engines

Sometimes I wish I lived in the USA, where the Ho Bao Hyper-21 engine (marketed under the OFNA name there) is available for as little as $120USD. Over here in the UK, the price for an engine of this quality is still extremely good - I paid �110 each which translates to about $175 in American. Still. the difference mounts up when you are buying 2 engines. In the US I would have made a $110 saving. Never mind ey? We don't get snakes here.

To the engines then. I have read practically nothing but praise about the Hyper-21 on the net, and I have to say my first impressions are that it is very good indeed. The other engines I have experience with are the Thunder Tiger Pro-21 series, and these Hypers are visually superior and appear to be of higher quality. I hope the power output is as good or better - the Thunder Tiger engines are impressive at their low price.

With the engines in the car and the throttle links made, I started the run in. I will do this 1 engine at a time, so I can hear the engine running and spot any problems. After the first start up of engine 1, it was clear that this was a good idea. After 15 mins of running at idle, my ears were ringing. This engine and pipe combo packs in some serious decibels. Also, the compression is MASSIVE. A new engine should be stiff as the piston and sleeve are a tight fit, but after fitting the glow plug the engine was very hard to turn over - I can see why so many people have broken pull starters on this engine. The trick is to be patient and not go crazy trying to fire it up. Another thing is the mixture screws. All of them were very stiff to turn, so that should be good for holding their settings.

Having 2 engines with a maximum separation of no more than 10mm is going to cause some heat issues. What I did not want is the kit air filters obstructing the heat sink head of each engine. What a crap idea - what I want is an external air filter that both intakes feed from. This means it will need to have a super large filter area. I thought of making a still air box after deciding to scrap the supercharger idea, as it would take up the same space under the body. Then it was suggested to me on an email so I figured I would give it a go. I have the foam for the filter and the silicone connector pipes. For the box, I will use a small electronics box from Maplin Electronics. Just have to make sure it can handle the high flow rate - these engines suck in excess of a HUGE 3 litres per second.
Some quick calculations show that at 20,000 RPM this car will be travelling at 27MPH and will be sucking 3 litres/sec of air. I purchased a black plastic box, and cut out a 8.5 by 5.5 centimetre are in the base. At this engine speed of 20kRPM, the air speed into the filter foam will be 64cm/sec. This is easily within limits, and will hold up well all the way to both engines maxing out at 38kRPM, not going to happen on the ground though. I machined 2 aluminium couplers to connect the air hoses to the box, each with 15 degree tapers (any more would turbulate the air flow too much, any less would cause a sharp step or an overall air restriction). The box's new hole was covered from the inside with a 1" thick sheet of open-cell upholtery foam (the densest open-cell foam I could find). The foam is not as dense as comes with normal RC air filters, but this will be compensated for by the extra-thick 1" depth and the use of super-sticky filter oil. There is then a fairly large volume of 'still air', between the filter foam and the aluminium air intake ducts - all in the name of performance!