The 1996-7 Passat B4V-TDI Wagon had the AHU-1Z version of the TDI diesel engine, indisputably one of the all-time best engines ever built BUT there were a few design flaws on some exterior engine parts that we have found ways to improve.

Some of those components we upgrade are:

Deleting the 5th injector system (good idea but it never did function correctly)

Replace the OEM rubber vacuum hoses with Viton German color coded lifetime hoses,

Replace the stock OEM plastic fuel lines with Bio-fuel compatible--Gates USA hoses,

Replace the OEM stock compression clamps on the turbo cooling tubes with stainless double clamps

Hi -tech rubber gaskets, seals, relays, bushings, bolts and epoxy-type glues

Audi TT torsion bar bushings---Corrado spindle bearings

Weld the back side of the upper clutch pedal bracket where the actuating rod of the brake slave cylinder attaches and the Turbo Downpipe modification described below.

If VW had built these B4-TDIs for a second year they would have surely improved these flaws.

Many of our improvements are due to modern technology coming up with far more advanced materials than were available 20 years ago.

The following will show you how we attend to one of those design flaws on the turbo downpipe.


This photo is of a typical 1996 TDI Turbo downpipe, part #180129654. This carriers the air from the air cleaner through the EGR and down into the turbo. Working on hundreds of these AHU-1Z engines has shown us that this downpipe has a design flaw that we have upgraded to provide superior efficiency.

The next photos show the end of the pipe that attaches to the turbo. There are two flanges with holes for the attaching bolts. Due to the vibration/shaking of the engine (especially at idle) these attaching flanges tend to break and the end of the downpipe will crack as seen in the photo.  When this happens (and it happens on most B4-TDIs) the pipe will stay attached but due to the crack it will suck in dirty air and that air bypasses the function of the EGR and the air cleaner. Not only is the sucked in air dirty but driving in the rain will allow it to suck in water and water in the turbo is obviously not good.


We have devised a good and simple modification for this design flaw. Seen in photos below #6035 and 6036 is the modified downpipe attached to the turbo. We cut off the flanged end of the downpipe and alter it to attach to the turbo with a high temp rubber hose with two stainless clamps. The rubber hose dissipates the vibration and its held tight with the clamps so no dirty air or water gets into the turbo.

You can also see the new bolts and stainless nuts on the exhaust side of the turbo. we have sourced out the highest quality upgraded stainless and hardened nuts, bolts and other fasteners for the external engine components.


The following photo is the front of one of our restored B4-TDI engines ready to install. This has new Bosch Glow Plugs and new Glow plug bridge, Fuel injectors with new nozzles and seals, new coolant outlet, new crank vent assembly - (seen unattached in photo#6029), serviced Bosch fuel injection pump, German Mahle oil filter, new oil funnel, new valve cover and gasket and a new Bosch alternator. The new German color-coded vacuum hoses are attached to the engine and ready to be attached to where they go in the engine compartment.

The next photo shows the back of the engine, the side that is against the firewall when installed. Here you can see the turbo with the modified turbo downpipe attached. Above that is the aluminum intake manifold that has been boiled out in carb cleaner to rid the interior if excess carbon. It’s installed with a new gasket and new bolts. Attached to the top of this intake manifold is the exhaust tube that connects to the exhaust manifold (also attached with all new bolts and gaskets) This pipe allows some of the exhaust to go back into the engine to help it get its incredibly high MPG. Driving habits affect the amount of carbon build up inside the intake manifold. (Contact us for info on this driving habits) Also seen here is the black exhaust manifold, cleaned and installed with new bolts and gasket.


The following photo this is the passenger side of the engine with the Timing Belt cover off. Here you can see the new Timing belt, new tensioner, new roller and new water pump with steel impellers as opposed to some with the inferior plastic impellers. Here you can also see the new German Serpentine belt and new tensioner hooked up to the Bosch alternator and other pulleys.


View the next photo. Here is a restored engine installed in a Grey B4V-tdi Wagon. Here you can see the new coolant reservoir and new W/S washer bottle, new Alaskan Battery, new Bio-fuel lines, new Bosch fuel filter and vacuum hoses hooked up.

We use VW OEM G12+ phosphate free coolant and German Pentosin Synthetic engine oil.


The next photo shows two turbo air tube clamps. The clamp on the left is an original VW B4 compression clamp. These are a spring-loaded clamp that squeezes the end of the hose in place. Problem is the "spring" sometimes is compromised after 20 years and the air will leak in.  The clamp on the right is what we use to replace the original clamps. This is an aircraft stainless "T-clamp," the highest quality clamp we could find. We double these up on the ends of the tubes to insure a tight no leak fit.

These final photos show these clamps installed on one of our turbo air tubes.


These are some of the ways we have found to improve the external engine components.

Let us know if you have any questions!