SWEAT THE DETAILS
There are three versions of LT1 timing covers--ours is the first one. There are also different versions of timing gears, distributors, distributor drives and crankshaft keyways for different years of LT1. You will need to visit your GM parts counterman to sort out this mess because it's too complicated to dive into here, but suffice it to say you will need several specialized seals, o-rings, and gaskets to properly complete your cam swap. We dug up a great web page on rebuilding LT1s and hope it's still there by the time you read this (see www.automotiverebuilder.com/ar/ar99928.htm).
Don't forget to reinstall the cam retainer plate before installing the new timing chain. You don't want to discover these leftover parts after you've bolted on the timing cover! Here, the oil pan is loose and connected by only two bolts at the back of the block. This allows the timing cover to be easily installed without pinching or damaging any gaskets. We also took this opportunity to swap in a new Mr. Gasket one-piece oil pan gasket.
It's also advisable to check the water pump drive and bearings for grooves. If there are grooves, there will be leakage and you can only blame yourself for not checking. Be forewarned, however, if you decide to change the water pump drive and drive gear, you can't just knock it into the block with a hammer!
GO WITH THE FLOW
The world of engineering is nothing more than a balancing act of compromises. Any design cannot be all encompassing. Nowhere is this better realized than when examining why the late-model enthusiast should consider the Edelbrock Performer LT1 cylinder over the popular GM LT4 casting.
All too often the finesse of cylinder head design is not realized by the consumer and instead they comparison shop flow numbers alone. Based upon the flow data for the Edelbrock Performer LT1 and stock LT1 and LT4 castings, the latter has the clear advantage. But there is much more going on in a cylinder head then can be documented on a flow bench with a fixed depression. That is where the Edelbrock casting shines.
When it comes to airflow, a cylinder head needs to provide an equilibrium between port velocity and volume. It is all too easy to develop big flow numbers on a test fixture only to have poor velocity and thus low volumetric efficiency and power when bolted to a stock-displacement engine. The qualifier the industry uses for intake port volume is cubic centimeters (cc). This is a liquid measurement of the volume of the port. By itself it can be deceiving since the entire port is what is being measured, including the bowl area. Given the confine of space available in a given application, the port volume can be used as a good qualifier of the expected velocity of the charge. Low volume usually equals high velocity. To this cause Edelbrock's Senior Design Engineer, Ulises Gonzalez, worked very hard to maintain the 170cc volume of the stock GM LT1 design while improving the airflow. In contrast, the GM LT4 casting undeniably flows more air but has a much greater port volume, pouring out at 195cc. At 0.500-inch valve lift, the Edelbrock Performer out-flows the stock LT1 design by nearly seven percent.
Intake flow is critical to power production but the exhaust port is just as important. Edelbrock recognized that more power can be produced if less is consumed evacuating the cylinder on the exhaust stroke or pumping loop. The Edelbrock Performer LT1 has the ability to flow fifteen percent more spent gasses at 0.500-inch lift than the stock design. A more efficient exhaust port creates less pumping losses in the engine and will produce more power for a given volumetric efficiency.
Other features of the Performer LT1 casting that make it a good choice are thicker walls by 0.300 inch for future porting, a thicker deck surface for stability, along with a 54cc combustion chamber and 1.94/1.550-inch valves on the intake and exhaust, respectively. In addition, the Performer bolts right up to the GM intake manifold and does not need extensive rework to align the air path as the raised-port LT4 requires.
If you are looking to upgrade your LT1 cylinder head, undeniably the GM LT4 is an excellent choice. The Edelbrock Performer LT1 offers better port velocity and increased throttle response and low-speed torque which are just the ticket for a stock displacement street/strip car.
With the Performer design fitting right in the middle of the GM castings, maybe the marketing mavens at Edelbrock should have called it the Performer LT2.5!--Ray T. Bohacz
|Cylinder Head Flow Data* |
|Stock LT1 |
|GM LT4 |
|*All flow data is at 28 inches of H2O with a radiused intake and no exhaust extension. |