DIY: Rear Mount Turbochargerby Richard Rowe
Do you have a car, an engine and a spare turbocharger lying around? If so, then you may have almost everything you need to fabricate a rear-mount turbo setup, give or take $500-$600. Though single rear-mount turbo systems often have problems delivering boost pressure at low RPM (a condition known as "turbo lag"), high RPM power is as good as with any engine-mounted turbo application.
Engine and Turbo
Because of their somewhat laggy nature, a rear-mounted turbo system would ideally be applied to an engine no smaller than 4.0L. Torque-deficient four-cylinder engines will prove difficult and frustrating to drive if turbo-lag is too great, and may require additional modifications to the gearing and drive-train to compensate.
Some of the best deals on used turbos come from agricultural machinery, diesel generators and over-the-road tractor trailers. Though these turbos are all but guaranteed to kill power below 3,000 RPM, they work very well with large V-8s. You could purchase a rebuilt turbo for between $250-$400 from online turbo retailers, but it will be difficult to find one to suit large-displacement applications for less than $500.
In addition to the turbo, you're going to need a high-flowing single exhaust system. Use mandrel bent pipes, and don't go any larger than 3". Too-large pipes will reduce flow velocity and increase turbo-lag.
The single most expensive investment in this installation are the oil pumps. you'll need two matching pumps; one to pull oil from the turbo, and another to send it back from the reservoir. Westech makes such pumps, which will run you $220 a piece, but cheaper pumps are available from Summit. Purchase 30 feet of 2.5"-3": aluminum tube, and 6-10 rubber couplings and hose clamps to fit it. Expect another $100 in expenses.
After installing your new single exhaust kit, fabricate a section of mandrel-bent tubing with a mounting flange for your turbo on one end. This tubing should be installed so that the turbo rests in a vertical position where the muffler used to be. Fabricate a bracket to support the turbo from your car's frame.
Mount your first scavenge pump as close to the turbo as possible, and slightly below it if you can. Connect the turbo drain line to the inlet side of this pump, and the outlet line to your one-gallon trunk-mounted oil reservoir tank. Mount your second pump next to the reservoir, and run a line from its output to the turbo oil inlet.
Run your aluminum tube from the engine's throttle body or mass-air sensor to the turbo compressor outlet with as many sections of rubber tubing as required. Keep the tubing as far away from exhaust piping and suspension components as you can. Install an oil-impregnated air filter onto your turbo's compressor inlet. Install a spring-loaded blow-off valve set to your desired pressure if you're using a diesel turbo.
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