Big bore kit or stock bore with High compression Piston

I getting mixed information.

This Info for 2000 YZ426

So if I going tear into it should I go Big bore 444 with stock compression 12.5 or the 13.5 High compression piston will the High compression run on Pump gas or do you need to run race gas.

Cams for a big bore Kit for me I already have the Hot Cam the stock motor will the Hot cam be enought for the big bore do you need a more agressive cam proflie for the larger displacment.

What I read the 444 big bore will have much more out the hole grunt but the motor will sign off sooner do not getting fuel and air into the motor that it need to get the most out the bigger bore kit you' choking out the motor a higher RPM's range.

On the Hot Cams you can Redergree the cams to give more botton or top end if you redgrree the cam for more topend how much low end will you lose if any do to the larger displacement.

Or is just better to run a high compression piston with the stock bore then once again can you run pump gas with this setup.

As for porting the head or just cleaning up the casting flaws to get the head to flow better or pay the money to have a full tilt Port job from a good shop not some bucther.

For me a desert rider more over rev would be ideal for what I need.

I read others say they hit the rev limiter I never had the bike hit the limter just runs out motor before it gets to rev that high.

I dont know for others this a long term project so more or less I not worried how much it cost I will save until I have the cash to do the motor it is my toy I also planning to put the WR 4th and 5th transsinon gears in the cases and a new crank as long I in there like I said no big hurry just like to know what the best bang for the buck.

I also up grade the crank to a 2001 or 2002 set up to have the spline type not the woodruf keyway.

I know I could buy a newer bike but why I end doing the same to it LOL.

I like the 426 I feel right at home on it so thats why I build the bike I have I ownned newer bikes but I like the Old school 426.

Edited by marv02

I've got both the big bore AND hi comp piston, along with hot cams on my 426. It's a beast. It does bounce of the rev liiter with little difficulty, and pulls like a tractor out of the hole.

Do have to run race gas or pump gas.

I've got both the big bore AND hi comp piston, along with hot cams on my 426. It's a beast. It does bounce of the rev liiter with little difficulty, and pulls like a tractor out of the hole.

My 2000 426/444cc motor has both hotcams and head work and runs perfectly fine on pump gas.

I have this motor in a hybrid custom quad chassis so it's much heavier then a dirt bike. If it was going to ping and act up on pump gas it would on mine way before a 2 wheeler I would think.

Edited by SWIGIN

Thanks for the info like I said I likre the 426 but it need more power to it I use to a 60+ H/P bikes.

I know it wont be as much but a couple more H/P sure going to be nice with out the draw back of the other bikes I had with the higher H/P.

Can you let me know what jetting are you using with you'r 426 big bore with high compession piston and ported head so I have a base line to go off of.

Mine, too, runs fine on pump premium (97 octane here in Cali). JD Jet Kit, red needle on 2nd clip from the bottom, 175 main, 42 pilot.

Mine, too, runs fine on pump premium (97 octane here in Cali). JD Jet Kit, red needle on 2nd clip from the bottom, 175 main, 42 pilot.

Thanks for the Info

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