Exhaust resonance when lifting throttle – cure?

Exhaust resonance when lifting throttle – cure?

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Discussion

chris watton

Original Poster:

22,477 posts

259 months

Thursday 21st May 2015
quotequote all
I had the ACT big bore full exhaust system fitted not long back, as I wanted a slightly quieter sound for normal cruising.
It is quieter, but once the exhaust gets hot, I still get terrible resonance in the cabin, usually when lifting off.

I have a feeling that the larger diameter is now touching the underside of the car in certain circumstances, causing the drone.

Has anyone had similar, and if yes, what can be done to cure it?

Cheers smile

starlight225

365 posts

210 months

Thursday 21st May 2015
quotequote all
My take would be to loosen the system off and try to get a bit more clearance between the exhaust and its surroundings, then re tighten it all back up. If you didn't fit it, take it back to who did.

T40ORA

5,177 posts

218 months

Thursday 21st May 2015
quotequote all
If it's touching I would have thought that you would also get knocking. Surely it's more likely to be caused by back-pressure, or general airflow issues?

Do you have decat pipes?

chris watton

Original Poster:

22,477 posts

259 months

Thursday 21st May 2015
quotequote all
I had brand new cats fitted at the same time, so everything was changed from the manifolds back.

starlight225

365 posts

210 months

Thursday 21st May 2015
quotequote all
Another thought, how are your engine mounts?

chris watton

Original Poster:

22,477 posts

259 months

Thursday 21st May 2015
quotequote all
starlight225 said:
Another thought, how are your engine mounts?
They are fine, they were sorted when I had the 4.3 upgrade.

I think I'll ask Dom to have a look when it goes in for its service next week.

I did think about wrapping all of the exhaust in exhaust wrap - but I can't get to the underside of my car, and I'd probably mess it up anyway...

gacksen

680 posts

142 months

Thursday 21st May 2015
quotequote all
should not have happend if outfit has test driven the car.
if its just a bit depending on exhaust config could be
getting better by the time you give it some beans or
could improve due to increased ear ringing biggrin

on my last t350 had the outfits rear cans and with closed windows
around 2000-2500rpm what a drone eek result bye bye rear cans and different
outfit custom exhaust no drone at any rev clap

jrb43

793 posts

254 months

Thursday 21st May 2015
quotequote all
gacksen said:
should not have happend if outfit has test driven the car.
if its just a bit depending on exhaust config could be
getting better by the time you give it some beans or
could improve due to increased ear ringing biggrin

on my last t350 had the outfits rear cans and with closed windows
around 2000-2500rpm what a drone eek result bye bye rear cans and different
outfit custom exhaust no drone at any rev clap
I don't have enough hours in the day for an internet argument but:

1) I think many feel that this is getting very boring.
2) Even if you personally disagree with 1) - your post has done nothing to help Chris with his problem.

I'm pretty sure you're coming close to forum rules and the moderators may think to review your future contributions.

gacksen

680 posts

142 months

Thursday 21st May 2015
quotequote all
jrb43 said:
I don't have enough hours in the day for an internet argument but:

1) I think many feel that this is getting very boring.
2) Even if you personally disagree with 1) - your post has done nothing to help Chris with his problem.

I'm pretty sure you're coming close to forum rules and the moderators may think to review your future contributions.
so seems a conclusion that you either didnt have a drone problem in your car
or never had a new exhaust fitted that had one. if not and the exhaust is new
and the car isnt fully run in as it is there is a chance it will sort itself.

forum rules are there and read. can´t see any violation there as we are talking
about facts not fiction but i guess you like SciFi where all the outfits deliver
perfect quality.

if so those postings wouldn´t exist at all would they ?

also if this would be all wrong i guess any outfit can speak
for itself.

for sure it will get sorted as the big bore system is not the cheapest one.



Edited by gacksen on Thursday 21st May 19:47

steveT350C

6,728 posts

160 months

Thursday 21st May 2015
quotequote all
Hi Chris,


So lifting off throttle causes problem?


Sounds similar to a problem I had:


An analogy is an issue I had re plumbing in my house....


Every time I hit the main pipe up in the loft with a heavy book, the boiler cut out. I spent ages on the internet trying to find out what was going on. I might as well have trained up to be a plumber myself with the amount of research I did.

Then I suddenly worked it out;


Don't lift off the throttle


biggrin

Edited by steveT350C on Thursday 21st May 21:45

chris watton

Original Poster:

22,477 posts

259 months

Thursday 21st May 2015
quotequote all
steveT350C said:
Hi Chris,


So lifting off throttle causes problem?


Sounds similar to a problem I had:


An analogy is an issue I had re plumbing in my house....


Every time I hit the main pipe up in the loft with a heavy book, the boiler cut out. I spent ages on the internet trying to find out what was going on. I might as well have trained up to be a plumber myself with the amount of research I did.

Then I suddenly worked it out;


Don't lift off the throttle


biggrin

Edited by steveT350C on Thursday 21st May 21:45
hehe

Thanks!

shep1001

4,599 posts

188 months

Friday 22nd May 2015
quotequote all

Check the cans/back box is not touching the diffuser and/or the body in the recess where the exhaust sits

chris watton

Original Poster:

22,477 posts

259 months

Friday 22nd May 2015
quotequote all
shep1001 said:
Check the cans/back box is not touching the diffuser and/or the body in the recess where the exhaust sits
The back box is pretty close to both the diffuser and exhaust/number plate heat shield.

I may buy some self adhesive thick heat shield to put onto the back of the of number plate shield and diffuser. Of course I never had this problem with the small separate bean cans.


Edited by chris watton on Friday 22 May 19:22

mr lock pick

536 posts

212 months

Friday 22nd May 2015
quotequote all
Chris

Have a chat with Mr Clive Ford, he may be able to offer you a few solutions. Many of us have experience droning, including myself.

By the way I love all your post as we all get to learn a lot, however I thought I could moan, I have officialy voted you No. 1 EXPERT PH moaner 2014-2015.

Keep all the mods coming and the post fella.

clap

chris watton

Original Poster:

22,477 posts

259 months

Friday 22nd May 2015
quotequote all
mr lock pick said:
Chris

Have a chat with Mr Clive Ford, he may be able to offer you a few solutions. Many of us have experience droning, including myself.

By the way I love all your post as we all get to learn a lot, however I thought I could moan, I have officialy voted you No. 1 EXPERT PH moaner 2014-2015.

Keep all the mods coming and the post fella.

clap
Moaner! Do I? Gulp - didn't realise - am I turning into Alf Garnet in my old age, and too senile to even know it! hehe

starlight225

365 posts

210 months

Saturday 23rd May 2015
quotequote all
Hi Chris, by some strange quirk of fate I currently have my complete system off the car. Just refitting cats after the car came decatted. Have found that my system was a big bore system having bought a pair of standard cats, but that's a whole different story. With it off I noticed that the system was rubbing on the rear diffuser and on the chassis under plate in front of the diff. There are some adjustable L shaped hanger brackets that were effectively set too low causing all the contact. Also you could put a few washers between the chassis and the cross plate to give a bit more clearance

chris watton

Original Poster:

22,477 posts

259 months

Saturday 23rd May 2015
quotequote all
starlight225 said:
Hi Chris, by some strange quirk of fate I currently have my complete system off the car. Just refitting cats after the car came decatted. Have found that my system was a big bore system having bought a pair of standard cats, but that's a whole different story. With it off I noticed that the system was rubbing on the rear diffuser and on the chassis under plate in front of the diff. There are some adjustable L shaped hanger brackets that were effectively set too low causing all the contact. Also you could put a few washers between the chassis and the cross plate to give a bit more clearance
Cheers smile I too had the larger bore Tuscan S/Sagaris OEM cats fitted.

I am taking the car to Powers on Tuesday for its post run in service, I shall ask Dom if he can sort the underside for me. I am pretty sure I can sort out the back box by fixing thick heat shield on the top of the rear diffuser and number plate shield.

Shouldn't have to though - just having the new system fitted cost me £360 in labour! They must see me coming...hehe

chris watton

Original Poster:

22,477 posts

259 months

Saturday 6th June 2015
quotequote all
Took the Tam out for a good run yesterday - and I still get the horrible droning resonance when lifting off (when up to temp)- making the whole car seemingly vibrate, ruining an otherwise fantastic experience.

I will buy new hangers and perhaps wadding to see if that helps, and self adhesive heat shield for the inside of the rear exhaust shield and diffuser, as the large ACT back box it very close to both.

On an unrelated topic, my wife had her first go in the Tam since the upgrades last night - too afraid to put her foot down, so everything was overtaking, even old Rovers ...hehe

chris watton

Original Poster:

22,477 posts

259 months

Saturday 6th June 2015
quotequote all
OK, I looked under the car, and there seems to be three possible culprits, what do you think:




gacksen

680 posts

142 months

Saturday 6th June 2015
quotequote all
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.