Weird engine tuning issues at the drag strip
Hey guys, I am having trouble figuring out why my car didn't pick up very much at the dragstrip when I upgraded some parts on my engine.
Parts that remain the same: 305 sbc, forged rotating assembly with flat top pistons, trickflow super 23 175cc cylinder heads (10:1 compression ratio in my case), 1.625" full length headers, 2.5" dual exhaust, borla straight through mufflers, 4150lb weight with driver, pac racing valve springs (155lb seat and 390lb open pressures), Morel 4602 high rpm hydraulic roller lifters.
Old setup: original bone stock Quadrajet carburetor, stock ignition, Edelbrock performer intake non air gap, Lunati hydraulic roller camshaft (219°/227° @ 0.050" lift, 112LSA, 106 ICL, 0.530" lift), 2400 rpm stall torque converter, 3.73:1 rear gears, 1.52 ratio comp cams rocker arms. Best quarter mile with zero tuning, 2.2 60', 6.1 330', 9.1 @ 79mph 1/8 mile, 14.0 @ 99mph 1/4 mile.
New setup: Quick fuel 650 cfm double pumper, MSD pro billet distributor, ported Edelbrock Victor Jr intake with 1" tapered 4 hole spacer, Lunati hydraulic roller camshaft (240°/252° @ 0.050" lift, 108LSA, installed at 105ICL, 0.590"/0.550" lift), 3800 stall torque converter, 4.10:1 rear gears, 1.6/1.52 ratio rocker arms on intake/exhaust. Tuned to run 12.5:1 air fuel ratio at full throttle. Best quarter mile, 2.1 60', 5.8 330', 8.6 @ 81 mph 1/8 mile, 13.4 @ 102mph 1/4 mile. Engine does not pickup any speed with more than just 27° of timing. Balancer zero mark is confirmed as being true TDC.
You would think with all the changes it would be a lot faster. Instead, I feel like almost all the gains are from a higher stall torque converter and shorter rear gear. Any ideas as to why this is? Exhaust back pressure? Valve float? I have no idea anymore.