Pistons and rods become one in the war on power. There's less piston in order to improve r
How does anyone get 409 ci from such a small package? Most folks stop at 347 or 355 ci using a stock block. Based on MPG's popular 355 and 377ci Boss stroker engines and modern Dart block technology, here's how Scott squeezed 409 ci into a 289/302-size block.
Cleveland 4V Vs. MPG 3V
Let's put the factory 351C-4V head alongside the MPG 3V head and compare. It's apples and oranges because the MPG 3V Cleveland head is a clean sheet of paper casting for Clevelands and Windsors alike. It's simply better than a factory iron 351C-2V or 4V head. The 3V yields technology that was unavailable in 1970. The trend in cylinder heads is toward smaller, more efficient heart-shaped chambers with plenty of quench area for improved combustion. This takes the ping out of hard acceleration and makes the most of the fuel/air charge. Behind the wheel, it means more power without engine suffrage.
Would you believe the MPG 3V intake port flows more air than the larger 351C-4V ports? Scott tells us improving port geometry does this. Not only has MPG improved intake flow with this head, but it has also improved velocity, which provides more torque. MPG achieves this with five-axis CNC port work-improving the short-turn radius and offering a better valve job at the same time.
To keep port velocity high, the finished intake runners aren't extensively modified at all. They remain a lot like they arrive from Australia. Scott hand-finished one short-turn radius and intake bowl, which improved flow during development. He took this information, digitized it, and made it part of his CNC programming. MPG coats each intake port with a special thermal coating to reduce intake charge temperature-which means a denser mixture and greater power. Scott learned he had to do little to the chamber. Exhaust ports have been raised 0.400 inch to improve flow.
Scott went with a mechanical roller cam from his own CamResearch company. A mechanical camshaft makes sense when we're going to spin it high and don't want the irregularities of a hydraulic roller cam. Pro Magnum 1.7:1 roller rockers from Comp Cams are also used. Here's the straight dope on this Engine Masters cam from CamResearch.
|Duration at 0.050 in: ||250-deg. |
|intake, ||252-deg. exhaust |
|Valve Lift: ||.744 intake, |
|Lobe Separation: ||106 deg. |
MPG opted for this rocker arm stud girdle from Jomar, which is mandatory for camshafts with fast ramps and high spring pressures. This keeps the valvetrain stable and safe.
Scott adds that seat-to-seat duration is short and lifter acceleration is fast. This means fast open and a lot of time at near full lift to fill the bore with the densest mixture possible. This means power across a broad band.
|MPG at the EMC |
|Displacement: ||409 ci |
|Bore: ||4.250 inch |
|Stroke: ||3.600 inch |
|Average Peak Hp: ||658 |
|Average Peak Torque: ||584 lb-ft |
|Average Hp |
at 2,500-6,500 rpm:
|Average Torque at |
|531 lb-ft |
These numbers came from three back-to-back dyno pulls made after three warm-up dyno pulls.