This is Loren's Chevelle. With a Rat and a decent gear, it has most of what it takes to ma
Loren Coate, via CarCraft.com: I'm a retired school principal with a stock 502 H.O. crate motor in my '70 Chevelle. It has Hooker 2-inch headers, an 850-cfm Quick Fuel double-pumper carburetor, 3:73:1 gears, and a 2,800-rpm converter. The car weighs 3,800 pounds with consistent 1.80 60-foot times and has run 12.50 at 109. The tire size is 275/60R15 MT ET street radials that are 28 inches in diameter. This is a stock 502 H.O. with rectangular-port iron heads and a nonadjustable valvetrain. I've noticed that acceleration tapers off noticeably after 5,000 rpm. Could you help me get to 11.99?
Jeff Smith: Don't you just love letters that get right to the point? I have lots of suggestions, but let's start with more background. The 502 H.O. (High-Output) GM Performance Parts crate engine is a 450hp big-block with 550 lb-ft. The engine uses an excellent steel 4.00-inch stroke crank, forged 8.75:1-compression pistons, iron rectangle-port heads (2.19/1.88-inch valves), and a conservative hydraulic roller cam with 211/230 degrees at 0.050-inch tappet lift, 0.510/0.540-inch valve lift, and a conservative dual-plane intake. The easy answer is to just dial in an Edelbrock Performer RPM Air-Gap intake and a cam with about 20 more degrees of duration and lift of around 0.550 inch. This will also demand better valve-springs and an adjustable valvetrain with good roller rockers. This will raise the H.O.'s horsepower peak from 5,250 rpm to around 6,000 rpm, and the horsepower will probably jump to more like 480. This is a good idea, but we have more.
Based on stated power and weight, our copy of Patrick Hale's Quarter Jr. dragstrip simulation provided some interesting information. The simulation estimates the Chevelle should run around 12.40 at 108 mph, which is very close to your current performance (I had to estimate weather and track altitude). However, the simulated 60-foot time was 1.63, and yours is 1.80. It also appears that the tall Mickey Thompson DOT drag radials tend to reduce the gear ratio a little. According to our simulation (and your mph), the engine is barely turning 5,000 rpm in the lights. At first, it might appear that adding a gear ratio such as 4.10:1 would help, but we tried that and saw barely a 0.10-second and 1-mph improvement, making it difficult to justify the cost. This minor improvement in e.t. and speed is because the engine is already making excellent torque but no horsepower to push the trap speed. That's why adding gear doesn't help the acceleration on the starting line. To take full advantage of the gear change, we have to make the above engine changes as well.
A better way to improve e.t. without spending money on the engine is to reduce weight. At 3,800 pounds, the car is heavy. If you are creative, there are many ways to reduce weight at very little cost. Pull out any unnecessary pieces. If the car has A/C, yank it all. Try a pair of inexpensive plastic bucket seats to replace those factory seats, and while you've got the seat out, rip out all that sound deadener under the carpet-that's probably 20 pounds. Does the engine use a clutch fan or-worse yet-a plastic flex fan? Those clutch fans are monster heavy, and the plastic ones are notorious power bandits. Replace the fan with a big OE electric-look for one of those huge 12-inch electric units used on a Lincoln MKVIII. They move a ton of air, and you could get a junkyard piece for next to nothing-saving weight and maybe freeing up some horsepower. Every 100 pounds you can pull off the car will trim 0.10 second and add 1 mph to the trap speed.
One way to get a double hit off any weight reduction is to run as light a rear wheel as possible. Your other photo shows you are using the 15x8-inch steel GM Rally wheel in the rear. Those are really heavy-on the order of 40 pounds for the pair. Find a light aluminum race wheel. If you're willing to buy some parts, a fiberglass front bumper isn't expensive and will pull a solid 20 pounds off the car. That's a good dollar-per-pound investment. A fiberglass hood like the one we used on our Chevelle last month from Glasstek will also remove 25 to 30 pounds.
Overall, unless you can remove about 300 pounds from the car, it will be tough to lower the e.t. to 11.99 without resorting to engine improvements. It appears it will take around 500 hp to push this Chevelle at 3,800 pounds into the high 11s. If you're really serious, pull 200 pounds, add the cam and intake, and you'll probably be close. Of course, the quickest, easiest way to get there is with a nitrous system-but you already knew that.
Glasstek; Naperville, IL; 630/978-9897; glasstek.com
Racing Systems Analysis (Quarter); Oshtemo, MI; quarterjr.com