Mailbag: How to Get 400+ Horsepower from a Chevy 400 Engine

Got questions?

We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re looking at ways to make over 400 horsepower from a small block Chevy 400.

B.B. Hastings, NE

Q: I have a 400-cubic-inch small block Chevy. I would like to be able to get 400-plus horsepower from this engine while maintaining my car’s drivability on the street. The vehicle currently has a Powerglide transmission and 3.88:1 gearing. Do you have any suggestions for parts combinations that might help me achieve this goal?

A: Obtaining the 400-plus horsepower you desire should not be a problem. Achieving more than a horse per cubic inch from most engines by using stock cylinder heads is almost counterproductive, though. An aftermarket cylinder head is almost a necessity—1966-69 Corvette “camel hump” cylinder heads being the rare exception. In addition to aftermarket cylinder heads with 2.02/1.60-inch valves—or very well-prepped OEM castings at the very least—here are some guildelines for achieving 390-415 horsepower at 9.5:1 compression:

• 1.5:1-ratio roller rockers
• 1 5/8-inch primary tube headers
• Dual plane high-rise intake manifold
• 700 cfm, 750 cfm, or 770 cfm carburetor
• Aftermarket camshaft: .484-.510-inch lift, 238-248 degree duration at .050-inch lift, 110- or 112-degree lobe separation

The combination of these parts should develop peak horsepower in the 5,500-5,800 rpm range and peak torque around 4,400-4,700 rpm. You didn’t mention torque converter or drive tire diameter, but factoring in the Powerglide and deeper 3 series gear, you should consider a torque converter with a 3,000 rpm stall rating and a maximum tire diameter of 25 inches. You may also want to consider 4.10-4.11:1 or 4.32-4.33:1 differential gearing.