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OHC heads for Small Block Chevy?!?!?

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Overhead cam and multi valve heads used on traditional domestic V-8s! Seems like an interesting topic of discussion, yet not seen on this forum with any sort of depth or seriousness that aI was able to uncover.

I recently stumbled across a pic of the Moser SBC DOHC heads and like the younger generation of today, was immediately distracted and dropped everything else I supposed to be doing at the moment to dig little deeper, for no other reason than curiosity…

In searching this forum I would’ve bet money this topic had been covered to some degree in the past but couldn’t find anything with any real substance. (Possibly my search techniques genuinely suck, which I’m sure someone will exploit...) :wink:


I'll start out with the probably the most well known of aftermarket offered traditional V-8 OHC heads, the Moser/Harvey Crane Jr, DOHC heads!

DOHC cam, 4 valves per cylinder heads for the SBC short block. Dyno tested to as much as 11,000 RPM back in 1970! :shock:


Mr Richard Moser bio;



Harvey Crane Jr, was instrumental in the development of these heads;



The HotRod magazine article, 4 pages worth;














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Next up, I stumbled across this very interesting concoction using the vintage small journal SBC 265, (road draft crank case breather system). :wink:

Has all the appearance of DIY from a small shop/garage. Like it! :2thumbs:

Note the cool cam oiling.


Anyone, (TonyD,) have any info/history on this set up? Possibly some old school Bonneville or drag race effort?









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I am getting wood over the vintage engine. Oooooh so badly it is desired...


The Moser is neat, but not in the same way the second one is!


My preference runs to Schubeck's DOHC Efforts. If you see it, you will see why.





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Look under the valve cover on the link I gave.


Look closely...




Rocker actuated valves vs direct actuation?

Pseudo hydraulic-mechanical lash adjustment system, hydraulic lifters adjusted with a .002" clearance for NO lifter preload, effectively eliminating any lifter pump up at elevated RPM's?

Edited by BRAAP
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Are these "just" DOHC, or do they use some form of variable-valve timing? One suspects that the better modern aftermarket conventional-style OHV heads outflow most of the 4-valve DOHC exotics. And the engine rpm is probably more limited by bottom-end stability than by the valvetrain. Maybe 4-valves offer mid-lift flow advantages because the valve curtain area is larger for the same valve lift? Do 4-valve heads have a combustion chamber advantages over canted-valve 2-valve chambers?


On a related note, what about multi-valve cam-in-block schemes? The advantage is short timing chain, compact design, no need to disturb the timing chain when removing the heads... but lower valve mass and possible combustion chamber advantages.

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a really well designed and properly manufactured 4 valve single or double overhead cam head could easily boost the hp potential of the chevy v8 engines a great deal.












2: 1.84 In. valves BB Chevy Intake Ports

BB 32v. 2: 1.840 IN. valves Pontiac Pro Stock 2.38 In. valve

0.1 94.4 0.1 70.8

0.2 206.5 0.2 147.5

0.3 312.7 0.3 230.1

0.4 375.24 0.4 277.3

0.5 448.4 0.5 342.2

0.6 472 0.6 395.3

0.7 494.42 0.7 436.6

0.8 494.42 0.8 448.4

2: 1.6 Ex. valves BB Chevy Exhaust Ports

BB 32v. 2: !.6 EX. valves Pontiac Pro Stock ! o Stock 1.9 Ex. valve

0.1 88.5 0.1 59

0.2 182.9 0.2 118

0.3 259.6 0.3 182.9

0.4 318.6 0.4 241.9

0.5 381.14 0.5 300.9

0.6 424.8 0.6 330.4

0.7 430.7 0.7 342.2

0.8 430.7 0.8 344.56














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Look under the valve cover on the link I gave.


Look closely...




Rocker actuated valves vs direct actuation?

Pseudo hydraulic-mechanical lash adjustment system, hydraulic lifters adjusted with a .002" clearance for NO lifter preload, effectively eliminating any lifter pump up at elevated RPM's?


The most mind-bogglingly supercool mega-awesome awesome awesome thing *I* saw about that engine was the cam drive/timing system as compared to the accessory drive system.


I cannot ruin it for you; you have to go back and look yourself.

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What is the technical advantage of double overhead cam engines? The newest corvette engine gets very good power with a Gen IV pushrod engine.


In the most basic sense, SOHC vs the in block design of a 2 valve head, advantages of OHC is more direct valve actuation with the possibilty of lighter weight valve train, at least as seen by the cam lobe. :wink:


Disadvantages are, for a V- engine, is the added overall wieght of an additional camshaft or 3 depending if it is SOHC or DOHC design, overal CG of the engine is higher with the cams being up on top of the engine, and common designs are taller and most of the time wider making the overall powerplant package physically larger, (modern Ford OHC V-8's are a good example of this).


Outside of that within the 2 valve constraints, OHC advantges are not very large and also carry just as many not large disadvantages as well. As you pointed out, GM is still succesfully employing the single in block push rod 2 valve design in some of the worlds most powerful and best performing cars in the world, Vette Z-06 and ZR-1. :2thumbs:


Where OHC really starts to shine is when utilizing multi valve technology vs the 2 valve. Valve area per CID is much greater allowing for greater breathing, (combustion chamber roof is more vale than head material allowing the cylinder to breathe easier with less aggressive cam timng vs a comparable 2 valve design). Now with seperate intake and exhaust cams, fine tuning of the intake valve timing independant of the exhaust valve timing can be accomplished, and add to that real time variable cam phasing of the seperate cams, a very broad power band can be had while maintaining decent economy and mileage. :2thumbs:

Edited by BRAAP
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I'd like to have a set of those Arao heads! I think that there is much room left in developing multivalve, pushrod engines. They flow quite a bit more on the top end, and the force of having to move the pushrod and rocker, etc back on a valve closing event would be shared over two separate sets of valve springs meaning that the valve spring tension wouldn't have to be so astronomical and they could rev higher!

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