Re: What ended the flathead engine?

Posted by RN on July 23, 2007 at 11:58:11 from (69.130.240.76):

In Reply to: What ended the flathead engine? posted by Sunny 4 acres on July 22, 2007 at 18:52:30:

Memories of 1937 ULH Harley, 1948 Ford sedan, 1960s G HD and KHK, WRs. Flatheads had a breathing restriction over 4000 rpm- the 180 turn from intake into cylinder- but had less valve train mass compared to pushrod engines so cam profiles could be quicker opening. Heating problems noted on Ford V8 - 6 cylinder inline didn't have exhaust crossing middle of cylinder bank and water jacket on exhaust manifold would help cool- still used on marine engines. Pollution laws getting some but a dual spark plug, HEI type ignition, lean fuel mix, and improved rings and slightly tighter piston/cylinder clearance can get through most emission laws now- may not in future. Flatheads were a compact engine design, when Chrysler went to OHV 6 in late 60s to replace flathead they had to slant the engine to fit in car body designed for flathead engine- the 'slant six'. 7 to 1 compression with a slant popup piston, relieved block at valve area and 90 octane gas was working fair, 6 to 1 or so with 80 octane gas common- Ford 9N was about that. Engine casting of a simple block and a small OHC head now a bit cheaper than casting multi cylinder block with valve design next to cylinders and simple head- especially if engine expected to run to 6000 rpm. some OHC Jap engines running 8000 rpm and short runs higher. HD KRs could hit 6000 rpm easily, pulled about 1hp per cubic inch- 45- for class C racing, but these were running high octane leaded fuel and were getting toward limit of design. RN

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