Pontiac Street Performance

Steve Coombes' 2003 462 Update

Steve Coombes has once again taken high performance to another performance plateau. This time his new engine configuration is tamer and more streetable and as a result it joins the ranks of other engines featured in the Torque Power section.

Don't be fooled by Steve's detuning effort as his 1970 Trans Am remains a top performer in any class. What is truly wild is that his TA runs as good as it looks. Below are the critical engine and driveline details.

Steve's engine received PSP's 1 to 1 Club honors on June 24, 2004. His engine clearly develops in excess of 1 hp per cubic inch of displacement. It rocks!

Technical Data
Block 1970 455 YH
Block Specs + 0.030" over bore; hard block to freeze plugs; Pro-Gram Engineering 4 bolt main caps with ARP studs and bolts. Note: bored and honed to piston manufacturers specs, using torque plate.
Bore/stroke 4.181"x 4.210" 462 cid
Heads Edelbrock #6056 90cc chamber volume (9.7 to 1 static compression); T&D shaft roller rocker system, 1.6 ratio on both valves; ARP head studs & bolts; Felpro 1016 head gasket and 1436 exhaust gasket. Port matched to Specialty Component Engineering intake gasket, 1.175" x 2.320"
Head Flow Nos. on SF 600 Bench, 28" of water .100":83/82
Valves Ferrea 6000 series SS intake:2.15", exhaust:1.77"
Lunati H-11 dual valve springs, 1.52" diameter; springs are PolyDyn performance coated
Crankshaft 1970 455 "N", 0.010/0.010
Rods Carillo 6.625" Forged Steel
Pistons JE forged aluminum
Rings JE ring package with Total Seal top ring.
Deck height +.001 (nominal); Pistons extend .0007 to .0011 above the deck.
Bearings Federal Mogul 3/4 groove mains and Clevite 77 on rods; both Calico CT-1 coated.
Timing gear Rollmaster billet roller 9 key
Harmonic Damper BHJ (SFI approved)
Cooling Meziere Electric (35 gph)
Camshaft Comp Cams Xtreme Energy Street Roller #P4876B/4876B SR108, 254/254 @ 0.050", .389/.389 lobe lift, .622" gross lift with 1.6 rockers, set at 104 degree intake centerline; 108 lobe separation angle
Pushrods Manton 9.150" length, 5/16" diameter x 0.83" wall, 4140 chromoly steel
Lifters Crower solid roller lifter with optional high pressure pin oiler
Holley 4150 HP950; Edelbrock RPM with plenum divider cut 1"; port matched to heads
Oiling System Canton 6 quart road race pan; Sealed Power 60lb. oil pump; Fram HP2 racing filter, Mobil-1 10w30 synthetic oil.
Ignition MSD system 7AL-3 box; Pro-Billet distributor; HVC coil and crank trigger; Taylor spark plug wires; NGK V-groove plugs
Emissions NA
Exhaust Headman headers 2" tube diameter, 10.5" collectors; 3.5" into 3" Dr. Gas X Crossover; full length 3" exhaust running gases through Dynomax 17792 mufflers.
Edelbrock IAS shocks on front and rear and front sway bar in place; Landrum 300 lb./ in. leaf springs with Cal Tracs traction bars, Moog 6-cylinder front coiled springs; Wilwood front and rear disc brakes
Fuel Unleaded premium
Weight 3750 pounds
Tires/Rims Front: FirestoneFirehawk SS20 P215/65R15
Rear: 275-60R15 Nitto NT-555R drag radial for street; 28x 12.50 M/T ET Street DOT tires at the strip
Rims: American Torque Thrust
Driveline features TCI, internally balanced flex plate (SFI approved); 10" Continental torque converter for the street (8 inch A-1 4200 stall converter for the strip); TH400 transmission with manual valve body; Earl's Performance 19-row transmission cooler; GM 12 bolt with Moser axles, C-clip eliminator; Auburn limited slip with 3.73 to 1 gearing; T/A rear end girdle

Location:Liberty Hill,Texas

Model:Trans Am
Exterior:Lucerne Blue
Interior:Bright Blue


Dyno results: 589.1 CB Torque @ 4400 rpms and 580 CB Power @ 5800 rpm

Quarter mile: (running 8" converter and 90/10 shocks on the front and no sway bar in place); 1.60 60" times, 10.88 ET at 124.28 mph (date: 11-21-03)

Although racing seats, safety harnesses, and a 6-point roll bar are now present, the interior modifications and upholstered seats were tastefully done to match the car's original interior. The 6 point roll bar looks like it should have been a factory option.
Copyright © 1997-2004, Bill Boyle. All rights reserved.