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.
Our block fresh from the machine...
Our block fresh from the machine shop (North Jersey Performance in Emerson, N.J.). For a grand total of $277.20, the shop honed the cylinders, installed new cam bearings, and performed an initial block cleaning. We'll do some block inspection and cleaning of our own before we begin assembly, just to be safe. Also pictured is an item you'll need that we didn't mention in our tools article (elsewhere in this issue): an engine stand. Readily available at almost any auto parts store, an engine stand allows the block to be rotated about its lengthwise axis during assembly.
In order to inspect the diameters...
In order to inspect the diameters of the cylinders and mains, a dial bore indicator is necessary. We'll be using the Powerhouse unit we discussed in the tools article. First, set the overall length of the tool to be just larger than the hole you are trying to measure. Do this by adjusting the attachments and shims included with the tool, and measure the overall length you get using a micrometer or caliper. When inserted into the hole in question, the tool indicates how much it is being compressed.
As it is impossible to visually...
As it is impossible to visually set the tool perfectly horizontal in the cylinder, the tool is designed to be rocked back and forth until the largest value is seen on the dial indicator. This indicates the value that needs to be subtracted from the measured length of the tool in order to get the actual cylinder diameter. Outside of the cylinder, our Powerhouse caliper measures the length of the dial bore tool as 3.927 inches. Subtracting the maximum value indicated on the dial indicator when in the cylinder (0.023), this means the actual finished cylinder diameter is 3.904.
Using our Powerhouse caliper,...
Using our Powerhouse caliper, we measure our piston diameter to be 3.901 inches. Since Lunati specified a piston-to-cylinder-wall clearance of between 3 and 4 thousandths for our particular set of pistons, we are right on the money with 0.003 inches of clearance.
Next, we measure the diameter...
Next, we measure the diameter of the main bearing bores. Since our block was not align-honed, we're not actually checking machine work here; just making sure these main bearing bores are within GM's specification for size and roundness. After torquing the main cap bolts to the proper spec in the GM service manual, our dial bore indicator tool is used to measure each bore in succession in both the vertical and horizontal planes. All measurements yield identical readings of 2.761 inches. While GM specifies production main bearing bore diameters of 2.750-2.751 inches, the discrepancy probably is due to limits of the measuring tool; the fact that all the measurements are the same is all that really matters. Plus, we'll be checking bearing clearances using Plastigage momentarily.
Now that we've checked everything...
Now that we've checked everything out in terms of measurements on the block, it's time to start our final block cleaning. Begin by inspecting all threads in the block, both in terms of bolt holes as well as holes for oil gallery plugs. Look for leftover sealant as well as any damaged threads. We discover that our head bolt hole threads are pretty gummed up from the thread compound GM used when originally assembling our LS1. This could interfere later on with proper installation of our ARP head studs, and could also prevent proper torquing of head bolts (if used in lieu of studs).