Dyno Parts-Juggle-Fest: 520 Hemi

Testing Exhaust Manifolds, Headers, Carbs and Air Cleaner

Last month we stuck one of Chrysler’s most legendary high performance engines on the dyno and juggled exhaust manifolds, headers and air cleaners to see what impact they had on power potential. Well, okay, last month’s Max Wedge test mule wasn’t really a vintage “426-V-MP-HC” 13.5:1, solid cammed, big port Stage III thoroughbred, but rather a poor man’s copy based on a 1977 Dodge motor home long block topped with modern reproductions of vintage Mopar Super Stock parts. But we did learn a lot.

This month we’re testing another iconic Mopar powerhouse – the 426 Hemi – to see what impact headers, manifolds, carburetor size and air cleaner efficiency have on output. And yes, like last month’s mill, this Hemi is something of a poor man’s copy. Rather than a numbers matching BS27R ’71 Hemi ‘Cuda convertible mill or a N.O.S. ’64 Race Hemi crate engine discovered in an old Virginia tobacco barn, this one’s a Stage V wedge-to-Hemi Conversion engine.

If you’ve never heard of the Stage V Hemi Conversion package, here’s a brief rundown. Back in the early Eighties, original Hemi blocks and heads were extremely hard to come by. Naturally all of this stuff was used equipment and there were no reproduction parts on the scene – the amazing Mopar Performance 426, 472 and 528 crate Hemi and parts program wasn’t even a dream yet.

So a guy named Eric Hansen conjured up Hemi heads that can be bolted to any RB wedge block with minor modifications. The heads are all-new castings that look and behave exactly like hallowed 426 Hemi heads – but they’re cast aluminum and have ports that out-flow the originals by a significant margin.

Yes, you still have to reload your 413, 426 or 440 wedge block with Hemi-type pistons (to fill the stock-size 175-cc combustion chambers), a Hemi cam (since wedges have a different lobe sequence than Hemis) and specific Stage V rocker arms, rocker stands and rocker shafts (to suit the altered pushrod angle forced by the wedge block’s tighter lifter valley-to-deck transition). But once you’ve “tuned” the wedge block thus, you’re free to bolt any Hemi-style induction and exhaust components you want. If they can be bolted to O.E. Hemi heads, they’ll fit the Hemi Conversion heads too.

Naturally this opened the door to lots of 440-based Hemi Conversion motors and the big break came in 1986 when Pat Ganahl visited Stage V Engineering and “put the guys on the map” with a full feature story in Hot Rod magazine. Since then, several hundred Stage V Hemi Conversion kits – and complete engines – have been built. And yes, mine is one of them. The ingredients list at the end of this story gives all the important specs and prices so I won’t use the space here.