23 Degree Heads VS. L98 Heads
Trick Flow's 23 Degree Chevy Head vs. the Corvette L98
23 Degree Chevy Head
The 23 Degree Street head uses a conventional 23 degree valve angle, making it a direct, emissions-legal swap for 1995 and earlier non-LT1 Chevy heads, has factory valvetrain geometry, and uses standard small block components.
The 23 Degree head features 64cc combustion chambers, 2.02"/1.60" stainless steel valves, bronze valve guides, and 3/8" screw-in rocker arm studs. The intake ports are 195cc and have a high velocity, small cross-section design that provides excellent low-end torque and high rpm power. You also get a choice of valve springs. The standard spring is a 1.25" single, as used on the heads we tested. They're good for cams up to .520" lift. The next step up is a 1.47" single spring, designed for cams up to .540" lift. And for the more radical cams up to .600" lift, the 23 Degree heads are available with 1.46" dual valve springs.
The Trick Flow 23 Degree Street head uses a conventional 23 degree valve angle, making it a direct replacement for 1995 and earlier, non-LT1 Chevy heads. The head features high velocity 195cc intake runners, 3/8" screw-in rocker arm studs, and bronze valve guides. Trick Flow also offers three valve spring choices: 1.25" single for cams up to .520" lift, 1.47" single for cams up to .540" lift, and 1.46" double for cams up to .600" lift.
This is where the 23 Degree heads really outshine the GM Performance L98s. The 2.02"/1.60" valves are a step above the L98's 1.94/1.50" valves, which means the Trick Flow heads can flow more power-building air. The 23 Degree's 64cc combustion chambers are larger than the L98's 58cc chambers, and thus yield less compression. Our 383 test engine had 10.1:1 compression with the Trick Flow heads, and 10.8:1 with the L98s. The extra squeeze gives the L98s a small torque advantage at lower rpms.
L98 Heads
The L98 aluminum head first appeared on the 1986 TPI Corvette, and was used up until the LT1 motors were introduced in 1993. Trick Flow used brand new GM Performance heads for the dyno test. The GM heads feature the same basic design elements of the production L98-58cc combustion chambers, 1.94"/1.50" valves, high-velocity 163cc intake runners for good throttle response, and D-shaped exhaust ports for better flow -- and come assembled with heavy duty 1.27" chrome silicon valve springs, 3/8" screw-in rocker arm studs, and guideplates. The heads also have angled spark plug locations, and no provision for EGR or an intake manifold heat riser.
Instead of using a set of tired old L98 heads out of a boneyard, Trick Flow went with brand new heads from GM Performance. The GM heads have 58cc combustion chambers, high velocity 163cc intake runners, and D-shaped exhaust ports like the production L98, but are updated with 1.27" chrome silicon valve springs and 3/8" screw-in rocker arm studs. The exhaust ports are also raised .100" from the stock location, which may require opening up the exhaust manifolds or headers to achieve optimum flow.
The 58cc chambers in the GM Performance heads have 1.94" intake and 1.50" exhaust valves. While those are fine for building low and mid-rpm power (especially torque), they cannot flow enough to sustain power production above 4,000-4,500 rpm.
