The part numbers for the LT4 intake manifold seem to bring much debate in many other forums. For this reason we have done some extensive research to nail down the truth about the LT4. Thanks to many customers whom have paid for us to gather this information you can now read on better inform yourself about the LT4.

The GM LT4 Engine got its start in 1996 with the Chevrolet Corvette. The most popular LT4 "Grand Sport" Corvette was the one painted blue with a thick center comp. stripe. This engine was rated at some 340 horsepower from the factory and had a red intake manifold part #12550630 which is now No Longer Available thru GM. The badge on the intake throttle body read "Grand Sport" and the LT4 engine found in the Grand Sport Corvette had a .477 lift camshaft with bigger LT4 heads. You can see more details about the LT4 heads our other thread.

Later GM Performance rolled out with a kit that was basiclly a bunch of parts pulled from the shelf and made into what is now known as the LT4 Conversion kit. It retailed for some 2800-3200 USD and bosted even more horsepower than that of the Grand Sport LT4! The power output was rated for this conversion kit at 420 HP. The great thing about this all in one kit is that you could put it on any LT4 and get serious horsepower gains. The kit included the special "Red" LT4 intake part # 12550631, LT4 heads, GM Perfromance HOT Camshaft @ .525 lift, 1.6 Aluminum full roller rocker arms, and a complete gasket kit. Once the Grand Sport intake manifold became NLA this kit followed.

Part Numbers at a glance-

LT4 Grand Sport - 12550630
LT4 Conversion   - 12550631
LT1 Stock           - 10108630

I also know there is a diffrent part number for the early model 93. These models did not have mass air and had a diffrent style intake manifold. More information to come.