1988 Pontiac Firebird Formula 396 Short Block Engine Install - Pumping Up, Part 1

Project Magnum TPI Gets A New Lease On Life WithA 396 Short-Block From Strope Speed Shop.

Johnny Hunkins Sep 1, 2001 0 Comment(s)

Step By Step

The basis for any high-horsepower street car is a good short-block assembly. Our 396 stroker small-block was built by the experts at Strope Speed Shop in Washington, PA. Fuel-injected GMs--and Chevrolet small-blocks in particular--are their specialty.

The basis of our bulletproof 396 cubic-inch stroker was a reciprocating assembly from Lunati (consisting of 5.85-inch 4340 forged Pro Mod rods, custom 4032 forged pistons with .927-inch floating wrist pins, a Pro series plasma moly file-fit ring set, main bearings and rod bearings) and a forged steel 3.875-inch stroker crank from Cola.

Our Cola forged crank (part No. COLA38753B1, $900) can take a lot more than we're going to dish out for now, but it's nice to know that if we want to add a blower, turbo or nitrous down the road we've got something we can use. The one-piece rear main seal is unique to '86-up small-blocks and features better sealing than it's earlier two-piece counterpart. Note the gun-drilled rod journals--this allows the rotating assembly to balance with considerably less weight, and less weight means better acceleration.

Here is the culprit which caused us to cut short our plans to add a blower to our stock short-block. These four rod bearing shells show a catastrophic wear pattern (pointed out by the tip of the pen). The small-block Chevy prioritizes oiling from the rear bearings forward; these bearings came off the front two rods which are at the end of the oiling chain.

The Lunati 4032 forging is a high-silicon design which is great for the street enthusiast. (A forging is much stronger than any cast or hypereutectic design because the crystalline structure is aligned during the forging process.) Its high-silicon content minimizes expansion, reduces cold piston slap and mitigates oil consumption.

Using a profiled rod like the Lunati Pro Mod piece is a good investment on a stroker motor. The contoured shoulders and caps make clearancing the block easier and leave more meat on the block. The guys at Strope also report that the Pro Mod's I-beam construction has proven to be just as strong as a more expensive H-beam rod.

Our Lunati piston features a wrist pin which intersects with the oil ring package. To preserve the integrity of the oil rings, Lunati uses a groove lock spacer to bridge the gap left by the wrist pin hole. A locking tab faces down inside the wrist pin hole, keeping it from rotating the gap over the hole.

This comparison of the stock piston/rod combo (left) with the Lunati stroker piston/rod combo shows the difference in compression height (the distance between the wrist pin and the crown of the piston). The longer stroke means we've gone from a compression height of 1.56 inches (stock) to 1.213 inches, a reduction of .347 inches. We've lost some meat, but by going to a forging we've gained all our strength back and then some. We've also lost a lot of reciprocating weight which translates into free power. Also note that our Lunati rod is longer by .15 inch.

The .1975 added inches of rod throw on our Cola crank (bottom) doesn't look like much (that's .395 extra inches of stroke), but it yields 46 more cubic inches with a .030-inch overbore.

After removing and disassembling our 350 TPI motor, the bare block was taken to the machine shop. After being hot tanked, our new Pro Gram Engineering billet caps were cut to fit the block (called setting the air gap) and the block was drilled and tapped for the splayed caps. The block was then align bored and honed with the new caps in place.

Our block was then bored .030-inches over. For final honing, a BHJ torque plate was torqued down with the same example of ROL gasket we'll be using for final assembly. This simulates the stress on the bore with the cylinder head torqued down. All bore distortions are removed in this process--this improves ring seal and power considerably.

Those who follow the exploits of our third-gen Firebird project car can be forgiven for wondering why we're changing directions as of this month. After all, isn't it our motto that when building a project car you should set your goals, make a plan and stick with it? When we initially got our 1988 Firebird Formula 350, we started modifying the Tuned Port 350 engine like many of you would: first the cheap and free stuff, then some easy bolt-ons, culminating most recently with a cam, ported heads, and a ported TPI manifold (see "Getting Serious," November 2000).

Our next plan for the engine was to push the bolt-on theme even farther with a Vortech S-trim supercharger kit and fuel system upgrades. But as fate would have it, days before the blower kit was supposed to arrive, we were greeted with the wonderful sound of rod knock. In case you're wondering, the sound of rod knock is not a good portent for adding another, oh, hundred rearwheel horsepower via a blower kit.

Behind schedule and faced with repeated driveability problems (see "Fine Mess," August 2001), we thought we were finally seeing the light at the end of the tunnel. Well, that "light" turned out to be a train. Our original goal of building a semi-affordable "bolt-on" car was going down faster than the Titanic. The idea was nice; many third-gen owners are on a budget and prefer to spend at a moderate pace when making upgrades. It's not that budget-minded enthusiasts like to go any slower than their rich counterparts, it just takes a little longer and sometimes takes a more tortuous route. (The word "tortuous" definitely applies to us!)

Perhaps if we were more virtuous, we would've located another used stock engine or perform a stock rebuild of the existing engine. We thought about it, but decided against either option. To make a long story short, we opted to go with a naturally-aspirated 396 cubic-inch stroker with bullet-proof parts and superior induction. (For the full story on why we chose a naturally-aspirated stroker, you can log on to www.gmhightechperformance.com.)

Making A Game Plan

The decision to build a stroker engine is fairly straightforward, the really hard part is selecting the right parts for the short-block, induction, ignition and engine management. As fun as it is to pick parts out of a catalog, more often than not, this can lead to disastrous results if you don't know what you're doing. And while most people like to think they know what's going on (us included), they really know just enough to get into trouble. For this reason, we asked the good folks at Strope Speed Shop (Washington, PA) to help select our parts and assemble our engine.

Having seen many of Strope's previous projects, we had a good idea that they were in tune with what we wanted. As the parts selection proceeded, we discovered that Bill Strope Sr. and his son Aaron were very meticulous. Our busy schedule offered plenty of opportunity for us to forget about the many minor needs of the project, but Bill and Aaron were on the ball with regular communication via fax and e-mail. They made sure that every part was ordered properly and every "T" was crossed. By the time we were ready for our short-block photo shoot, there was no stone left unturned. Of all the positive things we can say about Strope, the logistics and planning impressed us the most--a big factor for us given the long travel distance involved.

As we alluded to earlier, Strope specializes in building really hot fuel-injected street-legal GM machinery. In short, building this kind of stuff is not a side project, but the main deal. When we told them we wanted a stroker, they already knew what to do. The short version is that we wanted a street-legal naturally-aspirated EFI motor with a wide powerband that would be capable of pushing us into the high 11s. To get that, Aaron Strope recommended that we go with the biggest small-block practical with the cylinder case we already had.

Aaron says, "There's really nothing special about the number 396, it's just not any more expensive to build than a 383. The side benefit is that a 396 has a little bit more bottom end than a 383. When you go bigger, you get to the point of no return. If you go to a 409 you won't make that much more power because you can't use a SuperRam and you don't have a street motor any more. You can't really go up on the bore with a stock block, so you have to go with a bigger stroke and you need to do a ton more clearancing on the bottom end. The 396 is really the right size for a stock-block stroker." (We'll cover the induction in more detail in part 2, but it bears repeating that the SuperRam was a key breathing component for our stated goals. It doesn't make any difference how big the holes below the deck are if what's on top can't supply the air.)

To obtain 396 inches, Strope retained the original block, opting to machine it to handle the added bore and stroke. The stroke, in this case, came from a bulletproof Cola forged crankshaft with a 3.875-inch stroke. "This was our first time using a Cola crank, and the forging and the machine work looked really good," says Aaron Strope. "The fillets looked good and they did a nice job contouring the counterweights. They also radiused the oil holes and they lightened the throws by drilling the 1 and 4 rod journals.

"I was really impressed with the spec sheet--they measure each crank by hand and write it on this sheet. They also check the stroke with a computer. This makes my job as an assembler pretty easy. I think we'll be buying Cola cranks in the future for some upcoming projects. We weren't that happy with the packaging, however. The crank seemed pretty unprotected in its cardboard box, but it arrived just fine from UPS."

The Cola crank is one of the few in the industry to be offered with a one-piece rear main seal. Even though all OEM small-blocks made after 1986 came with a one-piece rear main, most crank manufacturers build the older two-piece design, citing the preponderance of race cars still using the older design. Late-model owners, however, are reluctant to retrofit the older design due to its poor sealing and frequent maintenance. Cola actually offers two styles: standard, and lightweight. The lightweight version (which we chose) features gun-drilled rod journals for greater power.

For reciprocating components, Strope chose Lunati. Among those parts were Pro Mod forged 5.85-inch rods. "Lunati stuff is really good quality," states Aaron. "We've used it before and it's really tough to find a good rod like the Pro Mod at this price. It's got a profiled contour which allows you to clearance the block easier, it's lighter and it maintains the same strength as a more expensive H-beam rod."

Lunati Pro Mod rods were teamed with a set of custom forged 4032 pistons. To get the desired zero-deck clearance with the 3.875-inch stroke, Strope specified a 1.213-inch compression height. This places the .927-inch wrist pin with our 5.85-inch rod just inside the oil control ring pack. To shore up the oil pack, Lunati uses a special bridge ring with a locking tab that faces down in the wrist pin bore. It's a rather elegant solution to a weak area in the piston. Strope also specified a 4.030-inch bore and dual valve reliefs (totaling 4cc) to produce a final compression ratio (with the intended 64cc AFR heads) of 11.69:1.

"The 4032 Lunati piston forging allows you to use a tighter piston-to-wall clearance and that makes the engine quieter," states Aaron Strope. "A race-series forging would have a lot of piston slap because it would have almost twice the piston-to-wall clearance. In terms of strength, the 4032 alloy is nearly as strong as a 2618 race piston. What little the 4032 gives up in strength, it gains in dimensional stability. I think it's the strongest truly streetable piston you can get."

With a sizable investment in the rotating assembly, it only makes sense to keep it all in place when things get frenetic. Consequently, Strope was absolutely insistent on the use of Pro Gram Engineering billet main caps. These four-bolt splayed pieces replace the stock cast-iron two-bolt caps and require the block to receive extra machining steps. The Pro Gram caps are not only far stronger than the stock ones, they also shore up the webbing by having an extra pair of splayed bolts on each of the interior caps.

While we were at it, we also ordered the 2-bolt billet front cap for extra strength. (Pro Gram also offers a billet rear thrust bearing cap which is excellent for power-adder cars, but Strope felt the stock rear cap was already sufficient.) We were happy to discover that Pro Gram offers their splayed conversion kit specifically for late-model applications where the stock oil pan and dipstick must be retained. This saved us a bundle because we didn't have to upgrade to a custom oil pan--an otherwise unnecessary expenditure for a low-rpm street application.

Last, but certainly not least, is the importance of a high-quality, high-tensile strength fastener. Once again, Strope was adamant, and insisted on using Automotive Racing Products' studs with 6-point nuts (for the inner cap fasteners) and 12-point bolts (for the outer splayed caps). We will also be using ARP fasteners for the remainder of the engine build-up including head bolts, oil pump drive, oil pump stud kit, balancer bolt, flex plate bolts, and torque converter bolts. As you can tell, we don't plan on stuff moving around much once we torque it down!

There's a lot more coming in the issues ahead. Next time we'll follow up with camshaft, valvetrain, oiling and induction. We'll look more closely at our horsepower and airflow goals and reveal our strategy for leapfrogging into the 11s.

For more info on the Magnum TPI 396 short-block, log on to www. gmhightechperformance.com. There's a lot more than meets the eye!

Short-block Components:
Cola crankshaft, part No. COLA38753B1 $900
Lunati Pro Mod connecting rods, part No. LAB1 $699
Lunati custom forged 4032 alloy pistons $599
Lunati ring set, part No. P14035 $99.95
Lunati rod bearings, part No. CR848HP $59.95
Lunati main bearings, part No. MB5142HP $59.95
Pro Gram Engineering main caps, part No. SB350C12 $239.95
Pro Gram Engineering front main cap, part No. SB350F $79.95
ARP 12-pt. main bolts (outer), part No. 234-5201 $136.95
ARP main studs (inner), part No. 134-5401 $43.48
machine work (block & balancing) $900
total: $3818.18

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