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Attention, 2.2 quick hesitation cure. YES IT WORKS.

34K views 168 replies 46 participants last post by  mr c 
#1 · (Edited)
My son (filby boy) after a year of 2.2 Brera car hesitation problems and a full specialist service which made no difference, considered fitting an exhaust system at a cost of nearly £800 to solve the problem. I said it can’t be that bad and took it for a drive, it was appalling, (especially after my 159, 2.4) so I said I would have a look.

I am an engineer by profession and a few years ago had to design a marine exhaust system to solve back pressure problems on 710 hp diesel engine installations.
Without going into boring details I looked at the air flow through the cats and first box including exhaust diameter and they were ok. I then looked at the baffle arrangements in the back box on each side and concluded there were too many U turns to allow the gasses to free flow when a sudden rapid increase in exhaust volume/flow was required. This would choke the engine until the faster flow was established around the baffles.

I concluded that a 14mm diameter hole through the side of the final baffle each side would be large enough to allow excess exhaust pressure to spill flow and reduce back pressure. I then drilled a 14mm hole inside both back boxes as shown.

The results were amazing. It is a different car, smooth acceleration, no jerking or coughing. You can pull away slowly or roar away with confidence and gear changes are now smooth. I cannot describe how different the car now drives and it was such an easy cure with only a slight noise increase at tick over.
This cannot be done on a 159 because of the exhaust shape.
If you don’t believe it, I am happy to show the difference if you are in the Yarmouth area.
In the pictures below I have sprayed silver paint in the exhaust to show up the hole which you would not normally see.
 

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#3 ·
Agree with Tata.
The mind boggles as to how AR got away with selling the 2.2 with its awful hesitation issue :confused::rolleyes:
And such an easy 'fix'.
Well done Filbyman :thumbs:
 
#4 ·
Interesting.
Im also an engineer and was thinking you needed to give a more flowing/open exhaust to eliminate this issue.
First i have looked (but not as yet) at removing the centre box to do this but this "fix" makes good sense.
How does the 159 differ to the Brera back box then?
 
#5 ·
The 159 back back box is the same but the outlet tail pipe drops down and therefore you are not able to position a drill inside where required, theoretically if you cut this off you could drill the holes but then you would have to re-weld the tail pipes back on. I have been thinking about altering my back bumper and fitting a pair of 2.4 diesel back boxes from a Brera onto my 159 including drilling the holes.
 
#10 ·
Does that mean they come out of the show room like that ?? When I got my S it to had hesitation issues, and was a pig to drive especially pulling away .. however mine was due to a fault with the inlet phase solenoid, I was getting sporadic EML, which I could reset however the hesitation was always there, after I changed the solenoid the car was a different car to drive :) Obviously the S has a different exhaust which probably sorts the issue with air flow
 
#12 ·
Hello Everyone, recently got a 2.2 Brera, and since been hovering around on here, great site, Fantastic car!!
Have noticed what I imagine is described on here as the hesitation issue, but generally not massively bothered by it, seems worse when cold, in the mornings. However I am tempted to try this, but being totally non mechanically minded, not sure if its something I can (or should) do? not doubting the op at all, but can it really be this simple? am I going to be the first Newbie idiot to take a drill to his exhaust?? any guidance appreciated. :)
 
#14 ·
Thanks for the response everyone.
It will not effect any exhaust emissions as the CAT is untouched. The holes are inside the exhaust silencer so it is not an MOT problem. The additional noise is only very slight on tick over and no different when reving. There is no power loss, it may even help power as there is less back pressure, but I doubt it because as the gas flow increases in speed it will follow the normal route around the baffles. It was only designed to allow the initial exhaust surge to be released.

You will also need a long drill as you need to drill quite a distance inside past the baffle lip as seen in picture one.
As I said in my post, if you are in the Yarmouth area, I happy to do this for you and you will see the difference.
 
#20 ·
Is that all there is to it? I just need to drill 2 holes at the angle shown via the outer exhaust pipe tips with a 14mm drill? Is it just a matter of making a hole in a thin piece of metal or do you have to drill through more of the exhaust?
I don't want to make a complete mess of things if I can help it...
 
#22 ·
Anybody tried this yet? I couldn't find a drill bit long enough so will have to buy one if I'm going to give it a go. I did mention it to ProAlfa and they weren't convinced it would work and weren't keen to try on my car. Fair enough, as it's not exactly something out of the repair manual..
 
#24 ·
I've done it... Two 14mm holes as shown in the exhaust and I really think the original poster is onto a winner with this one. I must say that at first I didn't think it had made much difference but I reckon that was because I was used to compensating for the hesitation. Now I've got used to the mod it does seem as if the hesitation is gone. There are a couple of junctions I use regularly that always seemed to bring out the worst in the car when moving off and they are much smoother now.

The exhaust noise isn't any louder apart from a slight difference in tone if you are standing next to the exhausts.

It cost me 15 quid for a long drill bit (a normal one isn't long enough) and I consider that money well spent..

Many thanks...
 
#26 ·
Well done DC.

I new people would think it was a bit of a strange thing to do, but it only took one brave person to prove my point.
I am going to get two second hand Brera 2.4 diesel back boxes and see if they are the same. If they are then I will drill out the holes then put them on my 159 (with bumper modifications) and see if I can squeeze some more HP from my already re-mapped and de-partial filter removed car.

This is not the first exhaust mod that I have been involved with. My sons first car, a 147 1.6 was also modified which he has since sold on.
 

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#28 ·
If you drill a larger hole then you will start to get noise from the exhaust especially when at speed as exhaust gas will escape through the larger hole and not flow past and go around the last baffle. The hole was made to remove the excess pressure pulse caused when you put your foot down which will push its way through the hole. A 14mm hole ( 9/16” in old money) could give a potential flow rate of around 65 cubic feet of air per min, at 4psi. But this will change with temperature and flow direction and of course pressure. I have not measured the pressure so the hole size is a guesstimate but it seems to work. Now there is a hole there, I could try and connect a pressure gauge and take an actual pressure and temperature measurement. I could then calculate the gas flow through rate being achieved, or I could go to the pub?
You could drill a bigger hole but I would not recommend it. 14mm seems enough.
 
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