As with many older vehicles, finding production replacement parts can be a challenging task. In many cases, original manufacturer replacement parts have been out of stock for years. This leaves engine builders no choice but to look at aftermarket solutions for their engine part needs.
For turbo Buick V6 engines, which include the 3. 8L and 4. 1L models, finding a replacement crankshaft poses unique concerns for engine builders. While many naturally aspirated crankshafts do exist, they lack the rolled radius which gives the crankshaft added strength for turbo charged engines. Science Journal While there are some engine builders that do use a naturally aspirated replacement cast crankshaft, doing so may result in premature engine failure under boost. Generally speaking, naturally aspirated crankshafts should never be used in a vehicle which utilizes a turbo.
Although the original turbo Buick crankshaft may be machined with a crankshaft grinding machine, preserving the rolled radius in each journal is critical in preserving the strength of this component. In most cases grinding the crankshaft to. 010″ under on the rods and. 010″ under on the main journals is acceptable. However, grinding more off of each journal may result in some of the rolled radius being ground away. Please keep in mind that on most production crankshafts, the rolled radius does not uniformly conform to the journal itself. On some areas of the journal the rolled radius may actually not be as deep as it is on the other side of the journals.
When an original turbo Buick V6 cast crankshaft can not be found or repaired, it is time to look at the aftermarket availability for options. At the present time there are two primary options for engine builders to consider. First, there is the 3. 400″ stroke crankshaft and a 3. 625 stroker alternative. Both of these crankshafts are steel forged and are much stronger than the original cast crankshafts.
Since turbo Buick V6 engines originally came with a 3. 400 stroke crankshaft, the forged 3. 400″ stroke crankshaft will be as close to a direct replacement as possible. However, most vehicle owners that want to produce as much horsepower as possible typically select the 3. 625 stroker crank as the added stroke adds to the baseline horsepower. This added stroke is essential when using a performance camshaft and cylinder heads. When all three of these components are combined, it removes any horsepower bottleneck within the engine itself.
Although the 3. 625 stroke crankshaft can produce more engine horsepower, the use of this component does require additional machining to be performed on the build. For example, the connecting rods will need to be clearanced so that they do not hit the camshaft. Additionally, the casting around the main oil galley in the block needs additional clearance as well. Most automotive machine shops insert a piece of tubing into the galley and then grind the casting away in a small area of the galley.
Regardless of which direction you take in replacing your turbo Buick crankshaft, there are options which are available. Depending on your desired engine performance goals, a forged crankshaft that matches the existing stroke offers the greatest savings. However, a stroker crankshaft will certainly produce much more horsepower and will allow your engine the opportunity to fully benefit from any additional performance parts that you use in your engine build.