Glassair / Lancair Installation

Airbox Design

The installation of the Ellison Throttle Body Injector ("TBI") on tightly cowled sport aircraft, such as the Glassair or Lancair, requires careful attention to induction system design. The air inlet, carburetor heat system, carburetor and intake manifold are all aerodynamic devices; for maximum performance these devices require the same careful design as other aerodynamic devices such as wings, flaps or ailerons. Careful planning and testing will result in an installation with maximum power, fuel economy and dependability.

The Lancair 235 cowl provides very little room for an efficient carburetor inlet airbox and will not accommodate an adequate air filter. The stock 1.5 inch high box induces a substantial pressure loses.  In the Jan/Feb 1990 issue of the Lancair newsletter, John Bittner reports of a 50 static RPM increase (about six horsepower) by simply enlarging the airbox and cowl a bit.  Clearly, for maximum performance, no matter what fuel metering device is installed, the stock airbox should be enlarged.

The sketch below shows an increase in airbox depth to about 4 inches. This will allow the original flapper type valve arrangement for carburetor heat and provide room for a proper size air filter such as a bracket filter.

Another possible inlet configuration would be to use a remote filter and airbox and a NACA scoop for inlet air. If air is ducted to the TBI with 2 hoses in a symmetrical arrangement, this should yield good fuel distribution even with a 2" deep air box at the TBI.

To gain much needed cowl clearance, Ellison Fluid Systems, Inc. has designed a plenum box which mounts to the standard Lycoming updraft sump and allows the TBI to be mounted horizontally with it's inlet facing forward. This plenum box gives excellent fuel distribution resulting in maximum fuel economy. The use of the plenum box provides about 3 inches more cowl clearance than a standard Throttle Body/airbox combination. Also, airbox design is now simplified because the induction air no longer has to make a 90 degree turn before entering the TBI.

Glassair and Lancair builders with 0-320 engines can use an oil sump from a IO-320-B1A which can be been modified to allow the TBI to be mounted to the front of the sump with it's inlet facing forward.

Basic design suggestions relating to inlet airbox configuration are available by clicking Inlet Airbox. Click carburetor heat for an explanation of its importance in a TBI installation.

TBI Orientation

TBI orientation that activates the throttle in a spanwise direction will generally yield better performance than one in which the slide moves fore and aft.

Ordering Information