If you've been following the buildup of GMHTP's project 2001 Trans Am WS6, you know that we've been hinting at an imminent displacement increase. While bolt-ons like our full exhaust, big intake, and direct-port nitrous system have gotten excellent power increases out of this Pontiac's internally stock engine, there's nothing like a bump in cubic inches to really wake things up.
Unfortunately, pumping up cubes usually means pumping many thousands of dollars in the direction of a speed shop's bank account. Highly competent shops exist throughout North America that will be happy to take your hard-earned cash and turn your late-model, Gen III-powered ride into an impressive performer. This is definitely not a bad way to go.
But putting together one's own high-power, stroked EFI engine can be just as--or more--rewarding than enjoying the end product. After all, anybody with a wad of cash and zero hands-on knowledge can drop his or her car off at one of the aforementioned establishments and drive away a few weeks later with a couple hundred extra horses under the hood. The more unique breed of person dreams of building and installing such an engine at home, thereby gaining the satisfaction of tackling a seemingly daunting task many would not dare. But can such an undertaking really be done in the average suburban garage? Or is this power-hungry do-it-yourselfer destined to spend thousands of dollars extra having a shop build and install this stroked motor instead?
The time has come to find out. We're going to double the fun and halve the cash by building a stroker in our own garage. Follow along as we transform our Trans Am's 346-inch LS1 into a 383-cube LS-wonder.
Stroker Parts Selection
As we've hopefully made clear, there are two interlocking themes to this story: build-it-yourself, and build on a budget. The two go hand-in-hand, as the do-it-yourselfer is likely building his or her own engine in large part to save labor costs.
The question of what one looks for when building a budget-conscious stroked LS1 can't be asked unless one knows how tight cash really is. Someone on an absolute shoestring budget can get away with cost-saving measures like reusing the stock cylinder heads and just having a simple port job done to them. However, when it comes to the parts to actually make the engine a stroker, there are minimums of what must be bought, and the major items include a crankshaft, connecting rods, and pistons.
Before we get into how to go about choosing components, keep in mind the single most important canons of engine building: inform yourself, set realistic goals, and stick with your decisions throughout the stages of selecting parts, engine assembly, and eventual enjoyment out on the road. Ignore these, and disaster is certain to occur. And while we'll guide you in the right direction of understanding stroker LS1 component design and selection, we'd be doing you a disservice if we purported to include "everything you need to know." We just don't have the room to cram it all in. So, do your research! We'll mention some good books to pick up, and of course there's a ton of info to be garnered from visiting LS1-oriented Web sites. It also helps to make sure you pick up a copy of GMHTP every month!
Crankshaft: The Heart of a Stroker
GM uses a 3.622-inch crankshaft from the factory in the LS1; so how much bigger should you go? For our application, we wanted to make sure we would still have a reliable, daily drivable car that wouldn't suck fossil fuel like there was no tomorrow. Therefore, we chose to go with a 4-inch stroke, giving us 383 cubic inches (6.3 liters). Though larger cranks can fit, our choice to forego "throwing in the kitchen sink" is based on a few things in addition to those we've already mentioned. First, clearancing of the block will be minimal, saving us headache. And, keeping our planned moderate nitrous usage in mind, we'll limit our horsepower level enough that we'll be able to safely stick with our stock steel main caps without worry that we should have shelled out cash for some expensive billet units--and the accompanying machining costs to fit them to the block.
The analysis doesn't end there. Absent an adjustment in rod length, increased crankshaft stroke will decrease compression height (the distance between the centerline of the piston pin and the face of the piston). With our plans for nitrous use, we wanted as much ring land strength as possible; the smaller the compression height, the less space there is for the rings, and at a certain point the top compression ring will have to be moved too far toward the face of the piston, exposing it and the now-thin ring land to more heat than they can bear. You'll see these dimensions explained further in the photo captions when we get to piston assembly.