Closed Chamber Heads

quote:

Originally posted by 22 Racer:

If I want to have an original appearance and the highest performance, are these heads the best way to go?

First, I hope your dieseling problem has been resolved, and the motor is now running fine on 91 octane fuel.

The part number "AE 3713 877126 32001" doesn't help me identify the heads.

I know you own a 1972 Pre-L Pantera, which would normally have a 1972 Cobra Jet motor in it, but I don't know if its equipped with the original motor or a replacement. So lets start from scratch, assume nothing, and cover the 3 best choices in stock appearing cylinder heads.

(1) If the motor in your Pantera is of the 1973/1974 variety, originally rated for 8.0:1 compression, and is still equipped with the dished pistons, the Australian 302C heads with 58cc combustion chambers is the most reasonable way to bring the compression up to around 9.9:1. Those heads have ARD1AE casting numbers. They have the small ports and small valves, but they aren't bad performers. Some guys like the lower rpm performance these heads provide to a motor better than the lower rpm performance the big port 4V vaiety of head provides to a motor. If the motor had dished pistons, these are the heads Jerry most likely installed. If these heads were installed on a motor with flat top pistons the compression ratio would be set at 10.4:1, which is a bit high for a typical street motor, but that much compression is actually a good match if the motor has a hot cam installed in it.

(2) If your Pantera's motor is equipped with flat top pistons the 1970/1971 variety 4V cylinder heads, casting numbers D0AE or D1AE, having either 63cc combustion chambers (D0AE) or 66cc combustion chambers (D1AE) will set the compression ratio at about 9.8:1 or 9.5:1 respectively, and that can be brought up to 10.0:1 with just a little bit of milling (0.012" to 0.030"). These are big port and big valve heads that can provide a motor with thoroughly good low rpm performance when used with the right cam, and the top end rush of a motor equipped with these heads is intoxicating and hard to beat.

(3) Scott Cook of Australia manufactures alloy heads and a matching alloy intake manifold that look identicle to the original castings externally, if you paint them Ford blue nobody would recognize them as aftermarket parts. The ports and combustion chambers of the heads, and the plenum and runners of the manifold, have been designed by Darin Morgan of Reher Morrison Racing Engines. He's recognized as a top authority on the subject of induction system design. This induction system would update your Pantera's motor with the most up to date technology, and is worth about 70 additional horsepower compared to unported 4V heads. The high swirl combustion chamber volume is 60cc, which would set the compression ratio of a motor with flat top pistons at 10.1:1. Scott's dual plane manifold amazingly gives single plane manfolds a run for their money at high rpm, while providing better response at low rpm; and the full height plenum provides the best possible manifold vacuum.

-G

quote:

72 Pantera #3939 production date 7/72

George: Does this shed any light on what motor I have? I have invoices for replacing the cam,lifters, intake, & carb, but nothing about the pistons being changed so I'm assuming they're original.

If your Pantera is still equipped with the original short block then its a 1972 variety Cobra Jet motor (Q code motor). It was originally equipped with a 750 cfm Motorcraft 4300D carburetor, open chamber 4V heads with the large 2.19” intake valves, and 75.4cc combustion chambers (D2ZE castings). The motor was also equipped with flat top cast pistons having two valve reliefs which set the compression ratio at 8.6:1. The hydraulic cobra jet cam lifted the intake valves 0.481”. It was rated for 266 net horsepower, but the same motor was rated at 280 gross horsepower the year before.

George: Considering the motor I have can you answer the following: What did the compression ratio get bumped up to with the closed chamber heads? How much did the horse power increase with the closed chamber heads. In your opinion, should I be able to run pump premium fuel with the higher compression brought on by the closed chamber heads.

We haven't figured out which heads are installed on your Pantera's motor, there's three possibilities:

ARD1AE head castings (Australian 302C)
new compression ratio = 10.4:1
additional horsepower = 15 bhp minimum

D0AE head castings (1970 M code)
new compression ratio = 9.8:1
additional horsepower = 10 bhp minimum

D1AE head castings (1971 M code & Boss 351)
new compression ratio = 9.5:1
additional horsepower = 8 bhp minimum

The minimum horsepower increases "assumed" there were no other changes to the motor (such as the camshaft), the heads weren't milled, and the motor had 8.6:1 compression before the heads were swapped.

I normally didn't just bolt heads on as-is, it was my custom to mill the heads to achieve a 10.0:1 compression ratio. I have a rule of thumb, taking a 8.0:1 motor to 10.0:1 will result in a 20 bhp minimum increase; taking a 8.6:1 motor to 10.0:1 will result in a 12 bhp minimum increase. A head swap on a Cobra Jet motor was usually accompanied by advancing the camshaft timing, Boss 351 valve springs, Boss 351 crankshaft damper, plus re-tuning the carb and ignition. That was a 320 bhp motor equipped with the factory cast iron exhaust manifolds; headers and good mufflers brought that up to a solid 350 bhp. And contrary to modern sensibilities, that is quite a powerful motor.

Even though Ford advertised the compression ratio of the early 351C 4V motors at 11.0:1 in 1970 and 10.7:1 in 1971, the actual compression ratios were 9.8:1 and 9.5:1, respectively. Its hard for some to believe, but Ford lied that much.

The compression ratio numbers I've quoted are "static compression ratio". The number that actually impacts the performance of a motor is the "dynamic compression ratio". Among the variables that alter the dynamic compression ratio is the point at which the intake valve closes as the piston is rising to compress the air/fuel mixture. The later the valve closes, the lower the dynamic compression ratio. It should be obvious that the camshaft specs heavily influence dynamic compression ratio, power output and the octane of the fuel required by the motor.

It is my experience the last 40 years that a Cleveland motor with 10.0:1 static compression, equipped with a camshaft that closes the intake valve around 70° ABDC, has a dynamic compression ratio of around 7.66:1 and will operate on 91 octane fuel quite readily, with a reasonable margin of safety. 10.0:1 is actually a conservative compression ratio for the 351C running on 91 octane pump fuel.

Among the benefits of swapping to quench chamber heads is an increase in mixture turbulence within the combustion chamber at low rpm and therefore an improvement in low rpm torque. This is felt as a little extra "kick" or improved throttle response at low rpm.

You can "hear" increases in compression ratio as a louder "pop" in the Cleveland's exhaust note when the exhaust valve opens. It sounds more "angry". The charging rhino snorts louder. Puts a smile on my face. Sound of a Charging Rhino

-G

here's something that helped me to identify my heads ....

http://351cleveland.wetpaint.c...der+Head+Spreadsheet

Philippe