426 vs stock size high comp JE piston

[buster024]

In previous threads I had a respone that I could use a stock size high compression JE piston as opposed to a re-bore since my bike is so new. Am I still gaining the same power gains by not re-boring? Do I have to re-bore if I want a true 426 or can I get the full gain by just adding the piston (and hotcam, port/polish). Do I have to add a sleave to avoid overheating if I don't re-bore?

[Chino886]

Originally posted by buster024
In previous threads I had a respone that I could use a stock size high compression JE piston as opposed to a re-bore since my bike is so new. Am I still gaining the same power gains by not re-boring? Do I have to re-bore if I want a true 426 or can I get the full gain by just adding the piston (and hotcam, port/polish). Do I have to add a sleave to avoid overheating if I don't re-bore?

Wow......lots of questions.....I will attempt to answer them the best I can (I am no expert).

You will gain power with just adding a high compression piston and cam, but you don't need to bore it. You will not gain the same power but it will be noticeable. You can do piston, cam, and port and polish without boring.

If you want a 426, you will have to bore and probably want to resleeve it. When you bore the stock sleeve to a 426, you are getting pretty thin on the sleeve walls and are losing reliability. You can also do a 416 and not have to resleeve. If you want to do a 426, I would invest in a sleeve at the same time.

My honest opinion is that if you are going into the top end, you might as well bore it to a 416, get a JE piston (I think its a 10.8:1) , cam, P & P, and a valve job. When you do that you will also want to possibly invest in better clutch basket since you are adding HP to the motor. The fibers should be fine since you said it was so new.

I hope I answered your questions, if you have any more questions, just post them and someone more knowledgeable should be able to help you.

Good Luck!

[boricua]

:huh

not exactly sure what youre asking. if you want to get a bigger piston, yes you will NEED to bore it. if you want a piston with higher compression, as long as its the same size, you should not have to bore it. will you gain power with a bigger piston, or with a stock piston only higher compression, yes to both.

was that it?:confused:

[boricua]

yeah, what he said.......

[jtjpilot]

why don't you just grow a pair and get a 300ex! That's were it's at!!!

[Ex'r Marlin]

Originally posted by Chino886
[B]... You will gain power with just adding a high compression piston and cam, but you don't need to bore it. You will not gain the same power but it will be noticeable. You can do piston, cam, and port and polish without boring.

If you want a 426, you will have to bore and probably want to resleeve it. When you bore the stock sleeve to a 426, you are getting pretty thin on the sleeve walls and are losing reliability. You can also do a 416 and not have to resleeve. If you want to do a 426, I would invest in a sleeve at the same time.

My honest opinion is that if you are going into the top end, you might as well bore it to a 416, get a JE piston (I think its a 10.8:1) , cam, P & P, and a valve job. When you do that you will also want to possibly invest in better clutch basket since you are adding HP to the motor. The fibers should be fine since you said it was so new.

Ditto. I also think the reliability of the stock bore/high compression piston or the 416 kit per above surpasses the reliability of the 426.

Note: I absolutely love my 416EX, and it has been great for several years now!:macho

Good luck!

[400exrules]

im about to go with a JE 416 soon, and i cant decide between their 10.8:1 or the 12:1. Is their a big power difference between the two compressions?

[Ex'r Marlin]

Originally posted by 400exrules
im about to go with a JE 416 soon, and i cant decide between their 10.8:1 or the 12:1. Is their a big power difference between the two compressions?

Even though I run 20% race gas with the 10.8 to 1 compression, you will most likely "need" to run race gas. Running 10.9 to 1 does not require running race gas... I run it to help keep her cool here in the Phoenix area.

Something to think about.

If you ask me, it is not worth going to the 12:1 compression for that reason alone.

Going with an FCR carb will also make a noticeable improvement once you get the 416 kit.:D

[400exrules]

im trying to get a good bit of power without sacrificing reliablilty, and having to spend a bunch of money on HD studs and a HD rod and stuff

[Chino886]

Originally posted by 400exrules
im trying to get a good bit of power without sacrificing reliablilty, and having to spend a bunch of money on HD studs and a HD rod and stuff

if you don't want to do HD rod and HD studs, do not go with the 12:1, go with the lower compression.

[400exrules]

Originally posted by Chino886
if you don't want to do HD rod and HD studs, do not go with the 12:1, go with the lower compression.

how much of a power difference is their in a 10.8:1 and a 12:1? is it worth the money?

[Chino886]

Originally posted by 400exrules
how much of a power difference is their in a 10.8:1 and a 12:1? is it worth the money?

Well, like I said before, I am no expert, but to me, I don't think it is worth the money. I am sure someone will come on here telling you it is. You have to figure in about $4.00/gal of gas also.

My calculation is:

$500 (HD rod, HD studs, labor to split bottom end, new rod installation, etc)....this does not include the cost of piston, gaskets, cam, and everything else you planned on doing

$8.00/each tank of gas that you run through it for 110+ octane (will be necessary for all comp ratios over 11:1 on 400EX).....

If you can afford it, I would say do it, otherwise, just stay below 11:1. If you want to mess with the rod/crank/bottom end, you might want to go with a low compression stroker, 416 + stroked = 440!

My 2 pesos......;)

[boricua]

yeah that about sums it up, only i think he meant 8 bucks a gallon, not tank. there is a big difference in power when going from 10:1 to 12:1. but there goes some of the reliability. cost to run will be higher.
you should be pleased with something between 10 and 11:1. add any other mods you do to it and it should put a smile on your face. the studs, rods....that you can do for reliability until you going past a certain point where it nearly mandated.......

[400exrules]

so how safe and reliable is it with a 10.8:1 416 piston? without studs and a rod and crap?

[Chino886]

You will have a :D on your face!

And it will be :macho and reliable!

[AL Elks]

NEVER, NEVER, NEVER, NEVER (getting the hint) go bigbore without doing all the other mods first or at the least same time. Going bigbore without an aftermarket exhaust, opened up airbox, cams, high compression piston (if you want high compression), larger carb if it doesn't have EFI and a good CDI or ability to adjust the EFI is a waste of good money. A bigbore needs these mods to take advantage of the bigger bore.


Man was that a run on sentance or what?


Anyway that's my opintion. :D

[400exrules]

Originally posted by AL Elks
NEVER, NEVER, NEVER, NEVER (getting the hint) go bigbore without doing all the other mods first or at the least same time. Going bigbore without an aftermarket exhaust, opened up airbox, cams, high compression piston (if you want high compression), larger carb if it doesn't have EFI and a good CDI or ability to adjust the EFI is a waste of good money. A bigbore needs these mods to take advantage of the bigger bore.


Man was that a run on sentance or what?


Anyway that's my opintion. :D

well i have a cam, pipe, filter already, of course. im not stupid

but my pipe is an hmf slip-on, and i might be going to a full sparks X-6 soon, to get even more power

[Ex'r Marlin]

Originally posted by 400exrules
so how safe and reliable is it with a 10.8:1 416 piston? without studs and a rod and crap?

Well... I too have a '99 400EX, and have the following done to it:

416 J&E Kit with 10.8 to 1 compression from C&D Racing.
Stage 2 Hotcam
Ported, but not polished
FCR Carburetor from C&D
K&N Air Filter
Yoshi Slip On,
No problem running High Octane pump gas, but I currently run 20% Race gas for where I ride

As for reliability... Had this done in early 2002... AND IS STILL running strong!:) :macho

Yes, I do race it, and I still ride it very frequently. I actually ride it more than my 450R because of the ride my 400 gives me with the aftermarket suspension. That may change once I get the 450R done...:eek:

As for a noticeable difference... Yes, noticeable improvement, a lot of fun to ride, and from my personal experience, extremely reliable!:D

Hope this helps. Good luck.

[400exrules]

thats good news!:D

pretty much the same setup im going for too, except or P&P and carb. how is the power increase with a carb? are they similar to stock, as in jetting procedure?