Inliners International Forums General Discussion Hi Performance Thinking out loud: rod ratios and intake velocity

It's late and I let my mind wander.

Got to thinking, if we were to run shorter rods to increase piston speed, would that help with the poor intake velocity in the 230-250-292 engines? They are not high rpm friendly engines anyways, and the problem (I would assume) is most prevalent at low and mid rpms. Wouldn't you get a snappier suction on intake stroke, helping drive velocity up? And throw in a cam designed to support it, as well as CR... I'm curious to know if anyone tried something like this.

Any engine built with the wrong components will exhibit those characteristics. Its not really a common trait for these engines as you mention, with the right stuff.

Most contemporary inlines have ports that are too small for performance applications.

If you use a shorter rod port velocity near TDC will increase more quickly and lead to meeting the ports limitations of flow sooner thereby making the engine even less efficient as speed increases. Its the wrong way to go.

As a correllary to that decades ago when drag racers built tiny displacement SBCs and other small V8 engines in the 220 to 265 cid range for the lower Gasser and Modified classes they(we) often used shorter rods and heads with ports sized for the larger 327- and 350-sized engines just to get the mixture moving more quickly down the oversized inlet tract. Just the opposite of our dilema with too-small ports.

Harley did the same thing in 1968 - the flathead 45" KR motor's ports were really big, so they made a 1" shorter rod set to speed up the vacuum cycle.