Meet Quadstar's version of the Optimizer 6500, the latest revision of the 6.5L diesel that is still in production today!  It features a 506 block design with piston squirters, like a GM casting, except it is cast with an improved metallurgy.  The heads have induction hardened seats and opened cooling passages between the valves to address all the issues GM engines traditionally had. Why buy from Quadstar? FORGED steel crankshaft, adopted from the P400 - STANDARD LATEST GEP head castings with improved cooling passages around the valves - STANDARD Less lead time!  We have local stock and rolling backorders to keep these moving out Pickup from our main location in PA or the factory in Ohio can be arranged Easy payment options. Financing Available! We can bundle every part you need to complete your build We'll talk you though it. Please get in touch and we'll reach out. No core or core fees required! These are 100% brand new direct from the USA AM General factory down to every single component and bolt.  Beware of imitations and misleading ads that abuse the trademark "Optimizer 6500".   *Specify correct configuration when ordering. The intake bolt angle in the cylinder heads is a key difference between options and whether the engine is for a GM truck, Van, or H1 Hummer. Turbo engines have DIAMOND pre-chambers in the heads Non-Turbo engines have SQUARE pre-chambers in the heads These were used in a lot more than just GM vehicles. Some examples are marine applications, buses, express vans. Please contact us if you need to cross reference which option is applicable to your situation. **Your payment method will be authorized when ordering but not be cleared immediately. We will contact you before clearing payment to ensure your order is correct and to review all applicable policies AMG = AM General GEP = General Engine Products. A subsidiary of AM General