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Discussion Starter · #1 ·
Some people know that I was slowly, in my spare time researching and plotting a sleeper motor build based on the 3v head made infamous by SDG. I wanted to see if an import build could be made to go toe to toe with a built Honda, which we know they can now, but specifically I wanted it to be an even displacement fight. I also felt there was potential in the 3v head itself and wanted to see how far I could exploit it.



This was going to be my attempt to match a Kitaco 124SE.



Well, I've since picked up a new project that's going to suck up a great deal of my time and money, and I ran up against a couple technical issues with the 3v planning that I haven't sorted yet. I figure I might as well toss this info out for the world to see what happens with it.



Anyone that makes it work had better credit me some though! :p



http://www.x386.net/TTR/Sleeper/3v.html

http://www.x386.net/TTR/Sleeper/motor-worksheet.html



These were my working notes. As you can see I was shooting for a shorter stroke motor, with high hopes that I could use high revs to get me the HP I needed.



I ran into problems though, both revolving around the SDG 3V head. The first is the head itself. Out of the box it uses two 19mm intake valves, which on paper should work like a single 27mm to 29mm unit. There wasn't any room to go bigger though, and worse, they are at a pretty steep angle compared to modern heads. Not to mention HEAVILY shrouded by poor combustion chamber design. I didn't consider this a show stopper, a bit of time with a carbide burr would fix the shrouding, and I could live with the included angle and limited valve size for now.



What did stop me from going my preferred bore x stroke setup is the size of SDG's dowel pins. A good mm or 2 larger than what a Honda or Lifan/GPX uses. There is no way to safely hit a 60mm bore let alone 61 like you can with the other big import mills. I figured I could bore the cylinder out for the sleeve, fill the stud paths (now exposed) with weld, press in a sleeve, and re-drill the stud paths, but not open them up for dowel pins. Instead I would drill the cylinder and head in a couple spots to use external locating pins, and try and do the same for the base. Still may not get enough of a sleeve to go 59mm.



Plus the added fun of trying to rework a 49.5mm crank for a 41mm stroke, no idea where to start on that process. : )



As to why I did all of this research and never lifted a wrench... I haven't got a whole lot of shop access, what little I do get, I need to make the most use out of. This is why I'm a theory nut, I want to have my ducks in a row before I settle on a build path so I can do the job once. Planning this much out, researching online, chatting with many here on PM, even though I've nothing to show for it was still time well spent. I've now got a much better understanding of what makes these things go, and how to make them go faster.



One result of this research:

http://www.x386.net/TTR/tech/cgi-bin/motorsim.cgi



Slower than death because it's on a 386, and not very accurate, but still fun to play with. Red on the chart is up to 75% volumetric efficiency, yellow up to 100%, Green is up to 115% efficiency.



There, how's THAT for over-sharing. : )
 

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A short while back there was a foreigner who posted a link to a 3v head that had lifan/jialing stud spacing if that really exists that would make your proposition possible.
 

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Discussion Starter · #5 ·
RcWannabe said:
A short while back there was a foreigner who posted a link to a 3v head that had lifan/jialing stud spacing if that really exists that would make your proposition possible.


I think I know where to get those heads, still have the combustion chamber and intake mess to clean up, and valve size restriction though. I was kinda hoping some cheap 4v import heads would hit the market, possibly with better combustion chambers and valve centers, but that never panned out.



If I get spare funds and time, I may just have to track one of those heads down.
 

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Discussion Starter · #7 ·
After trying the Pro Mini motor in a 70 chassis today for motard... WOOHOO I'ma gunna build me an import for my 70! I'll be selling off my stroker Honda motor after the current indoor series closes up in a month or so I think. I like to think my 51 x 54 motor is fast, but dang, it's no match for a 141 Lifan. I can't wait to try actual porting and other head work. :p
 
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