weatyGT

The miltek has no drown and I have a decat, with the oem cat it has none its almost like oem, all part of the manufacture process to illuminate unwanted drown, created improved flow and a preferred sound.

noodels

Adjustable may be the way to go as many variables including temperature
the OEM silencers has built in the Hemsoltz chambers also into the design.
some info here also
http://www.1addicts.com/forums/showt...=624797&page=2

CHIPPO

That is the sort of stuff I have been looking at noodles , hence my calcs point to 27" ish long , and I will be trying to fabricate a "trombone" arrangement to fine tune it

But for now that's on hold , bit of corrosion problem to sort now !

flanders

Here's a recent thread on the same subject https://www.s2ki.com/s2000/topic/109...sonator-design

CHIPPO

Interesting variation there , but keeping the same volume for the resonator. Those are the same calcs I looked at , well the same formula. Speed of sound as they says varies with temp etc as indeed it does depending air density / altitude , one and same thing

mattie170

I have made a Helmholtz resonator for my car and deleted drone from 3200-4000rpm. It has started a drone from 2800-3100. Idle is quieter. It needs to be larger than I made it. I used 2.5" pipe and teed it into the system just after where the decat would be. Well chuffed with how it worked seeing as I run a 3" exhaust with a single box. I am going back to a twin rear system again for flow but twin 3" pipes. I might even make the rest of the system in 90mm pipe if I need to. Once I have made the new rear exhaust section I will test for drone again but I think I need to make the Helmholtz resonator larger. When doing your calcs make sure you allow for 400c exhaust gases!!

Hope it helps people!

mattie170

Here is a picture



I think I was 4-6" too short but I ran out of space so will have to tee off the resonator to add more volume. It is 38" long for reference.

CHIPPO

Blimey that's much longer than the calcs would suggested , I worked it out to about 28" all in even allowing for temp , but it is the slug of gas up the resonator that makes the difference which will be at reduced temp as there is no flow through it . Your length would suggest you are trying to reduce drone at a lower frequency , my calcs suggested 130 hz which equates to around 3000 rpm for a four pot .
Nice job though , when I get round to doing mine it will have a joint for messing about with the length ., that locks like it is in a similar position to where I was thinking of putting mine.

weatyGT

Chippo... Have you thought of taking 2 manifold pipes and just keeping them right out the back.... Each side....

If that isn't clear....

2 manifold pipes go into one.... And they go right out back... So instead of 4-2-1 or 4-1 you have 2 of 2-1....

Does that make sense?? Have anyone e er tried that on the s2000....

CHIPPO

God know if it's been tried ,
I suppose ultimately using your logic why not 4 pipes all the way !

If 2 or 4 pipes would have an effect on drone I have no idea , as I say my understanding is it's all to do with the gas pulses generated by the exhaust gases being ejected from the engine via the exhaust and these have a frequency directly linked to engine rpm and the way that frequency reacts with other parts of the car , so stop or cancel that frequency and bingo no drone and the Hemsoltz supposedly does just that generating the same frequency but out of phase cancelling the pulses from the engine at approx 130 hz . It's the same effect as blowing across the top of a bottle , hence Honda must have had a higher frequency drone from the OEM pipe hence the 8inch resonator .