Exhaust resonance when lifting throttle – cure?

[chris watton]

gacksen said:

can you get the car on ramps ?

if yes second picture check the clearances of the exhaust between the chassis rails.
in case it drops on the protector plate you have some sort of metallish sound that is
very unique. easiest way would be get it up the ramp rev it till it drones while another person
takes a look from below.

I have no access to ramps

Would it help if I wrapped parts of the exhaust close to the chassis rails, and perhaps add spacers to the protector tray, or wrap that area of the exhaust too?

[gacksen]

you can try to leave off the protector for a short drive and hear if there is
any improvements. is it a mettalic drone you have e.g. often heard with old cars
if a heatshield is knackered or just the deep frequency drone ? is the drone
present with car in cold and hot condition or just once it is heated up ?

have seen the big bore act just off the car so i am not familiar with the clearances
but should be similar to my current t350 setting and there is not much space left and right
so there is a chance that the chassis can be touched by the exhaust.

[chris watton]

It resonates only when the exhaust is hot, so I assume it expands enough to touch another surface.

I bet it's hitting that rear chassis rail...

[chris watton]

OK, I bought 30 metres of exhaust wrap and have now wrapped as much as the two exhausts as I can (I never want to do that again!). I have also stuck self adhesive heat shield to the top surface of the under-car exhaust guard and the rear diffuser and rear exhaust guard.

I bought this:
https://www.merlinmotorsport.co.uk/p/exhaust-wrap-...
This:
https://www.merlinmotorsport.co.uk/p/thermo-tec-hi...
These:
https://www.merlinmotorsport.co.uk/p/stainless-ste...
And this:
https://www.merlinmotorsport.co.uk/p/zircoflex-ii-...

The only part of the exhaust I couldn't do is near the front, just past the cats where the pipes are on top of one another, rather than side by side. What are the chances it's the part I can't get to that's causing the problem!

Will try it out tomorrow morning, I really hope I've cured it..

[Fish]

It does look close to the under shield, I just had an ACT fitted and the under shield was packed off the chassis rails a little more than yours. All you have to do is unbolt and add washers to increase clearance...

Hope that helps..

[chris watton]

Fish said:

It does look close to the under shield, I just had an ACT fitted and the under shield was packed off the chassis rails a little more than yours. All you have to do is unbolt and add washers to increase clearance...

Hope that helps..

Cheers James. I did that, added a couple more washers to bring the tray down a little more. The exhaust is also wrapped quite well in that area.

knowing what I know now, I should have wrapped the whole system before it was fitted - I ache like hell now, trying to contort myself under the car!

[m4tti]

Resonance, if it is that rather than drone, is usually set up by vibration. It's probably tricky now you've wrapped it, but tapping along the length of the exhaust may show you where that vibration is originating from.

[chris watton]

m4tti said:

Resonance, if it is that rather than drone, is usually set up by vibration. It's probably tricky now you've wrapped it, but tapping along the length of the exhaust may show you where that vibration is originating from.

I did actually try that, but nothing. It only happens when the exhaust is hot, when it expands.

[chris watton]

OK, just got back from a 40 minute drive, and it's worked, no more horrible vibrations coming through the cabin! Phew!

Although I think I made a mistake in adding more Zircoflex self adhesive heat shield on the bulkhead, next to the manifolds - the glue was smoking like hell when I got back! Should I take it off?

[BuzzBillsberry]

Just be aware Chris that wrapping the exhausts moves the heat down the system so that'll be the rear boxes so you might find your boot rather warm so don't put any perishables in there or cold drinks. When I was running the standard silencer . The heat melted/distorted the rear number plate.... Even when I pulled the rear exhaust shield out it was still pretty hot

Buzz

[chris watton]

BuzzBillsberry said:

Just be aware Chris that wrapping the exhausts moves the heat down the system so that'll be the rear boxes so you might find your boot rather warm so don't put any perishables in there or cold drinks. When I was running the standard silencer . The heat melted/distorted the rear number plate.... Even when I pulled the rear exhaust shield out it was still pretty hot

Buzz

I remember seeing a pic of that Buzz - it was with that in mind I bought some more Zircotec heat shield and added it to the inside of the rear exhaust shield and the top of the diffuser, where the rear box sits pretty darn close.

My rear number plate is stuck on, not screwed, so I'll have to watch that. It was Ok with the separate bean cans, but the ACT rear box is pretty substantial...

[chris watton]

Just took a couple of pics of some of the wrap - it definitely works and is now a lot quitter in the cabin. As I mentioned, I couldn't wrap it all, most notably the pipe that is located above the lower one near the front, but I managed to get most of it. As also mentioned, not the best job to do when the exhausts are in situ!