How An Apparent Vendatta Against Higher Performance Engines Undermined Engine Development at PONTIAC

A sad tale of how GM stinginess may have cost in added pollution and fuel consumption, owing to some sort of apparent strange vendetta against Pontiac Motor Division's improved engine development

Pontiac had the supreme advantage by the later 1960s, with the debut of its rendering of GM's awesome 1968-1972 A body intermediates, specifically with its endura body colored front bumber available strictly upon its GTO.

 

The development of the overhead valve Pontiac V-8, initially debut for the 1955 model year, with its 4.62" bore spacings, had advanced to the point of its 389 cid V-8 which debut for the 1959 model year, received a larger bore for model year 1967, bringing its displacement with a 3.75" stroke to 400 cid.  Due to the higher emissions of the "closed" chamber cylinder heads, such as the 1967 "670" - Pontiac engineers introduced their "open" chamber cylinder heads for model year 1968, significantly reducing particle emissions.

 

In pursuit of greater performance, Pontiac engineers embarked upon two separate paths of cylinder head development- the round exhaust port Ram Air II, and the more radical Ram Air V- the latter with a revised exhaust port arrangement to no longer have the center two ports directly next to each other (good), though changing the firing order, therefore requiring altogether different camshaft sets.  But alas the RAV had tremendously oversized intake ports, rendering it largely impractical with inferior throttle response, and was thus never released as a factory installation.

 

The Ram Air II cylinder heads were a quite decent design, good enough to evolve as the Ram Air IV.  The Ram Air II came as a 400 cid, debuting spring 1968 in the intermediate sized GTO and the compact sized Firebird.  The Ram Air II would be super-ceeded by the Ram Air IV for model year 1969, again in the GTO and Firebird.  And for 1970, again in the GTO, as well as the new for 1970 1/2 Firebird Trans Am (and plausibly the Firebird Formula, though apparently non were ordered nor built- with the RAIV weirdly not appearing in the 1970 1/2 Firebird factory literature.

Alas, both the 1968 1/2 Ram Air II and the 1969-70 Ram Air IV were hobbled by a ridiculous mandatory rear differential ration of 3.90, and an even worse option of a ratio of 4.33- essentially tractor gears giving quite poor fuel economy and excessive engine revs at freeway speeds.  Why so?  Because the engineers selected a cam shaft with incredibly excessive valve timing duration of 308 and 320 degrees respectively intake and exhaust, great for higher revs, but terrible for slower revs.  So worse fuel efficiency with greater emissions.  And due to the excessive gearing, combined with GM's insane stinginess of refusing to provide Pontiac with FORGED rather than cast connecting rods, these engines were a warranty nightmare.  So for 1970, Pontiac sought to produce a Ram Air IV with better durability.  So the plan was to start producing the Ram Air IV with the improved more durable bottom end - forged rods, crankshaft and stronger engine block of the Ram Air V; of particular note being the RAV's improved design 400 cid engine block, so improved with its integral additional lifter valley, for securing the lifter lobes (the part that activates the pushrods which transmit the motion from the cam lobes to the valves).  By doing so, that is making the engine block's lifter lobes stronger, it becomes way more practical to develop somewhat steeper opening cam lobes, for greater engine efficiency (reduced emissions with greater power and fuel efficiency).

GM would of course block what we could call the "RAV 4" - that is, the improved bottom end of the Ram Air V, combined with the eminently more sensible Ram Air IV upper end.  GM would be too stingy to give Pontiac forged steel connecting rods and crankshafts, as such had to be devoted simply to its favored division Chevrolet.  But what about the stronger block?  Unlike the forged rods and crankshaft, the stronger block represented ZERO added cost, or what, perhaps 5 cent of extra cast iron per unit?  The development and tooling was already paid for.  So why not simply make the RAV engine block the standard issue?

 

Nope.  Instead, of utilizing the already paid for research and development of the RAV block, GM has Pontiac again redesigns its 400 cid block, changing from a one year only 979914 block for 1970 (which lacks the added lifter lobe valley cross ribbing), to a new block for model year 1971, the 481988 block (which also lacks the added cross ribbing).  It is a decent block, but why so develop yet another block that lacks the added cross ribbing, rather than use what was already researched and developed?

Nonetheless, intelligent minds within Pontiac prevail to establish such an improved stronger block with the development of the SD 455.  Due to the indisputably insane April 1970 dictate by upper level corporate GM management to lower engine compression ratios all the way down to about 8 to 1 (down from 9.5- 10.5 to 1), Pontiac shifted its development from the 400 cid engine to the 455 engine.  The reason given for this was to lower NOX emissions, nevermind that drastically increased CO and HC emissions, and resulting in automobiles getting 8 mpg instead of 13 mpg, while being able to use lower grade gasoline.  Hence we got such poorly tuned engines for 1971-72, such as what occurred with a road test by High Performance Cars during 1972, with a 455HO Firebird Trans Am, with a 4 speed manual and a 3.42 differential reportedly getting 5 to 8 mpg! 

The SD455 was essentially an improved version of the 455HO.  Representing a labor of love by Pontiac engine development, it was found to have considerably better fuel economy than the 455HO, at least according to a Spring 1973 SD455 Firebird Trans Am road test report by Car & Driver magazine, reportedly 13 mpg, as well as accounts of a model year 1973 preview caravan of Pontiac models, with the SD455 equipped automobile yielding that fleets 2nd best fuel economy.

People can read up more about the SD455 story in numerous places elsewhere.

The SD455 did have the integral cast additional lifter bore reinforcements.  Yet sadly the SD455 engine block was not only not adopted as the standard block, it was discontinued along with the SD455 engine by mid 1974.

Can we dare estimate the loss of potential engine efficiency, made possible with developing more efficient camshaft lobes, denied by corporate GM's failure to include the added lifter lobe strength?

 

How much extra automobile exhaust and extra fuel consumption did such a move so result?