For the past two issues of CCT, we've shown you how to build a powerful fuel-injected Chevrolet LT4 small-block for your classic truck project. Because the LT1 and LT4 are essentially small-block Chevys, they fit just about anything that can accommodate the Bow Tie V-8. Most LT1 and LT4 builds we've seen have successfully made 350-400 hp and an equivalent amount of torque. Trans Am Racing has taken our LT1 platform a step further with a 383ci stroker kit, an aggressive street roller hydraulic cam-shaft, and LT4 heads with commonsense port work. The result has been numbers better than we ever expected. Let's head out to Westech.
Buttoning It Up
We're going to wrap up our LT4 build with the induction system and a trip out to Westech to light it up. To refresh your memory, our induction system is a Corvette LT4 with a 58mm BBK throttle body. Coupled with the LT4 cylinder heads and a lot of clever port work at Trans Am Racing, we have a lot of potential for great power gains from good old-fashioned hot-rodding tricks.
To Tell The Truth...
Westech did a nice job dyno-testing our LT4. Instead of a factory GM PCM system, we opted for a F.A.S.T. system on the dyno from the terrific folks at COMP Cams. We struggled with some teething pains getting the LT4 up to speed, which is why we went with a factory GM PCM for this dyno pull.
During the first pull, we snapped two rocker arm studs, making it necessary to replace them all. Turns out the stock LT4 studs weren't long enough for proper valvetrain geometry, which is why we broke two of them. Mark installed 16 new ARP studs and torqued them to 45 ft-lb using Teflon sealer on the threads for proper sealing. He reinstalled and adjusted the rocker arms to the 1/2 to 3/4-turn standard.
We looked to PCMForLess.com for a specially programmed PCM for our LT4. Provide your vehicle's specifics (e.g., vehicle type, weight, transmission, axle ratio, tire size, with or without A/C, camshaft, induction system, injector size, displacement) and they will set you up with a ready-to-install PCM.
Mark specifies Fel-Pro gaskets on most of his builds. He suggests a thin film of gray RTV
To install the 58mm BBK throttle body, we need parts from the smaller factory throttle bod
...Mark removes the hot-water manifold from the original throttle body and transfers it to
...We need clean surfaces on both the hot-water manifold..
...and throttle body for a leakproof seal.
We like the bright red LT4 manifold, courtesy of Summit Racing Equipment. When Mark carefu
...Mark applies a bead of RTV at the block end rails. You don't need much here. As the RTV
BBK's 58mm throttle body glides into place with ease--a perfect fit. Summit Racing specifi
Our factory fuel rail has been fitted with Ford Racing 30-lb/hr fuel injectors to maximize
...Mark lubricates the O-ring seals with white grease and sets the fuel manifold in place.
What Sense In Replacing Sensors?
Whenever you're building a fresh computer-controlled engine, we strongly suggest the use of new sensors and controls in the interest of safe, reliable engine operation. This is the throttle position sensor, which gives the PCM (Programmable Control Module) feedback on throttle position. Elsewhere are sensors that detect coolant temperature, exhaust-gas oxygen content, inlet air temperature, and intake manifold vacuum. All these sensors need to be fresh because they each give the PCM specific feedback on a particular engine dynamic. Without that feedback, performance suffers badly.
We learned on the dyno that we needed a new Idle Air Control (IAC), which controls idle speed by creating a controlled vacuum leak at the throttle body. When we need a faster idle, the IAC creates a larger vacuum leak, which raises rpm. This happens when we turn on air conditioning or put the 4L60E automatic transmission in gear.
We like the flexible one-piece valve cover gaskets available today in Fel-Pro kits. They m
...Our LT4 has suffered some valve adjustment irregularities since it was dyno tested. We