View single post by discogodfather
 Posted: 08-29-2020 06:17 am
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discogodfather



Joined: 09-17-2007
Location: San Francisco, California USA
Posts: 221
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 Forced induction vs. NA probably plays a big role in the shape and size of the airbox, as well as the length of any trumpets/air horns you want to fit inside the airbox. Pipercross in the UK told me for any airbox, the length of the gap between the mouth of the bell and the wall of the filter or airbox itself needs to be at least 19mm. That gives a good idea of why Lotus made the airbox so deep, considering on the DHLA models the stock trumpets were around 30-40mm?

Pipercross also told me it's always advantageous to fit the largest box and largest filter that size constraints will allow, just as a general rule.

This Pipercross 600 pictured was too small for a higher performance high compression 907 (still 2 liter). It worked but the slim profile and cone filter, even with a full 4" ducting to the front of the bumper, caused some constriction in the system enough to need re-jetting, so I gave up on it. The cone filter was only 4.5" in diameter, kind of on the small side, and it was probably the major flow restriction. Even with the gap between the edge of the ram horn mouth and the airbox being 22mm, it didn't seem like enough.

I ended up just using a massive foam breadbox shaped setup and it doesn't need any adjustment with or without the filter, which I always have taken as the best indicator that there is no restriction in the system.