Comparison of A3 vs. A4 Intake Air Plumbing

[Ric Woodruff]

Over the weekend, at the first ever Central Florida GTG, I had the opportunity to compare A3 to A4 engines (thanks, jim wilson).

What we found was that the A3 had a constant diameter piping throughout the turbo to the intake manifold path with no restrictions.

The A4 on the other hand, has a area where the piping becomes flatened, and another area where it actually becomes quite narrow (near the intercooler). Both of the areas seem to restrict air flow.

An obvious cheap and easy upgrade to A4's seems to be to eliminate the air restrictions for better flow and therefore increased power.

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Ric Woodruff

Braumeister von Sehr Gutem Bier
Since the Last Millennium

1998 Jetta TDI Sport

"A man who stands for nothing will fall for anything"



[This message has been edited by Ric Woodruff (edited May 01, 2000).]

 

[Ric Woodruff]

BTW: The restriction just before the intercooler could possibly explain the condensing of oil vapors within the A4 intercoolers, resulting in a nasty sludge situation, where us A3's on the other hand, have clean intercoolers.

 

[Craig]

Hmmm. Perhaps we A4 owners should go back to A3 plumbing. Also I believe the plumbing on A4s has changed since inception. I have seen pictures of older NBs on this forum and there is a round tubing (hose?) beside the engine. On the newer Jettas, it is a narrow plastic duct. Obviously, there has been several mods by VW (cost reductions?) on the turbo ducting and each seems more restrictivbe that before. Bottom line is, the more recent the TD, the more there seems to be plumbing restrictions.

We need an upgrade kit for 2000 Jettas, Golfs (and NBs?).

 

[ThinkDiesel]

Hey Ric--

Did TDI Believer ever get to meet up w/ you guys?

 

[GoFaster]

Craig, you can't go back to A3 plumbing. Your intercooler is on the wrong side

Jim, you're on the right track by opening up the flow behind the intercooler. When I had a loaner NB for a week, I looked at the i/c setup in that car, and it's even worse off than my Passat was, for not having anywhere for the air to go behind the intercooler. Regardless of mods, you have to make sure that road debris can't get to the back of the intercooler, and that debris can't pack up inside the fenders where they could accelerate rust problems.

In my case, I trimmed off the bottom 3" of the fender liner a few months ago. Nothing hits the intercooler, and this past week I stopped after going up a good long hill with the trailer behind, 15 psi boost for a good couple of minutes. The pipe to the intercooler was so hot you couldn't hold your hand on it, and the one coming back from the intercooler was only slightly warmer than ambient!!! That's what we need...

Brian P.
'96 Passat TDI

 

[jim wilson]

Just want to make sure you know what I was talking about- I made the holes to the rear of the fenderwell the air can easily flow over the wheelwell but debris, if it could make it over the wheelwell wouldn't hurt the IC

 

[jim wilson]

I removed the inner cover of the right front fender this morning to try and find a way to increase the tube size. I removed the tubes. the turbo outlet is 1.5" yet one piece of the stock tubing goes down to 1" the tube leading to the intercooler is 2" I will have an adapter (1.5 to 2")to connect a new rubber hose (2") that runs from the turbos 1.5" to the intercoolers 2" by the end of the week. I noticed there is no place for the air flowing through the intercooler to goto. Instead of making holes right behind the intercooler for air flow (fear of road debris hitting IC) I made 4 1"x3" oval holes at the rear of the cover. I also removed the foam block that sits above the wheel well. This way the air has somewhere to flow and I don't have to worry about rocks hittting my IC. I think an 8" 500 CFM fan is all I need now. Oh and a tunning box,1.5 more twists on the vnt, and 2.5" turbo back exhaust.

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It's the area under the curve that matters.