1968 Pontiac GTO

[DeuceCoupe]

Originally Posted by Paul Ceasrine

Gene,

The main performance items in the 400/366 HP 'Ram Air II',,,

Cylinder Heads
* Casting #96
* Had larger intake ports, and re-designed round-shaped exhaust ports.
* Intake port volume (155 cc),,,,,,Exhaust port volume (162 cc)
* Combustion chambers 72 cc. ('spherized design' w/ shallow combustion chamber)
* Tulip-head shaped valves (2.11 intake / 1.77 exhaust) Extended length (5.20")
* Spiral-polished valves
* Dual high-rate valve springs
* Valve spring height (1.776")
* 11/32" Push-rod guide-plates
* 11/32" Push-rods (High-strength)
* 7/16" Rocker-arm studs
* 'D'-shaped port exhaust manifolds

* Note: The #96 casting heads are considered to have the best exhaust ports of the 400 heads.

Camshaft
* Code # "041"
* .491/.486 lift,,, 308*/320* duration,,, 115* Center-line,,, 87* Overlap

Note: The first computer-designed camshaft.

Carburetor
* Rochester #7028273
* 750 CFM
* Re-jetted, w/larger #42 Main Rod

Distributor
* Revised curve
* Hardened drive-gear

General Analysis:
The 366 HP 'Ram Air II' had a hell of a lot more than only 6 Horsepower more than
the '360 HP Ram Air I'.

"The 366 HP 'Ram Air II' had a hell of a lot more than only 6 Horsepower more than the '360 HP Ram Air I'"

I'm still learning and Gonkulating these combos but no doubt about THAT.
So far the Gonkulator is telling me that (refreshingly) the 400 GTO engines tended to be rated pretty close to their actual gross HP (iron manifolds, open exhaust, 60F 29.92 dry sea level air, no accessories).

Note that under that standard Gross HP definition of the 1960s, Ram Air adds ZERO gross HP - since all engines are dyno rated with 60F air into the carb. Ram Air adds NET HP, which is not how they were rated in the 1960s.

Of course that Gross HP varied a little since so many cams were used.
So far, a certain rough set of numbers comes out of the Gonkulator. These are NOT factory ratings, they're computed from my own Gonkulator model, based on flow, dyno data, etc. About +/- 3% typically.

335hp 066cam, log exhaust
340hp 067cam, log exhaust
344hp 068cam, log exhaust

347hp 067cam, HO/RA exhaust iron
358hp 068cam
370hp 744cam

394hp Ram Air II (041cam, heads, RA exhaust)
424hp Ram Air IV (041cam, 1.65RR, heads, RA exhaust, alum intake)

Note I can't distinguish between the RA1 and RA3 - is that about right?
RA1=360hp, RA3=366hp, but are the head flows etc really any different?
Comments welcome on all this!!

"Note: The #96 casting heads are considered to have the best exhaust ports of the 400 heads."

Well we can't ask Paul about that comment but he must have got it from somewhere. I've searched quite a bit for cylinder head EXHAUST FLOW - very hard to find especially on the #96 RamAir II heads.

I'm trying to compare factory exhaust flow, from the D-Ports vs RA2 vs RA4 (and even 455HO and 455SD) heads. Anybody know?