1975 Chevy Laguna S-3 Gets An Engine - Cup Car Power, Street Car Manners

Back in the day, when our replica Cup car Laguna was a current NASCAR entry, Talladega engines were unrestricted, and depending on whether they were early or late in the era, made between 560 and 585 hp. That's about 110 or so more than a restrictor-plate engine currently makes at Talladega, NASCAR's largest and fastest venue, but with the aerodynamically more blunt bodies of the '70s, the straight-line speeds where not too different from today's. For our Laguna, we wanted comparable power from a 350-based engine, but with everyday driving street manners and reliability. Also, all this had to be achieved without the use of a blower, nitrous, or a dry sump system. Another stipulation is that this engine had to be a bolt-it-together deal-in other words, all easily available off-the-shelf parts that sold for street car prices, not Cup car prices.

If the foregoing sounds like a tall order, it was-but certainly not out of reach if we add one factor into the equation: as many extra cubes as possible from a 350 block. The road to success with any engine build (where performance is the prime consideration) is the overall combination. In our case, since we're looking for a lot of power, everything gets just that much more critical. The carb must have sufficient flow capacity, as well as good mixture preparation qualities. The intake must flow well, as must the heads. The cam must open and close the valves at the right time to suit the combination (very important). Lastly, the exhaust system must be tuned to the rpm range, and the mufflers must not defeat the pipe length tuning. What this means is we have to pay attention to every aspect of the build from where the air enters, to where it leaves. A while back, we built a 408 stroker with T&L Engines in Stanfield, North Carolina, that was a great success on a moderate budget. (T&L's entry-level 408 makes better than 510 lb-ft and 505 hp, and sells turnkey for about $5,850.) We decided this should be our starting point.

Short-Block Assembly
The foundation of our T&L 408 was a sonic-tested late-model 880 hydraulic roller block of about 1995 vintage. These blocks have the advantage of being stronger, higher quality, and more consistent from block to block than the earlier pre-'87 blocks. Also, they come roller cam ready in stock form with a thrust plate to control the roller cam's end float.

Our block was given all the usual prep in terms of boring, decking, etc. After that, it was clearanced for the longer four-inch-stroke rotating assembly that was to be used. The clearancing of the 350 block is a critical issue. It takes the right combination of parts to accommodate 0.520 inch of extra stroke. Just diving in and grinding the block clearance without the right know-how will land you in the block's water jacket for sure, so here's how it's done.

After selecting an appropriate block, the next move to generating 408 inches is to go with the right rotating assembly, and the key component within this is the connecting rods. To get the job done, we went with a Scat forged rotating assembly, which uses their budget (about $290 a set) forged six-inch stroker rods (PN 2-ICR6000-7/16). Why this rod, and no other? It's all about bolt-head and rod-shoulder clearance. With a four-inch stroke, the bolt head of a typical rod will need so much clearance to be cut into the block that it will be well into the water jacket. The bolt head on the Scat rod is set way lower than usual, and thus requires far less clearance to be cut into the block. Also, the rod's shoulder where the bolt end is situated is more compact, and with minimal grinding, gives the extra clearance necessary for it to miss the cam when a four-inch stroke is used. It is because of the extra clearance afforded by the Scat rod that we can, with greater certainty, put a four-inch stroke into a 350 block without finding water. A point worth noting is that this rod, in a post-'87 roller block, will often allow the rotating assembly for 383 inches (3.75 stroke) to be done as a simple "drop in" procedure. That's a plus for the home builder for sure.

The piston for our 408 is an off-the-shelf Mahle item. For a stroker motor, piston and ring selection is more important to the engine's final output than it is with a shorter-stroke motor. The reason is piston-to-bore wall friction. The use of a longer stroke not only means a greater distance for friction to operate over, but also a piston-to-wall side-loading penalty because of greater rod angularity. All this means that some of the advantage of the extra cubes can be easily squandered to the evils of friction. The Mahle piston seeks to offset frictional losses, and past experience with these pistons shows they do just that. The most obvious move to reduce friction is the skirt coating, but that's only the start. The main deal is the ring pack used by Mahle. Instead of the usual 1/16-1/16-3/16 rings, these use a 1.5mm-1.5mm-4mm ring pack that installs into a much shallower ring groove. The result is not only a ring pack that weighs about 55 percent of the usual, but also a ring pack that requires less radial pressure on the cylinder walls to get the job of sealing done. I haven't done any back-to-back tests, but I have heard some engine builders talking a 15hp improvement with these pistons over a piston with a regular ring pack. The other nice thing is by the time the rings are figured into the price, (they come with the pistons), these Mahle pistons work out to be a good deal for what is essentially a real high-performance item.

The last item on the agenda for the bottom end is the pan. Stroker motors are a lot more sensitive here than a stock stroke build. With a four-inch stroke, the rotating assembly can more easily pick up and entrain oil, as well as hit the pan rail. To avoid this, a suitable Moroso pan is essential. Fortunately, Moroso has a variety of pans that will work with most chassis, so a phone call is all that's needed should you want to duplicate this 408 in any way.

Camshaft
Now here's something different. The cam for our 408 was from a new range that I've been working on with Comp Cams. So often, you can look through a catalog and the application given for any particular cam is really vague if you just go by what the catalog describes. (As if a cam described for a 262-inch small-block is equally ideal for a 400-plus-inch small-block!) It could be said that 99 percent of catalog cams are semi-generic. On top of this, it can easily take 20-30 minutes of studying the catalog to come up with a cam that, unless you are well-versed in the art of cam selection, may, at best, only be a passable selection. For those with less than professional experience, there is always a degree of uncertainly with the selection process.