Engine Rebuild

Common questions:

• Will a Chevy engine bolt in? No — the Pontiac 400 uses the BOP (Buick-Olds-Pontiac) bellhousing bolt pattern; Chevy is different. The Pontiac 400 is also Pontiac-specific — only Pontiac parts fit.
• Rebuild parts? Use Pontiac parts, not a Chevy kit. Sources include PAW and Summit, plus the hot-rod suppliers.
• Reaming vs. new pistons? Just removing the ridge at the top of the cylinder needs no new pistons; honing or overboring does.
• Oversize valves / cam parts? Depends on the cam — follow each cam maker’s recommendations; stock valvetrain is usually fine for a streetable grind.
• Is it still “stock”? Factory-original means stock; for drag classes the sanctioning body’s rules define what counts (NHRA Stock allows some aftermarket cams; lightweight pistons usually aren’t). On the street, it’s whatever you say it is.

Planning a mild, near-stock rebuild (example: a 326 H.O. with stock intake, exhaust manifolds, and points) — focus on breathing within those limits:

• Cam: a grind making power from idle to ~4000 RPM (a high-rpm cam will hurt with those restrictions); match it to the head work.
• Heads: mild pocket-port the intake bowls; plane to ~9.5–10:1 (run premium, don’t over-advance); add hardened exhaust seats for unleaded.
• Pistons: .030 over, flat tops; calculate cylinder + chamber volume to hit target compression.
• Block: decking is another way to raise compression — decide decking vs. planing with a builder.
• Balancing: small benefit at low rpm; weight-matching pistons and rods (heaviest piston on lightest rod) is a reasonable middle ground.
• Cadillac rear main seal: a popular upgrade (see the Dec. 1998 High Performance Pontiac article).
• Tuning: after assembly, experiment with jetting — a bigger cam and better heads may want a couple sizes up.

If budget allows and you’ll give up the stock look, aftermarket Edelbrock heads flow far more (close to 300 cfm out of the box vs. ~240 for ported stock) and keep gaining past .600″ lift — one member made 570 hp with them. Expect fitment work (mill the intake to match, round-port exhaust manifolds or headers, valvetrain clearance for high-ratio rockers), and don’t use copper head gaskets with them.