Mounting the Turbo (James – 02)

Now for the fun stuff!

When I built this car originally, I went to great lengths to get the stock S13 T25 turbo to fit under the stock steering shaft (aka death spear) so it would look as original as possible, and to keep the heat away from the hood and the brake master cylinder so we would not cook the brakes.

It takes a great deal of work to get the turbo to clear everything and there is just enough room to make it all fit – think building a ship in a bottle and you get the idea.

Most people who install SR20DET engines into their roadsters top mount the turbo. This is considerably easier plumbing wise, clears the steering, and can look quite sexy when done right.

The S15 SR20DET uses a T28 ball-bearing turbo instead of the T25 found on the S13 engine. This has a larger compressor housing that is quite a bit larger than its predecessor. This larger compressor housing makes it nearly impossible to fit the T28 under the steering shaft without serious modification or u-joint monkey motion.

We did not want to deal with that, so we decided to go with a top mounted turbo. I feel with appropriate heat shielding and dedicated fresh air, we can maintain the paint on the valve cover as well not cook the master cylinder, even with the larger T28 turbo.

Because we still have a solid steering shaft going through the left side of the engine compartment, we cannot use any of the commonly available aftermarket exhaust manifolds on the market, nor use the stock manifold. We have to build something custom.

This actually works out well as we can then place the turbo exactly where we want it. JGS Turbo makes a blank “log” manifold that allows you to cut exactly where you want to mount your turbo flange. Their kit comes in at just under $300 and gets you a fully-welded exhaust manifold and flange kit. You can see an image of what they do here: www.jgsturbo.com

Since the turbo is going to be top mounted, it needs to be “clocked”, which means that the snap ring on the compression side of the turbo needs to be removed to allow you to rotate the housing to get it pointed in the right direction.

The exhaust housing needs to be rotated as well. The four ½” bolts need to be loosened to allow the turbo housing to be rotated to suit your application.

When clocking the turbo, you need to pay particular attention to the oil and drain sections of the turbo. The oil feed needs to go on top, and the drain rotated straight down as it is a gravity feed drain.

Once the turbo has been re-clocked, you can figure out how it is going to fit on the manifold. What I wanted to do was to figure out what was a natural placement of the turbo with the down pipe (exhaust) attached.

Using a 2.5″ 304 stainless bend from Burns Stainless, and a stainless exhaust flange from Focussport, I was able to sort out how much room I needed to get the exhaust placed to where it had ample air room, good clearance to the firewall, and still had a natural curve.

This is a shot of the down pipe completed, but shows the general idea. What you want is to split the difference in room between the engine, brake master cylinder, firewall, steering shaft, etc. and not add any bends (if possible!)

As it turned out, the flange for the turbo would need to go right in the middle of #2 and #3 cylinders (right where you would want it to be!) The manifold was cut with the plasma cutter and the flange mocked up. I mounted the turbo at a little bit of an angle to compliment the exhaust down pipe and to aim the turbo compression housing a little more to the frame rail (just by a few degrees).

Here is what everything looked like when I was done:

Another side view:

We will cover the down pipe next!