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Chevy 409 Mark I Big Block Engine Build - Mighty Fine 409

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Happiness is a Long Stroke
In yesterday's heavy cars, the short-stroke 409 doesn't perform like a typical big-block, needing steep gears to get out of the hole. Fortunately, there's plenty of room in the block to increase the stroke. The 348/409s have the same bore-spacing, 2.20-inch rod journals, and rear main seal as the later Mark IV big-block. The front snout and seal is the same as a small-block. Only the 2.5-inch main-bearing journal diameter is unique. So the plan is to turn down the 2.75-inch big-block main journals to the 409's size, rework the snout to the 409/small-block pattern, and contour-grind the counterweights slightly to clear the oil pan. Drop in a suitably modified 4-inch stroke 454 crank with a 0.030-inch overbore and you get 474 ci-plus the missing low-end torque.

A 454 crank requires external balance weights. CH sells an aftermarket externally balanced small-diameter 7-inch SFI-legal 400 small-block damper that fits the now-small-block-sized 454 front crank snout while clearing the 409 water pump (however, its as-delivered timing mark location doesn't match the 409's timing pointer). At the flange-end, just use a 454 flexplate or flywheel.

Mate the 454 crank with CH's stroker pistons using modern big-block 3/8-inch-bolt rods-unlike the 7/16-inch forgings, they clear the block. With CH's custom replacement forged pistons, these longer and stronger modern rods are also a desirable upgrade for stock-stroke 348s and 409s.

Where's the Fire?

Pass the Gas
You can get serious heartburn trying to pass gas into and out of a 409. All the stock intake manifolds are weak and don't flow well. The production intake manifold runner-to-cylinder head entry forms a restrictive V-shaped intersection and porting them out only sharpens the V. An average ported intake runner actually flows about 10 percent less than a stock port through 0.400-inch lift! Port the exhaust and leave the intake side (especially the floor) alone (bowl work's OK). Serious guys will step up to a sheetmetal intake.

On the exhaust side, Hooker still offers a header set (PN 217) for '58-'64 full-size passenger cars. Most guys default to a set of production high-perf exhaust manifolds. If you can find them, pull $650 out of your wallet.

Gettin' the Digits
There's many a late model that'll have hell to pay going up against a stroked 409. With the Isky Z-33 mechanical cam, a 10.0:1-compression 481 (0.060-over 409 with a 4-inch-stroke 454 crank) equipped with headers and two late-style 600-cfm Carter AFBs installed atop the stock high-performance 2x4 high-rise made 499.3 hp at only 5,500 rpm, and 516.6 lb-ft of torque at 4,500 on pump premium unleaded gas with 34 degrees of spark advance. It produced in excess of 450 lb-ft throughout the entire test range, with over 500 lb-ft on tap between 4,000 and 5,100. With 41 degrees of timing, the Isky 0.620-inch lift roller and 1-inch carb spacer plates, an otherwise similar 474 (only 0.30-over) upped the output to 522.7 hp at 5,800 rpm and 538.4 lb-ft of torque at 4,300. Got any tree stumps that need yanking?

SOURCES
CH Enterprises
1044 W. Brooks St.
Ontario
CA  91762
909-988-9848
www.mr409.com
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