Yz 450 big bore

[jp]

I am considering fitting Vertex 500cc big bore kit to my 07 yz450. I have discovered the cases need modifying to fit cylinder. Has anyone done such a mod or know anything about it? How much work is needed to fit cylinder? What sort of performance gains can you expect? Is it worth doing? I can get a Athena kit which is 473cc which require no mods for virtually the same price but I'm thinking is a 23cc increase worth the expense? Thanks

[SM93]

if u want more power buy a honda!!

[mr_suzuki]

Or An aprilia :poke:

[Flash]

If you want to win MX races keep the Yamaha!

[SM93]

how much is the big bore kit so we have a point to work with???

[jp]

KIt cost $650 which includes cylinder, piston, piston pin, rings, circlips and complete top end gasket kit. All mods to be carried out to cases are able to be done with die grinder, so I've been told.

[SM93]

thats cheap!!! u doing the work yourself? will u buy a pipe or any other mods?

[jmcd]

You can doo iiittt!! Go for it.

[Doogs]

Personally I don't like big boring bikes, but if you felt an extra 5 kms per hour is worth it, do it.

I find it make them sound and rev sloppy at the bottom end and they lose the tight sound. Unless you are holding full throttle I would not open that can of worms, especially if you have to do case mods. You would want to some money for when the cam chain self destructs and the connecting rod sees daylight and the electric start cooks its self from trying to crank it over.

It is kinda like V8 syndrome, I'd take a V6 with a good turbo

Get a good header pipe and slip on instead.

[Flash]

I'd agree with big boring 2ts it isn't that easy but 4ts if your getting a whole barell Athena etc. then they have full thickness bore walls I believe so you shouldn't have a problem there and the rods aren't a problem unless they are standard.
If your auto decomp is working why would the started struggle that much more?
Have a read hear -.

http://www.maxpower-engines.com/default.htm

Plenty of info there!

[jp]

Thanks for the link. Very useful. At the moment I'm just researching the mod, to see if the slight increase in capacity is worth any performance gains against reliability. For a possible 2-3 hp gains is it worth building a potential grenade.

[Flash]

If you don't change cam compression and increase carb size there is no reason it should be less reliable! Unless the motor is suspect already!
It will be more than 2-3 hp gain! the 125's to 144 are getting more than that!

[devo]

As far as the KTM's go, the 525 has bugger all more horsepower than the 450 (<5 I think) but a fair bit more torque.

[Flash]

Yeah that's right Devo, not unusual. THe 510 huskies are the same but it's still a bit more the 2-3hp

[Doogs]

Any 4T larger than 450s sound sloppy, although the WR450s sound real sloppy compared to a 250F's tight reving sound. Although your YZ will be better than a WR

I personally would not do it and more so would not do it to a YZ MX bike
They are good enough is they are,

if the HP gain your looking for is for holding it full throttle at the SM track then the reliability will be an issue anyway with or without the kit.

[jp]

The main reason to do it is to more punch out of the corners. As I weigh 100kg I lose a lot of time exiting the corners to the lighter guys. What other cheap mods would give me performance gains for supermoto. I the only things I've done to motor so far is pro-circuit T4 slip on, slipper clutch and adjustable leak jet. Would cutting holes in the side of the airbox and installing a K&N high flow air filter make much difference. Thanks