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TeamScream

Max power out of a 426?

22 posts in this topic

Does anyone know what the factory guys were able to get reliably out of a pumped up 426 engine?

I am seriously thinking about 2 options for my supermoto endeavors.

1) spend considerable money with engine work to try and get over 50HP to the rear wheel and have it last a while if at all possible.

2) buy a KTM and start all over with a bigger displacement machine that has more room to grow.

What I am looking for is anyone with inside info from some of the builders that have seen huge power increases with head/bore/stroke work and can share that info or point me to a builder that can make it happen.

I have read the TT supermoto project bike page and noticed that they got 49+ hp with a big bore/carb/ignition upgrade, I am actually looking for more than that.

i plan on competing in the AMA supermoto races thsi year and would like to run my 426 since all of the other trick stuff is already done (susp, brakes,wheels etc.) wheres the super duper secret stuff kept?

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WOW SFO

I am so glad you saw my post and replied, thanks so much for posting those dyno runs, I greatly appreciate it!

I was seriously thinking of sending the whole motor to Eric Gorr and just letting him work the magic on it, what do you think abou that? would it be wise to get the crank balanced?

My motor only has roughly 800 miles on it now, the bike is still in virtually brand new condition, but I feel that it would be prudent to at least have all the bottom end stuff spec'd out along with the big bore kit.

It is amazing that the power numbers you show dont vary that much from pump gas to the Nutec, 2HP is not a whole lot, specially if the (your) bike runs as strong as it seems to with good pump gas.

Please let me know what else you found out after you did your engine that you would have done differently and I will take that path.

PLEASE feel free to email me, I would love to correspond with you on this project, do you plan on making it to the WSBK weekend this July @ Laguna?

I grew up in Carmel Valley, and my father still lives there, so maybe we can hook up??

Thanks again bro for the posts.....greatly appreciated!

Dauv McNeely

videoassistla@yahoo.com

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WOW SFO

I am so glad you saw my post and replied, thanks so much for posting those dyno runs, I greatly appreciate it!

I was seriously thinking of sending the whole motor to Eric Gorr and just letting him work the magic on it, what do you think abou that?

Sounds like a plan

would it be wise to get the crank balanced?

My motor only has roughly 800 miles on it now, the bike is still in virtually brand new condition, but I feel that it would be prudent to at least have all the bottom end stuff spec'd out along with the big bore kit.

It wouldn't be a bad idea to do a bottom end inspection, if those 800 miles are race miles I might consider crank replacement, but if Erics doing the work I would defer to his judgement.

It is amazing that the power numbers you show dont vary that much from pump gas to the Nutec, 2HP is not a whole lot, specially if the (your) bike runs as strong as it seems to with good pump gas.

I was surprised too, Yamaha really did there homework the ignition curve and and the chamber design doesn't allow hp increases with doped fuel. Even the vortex is not an improvement on the stock ignition with this set-up.

Please let me know what else you found out after you did your engine that you would have done differently and I will take that path.

The only changes I would run now are the KMPI SS valves and running '00 springs.

I am playing with a few head combinations to get more hp at higher rpm's but this is only suitable for DT and Motard.

I might consider a custom Thunder Alley down pipe,and when Hotcams comes out with their decompressor cam I will be running that too.

Bill

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Good work guy`s,what`s the script with the valves and springs,is doing the crank the only way to get them to run real smooth! :)

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What do you mean script?

I run the SS valves because of durability. The oem TI ones work fine but are expensive to replace, the ss ones are cheaper and refaceable.

I use the pre ti springs from the '00 model to bump the seat pressure up for the heavier valves.

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Ok SFO,

I just spoke with Eric Gorr, finally got a hold of him...he's very busy.

Anyway, you mention head work? what head work did you do to still keep it (the whole build) at roughly $800.00 ?

I would also really like to chat with you via phone? will you call me collect? I guess the thing that makes most sense for me to get ready for the next race would be to get the stuff done as fast as possible and Eric is like 3 weeks plus out right now on any work, so I think I will tackle this in stages, I will send the cylinder out to US Chrome for bore and plate, order the weisco 444 13.5:1 piston kit and order a thunder alley pipe, i have all the jets needed to get it close when I get it all together, but I would really like to talk to you about proceedure, I am an accomplished mechanic with enough skill and cleanliness to do the work, but I would like to know if yu found any work arounds, special 'tricks' that make the job easier, more flawless whatever?

Thanks for all the good posts and please email me with your # or so that I can email you with mine if you dont mind spending a few minutes with me on the phone?

Thanks!

videoassist@socal.rr.com

Dauv McNeely

im in Los Angeles.

Thanks SFO.

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Dauv...

I met you last year at Laguna, I'll look for you this year to see how your bike is doing. I just bought a 426 cylinder that I'm going to send out because I'm doing the same thing... the 97mm piston, and SFO has been providing me with info on another message board. I'm going to do the 444cc thing along with a new rod (I have to change the rod because my WR is a 400 not a 426) and new timing chain and valve springs. Then, next winter I'll probably do some mild headwork along with the bigger intake valves.

I am also waiting for the Hot Cams auto decompressor camshaft to come out. Starting my WR has never been a problem but once I got my CRF I fell in love with the simple "kick and go" and can't wait to get the cam for my WR, I'm buying one the day they hit the market.

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Ok SFO,

Anyway, you mention head work? what head work did you do to still keep it (the whole build) at roughly $800.00 ?

Forgive me for overstating the $$.

I used to think I wanted to do this for a living too, I see why I don't.

Try Mike @ EDCO for the headwork.

Tell him you read about him on TT.

Tell him Bill from SF sent you.

If enough Thumpertalk guys send work to him he might become a sponsor of this noble website and that would be good for everyone.

He can do a race prep of your head. Tell him your goals and application. He is really good. His wife Jenny answers the phone and is a smart woman too.

This is the fun part :):D :D

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Make sure that US Chrome has the piston in hand so that they can properly fit the piston to the new bore size.

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Ok i am getting all my ducks in a row for this project, i taled to Edco regarding headwork, I talked to Thumper Racing and Eric Gorr for the Big bore kit, Eric's prices are the best but hes got no exchange cylinders in stock, so he told me to go direct to US chrome for the bore and plating, called them and got a $213.00 price for the job + $192.00 for the piston kit (rings, pin etc). Looking in my manual it looks like the only tool I will need that I dont have is the wrist pin puller, does anyone know if this is a yamaha only part? or is there a craftsman/snap-on equivilant that will do the job?

It looks like its going to be a 2 week deal no matter what with shipping and the actual work etc.

I have heard from Thumper Racing that the high compression (13.5:1) piston is not really the best way to go, it locks you into race fuel and the difference between that and the 11.5:1 is insignificant bot seat of the pants and dyno numbers, any comments on that?

Excited?...you betcha

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I talked to Thumper Racing and Eric Gorr for the Big bore kit, Eric's prices are the best but hes got no exchange cylinders in stock, so he told me to go direct to US chrome for the bore and plating, called them and got a $213.00 price for the job + $192.00 for the piston kit (rings, pin etc). Looking in my manual it looks like the only tool I will need that I dont have is the wrist pin puller, does anyone know if this is a yamaha only part? or is there a craftsman/snap-on equivilant that will do the job?

I have not needed the wrist pin puller the manual talks about. The pins comes drift with a light nudge by a delrin punch.

I like to run a 2B fittment roll tap through the threads in the case just to have them cherry, also lubricate these same threads on the thru bolts that tie the head and the jug to the case with never seize or assembly lube and the washers under the bolt heads. Want to make sure we get a proper torque so we don't experience head gasket anomolies that are prevalent on the 97mm 426.

I never had issue with this.

Be scrupulous about the surface prep on the head gasket surfaces. Pre assembly cleaning with acetone or brake cleaner is a good idea. Retorque after initial run in.

It looks like its going to be a 2 week deal no matter what with shipping and the actual work etc.

I have heard from Thumper Racing that the high compression (13.5:1) piston is not really the best way to go, it locks you into race fuel and the difference between that and the 11.5:1 is insignificant bot seat of the pants and dyno numbers, any comments on that?

Excited?...you betcha

Any comments on that?

You bet. The dyno has proven this motor will run on 92 pump premium the same as it runs with Phillips B37 which is 108 leaded. Save the $$ and run pump. I also ran this motor 1400miles wfo through baja on my honeymoon. Many refills w/pemex and the local brew that is mouth siphoned out of a 5gal bucket w/a hose.

No evil side effects.

How is it versus a 12.5~1 motor?

Couldn't tell you.

If you don't like the 13.5~1 piston, I'll buy you a 12.5~1 to replace it.

Just for giggles :D:):D

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I also ran this motor 1400miles wfo through baja on my honeymoon.

What the hell? Where was your wife during all this? Were you trying to make a run for it and escape from her? :)

We could probably have a contest to come up with replies to that quote and they would be damn funny!

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What the hell? Where was your wife during all this? Were you trying to make a run for it and escape from her? :D

She was along side with her KTM200 wound tight! :)

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Okay SFO, I have yet again another question...

If I decide to buy a complete crank assembly from Yamaha instead of just changing out the rod, which one do I get? I know there was some kind of differences with the balancer gear or something... splined vs. keyed. Can I get a 426 crank that will use the balancer gear I already have or would I need a different gear as well?

Also, I just put this up on ebay but maybe I can use it in my WR instead!?! :).... ebay piston

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