So my understanding is this (and someone please correct me if wrong):

- Some cars run a turbo and have an airbox installed. The compressor side of the turbo is hooked up to the airbox. Even when not boosting, the air from the airbox travels through the compressor, charge pipes, intercooler, and intake mainfold through regular engine vacuum. When boosting, the turbo draws in even more air for more power.

- Some cars (such as drag cars) have an air filter directly on the compressor side and don't have an airbox. The same thing applies here when not boosting (air pulls in through regular engine vacuum).

For the second option, where would the MAF be? If there is no MAF here, how is air/fuel ratio controlled? In the first option MAF and ECU talk to each other to control this.

 

the FC is a fresh air duct, airbox, Air Flow Meter (AFM), hose (usually a TID, Turbo Inlet Duct), the turbo, intercooler, throttle, engine
the FD is the same, but it used a MAP sensor, so there is no AFM, or MAF

for a race car, you want to get rid of as many restrictions as the rules will let you... also if you run a bigger turbo none of the stock stuff will fit anymore

 

Both use an airbox. My question was what controls air/fuel mix in cars running turbos without an airbox, with a filter on the compressor instead? Where would it be installed?

 

Cars without a Mass Air Flow sensor run a different engine control strategy.

They use Manifold Absolute Pressure and Inlet Air Temp sensors along with an ECU pre-mapped with the engines volumetric efficiency at all load points with air temperature ( density) correction.

The FC uses MAF natively and the FD uses MAP natively. All a aftermarket stand alones for FC and FC use MAP as there is less restriction.

Regarding airboxes- depending on engine bay arrangements there may be an airstream available in the engine bay for turbo intake that has not passed through the radiator first.

In these cases the power loss from the restriction caused by an isolated "cold air" intake is greater than the loss of power from pulling in slightly warmer air.

Any restriction before the turbo adds to the turbos pressure ratio to achieve the same boost (vacuum to boost spread instead of ambient to boost spread), therefore the turbo is required to do more work putting more heat into the intake air.

 

Thanks for the replies.