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Discussion Starter · #1 ·
To start off I have a 06 Carb with a Miller ATV Ported head, 96mm 12.4:1 Wiesco Piston, barker exh, FCI and cam mod. My last dyno I had was with that new setup at it dyno at 47hp. Which I remember others saying this dyno runs about 3hp low but I feel thats not that true as I run the same as a newer efi yfz only with the big 3.

Here's my dyno chart on Previous Setup:

Now what I need help with is my piston and rings are worn and the cylinder has no cross hatching left. So I plan on buying a new cylinder, piston and new valves. Now this is the area of what direction to go with power but would like to still run on 93 octane pump gas.

Option 1 to go back to a new OEM factory jug with a 95mm 12.75:1 CP Piston and oem cams and valves.

Option 2 is to go for a big bore like a 470-480cc kit with a 12.75:1 CP piston.

Not sure how much I would gain from the big bore and if its better to make reliable power with a factory setup at close to what I had.

I also have done some reading in the threads where the 06 has the shorter connecting rod but has 10cc more because of the head volume. So from my understanding my current 12.4:1 piston is lower on compression that I originally thought.

I'm just at a loss for what to do because I have never ran big bore and don't know any one personally who had a "built" motor other than me. And my friend just got a '86 TRX 250r so kinda feel I need to up my horsepower so I don't get murdered with what I know he is building his motor too.

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The big bore kits are fun but they have a brief life. I would dare say that they seem to last half as long. Option 1 is what i would do and maybe reach out to Miller to see what cam options pair well with the port work they did or even get the head re-done with bigger valves and cams to match. Ultimately, I would reach out to a builder that still does the older YFZ's because they probably have a few good recipes.
 

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Discussion Starter · #3 ·
The big bore kits are fun but they have a brief life. I would dare say that they seem to last half as long. Option 1 is what i would do and maybe reach out to Miller to see what cam options pair well with the port work they did or even get the head re-done with bigger valves and cams to match. Ultimately, I would reach out to a builder that still does the older YFZ's because they probably have a few good recipes.
Thanks for the input! Yeah I think I may go the option 1 route but slight change. I also believe my my crank is bad causing some side wear on the piston. But any how I have been trying to get in touch with Geoff at MMAD to see if he can do my head work and maybe do a 1-2-1 combo from him. That way my head is done and can support any mods going forward on my engine. I tore the head apart and the valves look to be worn.
 
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