The day of reckoning is finally here! Any guesses as to what this 400 (406) will make on the dyno?
This motor is built for the pure stock drags and is based on the small valve 400 4-bbl available on both A & B bodies (non-GTO) that has 10.0 to 1 advertised compression, rated at 330 hp and 430 lbft torque. The stock factory cam is the 066 cam rated at 273/282 (200/210 @ .050” lift) and .413” lift.
The XV 400 motor build is finished, broken in on the test stand, and goes to the dyno tomorrow. To recap, the block is a late ’70 400 block (F240) that is .030 over (406 cu. in.) with Icon forged pistons (1/16” - 1/16” – 3/16” rings), RPM 4340 I-beam forged rods, stock N-crank, balanced with careful rebuild (not blueprinted). The pistons are off-the-self 400 + .030 pistons with the 1.720” pin (compression) height, 4.5 cc valve reliefs and .0015” in the hole. The head gaskets are Flepro 1016’s with .039” crush thickness for a quench of .041”.
The stock small valve # 16 heads (date castings D160 & E200) measured in at 78 cc’s after a slight clean-up cut (80 cc’s factory) with a calculated static compression ratio at 9.94 to 1. The stock pressed-in rocker studs were pinned (like in the good ol’ days) with stock 1.5 stamped rocker arms and factory pushrods. The valve springs are basic CC-990 with 120 lbs seat and 240 lbs @ .400” open pressure (5600 rpm max. shift points). The valves are 1-pc SS 1.96”/1.66” Ferrea’s with 45 degree faces/seats (no back-cutting of the valve heads). The heads weren’t flow benched, but other small valve heads flowed around 190-195 cfm intake/150-155 cfm exhaust stock.
The Q-jet carb we used on the dyno is a 7041264 (’71 400 auto application with 73/43 primaries and CC secondary rods to start out with) on an untouched ’70 cast iron intake manifold. The distributor is from a ’69 400 manual trans application with a Crane XRi electronic replacement ignition. The exhaust manifolds are the std. A-body log style with 2-1/8” openings flowing into Pypes mandrel bent 2.5” head pipes 4’ long.
The cam originally selected was going to be the Summit 2800, but we decided to go with the 2801 instead because of the higher compression to bleed off a bit more cylinder pressure since this is a street driven car 95% of the time. As discussed earlier, the Pure Stock Drags now base cam limitations on the engines ability to maintain 16 in. vacuum at 1200 rpm in neutral. The 2801 does that easily and (actually closer to 20 in.) and is very mild with minimal lope. It is essentially a high lift version of the factory 068 cam (214/224/112 @ .444”/.466” lift). Interestingly, the Desk-Top Dyno predicted 341 hp/445 lbft for the 2800 and 359 hp/429 lbft for the 2801, so very little difference and a trade-off of torque for horsepower. The 2801 was installed straight up as the DTD predicted the highest hp/tq and averages at -2 degrees with the 2801 valve timing specs anticipating timing chain stretch.
The ’70 small valve YH code 455 (462) I dyno’d a few years ago with the same compression and exhaust logs made 391 hp/512 lbft torque with the 2802 cam.
What you’re your predictions?
Dennis
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