How To: Install an APR Turbo Inlet Pipe on an Audi A4

By James Mackintosh, 30 June 2010

Perhaps the fact that most of my recent posts have been how-to articles tells you something about my preferred past time. While I like to write about cars, I love to work on them.  Sometimes that's reversed (see: Saab 900 water pump install), but besides driving, my favorite thing on this earth to do is turn wrenches on a car.  Now, if I didn't take forever and a day to do anything automotive-related, I could probably make some money with this.  But as a whole, I prefer writing about cars for a paycheck and wrenching on them as a hobby; I think if I added stress and deadlines to my wrench-turning escapades it would end in tears.

So whenever I get the opportunity to work on a car, I pretty much jump for it.  I figure any additional experience is a good thing, even if it's not on my own car.  Which brings me to my friend Jon.  Recently, Jon traded up from his 2001 BMW 325i (which I featured on my old, now sadly defunct website tehcarblogz) to a pristine, low mileage 2002 Audi A4 1.8 Turbo Quattro.  It's a peach of a car.  Base model with just a few options, 1.8L 20-valve turbo straight four (laid out longitudinally in the classic Saab tradition, thank you), Torsen full-time four wheel drive, 5-speed manual.  With only 64k on the clock and virtually no problem areas, it was like a clean, blank slate.  You see, Jon's just like me: he sees a stock vehicle and sees potential, rather than an end.  His previous 325i was similar in equipment, but was modified fairly extensively for a recent BMW.  Full Koni/H&R suspension and sway bars, K&N intake, AAW chip, full Borla exhaust with a high-flow cat, B&M shifter, limited-slip-differential with 3.46:1 final drive ratio, M5 clutch and 12lb single-mass flywheel...  it was a lot closer to a track car than BMW ever intended, and a whole lot more fun to drive without sacrificing livability as a result.  So it was expected that Jon's new toy (excuse me, daily driver) would stay stock for approximately as long as it took to drive to the nearest local software vendor.

This has proven to be the case.  We've been very busy turning the A4 from a mild-mannered European luxury sedan into a turbocharged cruise missile in a stealth suit - a sleeper, if you will.  To date (in the last 2 weeks!) here's what's been done.

  • Central exhaust resonator replaced with straight pipe
  • Unitronic Stage 1+ 93 Octane Software Installed (180/180 to 215/245 bhp and tq, 9.7 to 18psi)
  • Forge Split Diverter Valve (80% recirculate) installed
  • Polyeurothane Snub Mount (front motor mount) installed
  • NGK Iridium plugs, one heat range colder than stock, installed
  • Neuspeed Short Shift Kit installed

As you can see, we've been quite busy.  While some were quite easy (the software, for instance - a swipe of the credit card and 20 minutes with a laptop yielded massive extra power), some have been a bit of a pain in the ass.  The Neuspeed short shifter was a drastic improvement - which took about 5 hours to put in, including disassembling the damn thing after we've discovered there was no reverse gear.  Ahh, you live and learn.  But yesterday, Jon called me up and uttered the magic words "The APR TIP is here.  You wanna bust out the wrenches?"  Well, of course.  I also busted out the camera to show you, loyal readers, the joys of working on a recent Audi product.  Some sarcasm is intended in that statement.

Step One: Remove stock crap.

Here's the frankly terrible stock induction setup.  That big black plastic crossover pipe is actually the intake tube - about 6" wide but only an inch deep.  It feeds from the grille into an airbox with a flat filter underneath, which then passes air through the Mass Air Flow Sensor (MAF) and into the turbo inlet pipe.  The TIP feeds fresh, filtered air to the turbocharger where it's compressed, intercooled, and shot into the intake manifold creating happiness.  Problems here?  Plenty, as you can see above and below.  The stock intake tube is terribly restrictive, flimsy, and makes working on the car a bit of a pain in the ass.

The air passes through a small inlet, and into a thick air filter.  Then you get to the actual inlet pipe itself, which is what we're primarily here to replace.  It's made out of soft rubber.  While this doesn't sound like an issue (it's not pressurized!), it presents some unique issues.  On a stock car running stock boost, no.  On a Unitronic-chipped 1.8T, yes.  This tube is how the turbo itself breathes - when it's breathing normal amounts of boost, it's totally capable of providing sufficient flow.  When you're pushing almost double the stock amount of boost, it tends to collapse under heavy loads.  This is partially due to the restrictive airbox setup and partially because the turbo is asking for a lot more air.  Imagine breathing through a straw, sitting in a chair.  Now imagine breathing through the same straw running a marathon and you see the issue.  So, get to removing crap!

The weird UFO-shaped device in the center is the PCV (positive crankcase ventilation) valve, which needs to be removed.  Below that on the TIP (sticking out above and to the left of the PCV valve in the picture) is the N75 valve, which is part of boost regulation.  Both of these need to come out, and they're both a royal pain in the rear.  For those of you not familiar with VW/Audi single-use clamps, here's a tip: don't.  They are hateful devices, and should be banished from existence forever.  Most of the time spent on this install was fighting with cursed single-use clamps.  Twist, cut, swear, cajole, beg, and do whatever you can to get these things off.  There are two other fittings below these two that must be removed (I believe secondary air injection and EGR), which is made easier by simply loosening the TIP from the inlet side of the turbocharger.  Once you've got all four(!) fittings loose and the stock TIP removed, you'll see something like this:

Aww, hi there Borg-Warner K03 Sport!  You're so tiny!  I wanna give you a hug.  Would you like to meet your papa, the Garrett T3?  As you can see, it's a bit of a tight fit down there for those of us cursed with fat, awkward hands.  Also visible at the bottom of that photo is the Forge splitter valve installed about a week ago.

After this, it's time to get that whole stock airbox and heat shield out of there and stuff it in the trunk.  It's just a few phillips head screws and some rubber grommets, not too hard.  Really opens up the cramped turbo side of the engine bay, eh?

Step Two: Prepare New Parts, Hook Stuff Back Up

Here's the stock TIP next to the APR inlet pipe.  Boy is this car lucky it met us.  Notice the more gradual bend at the end leading to the turbo, the wider inlet, and the fact that it's heavy duty silicon and won't suck closed under boost.  This is quality stuff, in addition to being pretty and blue!

At this point it's helpful to jack up the passenger side of the car and put a stand under it to get some room to work underneath.  It helps to take off the intercooler pipe and diverter valve hose so you can access the underside of the turbo to tighten down the clamp that holds the TIP in place.  It's pretty under here!

Basically, once you've got the TIP aimed the right way, you need to get it on the turbo inlet correctly and tighten the everliving bejeezus out of the clamp so you don't have to go back and do it again.  Make sure all the clamps you can reach from here are tight, then reconnect the intercooler hose so you're not pressurizing the atmosphere.  Go back around up top, fight with all the connector, get everything hooked up, and Yahtzee!  You've got an APR Turbo Inlet Pipe!

From here it gets easier.  We picked up a conical filter and a small breather filter from our local FLAPS and some fitting hardware.  Unscrew the MAF housing from the airbox with a Phillips, and insert it the right way around into the end of the TIP.  Fit the conical filter onto the other end, and clamp down.  Now, see the black plastic pipe pointing up to the right of the TIP?  That's the Secondary Air Injection feed line.  We had an issue with the breather filter being a bit too small to wedge into the end of it, so we created a faintly ingenious home-made gasket to fit around the end of the breather and cram into the SAI line.  Using one of the fittings on the stock rubber TIP, we chopped it off and cut out about a half-inch of it to make a gasket.  Presto!  Tight-fitting breather filter!

Now that's bling.  We're almost done - remember that goofy stock intake tube?  We're gonna use a piece of it here as well - the front section that pulls cold air behind the grille mounts to the car with two Phillips screws and fits nicely above all this pretty intake equipment.  It helps assure the air getting to the filter is actually cold, although the lack of a heat shield is an issue we're going to have to fix in the near future as it's less than ideal.  Still, not bad for a few hours work, eh?

After everything's in place, go around to all fittings and make sure everything's all the way and tightened all the way down.  Then, go take it for a spin and enjoy!  The difference is definitely noticeable - stronger mid-range pull, more sustained boost to redline, and a most delicious whistle from the turbocharger that was significantly muffled by the stock induction system beforehand.  Another job well done, if I may say so myself.

Next article Jaguar XKR 75: Kitties' Got Claws!
Back to top