To try and give some indicative answers to what method of replacement filter to fit, ive recently fitted both a replacement K&N panel filter within the existing air box and a replacement Pipercross cone filter and ran them back to back on a rolling road.
My car is a Si with a 2litre zetec engine and on all the rolling road runs was fitted with a simple de-cat pipe and modified air box with 2 additional 30mm holes.
First run with standard air box and standard paper filter corrected 119BHP 136lb/ft


then removed the standard filter and installed the replacement K&N panel filter, power went up to 125.9BHP and 142lb/ft


finally removed the air box and fitted the Pipercross cone filter power went up again to 128.8 and 144lb/ft


As the cone filter produced most power this is what i stuck with as my car is purly for track day, however the replacement K&N panel filter also seemed to produce good results if you wanted to stick with the standard appearance, ive also now fitted a ducted cold air supply through where the spot light was to avoid any heat soak issues.


Finally i must add these were the results i gained on my specific car and may not be totally repeated on anyone else's but hope you find it useful. Also just fitted a Ashley manifold with more results to follow

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Will

Excellent piece of information. Love the induction pipe looks really smart.

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Tied

Thats suprised me.

I had green panel filter with drilled airbox on my RS1800 at the RR day and that got 128bhp

But in real world applications, I still think the air filter cone next to engine is a bad idea.

I'm creating one which goes in place of the battery but with a box around the back to reduce any heatsoak, might even put some air vents in the wing

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Daily isn't so Special. And it makes me sad.
Need space and time and I'll crack on with Jams si!

Catch me on Facebook as I'm rarely on here.

119bhp & 136lb/ft standard vs 128.8bhp & 144lb/ft with a pipercross?

I guess it's possible... Maybe. But that means these wild bhp claims can be true from the back of the box, when 99% of people know that it's not at all and always largely over the top. Looking at the graph, the wheel power changed by nearly 10bhp from standard to panel filter, yet the engine power it creates is less?

It's always possible, but if people knew how god damn easy it was for the tuner to change the figure to whatever he wanted it to be to satisfy the customer, most people wouldn't bother imo. Basically I'm skeptical lol.

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Rest in peace Ben "Jam" Elvin. Gone but never forgotten.

All the runs were done over about 1hour, and hopefully indicative of increases you would expect in that a panel filter is better than standard and a cone filter bit better still, the small variations in wheel power to engine power is down to the transmission losses which varied 2.5bhp between runs.
When it went on the RR i wasn’t buying any of the filters and hopefully no need for operator to adjust anything. All figures quoted are the corrected ones not the pub talk maximum which was 133.3bhp.
Also when done last trackday i removed the nearside headlamp to eliminate any induction temperature problems, but what i might of gained in cold air would expect i lost in aerodynamics!

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Will