Pontiac GTO 400 Engine Block Build Up - Poncho Honcho
Building A 506HP Street 462 From A 400
From the November, 2008 issue of High Performance Pontiac
By Doug Marion
Photography by Doug Marion
Given the current engine technology in the Pontiac hobby, building a big-cube Pure Pontiac engine from a 400 block is easier than ever thanks to the many stroker combo choices for 3.00-inch main engines. When Orwin Middleton of Santa Barbara, California, decided he wanted more power for the street to motivate his rare '61 Royal Pontiac Catalina, he pulled the transplanted '67 400 that sat in its engine bay and paid a visit to Joe Sherman Racing Engines in Santa Ana on the recommendation of storied racer and noted Santa Barbara engine builder, Bob Joehnck.
Coincidentally, Sherman was already in the process of building a Pontiac 455 with an Edelbrock top end featuring its aluminum heads, Performer RPM intake, 800-cfm AFB carburetor, a set of headers, and a street performance roller camshaft from Comp Cams. Sherman is known industry wide for incredibly strong street engines as well as top race engines. He even won the inaugural Popular Hot Rodding Magazine Engine Masters Challenge in 2002!
Middleton told him about his '61's proposed combo-a big-inch torquey, yet streetable, engine backed by a 2,500- to 2,800-rpm stall converter, a Turbo 400 and a 3.42 Safe-T-Track rear. With these specs in mind, Sherman devised a plan to have the block machined and bored 0.060 over to 4.181, and to use a 4.210-inch stroke, 3.00-inch main cast crank, stock length rods, 0.030-over 455 KB hypereutectic pistons and a Comp Cams hydraulic roller cam. The top end recipe would duplicate his other customer's 455 with Edelbrock parts.
Joe Sherman Racing Engine's...
Joe Sherman Racing Engine's cast crank features the 4.210-inch stroke of a 455 and the 3.00-inch mains to fit the 400 block. Installing a 455 spec crank in a 3.00-inch main block sometimes requires mild clearancing at the front of the block where the front counterweight will travel.
For the record, every block...
For the record, every block spec and dimension was checked out, noted, and blueprinted for the '67 WT-code block. To accept 0.030 455 pistons, the cylinders were bored 0.060-inch.
Stock 6.625-inch connecting...
Stock 6.625-inch connecting rods were press-fit onto Keith Black (KB) hypereutectic pistons. This type has the increased strength of a forged piston with the lesser expansion rate of a cast one. Less piston-to-cylinder wall clearance means better ring seal.
Sherman explained to Middleton that this 462 cubic inch combination would produce 500-plus horsepower at a livable 5,000 to 5,200 rpm with almost 600 lb-ft of torque. Though we typically see forged rods and pistons in these types of builds, Sherman also said that the hypereutectic pistons and cast rods would be cost-effective as compared to forged pieces, and durable in this application because peak power is made at just 5,200 rpm. Middleton was floored! To his old-world brain, these power figures bordered on Amtrak diesel territory! Sherman suddenly found himself with Middleton's Pontiac engine to build as well. Let's see how it all turned out.
The engine was dynoed on Joe Sherman Racing Engine's SuperFlow 901 engine dyno. For this pull, the fuel was 91-octane, the timing was set to 39 degrees and the jets were the same as listed in the engine buildup worksheet.
Joe related, "though the carb spacer normally does lean the mixture slightly, the out-of-the-box jetting was nearly perfect for this combo."
Here's the short-block buttoned...
Here's the short-block buttoned up just prior to fitting the oil pump. By retaining the two-bolt mains and stock caps and employing a cast 4.210-stroke crank, cast rods, and hyper-eutectic pistons, the budget is kept in check, while power for the street is generated. For added bottom-end insurance or higher-rpm potential, forged connecting rods can be used for your buildup.
Money was well spent on the...
Money was well spent on the benefits of a hydraulic roller camshaft from Comp Cams. The design of the roller cam lobes lets the valves reach maximum lift more quickly per degree of duration than flat-tappet cam lobes, which aid cylinder filling and evacuation, thus increasing power output. Less overlap required in a hydraulic roller as compared to a hydraulic flat-tappet to get this increased power can result in a smoother idle and improved low-speed performance. There's also a reduction in friction thanks to the roller lifters.
Roller cams generally don't...
Roller cams generally don't need any initial start-up lube, but Joe Sherman lubes the lobes and lifters anyway.
Edelbrock's No. 60579 aluminum...
Edelbrock's No. 60579 aluminum heads feature 87cc combustion chambers and can be ordered either bare or complete with valves, springs, and guide plates. Sherman chose the latter.
The oil pan is a Joe Sherman...
The oil pan is a Joe Sherman Racing stock-type replacement. This one is a later model that features a baffle in the bottom to keep oil at the pickup during high-g driving. That shouldn't really be a problem with the '61 Cat, however.
This 4.181x4.210 "undersquare"...
This 4.181x4.210 "undersquare" engine makes big torque and horsepower between 3,400 and 5,400 (max) rpm. At max valve lift, the heads flow 275-cfm intake and 185-cfm exhaust out of the box, which negates the need to port them for this combination.
Shown here is an Edelbrock...
Shown here is an Edelbrock bronze wall valve guide, a smooth as-cast pocket area, and hardened valveseat inserts for unleaded gas.
The 87cc combustion chambers...
The 87cc combustion chambers will provide 10:1 compression when combined with the 4.181 bore, the flat-top piston's compression height and valve reliefs, 0.005 piston-to-deck height, and the volume of the head gasket. A set of 2.11/1.66-inch stainless valves is included when the assembled head is purchased.
"D"-shaped exhaust ports were...
"D"-shaped exhaust ports were proven decades ago on GM Tech Center dynos to work best on high-performance engines. Though the heads are based on the round-port R/A-IVs, the exhaust port design was changed in the Edelbrock head to this D-shape. Nevertheless, the round-port manifold or header configuration is required when using these heads.
|Engine Buildup Worksheet|
|Block/Crank Combo||’67 400/4.210 stroker|
|Block||’67 GTO 400, code WT|
|Preparation||Bored and honed 0.060-over |
|Crankshaft||Joe Sherman Racing cast 455 stroker|
|Balancer||Aftermarket replacement, degreed|
|Rods||Cast, 6.625-in |
|Preparation||Size the big and little ends, install new rod bolts, balanced|
|Pistons||KB Hypereutectic, 0.030-455 flat-top with valve reliefs |
|Piston to Deck Height||0.005-inch|
|Piston Pins||KB press-fit |
|Piston Rings||Hastings moly top, cast-iron second|
|Balancing Spec||2,210g bob weight|
|Oil Pan||Replacement with baffle|
|Brand||Edelbrock aluminum, 60579, closed chamber|
|Modifications||As delivered from Edelbrock|
|Combustion Chamber Volume||87cc|
|Maximum Flow at 28 Inches of Pressure:|
|Intake||275-cfm at 0.700|
|Exhaust||185-cfm at 0.700|
|Angles Used in Valve Job||30-, 45-, 60-deg|
|Valve Guides||Edelbrock bronze|
|Rocker Studs||ARP 7/16-in|
|Roller Rocker Arms||PRW full roller, 1.52:1|
|Brand||Comp Cams hydraulic roller|
|Duration at 0.050||230/236-deg|
|Lobe Separation Angle||110-deg|
|Lifters||Comp Cams hydraulic roller|
|Valve Springs||Comp Cams dual|
|Seat Pressure||145 lbs|
|Open Pressure||395 lbs|
|Timing Chain||Comp Cams dual-roller|
|Intake Manifold||Performer RPM |
|Mods||Plenum clean-up |
|Carb||Edelbrock No. 1412, 800-cfm|
|Primary Metering Rod Size||0.071-0.047|
|Fuel Line||3/8-in diameter/No. 6 AN|
|Distributor||Stock-type, Pertronix conversion|
|Wires||ACCEL 7mm solid core|
|Brand||Mad Dog Exhaust Products custom |
|Primary Tube Diameter||1.875-in|
|Primary Tube Length||30-in|
|Collector Size||3 1/2x7-in|
You can see the 7/16-inch...
You can see the 7/16-inch screw-in rocker arm studs and included pushrod guideplates as the head bolts are torqued in sequence.
Valvesprings and retainers...
Valvesprings and retainers are Comp Cams-issued. PRW full-roller, forged aluminum rocker arms are plainly stamped with the engine size, stud diameter, and rocker arm ratio. Valvetrain geometry must be fully checked on every engine with aftermarket heads, especially aluminum, because spring pads and valve placement can be slightly different compared to stock, so proper roller rocker arm tip-on-valve stem positioning must be verified.
Since Pontiac never used round-port...
Since Pontiac never used round-port heads in a '61 model, Middleton had custom headers built to run the Edelbrock heads in his Catalina. Mark Delcamp, proprietor of Mad Dog Exhaust Products in Allen, Michigan, makes the company's headers one set at a time. He's been at it since 1989 and before that was a honcho at the legendary JR Headers in Detroit. These early Pontiac headers feature heavy-duty 16-gauge (0.065-inch wall) tubing.
A Pertronix electronic ignition...
A Pertronix electronic ignition conversion is hiding under the distributor cap. ACCEL wires deliver the spark to NGK FR-5 plugs.
Sherman adds a 1-inch spacer...
Sherman adds a 1-inch spacer to the Performer RPM intake manifold, which he says is worth an additional 10 hp. As well as providing WOT power, since the 800-cfm AFB carburetor features primary metering rods that work off engine vacuum, they can meter fuel 12 percent leaner or richer, benefiting performance or economy-depending on how the engine is being used. Hood clearance with the RPM intake and spacer might be questionable on some Pontiacs, but not Orwin Middleton's '61 Catalina.
Sherman had the new harmonic...
Sherman had the new harmonic balancer "degreed" from 10 degrees after top dead center (TDC) to 50 degrees before. After degreeing-in the camshaft, he had to make a new timing pointer. He also marked in white: TDC, the pointer tip, plus 30 and 40 degrees before TDC. Exact engine timing is a MUST! It should also be noted that the 455 had the benefit of being dyno-tested with no pulleys or drive belts, per se. This can save 6-7 hp.