SLS Standard Liter per second airflow (corrected for temperature and humidity)
SCFM Standard Cu. ft per minute airflow

VE = volumetric efficiency (generally volumetric effciency of small engines is inversly proportional to RPM so VE at Max HP (not torque) is the lowest VE. I would say 91.% is fairly good

Do you think the torque curve is Flat? I have not plotted it yet but I thought it was normal for an engine that is to be run at around 7000, peak power at 7600, low torque power peak 6200 or so RPM.

the specimen I have has significant downdraft on exhaust, 29 degrees on the top and 45 degree on the bottom wall of the exhaust manifold chamber. I have not measured it against TDC and piston center, but I am quite sure it is exactly alligned to the top of the combustion chamber.
It is done to aid scavenging effect as well as to bring the muffler mount lower and nearer to cylinder base. The idea is that as the piston moves down on the power stroke, the gas expansion follows the piston movement and achieves its highest expansion speed near the piston surface. As it reaches the exhaust port, it follows its downward and outward trajectory and has a smoother exit through a downward sloping exhaust manifold chamber. It is an excellent design element that increases the volumetric efficiency..
Industrial engines have straight box exhaust chambers. Larger glow engines such as Supertigre have lower surface of the box angled at around 15 degrees but zero degree on the top.

http://www.3mmodel.com.tw/yak-1.wmv
http://www.3mmodel.com.tw/0217yak54.wmv
http://www.3mmodel.com.tw/yak54.wmv
http://www.3mmodel.com.tw/

--------------


Yep, but not long after that, some young dudes with some machine shop experience will discover the new super cheap engines being made in India or Pakistan and they will begin offering those at 1/2 the price of the now expensive Chinese engines.

And that's Capitalism...


Ed Cregger

Sid,
Thanks for the explanation. Now the numbers come alive.
As to the angles of the E-port:
Sound pressure waves do not mind angles, however sharp. They dislike sudden cross section changes, which are evident with the just opened port whichever way you look at it. Angled ports don't help here.
Gas flow in a cylinder is rather stagnant, but it indeed follows the piston for the expansion front. The funny part is, that gas flow will not exceed piston speed, which is about 20m/sec at port open time. The gas flow speed out of the port however will be equal to sonic, as long as the pressure difference ratio is 1.4! That puny 20 m/sec now have very little influence, if any at all, because the speed is present before the venturi formed by the piston crown and port upper edge. Look at it like a slug of high pressure gas, ready to go any way it can.
I have experimented with port angles, and found no gain or loss in them.

I was refrencing the actual exterior mounting surface on the head, the internal chamber is angled. I have found no abnormalities on any of the engines I have gotten in stock from a basic visual inspection.
www.dawghouserc.com is up now and I hope to get some more of these engines in the field shortly. I also have a couple going out for extensive testing in multiple prop/exhaust configurations. I hope to get some good feed back on this to get out to the consumer...