Call it new tech by old NASCAR guys, conceived and executed by the long-time Winston Cup hands at Blue Thunder Racing Engines, chief among them, engine builder Harold Grady. About a month before Daytona Speed Week, Grady contacted Hank the Crank Bechtloff and the two formulated an engine package that would be showcased at the event--one that would include a lot of things that no other engine could claim, and one that would be built by seasoned NASCAR suppliers and bright thinkers.
Hank furnished the entire 9,000-rpm rotating assembly with the help of Carrillo's Jack Sparks and CP Piston's Barry Calvert, and Paul "The Rocket" supplied the box-and-box forgings, the latest Nextel Cup gimmick, which is lightweight and rigid to help the rings seal, and Fel-Pro engineer Greg West and Product Manager for Fel-Pro and Speed-Pro's Ron Rotunno provided the trick MLS head gaskets. Speed-Pro's Scott "Lord of the Rings" Gabrielson did the rings, and Harold Elliott applied his special coatings to all of the appropriate surfaces. Before the rotating assembly left The Crank's for the Blue Thunder shop, Automotive Balancing massaged the assembly. Additionally, HTC's representative in the southeast, Marty Cimaglia, oversaw the build and the testing of this project. Dig on that 1.8 hp-per-cubic-inch output, and you know that everyone involved dipped into their trick bags for this fierce small-block.
By nature, the motor was generously over-built, and therefore pricey due its extra-stout rotating assembly and the inclusion of nearly every subtle enhancement known to a naturally aspirated engine. Scrupulous attention to detail combined with things you can't see make a difference between just a motor and a killer motor that runs on the edge. And despite this mighty Mouse's intense racing flavor, it teems with ideas that could be applied to a small-block street engine.
The motor was constructed with the care and precision prevalent in all such extreme-duty applications. In this case, the bullet was destined for the Blue Thunder Super Late Model running under FASCAR (Florida Association of Stock Car Racing) rules. The restrictions include a 362ci (maximum) iron block, the first GM Bow-Tie Vortec big-port cylinder heads put into use (cast-iron and out-of-the-box stock save for thoughtful valve job; no changes allowed to runners, bowls, or combustion chambers), any flat-top piston design, an unaltered intake manifold-specific Holley carburetor (again without modification to alter airflow save for removing the air horn) and a mechanical fuel pump. Compression ratio, camshaft phasing, the rotating assembly, oiling system, and all the ways to reduce frictional drag are open to interpretation. With a 12.0:1 compression ratio and swilling Sunoco 110 race gas, this 355 made 632 hp at 7,500 rpm and 502 lb-ft at 5,900 rpm. Here's how it happened:
Grady began with a cast-iron, two-bolt main bearing block fitted with HTC steel billet mai
"We plug the oil galley that goes around the distributor and feed it from the front. We al
Because Grady wanted to use a ring diameter of 0.040-inch, he held the bore at 4.039 inche
Hank the Crank's billet arm is a jewel. Besides a Teflon-based oil-shedding coating (see s
Hank laid out the counterweights so the weight would be off the ends of the assembly and s
The mains are 2.300-inch (from 2.448-inch diameter main to a 2.2985-inch diameter) early-C
Grady likes Clevite products (PN CB1663-V) because he feels that they bed-in better than o
The stroke was finalized at 3.470 inches and realized via 6-inch-long Carrillo steel conne
The caps are secured with 3/8-inch Carr bolts that have a tensile strength of 285,000 psi.
The 100-gram Precision Products piston pins are 2.250 inches long with an 0.868-inch diame
Featherweight 390-gram CP pistons have a flat top, a cam-shaped skirt, and flat-ring lands
Ring seal is enhanced with a series of 0.062-inch gas ports (arrows). Scott Gabrielson bro
Original L31 Vortec casting. The new heads carry PN 25534371 and were the only ones in use
New GM Bow Tie Vortec Hank credits Lannie Barnes for securing them for Blue Thunder throug
The L31 exhaust port (top) looks like old tech;
GM Bow Tie port has definite D-shape, is raised up, and has a 77cc volume.
Grady puts them to the block with Fel-Pro 1144 MLS multi-seal gaskets. The 1144s have a st
Differences in the intake ports are dramatic. The new design is taller, narrower, flows st
The old port has 30-year-old technology (see Flow Chart).
The new combustion chamber is markedly different than the old. Grady: "It's a much better
We used 2.02-inch intake valves and 1.60 exhausts--with a 2-angle 45-degree valve job and
[I'll] Tell you, these new Bow Ties are the best 23-degree iron heads on the market." The
Stef's oil pan with a kick-out on the right side offers three scavenges with 1.450-inch po
The Weaver 5-gallon dry-sump tank holds 13 quarts of Mobil 1. The valley area is cleaned u
FASCAR rules leave camshaft phasing at the discretion of the builder. In this case, Grady
The PSI valvesprings provide a 320 psi on the seat and a whopping 705 psi open pressure--a
Crower rollerized shaft rockers (1.65:1/1.5:1) and the Crower rev kit (installed beneath
One of Danny Jesel's beltdrive systems kept the timing in check. A small-diameter, 4-poun
Unmolested intake manifolds are mandated, so Grady uses a single-plane Edelbrock Victor Jr
A CV Products mechanical pump handles the fuel delivery.
The DynaTech exhaust headers (1 3/4- to 1 7/8-inch step) sweep up and over the rear of the
Vortec Bow-Tie Brief
There are two versions of the new GM Performance Parts Vortec Bow-Tie cylinder heads: This one, PN 25534371 (bare) and PN 25534431 (complete), with the larger ports, and another with smaller ports, PN 25534351 (bare) and PN 25534421 (complete) with 185 and 65cc volume, otherwise, the architecture and improvements over the L31 design are the same. We will test the smaller version very soon in a dynamometer exercise. We were able to get an exclusive look at the big-port heads just as they were used in a NASCAR-type application.
Out of the box, they feature revised intake and exhaust ports and are machined for a 2-inch intake and 1.55-inch exhaust valves. The deck surface is 0.045-inch thicker than the L31s, and it has 65cc combustion chambers, a 206cc intake, and 77cc exhaust ports (see Flow Chart). The head is also machined for 3/8-inch screw-in rocker studs and a large valvespring pocket, and it will accept up to a 0.530-inch lift camshaft without modification. These castings are identified by the Bow-Tie logo below the exhaust port and the Vortec logo on top of the intake port area. The GM logo is also cast into the bottom of the intake port runners.
All concerned will be delighted to hear that the head includes intake manifold mounting holes for both early-model six-bolt and late-model four-bolt Vortec design. Mandated GM intake manifolds include a raised runner-type PN 10051103 (six-bolt type) or Vortec design PNs 12366573, 12496820, 12496821, 12496822, and 12499371 (four-bolt type). Though production cylinder head and intake manifold gaskets are acceptable, the hot squeal is Fel-Pro (PN 1142 for the MLS and PN 1289 for the intake). As per Scoggin-Dickey, pricing is: small port 4421 complete, $499.95; small port 4351 bare, $269.25; large port 4431 complete, $539.95; and large port 4371 bare, $293.25.
|Large-Port Vortec Cylinder Head Flow|
|The 355 Numbers|
Put Yur Coat On!
Harold Elliott knows better than most that the reciprocating parts must have an edge--a very slick edge--to compliment the engine builder's expertise and make his product a winner instead of an also-ran. He treated all the key elements of Harold Grady's bullet with a variety of friction-frying stuff. In a very brief explanation, this is how it goes:
Elliott coats the crankshaft counterweights with Teflon-loaded SL-11 in order so that the weights break the surface tension of the crank material so the oil won't stick to it and attempt to build up on the surface. The same goes for the connecting rods. He also uses SL-11 on the windage trays and the scrapers inside the Stef's dry-sump pan.
What he applies to the piston skirts, rod, and main bearings is called HM-30, which has is composed of a high percentage of molybdenum and makes the surface area much more durable in high-pressure areas. This allows the engine builder to tighten up his clearances as in the piston-to-wall area that will keep the piston straighter in the bore and aid ring sealing. Less clearance on the rods and mains means less oil leakage that will not collect in those areas, thereby not taxing the oil recovery system as much.
The HS-44 coating used on the tops of the pistons has a ceramic base, and therefore has very good heat-reflective properties. Keeping combustion heat away from the piston under the rings greatly improves the life of the piston and allows the builder to tighten the piston-to-wall clearance even more. Elliot does not stop there. Since the chambers, exhaust ports, and piston domes act as heat sinks during the combustion cycle and pull valuable power-producing heat from the area, he applies HS-44 to these surfaces as well. This coating is also applied to the tubular exhaust system in the interest of reducing under-hood heat and in presenting a very slick appearance.
Strict rules tend to initiate creativity and engender the NASCAR racers' credo of "being competitive." In this case, we're not talking about bending the rules or exploiting their interpretation, but simply using the most effective (and legal) means to reduce power-robbing friction, increase parts longevity, and enhance power output. In no particular order, the arsenal includes the gas ports that are drilled beneath the top ring land to ensure the best and most effective cylinder wall seal. This venerable helper is worth about 20 hp. The right rings, gas ports, and cylinder wall prep can release as much as 40 hp. Coatings and treatments for piston tops, skirts and pins, bearing surfaces, and crankshaft counterweights yield another 25 hp. The smooth counterweights are good for 5 to 6 hp, the small main journals 6 to 10, and the small rod journals 4 to 6 hp. Hank figures that the HTC Dyna/Rev special center counterweights are worth 4 to 6 more hp.