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Turbo Inline Six Engine - What's Your Problem?

Turbo Inline SIX
Jacob Potts, Mercer, PA: Here's something you may not hear too often. I'm seriously considering turbocharging one of GM's Turbo-Thrift 250ci L-6 engines for an early '70s Nova. I love the small-block V-8, but I'm looking to try something different - a turbo inline six. Would you please give me some information about the engine, including the exhaust runner size and if it is able to endure forced induction with whatever machine work is required? Also, are there any bottom/top-end kit parts available in the aftermarket? Your help will be greatly appreciated.

Jeff Smith: We did a little digging and discovered a guy by the name of Tom Lowe who is a member of Inliners International and has been building and driving a turbo inline six 292ci Chevy for several years. I spoke with Lowe, a fellow Iowan, and discovered he has close to 30 years of experience building these turbo inline six Chevys. You can see some of his handiwork on his website, 12bolt.com, since he repairs, builds, and sells Chevy 12-bolt rearends. But he also has massaged an interesting inline Chevy head modification that we'll get to in a minute.

The most critical component for the turbo application is a cast-iron exhaust manifold to mount the turbo. Lowe uses a T-4 turbo combined with a cast-in-place exhaust manifold built by a Brazilian company called SPA Turbo. The manifold places the turbocharger in the center and includes a built-in wastegate mount. The manifold is not light at 30 pounds, but it is durable. Lowe imports this manifold and sells it for $450.

Lowe runs a T-4 62-1 Turbonetics turbocharger on his 292ci six and is currently pushing 11 psi and still running the engine on pump gas. He says his 3,700-pound car and driver combination has run as quick as 13.8 at 99.9 mph at Cedar Falls Raceway in Cedar Falls, Iowa, with a 700-R4 automatic shifting at 4,800 rpm. Lowe has also built his own intercooler for the car and controls fuel with a Holley Commander 950 EFI system and feeds air through a stock 5.3L LS engine throttle body. With 42-lb/hr fuel injectors, the little six gets decent gas mileage. Of course, you could use a carbureted intake manifold mounted with a blow-through carburetor and go that route, which should be less expensive. If you do, we'd suggest talking to the guys at Quick Fuel carburetors. We have had great success with their blow-through carburetors on several occasions. They will probably suggest a relatively small-cfm Quick Fuel carb with annular discharge boosters. We recommend you follow their suggestions if you decide to try a blow-through carbureted application.

Lowe also has some suggestions for cylinder heads that work well on inline Chevys. The production inline-six-cylinder head uses a common intake port for two cylinders, which isn't very efficient from a performance standpoint. Compounding the issue is a head bolt boss that runs directly through the center of the intake port. Lowe suggests removing this boss using a reciprocating saw and then dressing the finished cut to improve cylinder head flow. That will then require an Allen head bolt conversion that he also sells. This alone will improve intake flow, but Lowe has created a Hi-Flow lump port kit that takes this initial modification much further.

The lump is a simple cast-aluminum insert that fits in the floor of the intake port and drastically improves airflow in all common port inline Chevy six- cylinder heads. The installation process isn't difficult, but it does require some machine work that might be better left to a professional machine shop. Or Lowe can perform the installation for you for a reasonable price. He has also created a how-to video online on YouTube. Search premium lump port Chevy inline-six 230 on the web and you can see the installation of one of these lump port kits. According to Lowe, the kit-along with a slightly larger intake valve-can drastically improve intake port flow. At 0.400 inch of valve lift, Lowe measured 164 cfm for the stock head, and with a larger 1.84-inch intake valve and the lump kit installed, the flow jumped to 208 cfm, a 26 percent increase in flow. The lump kit is available from Lowe's Autowerks website. We'd also suggest adding a set of forged pistons to the engine just to dial in a little insurance against detonation damage with the turbocharger.

More Info
Autowerks
Dysart, IA
319/476-2172
12bolt.com

Quick Fuel Technology
Bowling Green, KY
270/793-0900
quickfueltechnology.com

CC Quickies
Just For Old Time's Sake
Here's a vintage, '05 On the Rack shot pulled from the archives. It features crowd favorite Holly Weber tightly clad in a fine Detroit Muscle shirt. Ah, the good ol' days.

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