In Gragam Bell’s book on engine tuning he did tests on various filters/ airbox mods etc. His tests on bhp/torque for a simple straight swop to K&N show very little, if any, improvement. Perhaps only 1-2 bhp at higher revs. He did see airflow improvements but power gains were marginal if any. The tests were on a normally aspirated 4cyl smallish engine if I remember correctly.
One useful test series he described was mearuing flow in the ahole intake system to identify choke points/ flow restrictors, which helped in repositioning the flow meter. I will have to read it again to get details. He used manometers to measure it I think.
I like his testing processes as he uses mule engines/ strips down to check/etc with before and after results. Better than the off 5e cuff impressionistic/ marketing comments usually seen.
Last edited by sospan; 01/04/18 10:14 AM.
