Originally Posted by CurveTracer
An aluminum chassis assists the engine at achieving a constant temperature during racing because of the heat soak/transfer properties of the engine block and mounts. Could you help us understand why this property is a problem?
Also you mention only one engine test. What combinations of engines, racing conditions and ambient temperatures has the carbon fiber chassis been tested in to prove that it will not be detrimental to engine life?
This is something that I tested while working at Car Action Magazine and on engines run during National and World Championship events. So I've done so under some of the most strenuous conditions and the results are a surprise to most. In some respects, the "cooling" provided by the chassis can be more detrimental than helpful. I didn't test a carbon chassis, but rather steps that I had taken to insulate the engine from the chassis to prevent heat transfer from the block. On paper, the cooling from the aluminum chassis SOUNDS appealing, but I've experienced results that show that's not the case.
The chassis pulls heat mostly from the engine block. In all but the hottest conditions, that's not always ideal. In discussions with Dave Gierke, who is one of the most experienced engineers in the world as it relates to nitro engines, we talked about the fact that over-cooling the engine block can have a negative effect on the power and efficiency of the engine. The heat in the block helps to keep fuel vaporized, which makes it burn most effectively, producing more power and consistency. Tapping into the conductive cooling of the chassis can cool the block to the point that the air/fuel mixture condenses, which begins to effect all the aforementioned in a negative manner.
Speaking of conductive cooling, another undesirable aspect of cooling through the chassis is the amount of time it takes to saturate with heat. Tuning an engine in the amount of time available at most big events is guess work because the chassis is far from saturated in just the minute or two of warm-up time allowed. It generally takes about 7-8 minutes of running at full speed for the engine and chassis to completely saturate with heat and stabilize - in colder weather it takes longer. It means you basically have to guess at your mixture setting and this is the number one reason you see engines going lean during the course of a main. Once you get enough experience, it becomes easier to guess, but it's not ideal for the average enthusiast.
Insulating the engine from the conductive cooling of the chassis allows the engine to heat up and saturate more quickly, which makes tuning a lot easier and more accurate, so for practical purposes the engine is LESS likely to be damaged by someone who's not an expert tuner. Even as a skilled tuner (if I can say so myself without sounding too full of it) I preferred the behavior of the engine when insulated from the chassis. The acceleration was a little stronger, the fuel economy improved, and there was no measurable loss of engine life. The changes are subtle but definitely notable. Also keep in mind that ABC engines NEED heat to get the sleeve to expand fully, so there's no correlation between nominal heat increases and engine life. In fact I believe that the engine life is as good or better because when the sleeve fully expands (and faster than normal) there's less stress on the engine internals (bushings, bearings, etc.).
I continue to insulate the engine from the chassis to this day because of that experiment starting about 10 years ago. This isn't the same as running a graphite chassis. Graphite is a little more thermally conductive than the insulating material that I use, so it probably cools the engine block more than I would prefer, but certainly less than conventional aluminum mounts and chassis plate.