| L98 Mods vs Performance |
| Background Ref: Corvette Fever, Oct., 1994, "Horsepower Conspiracy", by Dave Emanuel Test Vehicle: 1990 Corvette, L98, 6-speed coupe, stock (??) gears Tires: Initially GY Gatorbacks, in Test #4 switched to GY Eagle GSC S, for traction Test Parameters: Launch @3,000RPM, Shift @5,000RPM. Test Condition: Test data was obtained from time slips obtained on a drag strip in PA. |
| Test Data Format Baseline: Test vehicle baseline results are shown in line item #1. Mods: Subsequent line items show results for each mod listed, chronologically. Table Layout: Ln # - is line item or test number. ET sec - Elapsed Time for 1/4 mi., in sec. Delta ET - change in ET from prior line item. TS MPH - Trap Speed for 1/4 mi., in MPH. Delta MPH - change in TS from prior line item. Mods Performed - mods done since prior line item. |
| Test Data Results Table Ln..ET......Delta.....T.S........Delta......Mods #...sec......ET........MPH......MPH......Performed 1...14.66...-----......97.10.....------......Bone stock, /w Goodyear Gatorbacks 2...14.50..-0.16......98.48....+1.38......HyperTech Power Pulleys 3...14.18..-0.32....101.27....+2.79......Air Foil, Bosch Plugs, TPIS wires, K&N cut lid, Stage II EPROM, 170deg Stat. 4...14.18......0......101.27........0........Goodyear Eagle GSC S tires (1) 5...13.47..-0.29....100.76.....-0.51......TPIS Super Profile cam @112deg ATDC CL (2) (3) 6...13.47......0......103.81....+3.05.....TPIS Super Profile cam installed @106deg ATDC CL 7...13.39..-0.08....103.66.....-0.15......ZZ-9 cam (4) (5) 8...13.12..-0.27....105.84....+2.18.....TPIS FlowMaster cat-back 9...12.93..-0.19....106.65....+0.81.....Big Mouth base, TPIS LT runners, ported plenum, 52mmTB 10..12.53..-0.40....109.43....+2.78.....TPIS Stage II heads, 7/16"studs, roller tip rockers, 2.00"/1.60" int/exh (6) (7) 11..12.32..-0.19....111.95....+1.52.....TPIS long tube headers |
| Notes (1) Back to back passes were made with Gatorbacks and with GSC Ss to verify that traction was not a factor in test results to date. Apparently drag radials were not available at the time in the 275/40-17 size. (2) Emissions with the S.P. cam were only 0% CO and 34ppm HC. (3) After Top Dead Center (ATDC) (4) Testing with base ignition timing at 0, 6, 8, 10, 11, 13 deg BTDC showed 11deg BTDC worked best. (5) Fuel pressure was varied from 38-55 psi and testing showed that 40psi worked best. (6) These heads are '88-'91 Corvette #113 Al castings that TPIS pocket ported/polished and installed new valve train components as indicated. (7) In Small-Block Chevy Performance" Dave Emanuel states that the stock #113 castings flow to support about 350 HP and that pocket ported they flow to over 400 HP. |
| Comments (1) Trap speed gains are proportional to peak HP gains, e.g. for a mild NA C4 Corvette a gain of 1 MPH is about 10 HP. (2) The performance gain from a mod may depend on preceeding mods and so may differ somewhat from those shown in the table.. |