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...
Mark specifies Fel-Pro gaskets on most of his builds. He suggests a thin film of gray RTV around the water passages at the intake manifold for added security.
To install the 58mm BBK throttle...
To install the 58mm BBK throttle body, we need parts from the smaller factory throttle body...
...Mark removes the hot-water...
...Mark removes the hot-water manifold from the original throttle body and transfers it to the BBK...
...We need clean surfaces...
...We need clean surfaces on both the hot-water manifold..
...and throttle body for a...
...and throttle body for a leakproof seal.
We like the bright red LT4...
We like the bright red LT4 manifold, courtesy of Summit Racing Equipment. When Mark carefully measured this manifold, he learned it's exactly the same as the LT1 casting except for the red powdercoating...
...Mark applies a bead of...
...Mark applies a bead of RTV at the block end rails. You don't need much here. As the RTV cures, it grows. Do not overtorque the intake manifold; it needs room to move with engine heat.
BBK's 58mm throttle body glides...
BBK's 58mm throttle body glides into place with ease--a perfect fit. Summit Racing specified the 58mm piece to jibe with 383ci and a hot hydraulic-roller cam. Take care to remember the hidden vacuum port located beneath the throttle body. We missed and couldn't get the engine to idle on the dyno--caused by a huge vacuum leak.
Our factory fuel rail has...
Our factory fuel rail has been fitted with Ford Racing 30-lb/hr fuel injectors to maximize the performance gained from 383ci LT4 heads and a more aggressive camshaft...
...Mark lubricates the O-ring...
...Mark lubricates the O-ring seals with white grease and sets the fuel manifold in place. He gently sinks the injectors into place and tightens the rail bolts.