PONTIAC 2.5L 4 CYLINDER
This engine has seen widespread use in a variety of GM products - notable from a performance standpoint are the Fiero and the Chevy S-10 "mini-trucks". The most frequent complaint from owners of these vehicles is that they could use more power. The 2.5L engine is also used in a number of rules limited oval track racing classes. The products listed in this catalog for this engine are targeted at delivering additional, reliable power for daily usage. When coupled with high flow cylinder heads and other performance enhancing products, these same parts can form the basis for a fairly stout street or track package.
The Pontiac V8 was the powerplant for a whole generation of "muscle cars", including the GTO and the Firebird Trans Am. As such, there had been considerable development of performance products for these engines throughout the sixties and seventies. Such efforts tapered off after production of this engine family ceased in 1979, but the increasing popularity of muscle cars has renewed interest in the rebuilding and modification of these engines. The performance aftermarket has responded by re-releasing many older products, along with several new items. Finding the parts necessary to put together a good running Pontiac should not be a problem.
Pontiac cylinder heads will physically interchange among the various engines, but careful attention must be paid to the piston to combustion chamber clearances. Pontiac used a wide variety of combustion chamber volumes to achieve the desired compression ratios and characteristics, some pistons may not be compatible with the heads you may select. The good news in this situation is that it is easy to lower or raise the compression ratio by swapping cylinder heads, as long as important clearances are maintained. One other critical issue in Pontiac cylinder head repair is related to valve length. When Pontiac changed the chamber volumes, they would shorten or lengthen the valves as required to maintain valvetrain geometry. This means that otherwise identical engines with different compression ratios will require different length valves! Since many of these engines have been previously rebuilt or replaced, the only way to be sure of getting the right length valves is to compare and measure your old valves prior to ordering replacements. The valvetrain in most Pontiac engines is a positive stop, non-adjustable type, which requires that the rockers be tightened to a specified torque against a step on the rocker stud. The heads can be converted to allow adjustment by changing
studs and using rocker adjustment locks.
There are a couple of important notes regarding the pistons we offer for the 455 Pontiac. The L24238F piston is designed to work with the Super-Duty forged connecting rod. If it is to be used with other rods, the area between the pin bosses must be opened up to 1.360â€. Our L2394F piston was originally designed for the Super-Duty or H.O. heads, but will now be compatible with several other heads. We have removed a couple of bumps previously forged into the head of the piston. These were originally intended to raise the compression ratio, but their elimination enhances flame travel and improves strength, resulting in a better overall product.
As in any engine, the Pontiac requires careful attention to clearances throughout the assembly. A minimum of .050 should be maintained between the piston dome and the cylinder head. Piston to valve clearance should be at least .100". These clearances will change if you mill the block or heads, use 1.6 ratio rockers, changes cams, or alter cam timing - check them carefully before running any new parts!