2.5/3" downpipes in relation to egt's

[DonGTI]

Can anyone please explain to me the effect a wide bore downpipe as opposed to a stock one has on egt's?
 
Also are there any pics in this forum of wider or fabricated downpipes? I would like to see how you people are doing yours with all this repeated emphasis of wider downpipes. I am just back from my silencer shop and we tried bending a 3" pipe to 90degrees for the pie that connects the turbo to the downpipe and as the pipe bends, inner diameter goes down to about 2.2"... what am i doing wrong? do you start with +3" pipe in order to allow for shrinkage whilst bending? Or do you use a 90 degree ready made elbow?

Material: Does stainless vs normal exhaust pipe have any effect on egt?

I don't have the time to plumb in the AAZ any time soon but I would like to have everything sorted out by the time i start... no loose ends or surprises or things i may have done better but didn't because just didn't know about them..

Thanks
Daniel

[haybayian]

Can anyone please explain to me the effect a wide bore downpipe as opposed to a stock one has on egt's?
 
Also are there any pics in this forum of wider or fabricated downpipes? I would like to see how you people are doing yours with all this repeated emphasis of wider downpipes. I am just back from my silencer shop and we tried bending a 3" pipe to 90degrees for the pie that connects the turbo to the downpipe and as the pipe bends, inner diameter goes down to about 2.2"... what am i doing wrong? do you start with +3" pipe in order to allow for shrinkage whilst bending? Or do you use a 90 degree ready made elbow?

Material: Does stainless vs normal exhaust pipe have any effect on egt?

I don't have the time to plumb in the AAZ any time soon but I would like to have everything sorted out by the time i start... no loose ends or surprises or things i may have done better but didn't because just didn't know about them..

Thanks
Daniel

The only way to make a decent 90 degree pipe in 3" is to buy mandrel bent units. This is a process by which the diameter of the pipe is preserved.

If someone could  tell me how to post pictures here I will show you what I have.

Haybayian

[DonGTI]

Can you explain regarding mandrel bent pipes? Is it the same as using a 3" elbow i can buy off the shelf from a steel shop and welding that to a pipe?

regarding pictures i was told to open an account with www.photobucket.com upload them there and then copy links to this forum...

[carrizog60]

use a server like imageshack to host the pics online
then copy the url they give(last one)and put him like this:
(hit img button),paste your url,(hit img again)

will look like this

[DonGTI]

I don't have pics of shrinkage that occured when i was bending the pipe myself however the factory item displays the similar problem


And another question... I thought that an exhaust system's effectiveness depends on its thinnest point/bottleneck. The factory turbo and its flange have a 2.3 inch hole, wouldn't a 3" system be pointless due to thinnest point being 2.3 inches and cause flow disruption/decreased back pressure ecc? Or do you replace the factory flange and widen the turbo housing to 2.5 or 3" ?

[burn_your_money]

Have you read this thread on exhaust size?

optimal exhaust size

[Vincent Waldon]

And another question... I thought that an exhaust system's effectiveness depends on its thinnest point/bottleneck.

I used to think this too, until I worked for a pipeline company and watched them replace short sections of a 500 mile 30" pipeline with 42" pipe.  "Why bother" I thought... the 30" stays the bottleneck.  Same with 16 gauge wire and then a little piece of 4 gauge... what's the point ??

Then I talked to some line engineers who smiled patiently.  Pipelines and fluids are not the same as wires and electrons... flow dynamics dictate that, in general, anything you can do to decrease restriction will decrease resistance to flow, which will improve flow overall.

So a 2" system with some 3" pieces offers the engine less restriction than a 2" system all the way thru.... hence why 3" cat-back systems give some people a noticeable improvement.

Or so I was told...   ;-)

Vince

[jimfoo]

Then I talked to some line engineers who smiled patiently. Pipelines and fluids are not the same as wires and electrons... flow dynamics dictate that, in general, anything you can do to decrease restriction will decrease resistance to flow, which will improve flow overall.
Vince

Actually it is exactly the same for wires and electrons.

[745 turbogreasel]

an overview of bender types
http://en.wikipedia.org/wiki/Tube_and_pipe_benders

[Vincent Waldon]

Actually it is exactly the same for wires and electrons.

Adding a short 4 ga section of wire to a 16 ga length doesn't increase the power-handling capabilities of the line, wouldn't you agree ?  The line will still melt at the capacity of the 16 ga wire.

Whoops... I think I'm hijacking a thread...  ;-)

[DonGTI]

Ok... so forgetting the electron issue, 2.5" or 3" tubing is the way to go...

BUT

Is there any significant performance difference between 2.5" and 3" systems? Your feedback please... for i was thinking 3" for the downpipe right down till the flexihose then 2.5 fron there to the backox (freeflow type stainless unit i have already).  

As regards mandrel bends, when i said i was considering using pre-bent sections fron a steel shop they are just like those on libybapa's link so i guess they are mandrell bent as well, will ask at the shop to confirm.

[haybayian]

Can you explain regarding mandrel bent pipes? Is it the same as using a 3" elbow i can buy off the shelf from a steel shop and welding that to a pipe?

regarding pictures i was told to open an account with www.photobucket.com upload them there and then copy links to this forum...

The best answer has already been provided to you by our forum colleagues. A mandrel bent pipe is more than just a bent pipe. The mandrel technique yields a pipe with a consistent diameter with no wrinkles. In making my exhaust system I have bought from a specialized shop an assortment of elbows (they gave me a bulk price). Yes I have mig welded the sections together. First tack welded in place and then complete welds on the bench.
Hope this is useful.
http://s273.photobucket.com/albums/jj208/VWSEVEN/
[IMG]http://i273.photobucket


Haybayian

[saurkraut]

3" inch is better than 2.5".

[DonGTI]

Yes I now know what is a mandrel bent pipe lol... seriously, just came back from the steel shop, he said he can sort me out with any bend i need, both pre-cut as well as long U sections. I showed him the pic of this fabricated manifold
http://vwdiesel.net/phpBB/viewtopic.php?t=10821
and he offered me to take the stock downpipe to him and he cuts me bits that when welded together acheive the same shape overall...

So my last 2 questions regarding the downpipe are:
A: Apart from not rusting/corroding are there any other advantages a stainless steel downpipe has over a steel one? (egt's maybe?)

B: On a mildly tuned motor will there be any significant difference between a 2.5" vs a 3" downpipe section considering i shall use 2.5 from the flexi-bit below the steering rack to the rest of the way till the backbox?

Thanks again
Daniel

[burn_your_money]

Do you know how to weld SS? I don't but from what I've read you need to fill the pipes with some gas to keep the back of the welds clean... or something like that anyways.

935racer explains it somewhere on here

If you an do the 3" I would, that way if you ever feel the urge to go bigger on the rest of the exhaust later you can