What happened to rear mounted turbos?

[Wadeski]

Ten to fifteen years ago, it seemed mounting turbos way down the exhaust system (under the chassis, in the exhaust ducting) was becoming a thing - especially on classic cars with larger displacement engines that already had a fair amount of torque, and slushmatic gearboxes to deal with said torque.

You saw it on classic American cars, but also big barges - I'm sure someone was running them on a Silver Shadow.

Jay Leno even had a video talking up how good it was on one of his classic cars. Then they completely disappeared, I haven't heard of anyone building a car this way in ages.

What happened to these?

[dxg]

Lag. People became intolerant of it.

[Magnum 475]

People wanted less lag to the point that the latest gen EA888 engine has the exhaust manifold integrated into the cylinder head, and the turbo appears to be mounted directly to the side of the engine.

Worse, BMW, Mercedes, and others created the 'Hot V' to eliminate lag, despite all of the heat management issues that go with it......

[Escy]

I don't think it's lag, we'd be talking about a couple hundred rpm. Mounting the turbos low requires an oil pump and they are really loud. I had one with a brass gear and at idle it was louder than my exhaust.

[stevieturbo]

Wadeski said:

Ten to fifteen years ago, it seemed mounting turbos way down the exhaust system (under the chassis, in the exhaust ducting) was becoming a thing - especially on classic cars with larger displacement engines that already had a fair amount of torque, and slushmatic gearboxes to deal with said torque.

You saw it on classic American cars, but also big barges - I'm sure someone was running them on a Silver Shadow.

Jay Leno even had a video talking up how good it was on one of his classic cars. Then they completely disappeared, I haven't heard of anyone building a car this way in ages.

What happened to these?

They are still very popular in the US. They have not disappeared at all.

Less so other places

[SystemOfAFrown]

Escy said:

I don't think it's lag, we'd be talking about a couple hundred rpm. Mounting the turbos low requires an oil pump and they are really loud. I had one with a brass gear and at idle it was louder than my exhaust.

Lag is a delay in spooling rather than a specific RPM issue, you might be thinking of boost threshold? Mounting a turbo at the wrong end of the exhaust means you lose of bunch of the thermal energy in the exhaust by the time it reaches the turbo, so it spools up more slowly even when you are well above the RPM that will provide steady state boost. Rear mount also exposes the turbo to damage from debris and thermal shock from water splash.