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GUNSHIPGUNNER -> Simple Method To Find T.D.C. (top dead center) (4/12/2002 6:55 AM)
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[QUOTE]Originally posted by Coulter_Dean
Sounds neat man:)
Just what can I expect to gain from porting a two stroke? and what size engine is this usually performed on? Thanks:D [/QUOTE]
Consider this regarding porting.
Most engines are designed so EVERYBODY can operate them with some measure of ease and success.
This everybody includes everyone from your basic Bonehead (according to 3 of my ex-wives I belong in that category)
to your basic genius. And all those in between.
So the engine MUST be easy to start, easy to get to idle reliably, produce reasonable power AND last more than a few flying sessions.
In order to fill the above requirements the manufacturers will always err on the conservative side when designing their engines for public consumption.
BUT!!
Specialty engine producers like Jett, Nelson and a few others don't need to be so conservative for a couple of reasons.
First is the price. Only a very small percentage of consumers are willing to pay the extra money these specialty engines can cost. This eliminates most of the Boneheads.
Secondly, these engine makers make it very clear that their engines are NOT suitable for nor are they intended for use by the average consumer. They also make clear the fact their engines require an extra dose of skill and caution to operate.
And they don't usually warranty them. A fellow who is unsure of his own abilities is less likely to buy one whereas experienced fellows don't give this lack of a warranty a second thought. The skilled engine user knows who does and who doesn't make good engines and they know what they are getting into when they buy from one of these specialty manufacturers.
Which leads me to the point of this post.
Your average RC 2 stroke Glo engine will respond very well indeed to a few simple modifications.
The extent to which you modify an engine can really be broken down into two categories.
The first category would include fairly mild mods to the engines port timing, compression ratio etc. While these mods are being performed to increase power output it is important to retain a reliable idle, fairly easy starting and end up with an engine that still lasts for a few flying seasons.
This type of engine can be an excellent choice for aerobatics flying, pattern type flying and in the especially demanding type flying that involves hovering, harriers and other 3d maneuvers.
The second category would encompass modifications based on obtaining maximum power output with little consideration for prolonged idling, ease of starting (that why God created electric starters!!:):) or longevity. These mods can include radical porting, bigger carbs, increased compression Etc.
This type of engine is better suited for Pylon racing, Warbird racing and other applications where speed is foremost.
I have been modifying engines that fit both of the above categories for several years with some success. Along the way I have made lots of mistakes and probably wasted more money than I should have. But I sure had fun (still am!!)
One thing to keep in mind about modifying these little engines is that someone has probably done it all before. Made all of the mistakes, had all of the successes. The key is to find out if these fellows bothered to document their experiences. If they did, find this info and study - study - study it. That's how I id it. (and still do) I read and re-read everything I can get my hands on.
Just recently I modified two of my favorite engine for use in a couple of my profile "Fun Fly" 3D type aircraft. I use APC 12.25X3.75 props almost exclusively for 3D flying. These props take everything a little .46 engine has to offer.
As I indicated earlier, 3D flying is extremely demanding. Throttle response is critical. So is reliability. If the engine "bogs" or dies when you wack open the throttle and you are in a low hover, the results can be catastrophic. 3D flying requires you to operate the engine in the upper mid RPM range, producing almost maximum power while receiving limited cooling airflow. So any mods have to be done keeping these things in mind.
The 2 engines I reworked are an MDS .48 and a .46 Raptor. I left the carb size stock but increased the exhaust duration (so they would better respond to a tuned pipe ), the inlet duration and the transfer ports duration. I also kept the compression ratio stock as I like to use a higher Nitro content fuel for the better throttling it can provide.
Both engines now produce a lot more power right where I needed it the most (3/4 throttle and above) They have almost perfect throttle response and operate at just under 400 degrees temp.
I hope this rather long winded post is some help to those flyers considering tinkering with their engines.
There are lots of experienced engine builders on this forum that I'll bet would be willing to help a fellow get started down this path.
Good luck!!
GSG
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