tech

By Ryan Lee Price
Photography: Robert Hallstrom, Ryan Lee Price

This is the turbo system as applied to a Mexican-built 1600cc engine, as it is roughly 500 miles into the life of the engine.

When people in the VW industry consider modifying their car to achieve more power, they automatically turn to the carburetors and exhaust, the two easiest (and some times expensive) ways to upgrade the performance of any aircooled VW. Some of the hard-to-find 48 IDA that are popular to use on today's street performance engines can fetch upwards of $1000, and the continual trouble of adjusting them is a perpetual nuisance.

Next to rebuilding the bottom end with expensive cams, boring, cranks, stroking, pistons, porting, pushrods, cylinders and an endless variety of expensive parts designed to go fast, another alternative is turbocharging, a quick, efficient and effective way to at least double the power of the engine that is on your car right now. Yes, double. It is easy to install, cheaper than a high-performance engine, definitely easier to maintain and...hold onto your hats... requires very little modifications to your current engine.

Can I Turbocharge My Engine?
Virtually all engines are capable of accepting a turbocharger. Though an in-line engine is ideal and presents the fewest problems in design and application of a turbo, a horizontally-opposed flat-four engine such as the aircooled VW engine is just as easy if the proper engineering has been accomplished, such with the Turbo City kit. Though this isn't without its drawbacks. Because of the nature of the aircooled engine, turbochargers in general will increase the head temperature of the engine, but Turbo City's kit is considered a mild turbo setup, creating an adjustable range of boost from seven to eleven psi. An aspect to consider before installing a turbo kit, is the transmission. Because turbos increase the amount of torque applied through the trans to the wheels, a Kennedy Stage Two clutch was installed to our project Beetle, but the transmission remained stock. A point of interest is that a higher octane fuel is recommended. With an engine compression ratio around eight to one (non turboed), 87-octane gas will suffice, and although they suggest that for every pound of boost added, the octane requirement should increase by one, it isn't necessary with this kit, as 91-octane is high enough.

What's Included in the Turbo Kit?
Turbo City, in Orange, Calif., offers their Rapid Response Turbo kit for the Volkswagen Beetle, a system that utilizes a Garrett parallel-wall diffuser mated with a curved-inducer impeller in a centrifugal-type compressor. The draw-through-designed unit forces compressed air from a Weber 40mm DCOE carburetor into the engine (a 45mm carb can also be used). Troublesome turbo lag in this kit is eliminated thanks in part to the Volkswagen engine's naturally low compression rate, the direct mounting of the carburetor close to the compression housing and the specially designed header that redirects the exhaust fumes through the turbine wheel.

This is the power horse behind the horsepower. The Garrett T25 turbo housing is best known for its work in Nissan 300ZXs, but its small turbo wheel and parallel-wall diffuser aid in the quick boost at roughly 1800rmps.		The two-to-one-to-one Header System is designed similar to that of a typical four-in-one header we commonly see on today's Volkswagens. This piece connects to the engine heads and provides the conduit for the turbo source of power, exhaust.		The Turbo Inlet Pipe drives the hot exhaust gases up to the turbo housing and turbo wheel. This pipe can get amazingly hot, roughly 1500 degrees.
The Inlet Tee connects to the stock end castings and acts as a conduit from the compressor housing into the intake valves and cylinders.		If you opt to remove the heaters boxes, like we did (hey, this is sunny So Cal), then the kit also comes with exhaust J-tubes.		The Turbo Outlet Pipe connects to the exhaust outlet pipe and removes the exhaust from the turbo housing and carries excess boost from the wastegate
The Exhaust Outlet Pipe is an unbaffled exhaust tube that fits underneath the left stock exhaust notch on the apron of a Beetle. You can option for dual exhaust pipes as well as the baffling for noise reduction.		The carburetor hardware includes bolts to attach the carb to the compressor manifold housing as well as the throttle cable linkage.		This hardware helps attach the Inlet Tee to the compressor housing.
The oil line fittings and hardware create a closed circuit oil system that links to the engine's existing oil circuitry.		What helps supply the fresh oxygen to the engine is this Weber 40mm DCOE carburetor.
		When boost exceeds wastegate pressure, the wastegate opens up the exahust valave (bottom) in the turbine housing, allowing exhaust gases to pass by the turbo housing, slowing down the spin of the turbine.

Turbo Troubleshooting

Symptom: Lack of Boost
Cause: Gasket leak or hole in exhaust system
Check: Block off tailpipe with engine running. If engine continues to run, there are leaks
Remedy: Repair the leaks, usually faulty gaskets

Symptom: Lack of Boost
Cause: Worn valves or rings
Check: Check compression
Remedy: Repair the faulty valves

Symptom: Lack of Boost
Cause: Butterfly doesn't completely open
Check: Check pressure in carburetor
Remedy: Adjust linkage

Symptom: Lack of Boost
Cause: Restriction in muffler
Check: Check turbine exhaust pressure
Remedy: Locate clog or remove baffles

Symptom: Lack of Boost
Cause: Dirty air cleaner
Check: Remove the air cleaner
Remedy: Clean or replace the air cleaner

Symptom: Gas odor during boost
Cause: Leak at compressor intake manifold
Check: Look for fuel stains around joints
Remedy: Tighten joints and replace gaskets

Symptom: Poor throttle response
Cause: Clog in carb
Check: Try richening jets
Remedy: Clean carb and check jet sizes

Symptom: Plugs miss at high power
Cause: Plug gap too large
Check: Measure gap
Remedy: Clean and reset to 0.025in. (or smaller if misfiring persists)

Symptom: Oil leak in turbine housing
Cause: Blocked oil drain
Check: Remove drain line and check for plugged or crimped line
Remedy: Clean and/or replace drain line and nipples

Symptom: Poor idling
Cause: Air leak between carb and compressor
Check: Listen for hissing around carb at idle
Remedy: Repair leak, usually faulty gasket