OV9

You may or may not have seen that I made an exhaust system for my S2000 in the fleet thread. It was all good apart from the most horrendous drone between 3 and 4k rpm. I used a spectrum analyser app to determine the worst frequency was around the 125hz range and made a helmhotz resonator of the correct volume to cancel out the 125hz drone, and it only fucking works.

The oem S2000 system has a 6 inch nob sticking out of the side for a similar reason, I initially replicated this and it helped, but didn't completely cancel out the drone.



So I found some calculations online and knocked up the correct sized canister like so...



There's some kind of wizardry going on in there I tell you.

Great work!

Awesome work, but is that shrouding the prop? Confusedification.

mik wrote: Wed Nov 25, 2020 11:14 pm Awesome work, but is that shrouding the prop? Confusedification.

I was going to ask this as well - I can't quite make out what's going on there in the photo

It’s floating just below the prop....the angle of the pic makes it look a bit confusing

Is the prop reflected in the end cap? I think that's what was puzzling me!

I'd never heard of a Helmholtz resonator before though - intersting stuff. I wonder how many other performance cars come with one OEM.

Yeah I just realised that’s probably what’s most confusing, it’s a mirror finish.

I don’t think it’s so much of an issue with most oem stuff as they don’t run straight through boxes generally, the silencers are usually chambered as it massively reduces noise at the expense of flow.

That’s top work

Tremendous stuff. Well done!

So is that open to exhaust gasses or is it just welded onto the side of the exhaust?

No wonder a poor NVH engineer can't get any work

Well done on doing the numbers.

You bastard.

That's a lot of volume and a long neck so super effective for your chosen frequency.

Phase 2 is to package that all circumferential to the main pipe.

“Hey Dan - what’s the redline on this thing”

“B-flat”

And yeah - what has Rob ever done to you?

mik wrote: Thu Nov 26, 2020 8:16 am “Hey Dan - what’s the redline on this thing”

“B-flat”

jamcg wrote: Thu Nov 26, 2020 6:55 am So is that open to exhaust gasses or is it just welded onto the side of the exhaust?

Yep its open, the main pipe blows across the inlet like blowing across a milk bottle.

mik wrote: Thu Nov 26, 2020 8:16 am “Hey Dan - what’s the redline on this thing”

“B-flat”

And yeah - what has Rob ever done to you?

You know the most amazing bit - the fact that you downloaded an app for your phone and that was what gave you the data to make the resonator. Measuring equipment was always interesting in my engineering days. Just using your phone, fucking hell.

well that's just awesome

I will await the before and after rolling road printouts before fully judging this creation

Good skills though

speedingfine wrote: Thu Nov 26, 2020 5:37 pm I will await the before and after rolling road printouts before fully judging this creation

Good skills though

Coming soon!

dan wrote: Thu Nov 26, 2020 6:37 pm

speedingfine wrote: Thu Nov 26, 2020 5:37 pm I will await the before and after rolling road printouts before fully judging this creation

Good skills though

Coming soon!