gain power with bore diameter?

[400thacker]

I am biulding a motor for my 400ex and the machine shop said it would cost 50 for a .040 over and 100 for .080 over. How far can I take a stock cylinder? would it be woth the extra money to go .080 over? If I understand correctly, you don't gain very much power with a bigger bore and compression is where the power comes from.
thanks in advance and any info is greatly appreciated.

[Homerx]

Yes you want to go .80 over or 2mm to an 87mm piston. Thats the 416 size. As well go to 11.1:1 comp and add a cam, theres you power increase in a nut shell. Also reliability is maintained.

[droppedmazda]

who is doin ur work in ky? yes the bore is gonna give u some power. go up on ur compression for sure. u can go up to 426 bore but i think a 416 is the best. .040 over is also a pretty good bore, it'll be a 406, then u could go to a 416 the next time u redo ur motor. 416 with like 11.5:1 compression is nice piston to go with. let us know wat u decide to go with.

[400thacker]

motorparts in ironton ohio is doing the work. number is 740-532-4433 they are located just across the bridge. I live in greenup ky so it is pretty close to me. cheap and good work.

does anyone know what the clearance should be? if i am useing a namura
tech 11:1 piston thats 86mm what should the bore size be? they want the piston too but I was going to order the piston tonight and drop the cylinder off today.
thanks

[Homerx]

I would really stay away from Namura, there is a reason they are cheap ! ! 86 mm is the 406 FYI.

[BigLuke]

I used the JE 416 12.1 piston deff wake up for the 4hundy specially since I already had a cam and exhaust.

[droppedmazda]

yeah u should really have the piston b4 u bore it so they can bore it to that piston. no piston is the same exact size so u need to bore to the piston u order. there is also a certain clearance they need to bore it to fit the piston(usually about .002). i agree with homer on the brand of the piston. i would get a JE, wiseco, or cp piston. 86mm is .040 over.

[jcs003]

1mm =.03937in. not .040in. a compotent machine shop will know this to keep the bore within tolerance to match the piston to the bore. they will hone the cylinder and will take approximatly .0005in. so the shop must have the piston and rings to bore the cylinder.

JE makes a superior piston and is worth the extra money. also, since you will have the head off you should have the port and polish work done by a shop with a flowbench.

[buck440]

im suprised no one said wiseco.......there the shizzel :macho

larger bores usually add more torque than anything. You will make your power with a new cam and a good exhaust/intake setup to get it flowing smoother. Port it and you should see your HP rise a bit

[rideracelivemx7]

well heres one way to look at it, i did a 11:1 440kit and stage 2 cam, it was a kit on ebay for 350, my friend spend 500 on a new jug and 440kit with out the cam, he had a ton of bottom end, it was a pain to keep on the ground but it completely fell on its face at mid range and top end. depends where you want your power, his kit was great for woods riding, but if you have an extra 180$ laying around then the stage 2 cam adds a ton of noticable hp that didnt just shine in one spot but over the whole powerband, personally id think if you did a 416 kit which is safe with out a new sleeve like i had to do paired with a cam will give you a sweet boost on a budget build

[hypersnyper6947]

My set up is in my sig, and it pulls like a mofo it puts down 37hp i have dyno charts to prove it and its only a 416.