Un-silenced is open around the bottom. a sikenced is a sealed unit. If you had ever driven cars with both you would know how much louder the un-silenced was. That is where it got its name .
A un-silenced style on a thermal-quad car is very obnoxious. The 70-71 style were designed to aim the noise from the carb suction front. This muffled the sound.
I have a silenced style for sale off of a 70 same as 71 but I didn't answer your ad with a PM because it would not have been what you are asking for.
you might want to change your title and remove "un-silenced" It would might change responses. Just trying to help you find the correct breather at a reasonable price.
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