How to Build a High Performance TBI Engine

by Don Bowman

A TBI engine is a standard engine with throttle body fuel injection. The throttle body consists of an air intake port and one or more fuel injectors, depending on engine displacement. The fuel injectors are located in the middle of the throttle body. This will give the best build up procedure for a significant horsepower gain, without sacrificing reliability and without a high cost.

Step 1

Install a high flow set of cylinder heads such as Edlebrock, Brodix or World Products. They will produce the most significant power gain when coupled with the following induction items. The thing to be concerned with is flow through the engine.

Step 2

Install a camshaft with a higher lift than standard and increase the duration to 292 degrees, regardless of the type or make of engine you are building. Racing catalogs will give you a description of different cams and at what RPM they are best at for power, torque and the type or quality of idle you can expect. The cams will be advertised with valve lift, which is how far the valves will open, the duration, how long the valves are open and the idle quality. Use the 292 for the length of time they are open; the rest is up to you as far as how radical you want the engine to be.

Step 3

Install a larger, higher volume fuel injector. It depends on cam selection, so tell the speed shop the cam you have chosen and it will supply the appropriate fuel injector for that application.

Step 4

Install the map sensor upgrade from the speed shop to provide the increased fuel flow needed for a high performance TBI engine. Throttle body injection relies on MAP sensors for fuel control. It measures atmospheric pressure as opposed to vacuum in the manifold. When the engine is at idle, the MAP sensor gives a low voltage signal to the computer and in turn the computer gives just sufficient fuel to idle at a mixture of 14:1. At idle, the engine produces an average of 18 inches of vacuum, but when you suddenly open the throttle the vacuum drops to near 0 and then climbs back, depending on acceleration and RPM. The computer recognizes this in the form of voltage rises and increases the time that the injectors are on, supplying more fuel for acceleration.

Step 5

Install a 185-degree thermostat and it will give an extra 3 to 5 horsepower--the computer thinks the engine is cooler and keeps a richer mixture. Install a good set of headers to get the exhaust out faster and a set of 2½ -inch exhaust pipes with low restriction mufflers.

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