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Discussion Starter #1 (Edited)
Hi everyone! New to this forum. I was looking for some input on my engine build ive been undertaking for awhile now.

Im all set for my 727cc stroker build (+5mm crank), done all my head work and +3 TB and I find my cylinder plating has worn through at the top. I sent it away to be replated, now everyone is tossing the 770cc Big bore idea at me and im a sucker for power. This is a great time for me to go 105.5mm bore and get a new CP piston without breaking the bank. But...

Is a 770cc MX/GNCC trail bike realistic? I mean ill blow the competition away times 20, but it seems I might do it in the 12 o'clock position the whole time. Im looking for any input from larger displacement guys. Thanks everyone!
 

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I would go to a 105 so you have a chance to have one rebuild before you have to start over on the cylinder.
 

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Discussion Starter #3
I think Kran and Gunz wanted me to talk to you about what piston to run in a 770cc. Im hearing 10.75:1, 14:1, 12.5:1. Emphasis on 14:1. Any thoughts?
 

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There are quite a few people out there that run a 770 for MX/XC, I am sure that you will get the answers that you are looking for.
 

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that should be about like running a cr500 out there on the track amongst 250's. In the open its going to be untouchable...in tight stuff, its going to be a handful.
 

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Portsculptor
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Devildog is runnin a 771 on his MX bike.
 

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Ive never known anyone to run a 770cc. Im clueless past 727 and 734 builds.
Yeah, the 770 is a pretty common build now. A lot of people have put the HR crank in since it is a cheap option and seems to hold up good.

I agree with 135boom though, with the extra power it could be a handful with the tighter areas.
 

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Portsculptor
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Correct, 70+hp and 55+ftlbs is a tiring ride(thats what I ran) and will give alot more arm pump than you would think and thats off a std bore/std stroke build much less a big bore stroker.
 

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Discussion Starter #10
Its really hanging on for dear life that gets exhausting. Its ok, I have 2 years to train for GNCC 2011, more like 2012 maybe. I still have the stock crank. If anything I can toss it back in and have a big bore bike on reg stroke if im overdoing it. I still cant get in touch with Kenny to swap out my std bore 11:1 for a 14:1 105mm. SO I might end up with std bore anyway. Hopefully devildog hops on and gives me some input.Thanks everyone!
 

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With my mid 70's build I get Zero arm pump and the motor is DEAD reliable. I'd do 105 and big compression and never look back.
 

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Discussion Starter #12 (Edited)
Preddy, am I looking at anything else aside from what ive got?

RJ cam
+5 HR crank
Dynatek programmable
PCIII
CNC P&P
+2 ferrera valves, kibble springs
+3 TB

then a 14:1 105.5mm piston
and have US chrome bore out to 105.5mm

Did you resleeve with an iron sleeve? Is that why you dont have to Nikasil the alum sleeve? My roomate did that with his 250 2-stroke, part of my winter build if its do-able.
 

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preddy has a 105mm build which is the 770. I run a 105.5 with a HR +5 crank which is a 777. I'm very happy with my big bore stroker build. The parts you have listed are a great addition but you'll be wanting a clutch as well. I'd go with a lock-up and be done with it. I'm taking mine back apart to add a lock-up and wish I'd done it from the beginning.
 

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I don't have the stroker crank, just the 105 bore. Its a iron sleeve, which I prefer.

parts list sounds good. I'll be looking for a new cam come winter time. Kinda leaning twards the Web4.
 

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I don't have the stroker crank, just the 105 bore. Its a iron sleeve, which I prefer.

parts list sounds good. I'll be looking for a new cam come winter time. Kinda leaning twards the Web4.

A WEB 4 for the track? or the 300FT Preddy? I just don't see a reason for the WEB 4 to go in a MX or GNCC bike:eyebrow:
 

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A WEB 4 for the track? or the 300FT Preddy? I just don't see a reason for the WEB 4 to go in a MX or GNCC bike:eyebrow:

I like the power that my bike has now, more than enough as it is. I really dont need more low end power, so the web4 seems to be the best choice.
 

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Discussion Starter #17
I think I was thinking 105.5mm because ive been shopping on Team Rocket Factory.com. Dangerous place for me to look :). I was talking back and forth with Kenny in April and we decided the WEBB 4 wasnt the best for what I was looking at as for MX/XC use. I cant get in touch with Kenny to change from my 11:1 std bore to a 105mm 14:1. Hes doing a build package with all the head work and TB and all that. If I cant get in touch with him by Monday/Tuesday. It wont matter what I want cause US Chrome will Nikasil my cylinder back to std bore 102mm.

Fingers Crossed...

I hear what you guys are saying with the lock up, that will have to be part of a winter build because im tapped for this mid season build. I was a hot cam stage 2 guy with an exhaust and filter. Im freakin broke now! :)
 
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