Mailbag: A Recipe for Making 600 HP in a 400 V8-Powered ’69 Firebird

1969 pontiac firebird


Q: I bought a 1969 Pontiac Firebird a few weeks ago. I has a factory 400 V8, which I’m told makes 345 horsepower. I’d like to get 600 horses out of this car, but I’m not sure where to begin. Any advice would be greatly appreciated!

A: We better to get to work, then!

Let’s start by getting more displacement. A 455 crank with the main journals ground down .25 inches to 400 main size, boring the block .030″ over, and some 455 pistons will get you up to 455 cubic inches.

A rebuildable 455 would also work and save you some cash. At this level, connecting rods like Eagle Specialties H-Beam rods would be useful.

To complement the greater displacement, you can install an Edelbrock Victor Intake and an 850 cfm double pumper carb, and Edelbrock cam and lifter kit, 1.61:1 roller rockers, 1 7/8-inch Hedman headers, and an NOS Cheater nitrous system.

Use the 150 hp jets, and you’ll have your 600 horses.

Use a 2,500 rpm stall torque converter and a 3.55 gear to put that power to good use. You’ll also want some subframe connectors and a roll cage to keep your Firebird in one piece.

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  1. One other option you may consider is an LS engine swap. I can appreciate wanting to keep the factory correct 400, but the bottom end of an LS block is alot stronger. Build it right, and you won’t have to worry about a connecting rod finding a way out of the oil pan.

  2. Changing heads is critical to get compression up a must do edelbrock

  3. Eagle Specialties also makes a stroker crank for this engine.

  4. is the 850 Holly double pumper a good street carb? I had one on my 496 BBC and it was more “race” than street. I decided to go with duel quads instead.

  5. Bored and stroked mine to 468. Kauffman racing equipment heads and intake with a lunati hyd roller cam. Just a bit over 600 horses.

  6. Charles Beaty says:

    Heads, Heads, Heads that’s where the power starts.. Get a nice set of Trickflows and nice cam and nice intake….

  7. Roy Haikarainen says:

    Keep the 400 block and put a Scat 4.250 4340 steel stroker crank and 6.800 H-beam rods in it. With a 0.030 overbore it’ll be a 461, and with a 0.060 overbore it’ll be a 467. Put a good set of 4032 forged pistons in for about 10.5:1 cr. A good cam may be the Comp Cams hydraulic roller that SD Performance sells as the Road Paver, with 246/252°dur @ .050″ lift, .608″/.608″ lift with 1.52 ratio rockers, 112° LSA. Top it off with a pair of SD Performance 325 cfm CNC ported Edelbrock aluminum heads, an Edelbrock Torker 2 intake port matched to the heads, and a QFT 950 carb. Spark it up with a complete MSD ignition system.

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