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The Demon Engines Low-Buck 454 Engine Build Part III

For The Last Installment, We Add A Little Boost To...

By Richard Holdener, Photography by Richard Holdener

Our new turbo came from the gang at Comp Turbo in San Dimas, California. It is important to get the turbo (or turbos) sized for the intended application. Contrary to popular opinion, boost and power potential from a given turbocharger are not unlimited. The turbo must therefore be sized to supply a given amount of power at a given amount of pressure. Fear not, as most reputable manufacturers offer compressor maps for their turbos and can guide you in your selection. Comp Turbo supplied a 74mm unit for our motor, which was capable of supporting more than 900 hp on our application. The 74mm compressor was combined with a T4 exhaust housing featuring a 1.15 A/R. This combination offered not only plenty of power but impressive boost response. Controlling all that wonderful boost pressure was a 45mm Hyper Gate from Turbosmart. Wastegates are another area not to skimp on, though, as mentioned previously, it is possible to find turbos in the wrecking yard with internal wastegates. All that was required for operation was a vacuum/boost reference line running from the bottom of the carburetor to the wastegate fitting. The internal spring was set to supply roughly 7 psi of boost.

Turbos rely on exhaust flow to accelerate the turbine wheel, which in turn spins the compressor wheel. The compressor wheel then provides flow and boost pressure to the motor. For all this to happen, we first needed to direct exhaust flow to the turbine housing. A quick trip to the local muffler shop netted the requisite bends, while we relied on a set of shorty headers from Hedman to serve in place of the stock exhaust manifolds. For the last word in low buck, it is possible to run the stock cast-iron exhaust manifolds, though plumbing can be more difficult, as most exit in the rear of the motor. Our shorty headers were for a street rod application and were dumped in the center. All we had to do was weld together a Y-pipe. Westech's Ernie Mena made short work of the project and finished up the Y-section with the T4 exhaust flange. We also purchased a wastegate flange and stainless steel gasket from a local muffler shop (also available from a variety of sources online). The nice thing about this do-it-yourself approach is that the turbo can be positioned anywhere in the engine compartment, and then the tubing can be welded together to feed the turbo in that location. A muffler shop can even be used to make the Y-pipe. Pay no attention to the need for mandrel bends or coated headers-just get the exhaust to the turbo. Make sure to leave room for the downpipe from the turbo to the exhaust system.

With the major portions of the homemade turbo kit completed, it was time to address the minor ones. A small section of 2.5-inch tubing was used to connect the turbo to the carb bonnet using a pair of silicone hose connectors sourced from eBay. It was necessary to drill and tap a hole in the pan for the oil drain fitting. A second brass barb fitting was used from the bottom of the turbo along with a short section of rubber heater hose to complete our oil drain back. The pressure line consisted of a 90-degree (-3) fitting in the top of the turbo, a section of hose (an old nitrous line works well here), and a second fitting in the block to provide oil pressure to the turbo. We employed a compressor bypass valve (or blow-off) valve between the turbo and carburetor and used a short section of 3.5-inch tubing for our exhaust. Naturally, it will be necessary to construct a downpipe from the turbo to your existing exhaust. Since the turbo motor will want and require less ignition advance, we simply moved the distributor to retard the ignition timing down to 22 degrees. A vacuum advance/boost retard pod on the distributor can be employed, or you can install an MSD BTR unit that allows you to retard the timing under boost.

By Richard Holdener
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