Oldsmobile 307 Engine - Analyze This!

When brothers Dale and Glenn Robinson decided to take up the gauntlet and enter the 2008 Engine Masters Challenge, they knew they needed every advantage they could get. They had to know all of the rules inside and out, and create a combination that could wow the crowd and still stay within budget. Their approach to building this little 307-based Olds mirrored their team name, Robinson Analytical.

Dale has been bracket racing with Olds power for a number of years, and is comfortable enough with the architecture of the engine that he knew its weaknesses and strengths. Talking with Dale, it is clear that he's a levelheaded player, and his philosophy was to break down the engine building process into two distinct focus groups: weaknesses and strengths. This, he figured rightly, would be the best way to approach the build.

The Robinsons started their analysis with a $50 core engine from an '84 Toronado. A little digging tells us that the 307 engines were popular throughout the whole GM family. All of the BOP and Chevy passenger cars received versions of the 307 for their mid- and fullsize cars from 1980 to 1990. Most Olds engines have the cubic inches cast into the side of the block, though the 307 has a casting of a 5.0 liter on the block. If you are looking for one in the junkyard and you spot a two-barrel carbureted V-8, keep on looking, as all 307s used a four-barrel Quadrajet. In fact, the 307 was the last passenger car offered with a carburetor in the United States (except some Crown Vic Police Interceptors, as we're sure someone will scream out).

For every Olds lover, the biggest struggle with the engine isn't necessarily making power, but keeping the engine intact. The 307, like the 403 and other Olds blocks, uses an open main-webbing design that saved the powerplants a good amount of weight, and GM a good amount of coin, but sacrificed structural strength. With a talent for machine work and an eye for details, Dale got started remedying this issue by building a structural support, connecting all of the mains to the block. He says: "I used a piece of 1018 flat bar with some blocks to connect it to the halo girdle, and I machined the caps and that's it. I bought the halo off J&S Machine and connected it all together." He used a set of spacer blocks between the J&S halo and the main girdle and used brass shim stock to set the preload to what he wanted. Finally, 3/8-inch Allen-head capscrews fasten the homebuilt girdle to the pan rail. In essence, he built a super-sized main girdle for the block. The beefed-up support had a secondary feature that helped move the oil pan further from the windage whipping around, thus better controlling the oil.

The crank used was one of the early 330 Olds forged-steel cranks. Coveted for their strength, the 330 cranks were quite popular to drop into small-inch engines. Dale spent a bit of time modifying and lightening the crank: "I took 3 pounds out of it. They're pretty hefty to start with. It weighs like 56 pounds, it was 59 when it was stock." Since modifying the SFI-mandated flywheel was out of the question per EMC rules, Dale also had to re-drill the bolt pattern on the rear of the crank from the oddball 330 pattern. After lightening and resculpting the shaft, it was balanced to a set of Eagle ESP Featherweight Chevy-style H-beam rods. "I went with the longest rod that was still within budget at 6.250 inches. Barely attached to the rods by a set of paper-thin 71 gram wristpins are some custom Ross full-round pistons. At the time the pistons were ordered, Ross didn't have the shape of the combustion chambers to go off of, so they were hand-tailored to fit once they showed up. With a small dome and the pistons sitting just out of the hole, it wasn't hard to come up with 10.4:1 compression. To prepare the block for those pistons, Dale made a custom hot-hone torque plate, allowing 125-degree water to pass-through the engine as it was being finish honed. That brought the engine to an honest 316 cubic inches. After the short-block was assembled, they took a torque wrench to it and were pleased that it only took a mere 7 lb-ft to turn it over.

At a passing glance, the casual observer more than likely wouldn't notice the size of the lifters in an engine, but when it is torn down next to another GM block, it stands out that the lifters sure look awfully big in this little 307. A little digging revealed that during the '80s, Olds moved into the world of hydraulic roller cams and used a big .921-inch diameter roller lifter. This made it legal to use lifters big enough to make Mopar guys jealous, even if they did have to use flat tappets per the rules. Further block details evolved as the Robinsons drilled small holes in the lifter valley to allow oil to fall directly on the flat-tappet camshaft. Also, raised vent tubes epoxied into the lifter valley keep the crankcase pressure equalized between the upper and lower end of the engine.

The cam that was used to motivate the mondo lifters was a COMP Cams grind using the MM Mopar lobes designed specifically for large-diameter tappets. The advantage here is that the angular relationship between the tappet and the cam lobe allows the cam to whang open and close the valves-technically speaking that is. "Looking back now, I wouldn't have gone that big on the exhaust lobe. I think I over-exhausted it."

As if the bottom end of this baby Olds didn't already have our heads spinning, looking at what was bolted on top of the block blew our minds. With an amount of consideration and effort that would make a Super-Stocker look like a bracket racer, Dale transformed the ordinary 5A casting heads into fully functional race heads. On the exhaust side, the center two cylinders share a common port, a terrible design for anyone wanting to make power. Using a block of iron to fill the main gap in between the two adjoining cylinders, Dale spray-welded iron to fill the remainder of the gap as well as to raise the floor of the exhaust port by almost a half inch. Similar treatment was given to the intake side as the floor was raised there by about 3/8 inch with epoxy instead of the spray-weld. "I've got about 10 pounds of epoxy in that motor between the heads and the intake manifold." Knowing he wouldn't need enormous runners for the amount of cubes, Dale kept the volume down. He says: "The intake port is way smaller than the original. I think the factory was 152 cc and now it's down to 145 and it's much higher. It's got a small cross section of 1.9 [square inches]." Final flow numbers ended up around 195 cfm on the intake and 170 on the exhaust. Though not huge peak flow numbers, he claims they were almost at those numbers by .200-inch lift. Just perfect for limited camshaft and rpm range applications.

Using experience and catalogs as his guides, Dale was able to round up a set of small-block Chevy 2.02-inch intake valves and 1.60-inch exhaust valves that he cut down to 1.55 inches, profiled, and back-cut. Both used lightweight 5/16-inch stems to reduce the amount of mass that the COMP Cams beehive springs would have to control. When determining the required spring pressure, this was their first solid flat-tappet engine build, so they took a stab at it and set it up with 130 pounds on the seat. But Dale says: "After looking at what everybody else used, I think I could have gotten away with less. Maybe I could have freed up some horsepower in the block then."

Having a set of T&D 1.65 rockers already on hand gave the Robinson Analytical team a head start, and they just bought a set of 1.8 rockers to swap onto the shafts for the intake side. Rocker arm geometry was right on the money as the roller tip sat directly in the middle of the valve with almost no movement.

Between the more-than-stock heads sat an equally modified Edelbrock Performer RPM intake manifold. Originally designed for a spread-bore carb like the factory Q-Jet, the manifold carb flange and portions of the runners were filled with epoxy to better fit the Edelbrock Thunder AVS square-bore carb and match the raised runners in the heads.

Once the Robinson Analytical team had their engine together it was time for testing. Normally a simple procedure for the Chevy and Ford guys, Dale says: "It was the first time we ever had an engine on the dyno and it was kind of a scramble. First of all, they didn't have an Olds bellhousing, we had to cobble up a Chevy one. Then we couldn't get it to butt up against the bellhousing. It's an old Superflow setup for a manual transmission crankshaft, and mine's an automatic crankshaft. So it took me an hour in the dyno room to grind a hole in the back of my crank to fit it up against." Once it got all lined up and fired, some basic timing changes and rod changes in the Edelbrock carb got the Olds where they wanted it.

With thousands of hours of thought and analysis, hundreds of hours of hard work, and four hours of testing, the Robinsons packed up their unlikely creation and headed from Grimsby, Ontario, Canada, down to the Jegs Engine Masters Challenge at the University of Northwestern Ohio campus in Lima, Ohio. When their time slot finally came, they hooked up their stock cast-iron headed 307 to the DTS dyno, while the crowd watched the closed-circuit TV in the main EMC lounge area. They didn't know that they were about to get their socks blown off. Where big-name engine builders broke or were DQ'd, the little Olds kept on. Where some ran hot and saw their scores shrink, the Robinsons kept making power, not dropping a point between their three final pulls. With over 435 hp and 430 lb-ft of torque from a tiny mid-'80s smog engine, the guys from up north proved that their analytical skills and attention to detail put them square in the middle of some of the best engine builders in the country.