Re: General 5-Star Build - Fast 50cc Single-speed

Mikey Antonakakis /
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Chapter 4 - The Engine

So, my searching for fast 50cc motors, at least those readily available in the US, led me to kids' dirt bikes. KTM 50 SX Pro Sr, circa 2001-2006 or so, seemed to be the best compromise. Parts are plentiful enough, and their clutches were frustrating enough to keep prices for motors somewhat low. The newer generation(s) of the KTM 50 have better cylinders and clutches, but they cost more, at least at the time. And the version I ended up with certainly ain't bad! Hard numbers are hard to come by, but seems to be something like 14,000rpm, 10hp, 9000rpm clutch out of the box. Not bad for a single-speed!

Of course, I am trying to nudge the limits of 50cc single-speed, so I dove into the beginnings of a plan to extract more power. More power would necessitate a better clutch, so I ended up with a Tomar Hole Shot. Apparently, much less frustrating than the stock 3-shoe, and a quality item. Of course, the real tough part of single-speed, well, speed, is balancing clutch meltdown/explosion with acceleration with top speed with durability. Pick two, maybe three of those. I'm sure many, many of you know too well.

But to start, I just wanted to see what kind of power could be extracted from the stock cylinder. It has pretty good ports, better than pretty much all moped kits, with a 3-port exhaust and 7 transfer windows (4 main, with the boost port broken into three interconnected windows). The main downside is the rather sharp bend in the main transfers, and less-than-ideal reentry of the auxiliary exhaust ports back into the main:

20160525_223631.jpg

I used these port molds to start modeling the engine for simulation in EngMod2T, a fantastic software. Some of the world's most accomplished 2-stroke tuners use it and it helps them push the envelope in their classes - think 50hp from a 125cc kart engine - they have found good correlation between the simulation and the dyno. Like any mathematical modeling, there are significant assumptions baked in (especially because EngMod is a 1-D simulation), but if you're in the ballpark, one of the most powerful aspects of simulation isn't the raw numbers (50hp from a computer doesn't mean anything), but the ability to compare design/tuning options back-to-back. That said, as with most things, garbage in = garbage out.

So at the time (May 2016) I explored some options - given a need for high clutch stall, should I go for a crazy high-RPM setup, or closer to the stock motor? If I'm going for raw performance, durability be damned, high rpm setup (exhaust duration increased about 20deg, transfers about 10, for a total timing of something like 205/130, with pipe to match) makes much more power under the curve:

7IgNAqy.png

As for progress, that was about as far as I got back then. For the next 3+ years, everything sat on shelves.

This single post is part of a larger thread. Start from the top or view this post in context.
Subject Written By Posted
  General 5-Star Build - Fast 50cc Single-speedTopic by: Mikey Antonakakis Mikey Antonakakis 09/03/19 03:20PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 03:32PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 04:14PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 04:21PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 04:46PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Overpriced Parts Overpriced Parts 09/03/19 05:10PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 05:19PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 06:08PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 06:22PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 06:32PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 06:41PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 06:49PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 06:55PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 06:59PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 07:05PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 07:13PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/03/19 07:43PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Aaron Blair Aaron Blair 09/03/19 09:23PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Johnnie Distefano Johnnie Distefano 09/04/19 12:39PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/04/19 03:44PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Chris Squid Chris Squid 09/04/19 08:25PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: ken gilbert ken gilbert 09/05/19 05:32AM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 11:03AM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 11:23AM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 11:39AM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 11:47AM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 12:07PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 12:19PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 12:25PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 12:32PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 12:37PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 12:43PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Brandon Weiss (Detective brandon to you) Brandon Weiss (Detective brandon to you) 09/05/19 12:44PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 02:17PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: alex . alex . 09/05/19 02:03PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 02:20PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 02:26PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: ken gilbert ken gilbert 09/05/19 02:22PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 02:33PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 02:41PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 03:09PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 03:15PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/05/19 03:47PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/06/19 01:18AM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/06/19 01:46AM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/12/19 11:03PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/14/19 10:21PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Born to be WillD Born to be WillD 09/18/19 07:33PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/18/19 07:49PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Alex Hedrick Alex Hedrick 09/21/19 02:30PM
  Re: General 5-Star Build - Fast 50cc Single-speedRe: Mikey Antonakakis Mikey Antonakakis 09/21/19 10:16PM

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