As an R/C vehicle lover, I often search eBay for the best deals on parts and complete models. However, I have found two items being sold that are more harmful than helpful to the operation of the model and should be avoided at all costs.

K&N R/C air filter. K&N does NOT manufacture a filter for R/C vehicles. The filters being sold are 1:1 auto engine breather filters. These filters are made of oiled cotton material and DO NOT provide adequate filtration for any model engine. Model engine filters are manufactured of high density foam made to capture the smallest particle. K&N filters don't provide this level of protection and it has been proven that their use will allow dirt into the engine - a costly mistake to make. Only purchase filters made specifically for model engines! Once again, K&N DOES NOT make model engine specific filters. The use of the breather filters on a model engine is HARMFUL!

Custom rear exhaust. (EDIT:  A recent search of Truck/Truggy Pipe/Manifold parts failed to turn up these terrible components. It appears as though they are no longer being sold here on eBay - good riddance to bad rubbish! I will leave the guide up as a warning in case they surface again) This has been available for the Traxxas T-MAXX for some time now. They usually come painted in bright colors. These "pipes" are not performance tuned pipes. They are run of the mill COPPER PLUMBING PIPE. They are not manufactured for a specific engine and they are not "tuned" to provide the proper backpressure and performance for any model engine. Their use will result in extreme difficulty tuning and can lead to a ruined engine if the tune isn't richened enough. But richening the tune to make these "pipes" work will cost performance. If you are looking to purchase an performance rear facing or dual exhaust, only purchase pipes made specifically for your application by reputable companies. CVEC and TSAIS are two that manufacture REAL tuned pipes.

Avoiding these two engine killers will save any model owner a ton of grief. Remember, not everything you can find on eBay is golden!