Editing Ford 335 engine (section)

===Cylinder heads===
The cylinder-head design for the 335 series engines is its most definitive design feature. All cylinder head variants were two-valve that use large free flowing ports with poly-angle or 'canted' valves.<ref name="V8Workshop"/> Having the intake and exhaust valves at separate angles allowed for very large valves to be used while reducing the port length and minimizing sharp turns within it,<ref name="Pantera">{{cite web|last1=Pence|first1=George|title=The 351 Cleveland Cylinder Head|url=http://pantera.infopop.cc/eve/forums/a/tpc/f/5650045562/m/4131047336|website=Pantera International|access-date=1 June 2014}}</ref> creating freer flowing heads than the Ford small block V8s.<ref name="351CHeads">{{cite web|title=351C heads|url=http://home.comcast.net/~jelerath/mustang/Specs/heads-fr.html|access-date=1 June 2014|url-status=dead|archive-url=https://web.archive.org/web/20131224193845/http://home.comcast.net/~jelerath/mustang/Specs/heads-fr.html|archive-date=24 December 2013}}</ref>

The 335-series engines used different cylinder heads for two and four barrel carburetors. The '''2V''' (two carburetor venturi) small port cylinder heads were used on 2-barrel engines while the '''4V''' (four venturi) large port cylinder heads were used on the 4-barrel engines.<ref name="CC 351C"/> The ports and valves on 2V heads were significantly larger than small block engines<ref name="351CHeads"/> and had excellent flow - actually slightly better than 4V heads at lower valve lifts.<ref name="CC 351C"/> The 4V heads had enormous ports which flowed very well, in particular at higher valve lift, and could out-flow Chevrolet Double Hump heads and Chrysler's high-performance 340 heads.<ref name="CC 351C"/> 

In addition to the two port sizes, the 335 cylinder heads used two style of combustion chambers, an open or a closed "quench" chamber. Both combustion chambers are very shallow, due to the shallow valve angles. The combustion chambers are almost a very shallow hemispherical chamber, rather than a wedge shaped.<ref name="CC 351C"/> The closed chamber heads enclose the valves more closely, reducing combustion chamber volume, to increase the compression ratio. However, both designs have the same [[thermal efficiency]] and resistance to detonation.<ref name="Pantera"/> The closed combustion chamber promotes better swirling of incoming air fuel mixture, giving it a low-rpm torque advantage, and requires less machining to obtain high compression ratios.<ref name="Pantera"/> However, the open chamber heads valves are less shrouded, which improves low lift airflow,<ref name="CC 351C"/> and they exhibit better emissions characteristics.<ref name="Cleveland"/><ref name="Pantera"/>

Most 335 series engines used stamped rocker arms with cast fulcrums that made for a non-adjustable valve train. The rocker arm design was originally used by the Ford 385 series engines.<ref name="CC 351C"/> However, the [[Ford_Mustang_variants#351|Boss 351]] and 351 HO had an adjustable valve train, using rocker arms mounted on screw-in studs and guide plates.<ref name="Cleveland"/><ref name="DIY Ford Valvetrain">{{cite web|title=Ford 351 Cleveland Performance Guide: Valvetrain|url=http://diyford.com/ford-351-cleveland-performance-guide-valvetrain/|website=DIY Ford|access-date=11 June 2014}}</ref>

Prior to the release of the 351C, the 335 Series cylinder head was used on the [[Ford Boss 302 engine]].<ref name="CC 351C"/> The Boss 302 used a large port closed chamber 4V cylinder head which required minor modifications to make the cylinder heads work with the 302 engine block.<ref name="Cleveland"/> The Boss 302 version of the cylinder heads used small 58cc cambers and large 2.23" intake valves. The valves were later reduced to 2.19" as used on the 351C 4V cylinder heads.<ref name="CC 351C"/>

{| class=wikitable align=center
|+'''335 Series V8 engine cylinder heads'''<ref name="Cleveland"/><ref name="V8Workshop"/><ref name="351CHeads"/>
|-
!Head type!!Chamber type!!Chamber volume!!Intake valve!!Exhaust valve!!Intake port!!Exhaust port||Application
|-
|2V||Open||74.7 - 79.9cc||2.04"||1.65"||2.02" x 1.65"||1.84"x1.38"||351C-2V, 351M, 400
|-
|4V||Closed||61.3 - 64.3cc||2.19"||1.71"||2.50" x 1.75"||2.00"x1.74"||1970 351C-4V
|-
|4V||Closed||64.6 - 67.6cc||2.19"||1.71"||2.50" x 1.75"||2.00"x1.74"||1971 351C-4V
|-
|Boss 351||Closed||64.6 - 67.6cc||2.19"||1.71"||2.50" x 1.75"||2.00"x1.74"||1971 Boss 351
|-
|351C-CJ||Open||73.9 - 76.9cc||2.19"||1.71"||2.50" x 1.75"||2.00"x1.74"||1971-72 351C-CJ
|-
|351C HO||Open||73.9 - 76.9cc||2.19"||1.71"||2.50" x 1.75"||2.00"x1.74"||1972 351C HO
|-
|351C-CJ||Open||73.9 - 76.9cc||2.04"||1.65"||2.50" x 1.75"||2.00"x1.74"||1973-74 351C-CJ
|-
|Australian 302C||Closed||56.4 - 59.4cc||2.04"||1.65"||2.02" x 1.65"||1.84"x1.38"||302C
|}