|
|
|
|
Original Message
|
| Small runner FE heads first appeared in 1966. |
| By Dave Shoe - 03/20/2002 5:24:10 PM; IP 12.2.11.131 |
The beginning of the 1966 model year marked a major change for FE production heads.
The very first small runner "velocity" heads appeared at the start of 1966 as a consequence of new emissions legislation. Prior to this, zero FEs got small-runner heads. Period. They didn't yet exist. Screw the misleading or erroneous literature that says otherwise.
The smaller runners and more aerodynamically shaped valve pockets of the new design allowed for efficient, powerful combustion at low RPMs, with some performance sacrifice at the higher RPMs.
Prior to 1966, every production FE engine had large runners. The CJ head simply inherited this 1958-65 runner design. Note that there was also an emissions "transition" head with only partial emissions mods in 1966-67 known as the C6AE-R which could be found randomly in any FE engine - there was about a 1-in-3 chance you'd find a C6AE-R large-runner head in your car or light truck these years. These had large runners just like earlier heads, too. All other heads in 1966-67 were all small "velocity" runners. By 1968 the C6AE-R was history, small runners were the norm, though the 427hyd and 428CJ would carry the old large-runner tradition into the '70s.
Recognize that all 428CJ heads, as well as 427LR heads, were cast to fit regular 2.03/1.55 valves. The cast heads were dressed out with a cutter to fit CJ valves. This makes CJ heads nothing more than 1959 332CID heads except they have stiffer valve springs, oversized valves, four extra bosses to fit exhaust gas reaction tubes, and eight extra bosses to fit Fairlane/Mustang exhaust manifolds, if required (this was another new feature in all 1966-later heads).
Since the 1959-1965 heads do not have restrictive thermactor bumps cast into them (which also first appeared in all 1966-later FE heads), a set of CJ valves will actually make these early heads flow better than stock CJ heads.
The magic of the CJ, however, is in the free-flowing intake manifold design. The MR/PI/CJ design was not available in the earlier years of the FE, so you'd never see CJ-type performance in an early 390.
As for the rationale of the machined chambers during the first three months of production, the idea was that equal chambers would provide for smooth engine operation, and would also allow maximizing the compression ratio because the combustion chamber size would be known nearly exactly. Unfortunately, the compressions were set for the planned octanes of the day, and these octane ratings were sometimes exaggerated. Because some gas failed to meet the rated octane at the pump, Ford was getting too many complaints about pinging. The extra cost was not worth it. Ford increased the combustion chamber size to reduce compression, and in doing so, they no longer needed to machine the chamber to an exact volume, saving money.
JMO,
Shoe. |
|
|
This thread, so far...
|
|
|
|
Post A Response
|
|
|
|
|
|