cant be made any better, full race suspension stock, race inspired stock pipe, race tires and wheel from factory, i mean.... why is hondas 450 so far behind, because honda made it so the aftermarket industry could survive with the competition going so far these days. thats my mind on "overlooking things" those details were probably purposefully overlooked and left alone to support the aftermarket industry.

any other ideas. this to me is very interesting, things like the z400 fuel injection and the nice shocks, and the liquid cooling, why cant honda keep up? because they choose to have it that way. its not just like any other quad on the market that way and theres room for personalization.

[F-16Guy]

Originally posted by 400man
... the head gasket trick sounds like a easy and cheap way to get extra power, but I really dont want to pull the head off just to change out the gasket.

Why not? Once you have the cam out, you're only an exhaust header and four head nuts/washers away from it coming off. It would take an extra hour worth of work at the most to do the head gasket.

[IcutMetl]

Back when I had my 400ex, my riding buddy swapped a stock piston for a Wiseco 10.5:1, and it woke it up big time w/o even changing the cam- he also put in a Sparks 6 degree key. I had a 6degree key and slip on, and after just the piston, it was no longer a close contest.

If I were you, go to a 416 overbore (still leaves some room), 10 to 10.5:1 forged piston, and either ann XR400 or HotCams stage 2 cam. Compression adds power everywhere in the RPM range, and without going over 11:1, I believe you can still safely run premium pump fuel. That should give you a very strong engine with plenty of low end, but one that still craves the revs. I've always read that the increased RPM limiter CDI boxes don't really do much unless your engine is tuned way out. The 400ex has great low end torque, so I think you could probably get away with a lightened flywheel just fine; it won't give any more or less power, but it will get into that power quicker. Either way, I would recommend an advanced timing key, an open airbox (or vented lid), a 450r carb if money permits, and a good full system if money permits or a ported stock header and slip-on. Good luck!!