Well a quick update after I gutted the back boxes on the Avant. As you can see I went from this restrictive baffle setup...
To a straight through piece of 2.5" perforated Stainless tube (Sorry I didn't take any pics after the one above) that I wrapped in a layer of stainless steel wire wool and then packed the remainder of the back box with glass fibre loft insulation. I used glass fibre insulation as it's an oil burner and the back boxes in theory won't reach the 600° melting point....whereas if it had of been a petrol I would definitely gone the Rockwool route that I was originally going to go as this is ok for over 1000°.
The reason for going a bigger size perforated tube over the original size was that it would still be quiet on tick over, plodding about round town or sat at 70mph on the motorway....but when under full load it should become basically a straight though pipe.
Anyway once it was all welded back up and put back onto the car and it seems to have lost a funny sound it had when Idling....I always thought that it was gearbox noise resonating through the exhaust as it's bolted directly to the gearbox at the front of the car, it was obviously the gasses passing through all the silly holes, slits and sections of the baffles in the boxes and restricting flow.
I revved it a few times and it was still quiet so on one hand I was disappointed that there was no increase in noise or tone at the front of the car......but it hadn't had time to carbon up as yet.
I took the Mrs to work a few hours later and I immediately noticed that the car was more responsive, even without putting my right foot down....it seemed a lot smoother. Even the Mrs said it felt different from the passenger seat which is a first!
No sorry that's not right....that's the second time she noticed something, the first was when I put the new Barum boots on the car.
Once I'd dropped the Mrs off at work the car was nicely warmed up so I took a detour to one of the local test tracks and opened her up.....I was pleasantly surprised that the car did in fact feel more responsive through all the gears. Quite a noticeable difference if I'm honest and it was much smoother through the full rev range.
I also noticed that the exhaust note had changed to a nice deeper tone, so it went from the only way I can explain it is say the letter F once and keep it going. (It sounded like air being forced out) you'll get what I mean when you do it....and it's also got an ever so slight burble at idle now that it's getting a few miles on it.
So am I happy......OH YES! Especially after I'd heard quite a few that had straight through pipes on Youtube on the same 170 BRD engine as mine and they sounded awful and way too noisy for my liking.
I'll try and get a sound clip done of it soon.
To a straight through piece of 2.5" perforated Stainless tube (Sorry I didn't take any pics after the one above) that I wrapped in a layer of stainless steel wire wool and then packed the remainder of the back box with glass fibre loft insulation. I used glass fibre insulation as it's an oil burner and the back boxes in theory won't reach the 600° melting point....whereas if it had of been a petrol I would definitely gone the Rockwool route that I was originally going to go as this is ok for over 1000°.
The reason for going a bigger size perforated tube over the original size was that it would still be quiet on tick over, plodding about round town or sat at 70mph on the motorway....but when under full load it should become basically a straight though pipe.
Anyway once it was all welded back up and put back onto the car and it seems to have lost a funny sound it had when Idling....I always thought that it was gearbox noise resonating through the exhaust as it's bolted directly to the gearbox at the front of the car, it was obviously the gasses passing through all the silly holes, slits and sections of the baffles in the boxes and restricting flow.
I revved it a few times and it was still quiet so on one hand I was disappointed that there was no increase in noise or tone at the front of the car......but it hadn't had time to carbon up as yet.
I took the Mrs to work a few hours later and I immediately noticed that the car was more responsive, even without putting my right foot down....it seemed a lot smoother. Even the Mrs said it felt different from the passenger seat which is a first!
No sorry that's not right....that's the second time she noticed something, the first was when I put the new Barum boots on the car.Once I'd dropped the Mrs off at work the car was nicely warmed up so I took a detour to one of the local test tracks and opened her up.....I was pleasantly surprised that the car did in fact feel more responsive through all the gears. Quite a noticeable difference if I'm honest and it was much smoother through the full rev range.
I also noticed that the exhaust note had changed to a nice deeper tone, so it went from the only way I can explain it is say the letter F once and keep it going. (It sounded like air being forced out) you'll get what I mean when you do it....and it's also got an ever so slight burble at idle now that it's getting a few miles on it.
So am I happy......OH YES! Especially after I'd heard quite a few that had straight through pipes on Youtube on the same 170 BRD engine as mine and they sounded awful and way too noisy for my liking.
I'll try and get a sound clip done of it soon.
Last edited:
