Less restrictive downpipes

ddeeble

Well-known member
Joined
Apr 27, 1999
Location
West Sacramento, CA
I recently came across a thread either here or on VW Vortex that discussed dyno results of increasing downpipe diameter to 2.5" as well as improvements to cat-back exhaust mods. The overall result appeared to be that a 2.5" downpipe combined with stock exhaust resulted in appx. 13-15 HP increase accroding to repeated dyno testing. I contacted Euro Sport Accessories (www.eurosportacc.com/vw/vw-html/vw.html) about this modification (I was looking for a drop-in replacement for the existing downpipe) and received a response back saying that they do not currently make such a mod, and would need to sell about 50-75 such units to make it feasable. Anyone interested in this type of modification should email Jason at Euro Sport Accessories (raffi@eurosportacc.com) and let them know you'd like to see it!

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1974 Super Beetle
1969 Beetle
 

ddeeble

Well-known member
Joined
Apr 27, 1999
Location
West Sacramento, CA
An interesting note to the testing that was done - it appears that the 2.5" downpipe coupled with the stock cat-back exhaust system performed better than the same car with 2.5" downpipes and 2.5" diameter exhaust. It was also interesting to note that removal of the catalytic converter only produced a appx. 1-2 HP increase regardless of which layout (downpipe/exhaust) was installed. If memory serves me correctly, the vehicle being dynoed (sp?) was a UK Golf TDI - the same vehicle was used for all dyno testing and parts were simply swapped on and off between tests. This mod, coupled with wrapping the intercooler plumbing with heat-resistant insulation could realistically yield 13-20 HP depending on design, etc... Seems like a cheap and easy way to beef up a TDI!

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1974 Super Beetle
1969 Beetle
 
M

mickey

Guest
The modest power gain from removing the catalyst doesn't surprise me. Diesel cats are a different, and much less restrictive, design than their gasoline cousins. My dad's Powerstroke cat only causes 3 or 4 pounds of backpressure. He removed it anyway, but doesn't notice any difference in power.

But, holy s**t Batman! 13-15 hp gain just by changing the downpipe? That'd have to translate to 25 pounds of torque, or so! That just can't be right. Why wouldn't VW invest in the extra penny's worth of steel for the bigger tube in the first place? Maybe they're deliberately trying to slow the cars down. I don't know, but I'll tell you one thing: If these performance claims are true, sign me up!

-mickey
 
M

mickey

Guest
I just thought of something. (It happens...) Is there anything complicated about the downpipe? Why couldn't any good custom exhaust shop make one for you? It shouldn't be all that tough. Just an idea. Probably won't work. Don't know why I even mentioned it. Oh, good night.

-mickey
 

Keith

Veteran Member
Joined
Mar 13, 1999
It could get expensive really quick to have a muffler shop do the 2.5" downpipe. The 90 deg. bend at the turbo is really sharp and a 2.5" 90 deg. mandrel bend must be welded to the flange, then straight pipe welded to the 90 deg. bend and etc. All this can be done alot cheaper on a jig for a bunch of cars.

Here's an idea: Anyone know of 2.5" aftermarket downpipes for the 1.8T Beetle? It would be easy to adapt that to the TDIs.

Keith.
 

Peter Cheuk

Gasser :P
Joined
Aug 31, 1998
Location
Daly City, Calif., USA
TDI
'06 Jetta GLI
I posted this information on the VWVortex website and forgot to put it here (so flame me! :p). Anyways, it goes something like this:

I got this information from my friend who works for Dinan. There are three ways to make this part. One is to have a muffler shop take some straight 2.5" tubing and 'crush bend' it into shape. Problem there is that the bends would reduce in diameter and be restrictive. The second way is to use premade mandrel bent tubes and cut and weld them into shape. No restrictive bends but the welds are weak points that will break eventually given the way the motors are mounted. The third way is to have the entire thing mandrel bent from straight tubing. While this is fine for production numbers, making one or two is very expensive. Dinan uses the second method for prototyping and then takes the prototype to have the final products produced.

Let's not forget that a flex coupling is needed to avoid breaking this item down the road. This could turn out to be an expensive piece. A shop like Techtonics, who specialises in exhaust systems and has the dyno facilities may be a better choice to create and make such an item, IMHO.
 

ddeeble

Well-known member
Joined
Apr 27, 1999
Location
West Sacramento, CA
Let's start emailing Techtonics as well - can't hurt to have multiple shops working on it!




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1974 Super Beetle
1969 Beetle
 

ddeeble

Well-known member
Joined
Apr 27, 1999
Location
West Sacramento, CA
Sent an email off to Techtonics just now - let's see what they think of the idea! Keep those emails to Euro Sport and Techtonics coming!

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1974 Super Beetle
1969 Beetle
 

Olli

Veteran Member
Joined
Feb 19, 1999
I too have sent an e-mail to Techtonics. I also invited them to visit Fred's TDI page so that they can see that there is a very enthusiastic following of the TDI. And that, YES ,we are also performance enthusiasts!

Olli
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, Massachusetts. USA
TDI
idi: 1988 Bolens DGT1700H, the other oil burner: 1967 Saab Sonett II two stroke
But is a flex pipe nesessary? Another thread concerning exhaust system resonation has one camp touting the newer solid pipe as the solution, while another faction is bending the flex pipe to free it up to its former limber condition. Mine is,(and has always been), resonating right at 2250 rpm. I also have a rear muffler that is rusting through the skin. I'm going to need a replacement soon. Do I get a flex pipe or the newer solid one? Stock or 2.5 in.? cat or no? Mid muffler or no? Decisions, decisions.

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Jonathan Bartlett
 

Peter Cheuk

Gasser :P
Joined
Aug 31, 1998
Location
Daly City, Calif., USA
TDI
'06 Jetta GLI
VW uses a flexible braided flex joint while Techtonics uses a spring loaded contraption (at least that's what I remember) to handle the flexing. I would think that the Techtonics solution would give better results. As to why use a flex coupling, well, blame the motor mounts for letting your engine rotate back and forth in the engine bay. That motion will cause breakage in the exhaust if it wasn't allowed to flex somewhere. If you never take advantage of all of that wonderful torque then a flex coupling may not be so beneficial to you. But, for me, the flex coupling will mean the difference between buying one or not as I'm having way too much fun with my car to be worried about breaking the downpipe the next time I come upon an unsuspecting honduh.

[This message has been edited by Peter Cheuk (edited June 02, 1999).]
 

Sooty

Veteran Member
Joined
Apr 29, 1999
Location
Midlands, UK
Don’t get too excited mickey, the claims are true but you may not have read the small print!


I did say in the original posting that the 16 hp increase was measured with the aid of a modified air intake system, K & N 57i kit (from a VR6) this would account for some of the increase, it wasn’t all down to the exhaust.

Tests where performed on ‘modem superchip’d car. The chip set adds an extra 30hp to the original 90hp, making 120hp (with the standard exhaust and air box) don’t you just love it when you actually get the boost that is claimed by a manufacturer. The extra 16hp is made up by the air intake and exhaust, I left the air box on while testing because I know that the chip will take advantage of all of the air that it can pass.

What difference the exhaust mod would make without the chip and air intake I don’t know. I am guessing that the air intake would add about 5-6hp and the chip may account for about another 2-3hp. So I think that you may get about 8hp for the exhaust only – well that’s my guess anyway.


For those interested the pipe was a single 2.5” bent into shape via a mandrel, with flanges welded for mounting etc.



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Andrei Rinea

Veteran Member
Joined
Jan 21, 2002
Location
Europe, Romania, Bucharest
TDI
VW Tiguan 4Motion 2.0 TDI 170HP (engine CBBB)
Practically a downpipe replacement would add very small power increase... right? That's what I'm getting anywayz (no cat, 2 cherry-bomb - see through mufflers and 2.25" exhaust) 1 maybe 2 HP increase. And I have a chip and Sprint 520.
 

jthesby

Veteran Member
Joined
Dec 23, 2005
Location
Concord,CA
TDI
'01 Silver TDI Golf
Wow, i haven't seen Peter Cheuks name on here in years.... not sure if you all heard what happened but his tdi got totaled... sold the wreck to a buddy of mine and he put it in a shell, and the motor lives on:)...Think Peters rollin a GLI nowadays..

But to the actual topic, I do believe it helps the EGT's.......
 
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