In an effort to reduce my noise levels to get past the Donington sound gestapo, I have constructed and fitted an airbox. It's basically an alumium box with a cone filter attached to the end of it (see photo - sorry the phone was the only camera I had to hand). Using my LC1 wideband air / fuel meter I have rejetted the carbs (honda blackbird) from 170 mains they were running with the foam sausage filter to 155 mains and it's still running a little rich (I'll order some 150's in the morning). The question is does this change in jet size sound about right / normal? The car is certainly down on power but it's much quieter. I guess you can't have it both ways.

thanks
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hmmmmm, shouldn't be down on power.......that filter must be restrictive if it is.

More money but I would have gone for a K&N cone, one of the large ones, should be good for no restriction up to 400hp or so

what Diameter pipe do you have from the filer to your airbox???.

Ray

The pipe is 70mm diameter (couldn't get a bigger pipe to fit). The filter is a Pipercross cone which is pretty big. Something is definately strangling the carbs though not sure if it is the airbox (which should be big enough) or the filter. With the original 170 main jets the car just bogged down at 4000rpm and refused to go any higher. The wideband meter confirmed that at this point the AFR was about 8.9 - 9!

I have in front of me a Green cotton induction kit designed for a Golf 2.0 GTi 16v (very cheap ebay buy - someone couldn't spell induction properly). Included with this is a large cone filter, I am going to try this and see if it flows any more air.

What size is the airbox? It looks a bit small to me. from the picture I'd say 100mm x 150 x 400 which is 6 litres.

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Originally posted by smart51
What size is the airbox? It looks a bit small to me. from the picture I'd say 100mm x 150 x 400 which is 6 litres.

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The R1 comes with a box that is 8 litres in volume. It is a 1 litre that revs to 12000 and so draws the same volume of air per second as a 2 litre that revs to 6000, except that your 2 litre takes bigger gulps and so lowers the pressure more for each pulse. I personally am making a 9 litre box for my enigine ready for when the repair shop fixes it. I guess 6 litres isn't bad and it looks well made so would be a shame to mess with it or replace it. First thing I'd do is see if I could replace / bodge a different filter on to it to see if it is that, An offcut of pipercross filter foam or something. If that's OK then I'd be tempted to leave the box alone.

If your inlet pipe is 300mm long then your box is tuned to 3000 RPM. If it is 350mm then it is tuned to 2800 and if 400mm long, tuned to 2600 RPM. You should find that the engine breaths very well at the tuned speed, quite badly at 2/3 of that speed and quite well at half the speed. A smaller box accentuates the effect. From twice the speed and upwards, the inlet port to the box becomes accustically opaque, keeping the noise in. A bigger box lowers the speeds.

I think the main problem with a small box is that each gulp of air lowers the intenal pressure more than it would in a larger box so restricing air flow slightly although the port diameter is nice and large.

If you've noticed a difference and you've changed to a box and changed the filter, change the filter again to see which has caused the problem.

Thanks, I spent quite a lot of time making the airbox, but to be honest if I didn't like trackdays and live 15 minutes from Donington I wouldn't have bothered. I am going to try the green cotton cone filter tomorrow and hopefully with the main jets at 155 - 160 ish it should run OK. Fitting the airbox hasn't made the car slow, just noticeably less 'pokey'. It still pulls well and makes just over 100mph (private road test). I can live with a few less bhp if it means I don't get asked to leave for being too loud. The foam sausage filter and the 170 main jets will be going straight back in when I get back home after each quiet trackday I do.

Out of interest, I'd like to know the before and after noise figures, to see how much effect is has. I'm led to believe that it mostly affects drive by noise, which is good for donnington.

Yup, drive by is what they always get me on.

With the foam filter on they have got me at 101dB with a silencer practically empty of packing.

With the foam filter and a well packed exhaust they have got me at 99dB

Covering the foam filter with cardboard and gaffer tape with a well packed silencer they recorded me at 97.5dB.

So here's hoping the airbox can get me down to 96dB ish.

I don't know if I'd dare to ask what sort of level I an getting to, if they don't throw me off that will be enough for me.

Well the Green Cotton Filter sorted it. Still running the 155 main jets however the car pulls cleanly all the way to 7000rpm. Still feels a little down on power but nothing I'm going to worry about. So the verdict Pipercross cone filter 0 Green Cotton Cone filter 1.

Here's some decent pictures of my efforts too.
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and another - thank you ebay that filter only cost me £21!

[Edited on 26/10/06 by givemethebighammer]
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