S&S T143 Long Block Engine for 1999-'06 HD big twins (except Dyna models) as 143" displacement yet fits in a stock chassis. If Bigger is Better, the T143 is the Best, The Biggest, baddest, bolt-in for a Stock Frame. All joking about size aside, it does matter. The S&S T143 Long Block engine for is the largest S&S engine that will fit in a stock Harley-Davidson chassis. It's big, 143 cubic inches. At double the HP of a stock motor, the power of the T143 requires technical expertise for the installation and tuning along with an experienced rider. This is an ultra performance/race engine. Longevity, engine noise, vibration and throttle sensitivity have all been compromised to reach this level of performance while fitting in a stock chassis and as such is not suitable for every situation.