Corvette Engine Build - The Power Principal, Part 2

On the first installment of our 383 engine build, we covered the rotating assembly. Now we'll put the finishing touches on the engine assembly so we can install it. we wrapped up Part 1 by handling the clearance issues with the cam and rods. Now the cam timing should be checked. We're concerned with maximum power potential, and cam timing is critical.

Most things in life are a balance-when you make a performance gain you lose somewhere else. Cam timing is no different. Retarding the cam typically makes more power at high-rpm and makes the idle choppy. Advancing the cam allows better low-rpm throttle response and hurts horsepower at the big end. This is where our Virtual Engine dyno software came in handy. We could advance or retard the camshaft to see power gains and losses. Be careful to look over the entire rpm band, watching for the changes in horsepower and torque when cam timing is adjusted.

To start, you need to be sure the cam timing is correct according to the camshaft manufacturer, then make changes if desired. There are many informative web sites that discuss cam timing. Take the time to read the theory and then put it into practice. Today's cam manufacturers have precise equipment that is rarely incorrect, but a slight indexing error will make cam timing off. It could be multiple things, including crankshaft index, cam gear, crank gear, or even timing chain variations, causing cam timing errors.

There are also other factors to consider. For instance, in our engine build, the Keisler-supplied, Tremec five-speed with 3:27:1 First gear, along with 10.4 compression, and the 3:73 rear axle ratio allows us to benefit from some cam retard to help top-end power. If we had an automatic transmission with a 1,400-rpm stall speed torque converter and 2:59 rear gear, advancing the cam would be in order to give some off-the-line zip. To ensure our cam would stay in perfect timing for many hours of engine operation, we used a Comp Cams High-Tech Roller Race timing set; Comp Cams pushrods and rocker arms actuate the valves with precision at high rpm.

Now the timing chain cover is on we could cover up the bottom end, but we had concerns about oil capacity. There aren't many alternatives when it comes to extra-capacity oil pans, especially in the '84-'86 Corvette cast-iron cylinder head engines. These early C4 engines have the two-piece crankshaft rear main seal, leaving these engines in an oil-pan quagmire that no one wanted to deal with. That is until Canton Racing Products stepped up and custom-built a Road Race oil pan with adequate ground clearance. The Canton oil pan has an 8-quart oil capacity and a built-in windage tray with the same 7-inch depth as the original GM pan. Canton now offers the oil pan in one- and two-piece rear seal versions with the dipstick on the right or left side. For those of you that have the later '91-'96 L-98 and LT engines, you can also use their pan since they provided a provision for the oil level sensor. The original clunky Delco starter can also be used.

Moving on to the valvetrain-smallblock cylinder head design has become huge over the last few years. We all know that combustion engines are air compressors. Efficient air flow equates to power gains. Edelbrock Performer RPM aluminum cylinder heads (PN 60999) completely assembled had been purchased previously for this project, so all we had to do was clean them for installation. The Edelbrock cylinder heads have 64cc combustion chambers with 2.02-intake and 1.60-exhaust valves, allowing .575 valve lift, so an aggressive lift camshaft can be used. GM D-port heads will coil bind at .495 valve lift in most cases when using stock components. Always check for valvespring coil bind and piston-to-valve interference, no matter what the numbers say.

The stock tuned-port induction system that produces great low-end torque but severely restricts high-rpm horsepower was previously replaced with an Accel SupeRam plenum and runner kit intake-manifold assembly. The large SupeRam plenum provides low-end torque, and the shortened, large-diameter runners allow high-rpm breathing. We dumped the '85 Corvette fuel-control system and went with the FAST bank-to-bank, fuel/igniton, computer-control system to get as much power and low-speed drivability as possible. Laptop tuning makes the system very user friendly, and the computer's operating speed is greatly enhanced over the OE '85 system.

A key component when adding any induction system is figuring out the proper fuel-injector flow rate so we don't lean out the engine at high-rpm and have a meltdown. Having too much fuel is not as catastrophic, but low-speed drivability and throttle response would suffer. High-rpm performance wouldn't suffer, but you have to get there, and unless you're driving there all the time, fuel efficiency would be terrible. RC Fuel Injection has a great web site (www.rceng.com) that has the formulas necessary to size the injectors correctly. When we loaded our desired 475 crankshaft horsepower, number of injectors (8), 50-psi fuel-rail pressure, 0.80 injector duty cycle, and our 0.47 brake-specific fuel consumption desired, our combination required 32 lb/hr or 320cc/min injector flow. This flow rate addresses wide-open throttle performance which will be limited to short intervals. With this info, we then decided on 30-lb/hr fuel injectors to keep the throttle response crisp. If we planned on running a long-distance, wide-open throttle race, we could increase our fuel pressure to 75 psi, giving us plenty of fuel at top end.

The next question that needs to be answered is what injectors do we buy? Aftermarket Bosch clone injectors are reasonably priced, so we got a set of 30 lb/hr and sent them to Cruzin Performance for a quick injector performance test to be sure of equal fuel delivery to each cylinder. The results weren't good: 12-percent flow differential and one injector cap was leaking fuel already, and the injectors were never run in an engine. We opted to try a fresh set of Bosch EV 1 fuel injectors, and the results were much better: 2-percent flow differential and no leaks. Using the original Bosch injectors cost more up front, but the engine and engine compartment will not suffer from smoke inhalation or shrapnel.

The only ingredient left is the ignition system. We used the Performance Distributors Mini VIP voltage step-up regulator that boosts system voltage to the precision-built Performance Distributors computer-controlled distributor. Their Mini VIP step-up voltage regulator will boost our coil voltage to 18 volts under high-rpm to light our Bosch Platinum Plus Four spark plugs with ease. We're glad we have the Performance Distributors Live Wires to keep all the voltage contained. One wrong touch with an inferior set of wires, and we'd be knocked to the ground

You'll notice from our photos that we have the engine installed less the intake and distributor. Since we had to run some additional wiring under the intake, this was the easiest way to assemble the complete engine.

All that's left now is the dyno run. Stay tuned!

On The Web
* Bosch
www.boschautoparts.com/Products/SparkPlugs
Spark plug info

* Cruzin Performance
www.cruzinperformance.com
Fuel-injector performance test facility, Fuel-injector cleaning facility

* RC Fuel Injection
www.rceng.com/technical.htm
Technical information injector-flow rate charts

* Virtual Engine
www.virtualengine2000.com
Dyno software