The key to VW's "high output" 1.6TD engines (RA and SB) was the intercooler, also called a charge-air cooler, or aftercooler.  The intercooler serves to cool the intake air after it has been heated by being compressed by the turbocharger.  This benefits the diesel engine greatly, as it thrives on excess air, and the cooler and denser the charge is, the more air can be forced into the cylinders.  This extra air enables more fuel to burn, which in turn reduces smoke, but also allows for an increase in fuel delivery to the cylinders, which in turn results in more power.

VW's TDI engines also use intercoolers for this reason, as do most other modern turbo diesels.

I am currently (Feb '03) working on fitting an intercooler into the Scirocco TD.  The unit I have chosen is an intercooler from an 86 Audi5000 Turbo.  This is a dual pass intercooler, which will be mounted in front of the radiator.

In order to keep piping short and direct, I've opted to mount the IC upside-down compared to its orientation in the Audi 5000 (original mounting diagram can be seen here) and on the left hand side of the car.  This will avoid having to run boost tubes between the engine and shock tower (space is tight) or over top/around the engine, as would be necessary were the intercooler installed on the right hand side.

After some more test fitting, I determined that it is possible to use the A5K IC in front of the rad on the left hand side of the car, however some changes will be necessary to accommodate the 675mm radiator. The right side of the rad will be moved to the A/C condenser's mounting point (moving it even further forward and to the right than it already is. The left side of the rad needs to be located back from the stock mounting holes to increase clearance for the plumbing. It will be necessary to manufacture a lower support and new upper bracket. The changes to rad location will require new rad hoses as well. The upper rad hose is a trimmed A2 upper hose from a 675mm rad (non-ac) and the lower hose is a 16V Scirocco lower hose. I should be able to get away with using another trimmed A2 upper hose (only less trimmed off this time) and will probably be able to use a lower A2 hose as well (which is what I originally used on the car when I put the 675mm rad in, before the 16V lower hose came in at the dealer.)

In addition, it will be necessary to re-orient the battery in order to allow space for the intercooler plumbing. With some modification to the lower battery tray, it will likely be possible to turn the battery 90 degrees to provide the necessary clearance.  One option is an A3 lower battery tray (they're plastic and bolt onto the side member.)  Alternatively I will be investigating putting an Optima RedTop battery in the rear hatch area.

Below you can see the intercooler test-fit with the 675mm rad. The rad has been moved over to the right by moving it into the forward-most condenser mounting hole. The cable tie is holding the upper bracket roughly where it needs to be mounted to provide clearance for the hoses. You can also see that I have trimmed the inlet of the intercooler to allow it to clear the upper rad support. Although it is not visible in the photos, I also trimmed the lower mounting post on the side of the intercooler's end tank so that it could be positioned right up against the left bumper tube.

Installation of the  Intercooler-intake manifold hose: (March 16 2003)

Intercooler tube route take 2 - test fit completed: (March 29 2003)

Intercooler mounting completed (April 12 2003)

Intercooler bracket detail:

Radiator detail:

Alternator modifications underway (April 18 2003)

Because of clearance issues between the alternator bracket and the radiator's lower outlet, I opted to modify the alternator mounting.  I aslo cut the extra "ear" off the alternator casing as well.  The alternator adjusting bracket was made from an 8V non-air bracket with the end cut off, so only the slotted section remained.  The bracket bolted to the cast alternator bracket was cut off of the left side lifting bracket from an 8V engine as well.  I am using an 11X925 belt instead of the 10X965 that was on the engine before.  The belt fits tight enough that it is necessary to remove the top mounting bolt for the alternator to install it.  As the belt stretches, there will be room to adjust it without interfering with the lower rad outlet, although clearance in this area is still tight.

Battery Tray modifications (May 4th 2003 - I can't believe it's May already!)

Battery relocation was necessary due to the location of the intercooler and intercooler piping.  Originally I'd hope to relocate the battery to the rear hatch, however time and funds are both things I've run out of... :)  The simpler solution was to turn the battery on the existing tray to allow it to clear the intercooler plumbing.  This was done by simply drilling out the spot welds on the rear hold-down angle bracket, and re-welding it at an angle on the tray.  I then drilled a new hole in the tray and welded a nut on the underside for the hold-down clamp.  The following shots are difficult to interpret due to the high-gloss paint everywhere - I'll take a few more with the battery actually installed.

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