Thread: Allison 6 Speed GMC 401
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Old March 31st, 2018, 03:19 PM
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Default Re: Allison 6 Speed GMC 401
While I believe the 4BT's can be upgraded for more power, the torsional vibration of a big powerful 4 could become a problem with driveline/rear axle components. I recall some years ago, the 4BT conversions were popular in lighter vehicles but the torsional vibration created all kinds of breakage issues.

Years ago when I drove for Greyhound, we had some MCI 12's I believe that had the 4 cylinder series 50 Detroits. Sluggish of the line but held road speed well, even on grades. On the road, it felt much bigger than it was.
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