Q&A: Hot-weather racing

Radio Control Car Action, Sep 2000

Chris,

Q I love my HPI Nitro Star 15 engine-when it runs. I hate that I can not prevent it from overheating and keep it running. I live and race in the Atlanta, GA, area, and it gets very hot during the day. We race in a open parking lot with typical afternoon temps of over 95 degrees. I have tried several solutions, but I can not figure this engine out.

Richening the fuel mixture does not seem to affect the running temperature but it does make fuel consumption much worse-so bad that the car can't complete a 5-minute qualifier. I also installed a taller second gear in an effort to improve fuel economy and lower the rpm to keep the engine's temp down. That did not solve the overheating problem.

Then I tried 10-percent-nitro (down from 20 percent). I ran the engine rich to ensure enough lubrication, but it still overheated in the afternoon (although I was able complete the first qualifier early in the day). I have talked with other club members who run this engine, and all have similar problems.

My next question concerns the cylinder head. This may seem like a stupid question, but is the stock head cast or machined? It appears to be cast. I have talked to several drivers running other NovaRossi engines, and the only difference that I can see is the cylinder head. They don't have overheating problems. If you have the time, I would love to read your solutions to my problem. I'll be patient; I can only imagine how many emails like this you receive in one day.

Kent Easterday

A OK, Kent, let me first say I like HPI products a lot, but all products have their strengths ,and weaknesses. In HPI's case, it's the small, stock, cast head some of their otherwise good engines are equipped with. So you were quite right to look to your engine's heat-sink head as a potential source of your overheating problem. In moderately warm temperatures, this head does a fine job of cooling, but once you get into the gos, it just isn't up to the task. If you add high humidity to such a high ambient temperature, you're really in trouble.

Remember, alcohol is the main component of glow fuel, and unlike gasoline, which is hydrophobic (repels moisture), alcohol is hygroscopic (absorbs moisture), and that further raises combustion-chamber temperature. Unlike the Nitro Star iSSS, which has a tall, machined, heatsink head, your Nitro Star 15 has a cast head. Get rid of it and install a good, machined, heat-sink head. HPI and other companies offer one for your engine. That's heat-busting modification number one.

Next, if your car doesn't already have one, install some sort of tuned muffler system. Some HPI cars have one; some don't. If you car is equipped with one of those small expansion-- chamber mufflers with a hateful, heat-causing extension tube, don't run it even once more with this restrictive setup. For optimum cooling, a 2-stroke alcohol/nitro engine needs to breathe freely at both the intake and exhaust ends. That horrible little muffler with its extension tube is choking off the exhaust end and driving the temperature up. Get a good tuned system and you'll gain more power while experiencing lower running temperatures. Who could ask for more?

With these two changes, your car will be equipped for hot-weather running. But remember: this doesn't mean that you can now lean your engine out to the last rpm. Run it rich, Kent.