400ex bore sizes??

[jarfly]

Okey some stirght answers PLEASE! I have been looking at a big bore for my ol bike. It turned out to be stock,but my jug is junk so I want to bore it. Was going to go to a 426 but have been told there .120 and .80 So what is what?

or should I go for broke with the 440?? there not a lot higher than the 426 and about boreing to the limit I don't mind I won't keep my ex long ehough to need a rebore. I'm going end up trade for a 450 or a 250R. So just some help kinda keeping my budget down. I do trailes and that is all. I don't want something i'm going have to run race gas or have to work on all the time. So what iv read a 426 with 11.1 piston?

[ish416]

Stock - 85mm - 397cc

.040 or 86mm - 402cc

.060 or 86.5mm - 406cc

.080 or 87mm - 416cc

.120 or 88mm - 426cc

.160 or 89mm - 440cc


440cc with an extra 4mm stroke = 460cc

416cc with an extra 4mm stroke = 440cc



Just bore to the next size that's available and go with a good 11:1 piston (requires 93+ octane) either Wiseco or JE. Namura pistons are junk so I would advise against them.

*EDIT* Also, the stock sleeve is maxed out at .120 or 88mm - 426cc. For anything more, you will have to resleeve.

[DragonGunner]

Stock - 85mm - 397cc

.040 or 86mm - 402cc

.060 or 86.5mm - 406cc

.080 or 87mm - 416cc

.120 or 88mm - 426cc

.160 or 89mm - 440cc


440cc with an extra 4mm stroke = 460cc

416cc with an extra 4mm stroke = 440cc



Just bore to the next size that's available and go with a good 11:1 piston (requires 93+ octane) either Wiseco or JE. Namura pistons are junk so I would advise against them.

*EDIT* Also, the stock sleeve is maxed out at .120 or 88mm - 426cc. For anything more, you will have to resleeve.


Yup....plus the bigger bore you go the more $ for the bore. I've had all of them at one time or another except for a stroker. 406 or 416 is my suggestion.

[jarfly]

Thanks alot. IV really wanted the 426 but leaning towards the 416 now. Its 50 at my local shop to be bored .1 or. 120 if I go 11.1 piston do I have to run race gas or will 93 be fine I'm going to run stock cam for now until I can get one. Really want a good trail motor but want something I can slightly.g like no tomarro. Was wanting 440 but it just seems out of my price range

[DragonGunner]

Your ok with 93 octane. My favorite bore was a 416 with a 10.8:1 JE Piston. By the way in its first yr. a 416EX with I believe the JE piston won the Baja 1000 in its category....it'll run hard forever...unless you don't snug down a oil line like this bonehead forgot to do.

[CJM]

No reason to bore much, larger bore on these really doesnt equate to a huge power gain. Higher compression piston makes better power. Id do a 402 or 406.

[81dasher81]

you dont have to run any higher than 93 until you get up to 13.5:1 then you will need race gas. if youre running 93 anyways then i'd go with 12:1 just for extra kick.. i ran 93 in my 426 with a JE 13:1 piston and it ran great with no preignition

[CJM]

you dont have to run any higher than 93 until you get up to 13.5:1 then you will need race gas. if youre running 93 anyways then i'd go with 12:1 just for extra kick.. i ran 93 in my 426 with a JE 13:1 piston and it ran great with no preignition

This depends on elevation, fuel quality, bike setup (air intake, cam, etc). It is best to not chance it and 100+ octane with 12:1 or higher. 11;1 is the safe cut off for 93.

[2001400exrida]

I would go for the 426 its a solid build and just as reliable as the small bores. My bore guy charges the same regardless of how big. I would not run anything but 100+ on an air cooled 400ex over 11:1. The liquid cooled 450s can run 93 on 12.5:1 and sometimes 13:1 but the old 400 needs High octane after 11:1

[81dasher81]

This depends on elevation, fuel quality, bike setup (air intake, cam, etc). It is best to not chance it and 100+ octane with 12:1 or higher. 11;1 is the safe cut off for 93.

right, i guess i was just assuming if you building a motor, you would be sure not to go cheap on fuel (even though it is just 93), and set up the rest of the bike accordingly.. you really need to make sure you have it jetted right, so it doesnt get hot, that will cause it to ping.

like i said i never had any problems with 13:1 on 93 octane.. like cjm said, it depends on how the rest of the bike is set up.

cjm is also right, power comes from compression, not bore. i'd save your bores and just go to a 406 or a 416. if you go any higher than stock compression i would get HD head studs, its cheap insurance

not tryin to start an argument, just sharing how i have my 400 set up!

[ish416]

you dont have to run any higher than 93 until you get up to 13.5:1 then you will need race gas. if youre running 93 anyways then i'd go with 12:1 just for extra kick.. i ran 93 in my 426 with a JE 13:1 piston and it ran great with no preignition

I doubt that you are able to run 93 octane with 13:1 compression without retarding the timing or running excessively rich. The 400EX would ping like crazy and overheat on 93 octane with 13:1 compression.

The 400EX is an air/oil cooled engine with an aluminum head. It's maximum safe compression ratio for pump gas is around 11.5:1. Generally in the woods, the engine will run a little hotter than normal so that is why 11:1 and 93 octane are generally considered the maximum safe compression ratio / octane. 12:1 or better would require race gas or something like 100LL.

[81dasher81]

umm.. i didn't retard the timing at all, but i did have it jetted a little rich, but not "excessively" rich. my 400ex does not ping like crazy or overheat on 93 with 13:1.

i am aware of how the 400ex is built. as stated above, im just telling you what ive done. youre right, in the woods, you will have less air moving, due to lower speeds therefore it will be more easy for it to overheat. i also put a second in line oil cooler on mine just for insurance. i didnt build my 400 to be a woods machine, i built it for mx.

i know what is "generally considered the maximum safe compression" by most guys on this forum, but like i said, this is just how found to make the most horsepower, without running race fuel.

i would have nothing to gain by making this up, i have nothing to prove lol.

[Thumpin440ex]

Dynamic ratio is what means the most. The 11-12-13 to 1 is a static number. Cam and valve events can change this depending on the cam. So yes you could get away with it depending on those things.

John

[81dasher81]

well i run stock valves with a stage 2 hotcam, so really it isnt anything special, with stock cam timing

[CJM]

The hotcam and your elevation are probably helping you.

[81dasher81]

the only elevations ive ran this engine are between 500 and 1000 ft, motocross, sand dunes, and a few trails over the past summer.. most of its life have been around 750ft..

sorry to hijack your thread man, i was just tryin to help you out by giving you some advice on what has worked for me in the past.

[2001400exrida]

like i said i never had any problems with 13:1 on 93 octane.. like cjm said, it depends on how the rest of the bike is set up.
i truly hope nobody reads this and thinks it's ok to run 93 octane on a 400ex motor that is 13:1 compression. BAD BAD BAD! your elevation and motor mods still equal a big no no, wait till that thing detonates, you'll be sorry.


cjm is also right, power comes from compression, not bore. i'd save your bores and just go to a 406 or a 416. if you go any higher than stock compression i would get HD head studs, its cheap insurance
not much power comes from upping compression, or bore for that matter. You might get 2 horsepower from going to 11:1 compression, maybe 3-4 horsepower if you go all the way to 13:1. A big bore will give you just about the same amount of power as going up in compression on stock bore. This is why if you go with a 426 plus a higher comp piston you will get a noticeable gain in power. port work will yield the most power gain, more than just upping the compression or upping the bore. You really do not get much power from compression.....like i said, maybe a few ponies. It's the whole combo of exhaust, port work, compression, bore, cam, and air intake that will give power gains. compression does not give much more power than bore, i would say they are very close. a 440 with 11:1 is going to have noticebly more power than a 406 11:1.

[DragonGunner]

i truly hope nobody reads this and thinks it's ok to run 93 octane on a 400ex motor that is 13:1 compression. BAD BAD BAD! your elevation and motor mods still equal a big no no, wait till that thing detonates, you'll be sorry.


not much power comes from upping compression, or bore for that matter. You might get 2 horsepower from going to 11:1 compression, maybe 3-4 horsepower if you go all the way to 13:1. A big bore will give you just about the same amount of power as going up in compression on stock bore. This is why if you go with a 426 plus a higher comp piston you will get a noticeable gain in power. port work will yield the most power gain, more than just upping the compression or upping the bore. You really do not get much power from compression.....like i said, maybe a few ponies. It's the whole combo of exhaust, port work, compression, bore, cam, and air intake that will give power gains. compression does not give much more power than bore, i would say they are very close. a 440 with 11:1 is going to have noticebly more power than a 406 11:1.


My 406EX and when it was a 416 were both faster with 11:1 than when it was a 426 with same compression and faster than when it was a 440 12.5:1. The only thing I can think of is that I have read that with the bigger bores you have to consider you are now running a heavier piston, the lighter the piston the faster it will rev, this also has to be considered. I would agree that a bigger bore would create more hp, or torque. But they may not always equal more speed.


I'm at 750 ft. and the 12.5:1 I tried running with 93, Wiseco said it would work....it was pinging more than a M1 Garand....lol.

[2001400exrida]

My 406EX and when it was a 416 were both faster with 11:1 than when it was a 426 with same compression and faster than when it was a 440 12.5:1. The only thing I can think of is that I have read that with the bigger bores you have to consider you are now running a heavier piston, the lighter the piston the faster it will rev, this also has to be considered. I would agree that a bigger bore would create more hp, or torque. But they may not always equal more speed.


I'm at 750 ft. and the 12.5:1 I tried running with 93, Wiseco said it would work....it was pinging more than a M1 Garand....lol.

more hp with the same weight quad = more speed.

So just to make sure i read this right. your 406 11:1 was faster than your 440 12.5:1? You had some tuning problems if that's the case.

[81dasher81]

well i really dont have anything to prove to any of you guys, like i said, im just sharing my setup,

and yes, if you were slower with 12.5:1 than 11:1 you definitely had tuning issues.

[JOHNDOE83]

If bore size doesnt matter power wise, then how do you explain my 10:1 440 running 16/39 gearing with 22in tires running 70mph in 4th gear with massive amounts of power to pull 5th, I ran a 8.3 in the 8th mile with this setup?

Any reg bore size or even a 426 wouldnt even be able to turn those tires with that gearing.

So FYI, bore size adds HP and torque and a 440 properly tuned will blow away any 426 or 416.

I am living proof of this! Just watch my racing videos!

[DragonGunner]

more hp with the same weight quad = more speed.

So just to make sure i read this right. your 406 11:1 was faster than your 440 12.5:1? You had some tuning problems if that's the case.

Rest assured it was tuned good. More HP does not always equal more speed either, that piston is only going to go up and down so many times, turning the transmission gearing that stays the same turning sprockets and tires if they continue to be the same also....with more HP you can go higher gearing and taller tires to equal more speed on the top end. What I'm saying everything staying the same a lighter weight piston is going to rev faster than a heavier piston getting the quad from point A to point B faster. So ya more HP plus sprocket change plus taller tires will run faster on top....but not all races are won by top end speed.

[JOHNDOE83]

Guys Im just trying to make a point here so please do not take it the wrong way.

Saying a 440 revs slow because the piston is heavier is like saying a crf timing chain will retard timing because its also slightly heavier.

Or like saying if you put +1 or +2 valves they will open slower because they are heavier.

Or your cam wont turn as fast because its a stage 2 and that makes it heavier.

Well honestly according to the info provided about piston weight, if you have all of those your quad should be slower then dirt, because the motor just got to heavy for the quad.

[2001400exrida]

Rest assured it was tuned good. More HP does not always equal more speed either, that piston is only going to go up and down so many times, turning the transmission gearing that stays the same turning sprockets and tires if they continue to be the same also....with more HP you can go higher gearing and taller tires to equal more speed on the top end. What I'm saying everything staying the same a lighter weight piston is going to rev faster than a heavier piston getting the quad from point A to point B faster. So ya more HP plus sprocket change plus taller tires will run faster on top....but not all races are won by top end speed.

Let me ask you this. Do you think big bore motors have more HP but are slower than smaller bores? That's news to me. More HP across the board means just that. HP doesn't only increase a machines top speed in fact with gearing the same it won't increase top speed at all. People do big bores because they get more power which in turn means faster.

[powerbomb400]

Can't forget "Power to weight ratio" on getting top speed. Compression is going to give most bang for power.

[Thumpin440ex]

I have found my set up has been faster then 416 and 426 bikes. GIVEN, Tuning, ect has a bit to do. Comp will almost def give you more power then bore. The added cubes will help in TQ. Make the set up work, you will have a fast bike. Every set up is diff. We can piss away forever what is the best. Figure out what you want and go with it. I chose the 40 set up for TQ, it with my combo and set up, will dog on modded 450 bikes. NO BS

John