The Maximum Overdrive concept started at the winter '04 NCRS meet at OldTown in Kissimmee, Florida. Jerry Pitt, during a previous conversationconcerning improvements for the early Corvettes, mentioned the Keislerfive-speed overdrive-equipped Corvette. He had driven the car and feltthe OD transmission was a major improvement over the OE Munciefour-speed.
We heard Keisler was modifying the Tremec transmission for installationinto early Corvettes, and it sounded like a smart move. Tremec suppliesthe transmission for the C5. Shifting is easy and has proven reliablewith high-torque applications. We wanted to drive the car to feel thetransmission and hear the change in noise level from the reduced rpm.
The original numbers-matching...
The original numbers-matching engine was in fair shape with many correctparts. There was a mix of correct replacement parts along with someinteresting quick fixes. The plastic fuel filter and rubber hose couldbe dangerous. Even a small fire can burn through the plastic fuelfilter. The engine ran OK but was a bit fuel rich at low engine speeds.
We met Shafi Keisler at the Old Town show and, after a short discussion,were handed the keys to the '65. The road test proved the Tremec was theright choice. It shifted smoothly with positive feel. Highway cruise rpmwas 2,200 at 70 mph and the sound level from the small-blockside-pipe-equipped Corvette was certainly livable.
After the road test, we discussed a possible engine change to complementthe OD transmission. Shafi wanted to bring his '65 Corvette coupe intothe 21st century. We discussed possibilities and other enhancements thatwould be necessary. We wanted good fuel mileage and power with hightorque to eliminate excessive shifting and lugging.
The Ram Jet looked at home...
The Ram Jet looked at home in the '65 engine bay. A paint stick was usedto check hood clearance with the original small-block hood. There washalf an inch between the intake and hood at its closest point. GM placedthe engine closer to the passenger side of the frame, so throttle-bodyclearance was an issue. The hood would not close because of the throttlebody.
We compiled a list of pieces that would work well together along withpossible options. We met Shafi at the Knoxville Corvette Expo; he likedour plan and thought it would be a good idea to have the new enginefeeding on cold, cowl-inducted air.
We decided on a serpentine-belt accessory drive system with Vintage A/Cfor cockpit cooling. The engine would be the 383ZZ425 unit (383 ci, 425hp) from GM Performance Parts. We also had a lengthy punch list ofunderhood and interior items that required attention. After a call to asome friends at GM and a few conference calls with Shafi, we decided touse the GM 350 Ram Jet electronic-fuel-injection Performance Parts crateengine. Even though the horsepower numbers were lower than the ZZ425engine, the torque number was 400 lb-ft at 3,500 rpm, which would beenjoyable shifting through the gears.
The 350 Ram Jet achieves high torque numbers with the help of the largeintake plenum feeding Vortec cylinder heads and a new MEFI IV enginecontroller (computer) handling fuel and spark delivery.
Removing the throttle body...
Removing the throttle body allowed closure of the small-block hood. Withmodification of the X-frame at the location of the throttle body andthrottle lever, the small-block hood could be used. Keep in mind, eachfitment situation is different depending on body-mount condition andbody shims used during assembly.
The MEFI IV engine controller uses a heated oxygen sensor for quickclosed-loop fuel control. All the engine sensors are reliable GM pieceswith weatherproof sealing. The MEFI IV also uses a knock sensor forengine- detonation protection. The controller is small, compact, and athome in the engine compartment.
The GM 350 Ram Jet was the best choice for other reasons. It's acomplete package, including wiring harness and computer, requiring onlyfour wires to connect to the existing mid-year harness. We could use theoriginal ignition shielding and all hardware. Plus, the 350ci Ram Jetwould be easier to cool considering the limited radiator area and addedheat load from the A/C system. Best of all, the engine would look likethe sought-after early Ram Jet mechanical fuelie engine.
The Ram Jet 350 would fit in the early Corvette, but the stocksmall-block hood would require minor surgery to the inner X-frame toclear the throttle body without any external modifications. The stockhood would also allow use of the air filter that came with thePerformance Parts engine.