Reference Manual

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Chapter 1: Engines: Oldsmobile V8s: 13-second 307 recipe

A low 13-second recipe would be a stock short block 307 with the following mods:

• Get some cylinder heads from a 1967 330 and have them drilled to accept the larger head bolts. The heads would receive a Mondello bracket porting job, and be fitted with the 1.995" intake valves and 1.62" exhaust.
• The heads would be milled for a true 9.5:1 compression ratio.
• The camshaft would be a Mondello JM-22-25 cam which works out to 274 degrees of intake duration and 280 degrees of exhaust duration, an intake lift of .523" and exhaust lift of .541", and lobe centers of 110 degrees. A full roller adjustable valve train would be installed.
• Complete Mondello oiling system with a full length windage tray and crank scraper.
• The intake manifold will be a slightly modified Edelbrock Performer RPM with the plenum divider ground away 2" wide and 1" deep.
• A 600-cfm Holley double-pumper and mechanical fuel pump. Mallory Unilite distributor and coil. Hooker headers with 1-5/8" primaries, and 3" collectors.
• The short block would receive the traditional hot treatment (prepped rods, forged pistons, zero-gap moly rings), and of course, a forged 330 crank.
• For the transmission, I would use a full manual TH-350 with a 3500 stall converter, and a Ford 9" differential. Start out with gears ranging from 4.33 to 4.88, depending on the altitude at which I would race.
• I think that would be one hot little 307. I would keep the shift points between 6500 rpm and 7000.

Be careful about wanting to use too much cam for a street 307. Especially with those sad 7A heads. No matter how long you hold those valves open, it's still sipping through a straw.

Since the computer only controls the primary side of the electronic carb, as well as the ignition advance, there's no reason to discard it. If the 307's intake manifold is being replaced with one with larger runners, you'd probably have to change the size of the jetting on the primary side. You might also want to use a non-computer carb on the car, and see if this makes a difference.

A high-stall converter is a good idea, but the real gains would come from swapping in some 5A heads with a Performer intake. No matter how much you open up the induction or exhaust system, with the small-port heads you're really being held back.

To realize any significant power gain, you'll have to open up the motor. Try a K&N filter, perhaps an aftermarket exhaust, and fine-tuning the secondaries on your carb.

The problem is not that the carb or exhaust is too small; the restrictions lie in the valve/port size, the lift and duration of the camshaft, and most significantly, the highway rear gears that keep your engine revving much lower than any speed at which you can take advantage of those modifications. (4)