Let's get back to booming V6 exhausts.
 

This is rapidly becoming the bane of my life entailing many hours underneath my X-plate 2.5 cursing the exhaust, the car and life in general.

The factory fitted rear box disintegrated at around 90k and I've spent the last 12000 miles fitting and removing a succession of replacement boxes all of which produced a loud resonating boom between 1200 and 2400 revs, louder than the engine in many cases which is a shame when the engine sounds so nice.

I've tried fitting additional soundproofing to the boot and that has improved things a little but I'd love to have some suggestions as to how to fix it.

Is it resonance in the boot/rear bumper area?
Is it the result of the pipes being too short and the bumper magnifying the sound?
Are the hangers too short (and if so how to fit longer ones while avoiding the pipe-knocking-on-the-crossmember sound)?

To be quite honest I'm running out of ideas so any suggestions would be gratefully accepted.

I hate that resonance, it's low frequency so the usual sound proofing probably won't help much, it might be transmitted through the body shell.



My V6 has an 'after market cat' and Dave in Fencehouses suggested an original might be quieter. When he reset the engine warning light he suggested it might be caused by the cat or dodgy fuel. But thinking about it I did fill up in Liverpool.


Pete

How about trying something like this?

https://www.ebay.co.uk/itm/4-x-14-CL...cAAOSwvT5dW6sv

Simple really, the aftermarket boxes are just that, something that fits but does not really MATCH the original design requirements, i.e. size of internal pipes and exactly the same construction.

Had a similar problem a few years ago when the company car leasing company insisted (for £ reasons) that an aftermarket final box had to be fitted. It was awful, after a bit of argy bargy they agreed to have the MGR parts fitted, all was returned to normal silence.

:wot:
A forum member was in the process, last year I think, of commissioning a replica of the original MGR clamshell KV6 rear silencer/tailpipe. An excellent initiative but as is so often the case, it's all gone very quiet. :cool:

Simon

Thanks for the replies so far. Purely from a cost point of view, if the answer is to fit a factory-spec rear box or some sort of resonator to the existing ageing system then I may as well wait until the world returns to some sort of normality and have the stainless cat-back that I was quoted around £300 for. When I had one from the same people for the Outlander I was able to specify what sort of exhaust note I wanted and they removed/moved resonators and changed tailpipes accordingly.

However, now I'm obliged to work from home half the time I hope to have the opportunity to continue playing with it. So if I stumble across any undiscovered answers I shall let everyone know.

I had an aftermarket box on my KV^, which was "boomy" at speed, and also at idle. I did notice, at idle, if I lifted my foot up to 1 of the tailpipes, it went quieter. So a spud was stuffed up it, and a quick drive proved it was quieter, though the spud didn't last long! Sadly this experiment wasn't continued, as circumstances changed and I got the present car instead. Maybe there is something about blocking off one of the tailpipes?

Stewart

I also saw something about stuffing one of the pipes with glass fibre, and another one about "manufacturing" an external baffle from an old fizzy drink can. Got to be worth a try I suppose :}

I must have been lucky - my garage fitted an after-market rear silencer to my 2.5 V6 ZT last December, and it sounds just like the original which had lasted 17 years (it still had MG on it!). Didn't use any exhaust centre (like Quick fit etc.) and didn't specify what I wanted as it was just before Christmas and I was desperate to have it done. Labour was not cheap, but the exhaust was about £55 which I thought reasonable, and the result is that lovely V6 burble.

Further to the "spud", when I swapped the car to the present on I thought I'd got another boomer. I tried a temporary experiment (which did look promising) with sound/heat insulation tape off ebay - plenty on there. Basically, I removed the silencer, then wrapped it in this tape. I then covered it in aluminium foil (actually kitchen foil, which was really too thin), for protection; the latter held on by metal cable ties. With it back on the car, it seemed a fair bit quieter, but a week later, it got very noisy. I removed it again, abandoned the experiment, and fitted a replacement (from Euro or CarParts4Less I think). The replacement is quite acceptable. The experimental one had blown a hole btw.