A2 1.4TDI AMF BHC Downpipe - what is the ultimate design - buy or make?

dieselfan

dieselfan

A2OC Donor
Have searched for a decent downpipe for my AMFs. Have not found any and have made two attempts my selves while waiting for the ideal design.
If it is available to buy... thats good, but if any have a clear idea wrt design that is also worth its weight in gold (bhp) :)

The big disadvantage with what I have made until now is that I have not done any dyno before and after so I have no clue of the improvement numbers... I did first attempt in 60.3mm x1.5 (2.36 inch) down to cat.
This version "feels" to improve low rpm response and ease breathing in general.

1. What is the ideal diameter for a downpipe that shall handle up to 110-120bhp ?

2. Are there any downpipes available to buy that are

3. Have any of you done any dyno testing so you know the benefit of standard vs tuning downpipe ?

4. Any that have tested if there is a benefit to increase bending radius from 3xD to 5xD ?

5. Do any of you have pictures or links to a downpipe that looks promising ?

I hope a lot of you want to participate to the evaluation :)

Cheers
dieselfan
 
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dieselfan said:
Have searched for a decent downpipe for my AMFs. Have not find any and have made to attempts my selves while waiting for the ideal design.
If it is available to buy... thats good, but if any have a clear idea wrt design that is also worth its weight in gold (bhp) :)

The big disadvantage with what I have made until now is that I have not done any dyno before and after so I have no clue of the improvement numbers... I did first attemt in 60.3mm x1.5 (2.36 inch) down to cat.
This version "feels" to improve low rpm response and ease breathing in general.

1. What is the ideal diameter for a downpipe that shall handle up to 110-120bhp ?

2. Are there any downpipes available to buy that are

3. Have any of you done any dyno testing so you know the benefit of standard vs tuning downpipe ?

4. Any that have tested if there is a benefit to increase bending radius from 3xD to 5xD ?

5. Do any of you have pictures or links to a downpipe that looks promising ?

I hope a lot of you want to participate to the evaluation :)

Cheers dieselfan
Click to expand...
Darkside Developments have a 2.5 Inch Decat Downpipe for an A2 TDI AMF
 
Don't have a clue what could be the best design (as straight as possible?), but I've replaced my shot/leaking flex bit on the downpipe of my former Arosa TDI (same AMF engine).
I welded in a flex pipe with a bigger diameter, and it picked up rev's quicker......... but I must say that when i was busy with it, I also removed the cat, which is a greater restrictor then the downpipe itself I guess.
Going larger in downpipe diameter is only a plus if you would install a bigger turbo and remove the cat, but I could be wrong.
 
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You might also need to be a bit careful - bigger isn’t always better because you do need some pressure wave movement for scavenging I’d exhaust gases on the next stroke I think. If you have a choke point it’ll cause rebound too.

It may be less relevant for turbo engines but Engineering Explained has a brilliant video on the function of the exhaust in assisting engine power and the role of performance exhausts. I’ll see if I can find it.


I love this guy’s channel.




Sent from my iPhone using Tapatalk
 
I had a custom decat down pipe made up on on my last project car by a company called Longlife exhausts. 2.5 inch stainless steel and it really made a difference to the pickup on the turbo. It cost £250.
 
Well, time to sum up and move to production phase :)

There is limited space for the downpipe, so the routing is given, unless one relocate the turbo. That is too comprehensive at this stage.
I have sourced 60.3mm AISI 316L bends and tubing. Flexi section is 304, not ideal but probably good enough.

Since I made the last one in 2008, many tools that I did not use and some parts with low " have to have them" factor, are now sold and a new AC/DC Kemppi is bought for the money.

Turbo outlet flange was made this week from 10mm plate. I did the outer shape the slow way... marked the shape with a pencil and drilled 80 holes along the line while I listen to old 10cc albums (probably none of you that are so old that you have heard about them ;) )

Flange holes were done in a milling machine to increase accuracy. Holes are only 0.1mm larger than studbolts. Then flange was bolted to turbo and the under size exhaust hole was grind up match the exact shape of my turbo on my project car "Letty" Gasket is also fitted and was therefore trimmed in the same operation.

Then I tack welded the first bend to the flange. I machined a diameter same as outer tubing , down to half of the plate thickness (5mm) Then next is to weld a full weld over the tacks and then dress a nice 10 deg taper.

Now I need to lift in the engine into Letty so I can verify correct position of next bend and the the flexisection.

A2 Letty SS downpipe flange.jpg


A2 Letty SS downpipe flange tac.jpg
 

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@dieselfan,
Whooop, yess, Here a 10CC fan! My first album bought from my money as a paperboy!
Sold my trusty old Elektra Beckum TIG 260Cdi and in return bought an ac/dc Sherman 206P..... ❤
 
A2Steve said:
I had a custom decat down pipe made up on on my last project car by a company called Longlife exhausts. 2.5 inch stainless steel and it really made a difference to the pickup on the turbo. It cost £250.
Click to expand...
Any idea if you did get any extra ponies from the new exhaust ?
 
Any that have done dyno and have an idea of what kind of increase one can expect ?
or have got promise's from manufacture's ?
Cheers
dieselfan
 
A2Steve said:
There’s no requirement for a CAT on this age of diesel, only a smoke test.
Click to expand...
Really? Your car still needs to meet it's original emissions requirement. Not doing so would invalidate your insurance.

RAB
 
I agree as there is only a smoke test required for the mot. This is straight from the mouth of my mot tester too.
 
RAB said:
Really? Your car still needs to meet it's original emissions requirement. Not doing so would invalidate your insurance.

RAB
Click to expand...

I would think that the modification would need to be disclosed to your insurance i.e the de-cat, but I cannot see any way that they could determine emissions standards and therefore invalidate anyone's insurance.
 
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