Engines: Oldsmobile V8s:

The 307 was built from 1980 through 1990, produced from 140hp to 180hp, and was installed in just about every car Oldsmobile built in that period, at one time or another, to include the Cutlass (1982-1988), Delta 88 (1980-1985), Regency 98 (1980-1984), Toronado (1980-1985), and Custom Cruiser (1980-1990). (3)

The 307 shares the same stroke as all the other Olds small-blocks (3.385") and has a bore of 3.800" for a total of 307.12 cubic inches. It was used in cars from every GM brand (Buick, Cadillac, Chevrolet, Oldsmobile, and Pontiac). The 307 was also the last carbureted V8 that General Motors manufactured.

         Technical overview of the 307

         Cleaning out the EGR passages

         Differences between the 5A and 6A/7A heads

         Differences between the Y and 9 engines

         Modifying: 13-second 307 recipe




Engines: Oldsmobile V8s:
Technical Overview of the 307 Engine

General Specifications




90-degree V8


5.0 liters (307.12 cubic inches)





Compression Ratio


Firing Order


Sales Code

LV2 / LG8 (1987 9 engines)

VIN Codes

Y and 9

Cylinder Head


Head ID Number

5A / 7A

Combustion Chamber Volume

67cc / 64 cc

Intake Port Height

2.03" / 1.30"

Intake Port Width

1.30" / 1.30"

Int. Valve Face Angle

44 degrees

Int. Valve Seat Angle

45 degrees

Int. Valve Head Dia.


Exh. Valve Face Angle

30 degrees

Exh. Valve Seat Angle

31 degrees

Exh. Valve Head Dia.


Valve Train


Lifter Bank Angle

39 degrees

Lifter Diameter

.842" hyd. / .921" roller

Pushrod Length

8.265" hyd. / 7.718" roller

Spring Free Length

1.960" Y / 2.090" 9

Spring Pressure @ 1.670"

76-84 lbs. Y / 85-95 lbs. 9

Spring Pressure @ 1.270"

180-194 lbs. Y / 203-217 lbs. 9



Rocker Arm Ratio


(Y) Intake Valve Lift

.400" hyd. / .395" roller

(Y) Exhaust Valve Lift

.400" hyd. / .402" roller

(9) Intake Valve Lift

.440" hyd. / .000" roller

(9) Exhaust Valve Lift

.440" hyd. / .000" roller






Quadrajet (4-bbl)

Primary Venturi

1 3/32"

Primary Bore Dia.

1 3/8"

Secondary Bore Dia.

2 1/4"




High Energy Ignition

Spark Advance


Spark Plug Type

R46SZ hyd. / FR3LS6 roller

Spark Plug Gap

.080" hyd. / .060" roller



Oil Capacity

5.0 qts. (w/ filter)

AC Oil Filter


Pressure @ 1500 RPM

30 psi. (206 kPa)



Engines: Oldsmobile V8s:
Cleaning out the EGR passages

The 307 engine is very sensitive to EGR flow; even a 50% reduction is enough to cause pinging headaches. Your car should run fine on 87 octane fuel. Mine with 50% blockage still pinged on 93 octane, with the timing set a 20 degrees, as factory-specified. Want a cheap performance boost? Remove the carb, and run a 3/8" drill bit to clean out the EGR passages. Mine picked up a lot of power with that, and I started running 87 octane again, with no pinging. The 307-Y likes EGR. This engine (ECM Program?) is VERY sensitive to EGR.

Remove carb, run a long 3/8" drill bit down the EGR tubes, drill out the carbon. If really bad, remove EGR valve and run a piano wire through the passages. You can remove the EGR tubes and clean them that way as well. You will see the build up.

My 307 ran MUCH better after I cleared the passages. Of all things, EGR to help power!




Engines: Oldsmobile V8s:
Differences between 5A and 6A/7A heads

Three types of cylinder heads were installed from the factory on the 307s with codes of 5A, 6A, and 7A. The 6A heads are fairly rare, but they are out there on some mid-'80s 307s (all with roller cams). Because they are so hard to find and rarely used, they will not be covered in this manual.

The 5A head is of a conventional Oldsmobile design, with large rectangular ports (about 1.3" wide by 2.0" tall). The combustion chambers are 67 cc and valve sizes are 1.75" intake and 1.50" exhaust. By comparison, the 7A heads have square intake ports (about 1.3" square) with 64 cc combustion chambers. Valve sizes are the same as the 5A heads'. The chart below outlines the differences between the two heads:

Head Code: 5A

Head Code: 7A

Combustion Chamber Size

67 cubic centimeters

64 cubic centimeters

Port Size

1.30" x 2.03"

1.30" x 1.30"

Valve Size, Intake

1.75" diameter

1.75" diameter

Valve Size, Exhaust

1.50" diameter

1.50" diameter

On paper, the 7A heads may seem like junk, good only as boat anchors. And from a racing standpoint, that is largely true. However, they do offer characteristics that the 5A heads just cannot give.

The intake ports on the 7A heads are "swirled", and smaller than conventional ports, which equates to lower overall flow, but higher velocities than normal ports offer. Higher velocities results in higher torque output and increased atomization of fuel, especially when cold. In fact, the 7A 307 engines are rated at 10 more lb*ft than the 5A engines are. Drive ability is markedly better with 7A heads than 5A heads -- it almost feels as smooth as fuel-injection!



Engines: Oldsmobile V8s:
Differences between the Y and 9 engines

A total of four basic Oldsmobile 307 engines were installed in Oldsmobile G-bodies. Early engines had regular flat hydraulic lifters and later engines used roller lifters with shorter pushrods and matching camshaft. There are also performance versions of both types. The chart below outlines the model years each type of engine was used:


Y Heads

Y Intake

9 Heads

9 Intake




































"hyd" = Hydraulic camshaft/lifters
"rlr" = Roller camshaft/lifters

There are surprisingly few differences between the Y and 9 engines. The camshaft and dual-snorkel air cleaner are the only power "adders" in the engine and the rest of the part differences are in place to allow for higher rpm use the 9 engines will most likely see. Below is a chart which outlines these parts:

Part Description

GM Part Number (not verified)

Long duration camshaft


High-rate valve springs


Harmonic balancer


Rochester Q-jet carburetor

17083553 (and 17084553)

Dual-snorkel air cleaner assembly


Intermediate exhaust pipe (y-pipe)


Muffler/tailpipe right


Muffler/tailpipe left


Higher stall converter


The 307-9 spends much more time in the upper rpm band than the Y versions do because of the rear axle ratio. All Hurst/Olds and 442 models got an 8.5" (except for 1983, which had a 7.5") ring gear which had a ratio of 3.73:1 with the pinion gear. This gear was a big part of the performance of these cars. The 307-9 versions are rated at 30 horsepower more than the Y and 5 lb*ft fewer than the Y (likely due to the camshaft).




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'll 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.


A special thanks to www.OldsGMail.com for the information.