[ca412686]

Hey guys. I got a 02 YZ426 in SM trim. Im racing at a road race track and I seen to need a bit more power. I can pull away from the guys in the turns and even have a better drive off the corners only to have them catch me on every straight. The other bikes are 450's with motor work done as well. All i really have done to my bike is the standard free mods and a full exhaust system. Im planning on doing the motor after the next round and trying to figure out what would be a better way to go. High comp piston, Big bore, or maybe even both? Im wondering if anyone has done this before and if it would be at all reliable for running on a road course at higher RPM's most of the time. Any help would be great. thanks guys!

 

[PowerFiend]

Truthfully, you would be better off putting your money toward a 450. All your motard gear will swap over.

I may eventually add a +2mm flat top piston(not the 13.5:1, that will probably require race gas) with squish clearance set a ~1mm, adding the HotCams int. (I already have the HC auto ex. cam, and a pipe.), and some minor port work to mine. But my bike is CA street plated, without a newer option.

 

[PowerFiend]

P.S. If you do decide to put in a new piston, there have been several reports of the Wiseco's failing. I personally would order one up from cp pistons. :thumbup:

 

[ca412686]

Truthfully, you would be better off putting your money toward a 450. All your motard gear will swap over.

I may eventually add a +2mm flat top piston(not the 13.5:1, that will probably require race gas) with squish clearance set a ~1mm, adding the HotCams int. (I already have the HC auto ex. cam, and a pipe.), and some minor port work to mine. But my bike is CA street plated, without a newer option.

Hmm, not quite sure a 450 is close to the price of some work done to the bike. Especially if I have to sell my 426 as stock....but thanks for the help

 

[MexMex]

Hey guys. I got a 02 YZ426 in SM trim. Im racing at a road race track and I seen to need a bit more power. I can pull away from the guys in the turns and even have a better drive off the corners only to have them catch me on every straight. The other bikes are 450's with motor work done as well. All i really have done to my bike is the standard free mods and a full exhaust system. Im planning on doing the motor after the next round and trying to figure out what would be a better way to go. High comp piston, Big bore, or maybe even both? Im wondering if anyone has done this before and if it would be at all reliable for running on a road course at higher RPM's most of the time. Any help would be great. thanks guys!

I would go big bore only.

Otherwise you are in the business of (very) expensive race gas, and precise jetting.

M.

 

[Big Zero]

If you are looking for the ultimate from your 426 motor, you should go with a total engine rebuild from a engine shop that knows four strokes. Steve Polk at Pinit Motorsports does engine rebuilds including crank work, big bore, headwork, and matches that up with carb set-up.

If you tell him what you want, he can build the engine to match your needs.

A friend of mine has an old YZ400F motor with stroker crank, big bore kit, headwork, cams, and exhaust that puts out 62HP at the tire. That is plenty to run with any 450 out there.

It all depends on what you want to spend. If you are happy with the bike, other than the lack of power, just buy more power. If you aren't that sold on the bike itself, sell it and start from scratch with a bike you do like. I saw a new in the crate 03' YZ450F for sale for $4800.00. That would be a good starting place, plus all your parts would swap over. Even with a newer 450, you will still need to dump in the cash to get the performance up. Cams, exhaust, etc. you will still be looking at $1500.00 easy.

Later

Paul G

 

[MotoMartin]

426 Power Upgrade

From Thumper Talk:

"You can get a 13.5:1 version of the 97mm Wiseco piston that will bring the displacement to 444 after a rebore/replate of the cylinder. If the rest of the engine is done right it will run with the newer 450s .
Here's a dyno chart of SFO's 444 running stock cams (reindexed) and stock valve sizes. At 52 horsepower on pump gas and 54 on Nutec it can stay with the 450s no problem."
http://www.four-stroke.com/Dyno_runs/SFO_index.htm

Also click on the Jon Escombe link at the bottom of the page, it looks like 55 HP is possible from the 444 cc kit, race pipe, HotCams and race gas. :clap:
This may be the way to go with a 426 like ours. I'm going to research costs (Wiesco, 13.5:1 piston, 2mm overbore, $142, rings $20, from Chaparral ), and shops that can do the cylinder work. Looks like Max Power in Madison, Wisc. will do the sleeve, Xtreme piston, and top end gasket for $550. http://www.maxpower-engines.com/bb-FourStroke.htm
444 sounds cool too like Ducati 999 :lol:
You might want to have your bike dyno'd just to see where you are in terms of HP. Stock 426 with a pipe should be in the 44 to 46 range if running correctly. A dyno run is about $50 out here in So Cal., it may point out carb issues.
Remember a stock 450 has about 48 HP so its not like a massive HP disparity, check your gearing maybe that's why they are pulling you on the straights!

 

[darrkrider]

P.S. If you do decide to put in a new piston, there have been several reports of the Wiseco's failing. I personally would order one up from cp pistons. :thumbup:

just curious whats happening with the wisco pistons?

 

[brian]

I have put many hard hours on my wiseco in my 500, pulled the topend off 2 months ago and it looked in perfect condition as my rings did as well......I too have heard the ugly stories...??? I run race gas with 40-1 synthetic and I have clean plugs and very good power (stock slug size (60 hp at rear) Not promoting the product at all but just letting you know of my findings with a 2 stroke engine.....someone told me the forged pistons are more stable and don't expand and contract as fast as the stockers..... ? just my 2 c's

 

[dbateman]

just curious whats happening with the wisco pistons?

people build a engine that is not set up for what thay need
piston to cylinder clearance is critical with forged piston
so you need to be fussy when you do your engine

 

[T-Bone]

Port and polish the head and toss in some cams and go

 

[fastkevin]

They say "there's no replacement for displacement", but a lot of times, both of your ideas end up giving more bottom end than anything else. If you wanna run down the straights, I would think a little more compression, but some head work. Get more fuel into the pump. Cams, carb or carb work, and port the head. I'd be also running oxygenated fuel.

 

[lrrs/uscra#517]

How is your gearing? After all, the straights are drag races. Not the sexiest thing to look at but cost efficent.

 

[someoneusedmyname]

A friend of mine had a totally stock '01 YZ426 in mx trim and nobody could catch him. Everyone else had sm trim, including my other friend with a 510 husky. The straights weren't too long but nobody could pull on him there either. I would make sure your jetting and gearing is where it should be.