Butler Performance 407ci TorqStorm Supercharged Pontiac Crate Engine — PUMP GAS 708 HP / 671 LB-FT, Dyno Tested

708 horsepower and 670 lb-ft — measured, not calculated

A Butler Performance in-house build: 407 cubic inches of Pontiac V8 under a TorqStorm centrifugal supercharger, fed by Holley Terminator X multi-port EFI. Assembled and blueprinted here in Lawrenceburg, run on our own engine dyno, and the numbers below are what it actually made — corrected, in our cell, on the day.

Why the curve matters more than the peak

A centrifugal supercharger builds boost with engine speed, and this combination is set up to use that. Boost comes in at 4.1 psi by 3,700 rpm and climbs steadily to 10.4 psi, so the engine is pulling hard from low in the range rather than waiting for the top of the tacho.

That is a very different engine to drive than a big-inch naturally aspirated combination that signs off early. It pulls hardest exactly where a street car spends its time when you ask something of it.

Built from a 350 block — and that is the interesting part

This started as a Pontiac 350 casting. It was drilled and tapped for four-bolt mains with a Pro-Gram billet front cap and Butler steel centre caps on ARP studs, rebored and honed with a torque plate, square decked, align bored across four caps, align honed, thermal cleaned, magnafluxed and sonic tested before a single part went into it. With a 4.250" Eagle forged crank and a 3.905" bore it comes out at 407 cubic inches.

Most people write the Pontiac 350 off. Prepared properly, this one makes 708 horsepower.

Why 9.5:1

Compression on a boosted engine is a decision, not a leftover. TorqStorm's own guidance for this kit is 9.8:1 maximum on aluminium heads, and for 93 octane pump gas they suggest 8.75–9.5:1 depending on pulley size and boost level. This engine sits at the top of that window — 9.5:1 on aluminium Edelbrock heads, with Butler forged pistons carrying a −16cc dish and a .040" Cometic MLS gasket getting it there.

That is why it takes 10.4 psi without living on the edge of detonation. Build the same engine at 10.5:1 and the blower becomes a liability instead of an asset. The camshaft follows the same logic: a Butler/Comp Power Adder grind, 236/244 duration at .050" on a 114 lobe separation, which keeps cylinder pressure sensible under boost and gives the blower something to work with.

The supercharger package

This is the TorqStorm Plus serpentine system for the Pontiac 326-455, passenger-side mount. It is a complete system rather than a charger and a bracket:

• Keeps your accessories. The serpentine layout drives air conditioning, power steering and the alternator alongside the blower — you are not giving up A/C to run boost.
• Everything to install it. Supercharger, brackets, pulleys, hoses, tubes, blow-off valve and hardware.
• Limited lifetime warranty on the supercharger.
• A bung for water/methanol injection is provided if you want to go further later.

Pulley size is the boost lever. As dyno tested this combination produced 4.1 psi at 3,700 rpm rising to 10.4 psi at the top of the pull. A smaller pulley spins the blower faster and makes more boost; that is a conversation to have with our tech department alongside compression and fuel, not a part to change on its own.

Crankcase evacuation — the part nobody photographs

A boosted engine puts more pressure past the rings than a naturally aspirated one, and that pressure has to go somewhere. This build runs a GZ Motorsports Super Pro billet vacuum pump off the crank mandrel, with a breather tank, a billet hi-flow control valve and a Butler billet evac baffle in the valve cover.

Pulling the crankcase into vacuum improves ring seal, keeps oil where it belongs and stops pressure finding its own way out through a gasket. It is not a glamorous line on a spec sheet, and it is one of the reasons this engine made the numbers it did without drama.

Specification — as built

Built the Butler way

Butler has been building Pontiac engines since 1974. Every engine that leaves here is assembled and blueprinted in our own shop and run on our own dyno before it ships — we don't ship an engine we haven't heard run. The dyno sheet goes with it.

Boosted Pontiac combinations are not a parts-list exercise. Compression, camshaft, fuel system and ignition all have to be chosen around the boost level, and getting one of them wrong is expensive. If you're considering a supercharged build, talk to our tech department before you buy parts.