672 Horsepower Pontiac 350

The Pontiac doesn’t get much respect. Eclipsed by the larger 389, 400, 421, 428, and 455 engines, the 350 is the Rodney Dangerfield of Pontiac motors. The only thing going for a Pontiac 350, so the pundits say, is that a 400 or 455 bolts right in its place.

But it’s been over 20 years since GM produced traditional Pontiac V-8s, and the supply of desirable big-inch blocks is drying up. Yet the orphan 350–produced from 1968-1979–is still fairly common, precisely because no one wants them. Pontiac’s 350 shares the same external dimensions with its larger brothers.

Heads–including Edelbrock’s popular aluminum castings–interchange. It uses the same 6.625-inch center-to-center Pontiac rods as the big motors, yielding a great 1.77:1 rod/stroke ratio, even with its relatively long 3.75-inch stroke. The major drawback is the small 3.875-inch standard bore, which restricts ultimate breathing potential and creates valve-to-bore interference with big valves and high-lift cams.

Valve To Bore Contact Is Most Likely To Occur On The Exhaust Side. Grind Clearance As Needed. Maintain 0.025 Inch Clearance Between The Bottom Of The Notch And The Top Of The Piston Ring Land At Top Dead Center.

All right, beggars can’t be choosers. For many die-hard Pontiac lovers, the 350 is all they can find and afford. Could a modern cam, pistons, rings, cylinder heads, and nitrous oxide technology get this Indian off the reservation? “Yes!” responds Bruce Fulper, the owner of Rock & Roll Engineering (RRE)–a leading Pontiac high-performance parts supplier and race-engine building facility. Other than the relatively rare ’68-’69 350 H.O., Pontiac never saw fit to develop the 350’s performance potential, yet Fulper has assembled an awesome package that makes nearly 540 hp on the dyno and runs high 11s in the quarter–without nitrous. Adding just a small amount of squeeze boosted the output to 670 hp and mid-10s. Here’s what goes into making a brave little Indian (or is that a little Indian brave?).

Bottom End:

Stock Pontiac iron cranks can handle anything you throw at them if properly prepped. The 326, 350, 389, and 400 Pontiacs all share the same 3.75-inch stroke, and a crank from one of these other engines works in a 350 if rebalanced. When swapping cranks, be aware that there are three different crank flywheel-mounting flange pilot diameters – ’63-and-earlier, ’64-’76, and ’77-’79–which must mate with a matching flywheel or flexplate. The crank used on this engine is 0.020-inch undersize on both mains and rods, though beefy Pontiac cranks can go 0.030- and 0.040-under on the mains and rods, respectively, without problems. This engine uses Dana-Perfect Circle rod (CP-758P-20) and -groove main bearings (MS-483G-20), which are available in common oversizes.

RRE Believes Conventional Windage Trays Actually Block Oil From Returning To The Sump. Instead, A Crank Scraper (RRE PN 4223) Is Used To Wipe Oil Off The Crank. It Installs On The Passenger Side Oil Pan Rail And Must Be Trimmed To Fit Within 0.050 Inch Of The Crank Throws.

All 350s can safely be bored 0.060-over. The most desirable blocks to look for were made from 1968 through early 1970. They may not have the correct mounting bosses needed for some later applications, but their larger cylinder-bore valve chamfers require less notching for valve clearance with big cams. Check for valve-to-bore contact by placing the valves, retained by clothespins, in the heads. Coat the potential bore-to-valve interference areas with machinist’s dye, place the head (with no gasket) on a bare block, and carefully drop the valves to establish the contact point.

Said to enhance sealing by 6 percent, this engine uses the latest Total Seal gapless top rings, conventional cast-iron second rings, and a thin but standard-tension oil ring assembly. Not subject to gap erosion, the gapless design can maintain optimum sealing properties longer than traditional rings. The rings seal 0.060-over CP lightweight flattop pistons that, together with the heads’ 72cc chambers, zero piston deck height, and Fel-Pro 1016 head gasket, bring the compression ratio in at a pump gas-friendly 9.5:1. Fulper ordered the custom slugs with the top ring lands positioned 0.300-inch below the piston deck to both enhance durability with nitrous oxide and to provide additional clearance for the valve notches required by the 350’s small bore-size.

The Stock Cast Rods Are A Weak Link On All Pontiac V 8s. CAT’s 4340 Steel H Beam Rods Are An Affordable Solution. The 500 Gram CP Pistons Have Precision CNC Machined 1/16 1/16 1/8–inch Ring Grooves For Enhanced Sealing. Double Spirolocks Retain Full Floating 0.980×2.750–inch Wristpins.

The Gapless Total Seal Compression Ring Is Actually A Two Piece Design That Must Be Installed Staggered With The Top And Bottom “rails” Offset 180 Degrees In A Manner Similar To The Oil Ring.

High-volume oil pumps aren’t required. The 60-psi Ram Air IV pump driven by a heavy-duty pump driveshaft is sufficient if you control bearing and rod side clearances. Excessive volume and pressure just increase parasitic losses and make the rings work harder. A 6-quart (with filter) replacement oil pan is filled with conventional SAE 30 oil for initial run-in, 0W-0 Royal Purple synthetic oil at the track, and 20W-40 on the street.

There Is A Mismatch Between The Oil Pump And Cylinder Block Transfer Passages. Elongate The Block Oil Hole As Shown To Match The Gasket Contour.

Resource:

Hot Rod

Rock & Roll Engineering (RRE)