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430 and 455 Cylinder Heads

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Normally, in taking about cylinder head improvements, the conversation usually gets into head flow and porting to better achieve improved cylinder filling.  This is important, but for increased efficiency and power, "combustion dynamics" than come into play.  I have watched several of David Vizard's recent videos on "quench" as a part of combustion dynamics.  Plus other things related to combustion chamber shapes between the quench pad and the exhaust valve.


From posts in the BCA Forums, I have determined that the Buick 430 engine was apparently a "sweet spot" engines with great highway fuel economy and good power.  But when the compression ratio was decreased and the bore size increased, something got "out of whack" as to the earlier "sweet spot" of things.


Has anyone done any significant combustion chamber re-shaping and combined that with particular piston crown shapes, to get the CR back into the nines?


Just curious,


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My understanding is that higher compression (within reason) improves gasoline engine efficiency.  So, comparing a 'high compression' 430 (10.25:1) to a '71 or later 455 is a bit unfair.  The larger displacement of the 455 helps compensate for lower compression as compared with a 430, however, the larger displacement requires more fuel to maintain stoichiometry.  An 'apples-to-apples' comparison would be the 430 against a 1970 455 (10.0:1).  In that case, Buick did claim a horsepower increase for the 455 over the 430 (370 vs. 360).  So, theoretically that 455 could be as efficient if the driver is able to use only enough throttle to match the highway speed of a 430-equipped car (assuming both need the same HP to maintain a given speed).



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When the engines were in development and production, larger generally meant more horsepower and torque.  Just from more air/fuel mix getting ingested and fired.  In more recent times, we have seen smaller naturally-aspirated engines make more power than the prior engines did.  It is that kind of dynamics which I suspect will go beyond what is normally considered as "good".  Bigger ports can work, but then what happens once the spark plug is ignited, completes the cycle. 


Yet we know that big ports are not always the answer.  Maybe for top-rpm dyno horsepower, but not so well for 3000rpm torque, usually.  I have also observed that most of the current high-horsepower engines usually have a bore diameter of approx 4", which relates to the burn time of the mixture.  As if the 4" bore size coincides with all of the fuel which can be burned efficiently with each spark produced, no matter the brand?


One thing which seemed to hurt the "emissions engines" was their lowered CR.  In the case of the Chrysler open chamber heads for 383s, 400s, and 440s with the open chamber heads, as with other similar heads from other makers, some piston manufacturers sought to get back some performance with "quench dome" pistons.  Pistons with a specifically-placed raised area to effectively make the open chamber heads into a closed chamber head with more quench and more chamber turbulence as a result.  Perhaps such pistons might be what the 455 chambers need?  THEN add in a good plateau honing job with "MM" piston rings for even better power output


In reading about the glowing reports of the HC 430s in Electras that would get 20mpg on the road, but with the later 455s it seemed that that suddenly dropped to the 12-13mpg range, by observation.  Driving 55mph might have increased that a bit, but still a lot of mpg loss with only 25cid difference in engine size.  A lot even for sub-optimal spark timing calibrations, too.  One factor that could be at play is the QJet carb, as it seemed that at some air flow levels, the triple-booster primary venturi became super-efficient as to fuel metering, which helped some engines get outstanding highway fuel efficiency, but that seemed to not be universally true from reading road tests of the later 1960s.


I have been curious as to what a modern EFI TBI fuel system, letting the EFI controller run the ignition system calibrations might increase fuel economy (by itself), but making the combustion chamber more efficient in the process might result in enough additional mpg increases to start to make the EFI system worth the price?


Other than engine efficiency, obviously a '67 Electra is more aerodynamic than a '73 Electra, which can count for about 2-3mpg on themore-level roads.  A cruise situation where vehicle weight is not that critical, unlike in acceleration situations or hilly terrains.


As much as has been learned from modern port flow/combustion chamber dynamics/valve lift dynamics with later-model Chevrolet heads, I'm curious how applying such evolutionary discoveries to a 455 Buick head might make it better in the process?  With the added benefits of more efficient power production and decreased fuel consumption at the same time.  I somewhat doubt that anybody without "5 mile deep" pockets might get excited about funding such research, but it's still something to think about, to me.  Another "idle time" "What if . . ." situation.


Just some thoughts,




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