CampStewart
Observer
did a gypsy hypnotize you and put you up to this?
Unicorn: a 4 Valve Head Pushrod Engine
- Thread starter nicholastanguma
- Start date
nicholastanguma
New York City
Interestingly, the aftermarket does provide a 4 valve LS head...and attaches a DOHC valvetrain to it. From Mercury Racing. Not really a LS in spirit anymore, methinks, but that's just an opinion.
All of Mecury racing's engines are 4V, and boat motors need a lot of torque down low. Wierd LOL. Of course the blowers help with that.
CampStewart
Observer
And that is where OHC really pulls away from pushrods due to valve float.
Reduced mass is the big advantage. With less reciprocating mass you can use lighter springs and longevity goes way up along with perfomance. Pneumatic valve springs is where it's at. Or the freevalve.
On a side note, anybody remember the Coates spherical valve head?
Buliwyf
Viking with a Hammer
Reliable 1000 horsepower from a 3.0l v12.
50% thermal efficiency from the modern 1.6l v6 used in F1.
A 450cc dirtbike that can jump over a Boeing 747 (parked).
Nearly 500hp and 1000tq from a 6.7l diesel that meets retarded EPA specs.
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nicholastanguma
New York City
This is exactly my point. Even without forced induction a 4 valve head breathes better than a 2 valve head, even when that 2 valve head breathes fabulously well. At this point I'm almost certain that GM went with 2 valves simply because of manufacturing cost being more affordable than 4 valves.
Thank you all for your varied insights and opinions. I think my question has been well answered now, and I'm pretty comfortable with my idea that a pushrod mill with 4 valve heads would indeed be the "best" streetable configuration for mechanical simplicity, dimensional compactness, and idle-to-redline power.
Of interesting note: I think a 4 valve head also helps compact an engine's dimensions more than a 2 valve head, as well. Admittedly, perhaps this only pragmatically applies to motorcycles, where measurements between engine rocker boxes and frame backbones/fuel tanks is at a premium, often tight by mere centimeters of space. Back in the '90s when the Fueling 4 valve heads were available for Harley-Davidson Evolution powerplants they were a bolt-on affair in place of the factory 2 valve heads...and despite their extra valves and commensurate extra performance came in at .25" shorter in height than OEM heads.
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javajoe79
Fabricator
yup. I remember the adds in car mags.
javajoe79
Fabricator
None of those apply here though. I’m not trying to say nothing is better than a 2v pushrod engine. To the OP’s point, complicating a simple engine like an LS or other pushrod 2v engines, takes away part of what makes them great. Maybe you’ll gain a little here or there but at a cost and you probably don’t need it.
javajoe79
Fabricator
Exactly. Why complicate it and add more expense when you don’t need to?
Mechanical simplicity? No. Again though, unnecessary. If it was necessary, gm would sell them like that or they would be a common aftermarket option.
This could easily be from an unrelated difference between the two engines though. Thinner castings for the valve covers or even a tighter fitted casting, valve angles on those particular heads, etc
toylandcruiser
Expedition Leader
toylandcruiser
Expedition Leader
How is an ohc more complex? It has less moving parts.
85_Ranger4x4
Well-known member
If it is a V type engine greatly complicates an engine bay though, especially one not designed for said engine.
Pushrod/OHC/DOHC inlines are kind of a "who cares" thing as far as footprint, the width difference isn't a big deal.