[DeTomaso] SPC - Do headers affect scavenging in individual cylinders?

[Daniel C Jones]

> Might be an argument for equal length 180 degree headers on an EFI motor.

Even on a 351C with equal intake tract lengths, header lengths, combustion
chambers, cylinder runners, et. al. the cylinders will not have identical
power curves because the engine has an unequally spaced firing order since
it does not have a flat plane crankshaft.  180 degree and tri-y headers
are attempts to space out the adjacent firing cylinders in the collectors
to minimize the effect of the unequally spaced firing order.  You can also
attempt to minimize cylinder-to-cylinder variation by tuning and blueprinting.
Vizard has reported as much as 40 HP increase on a carb equipped 350 SBC by
minimizing cylinder-to-cylinder variation.  Each primary tube was fitted with
a thermocouple and an O2 sensor to test the effect of the tuning changes
(carb stagger-jetting, intake manifold modifications).  Presumably, IR EFI
and 180 degree headers are going to have less variation to begin with
(compared to a plenum carb and 4-into-1 headers) so I'd expect the payoff
to be less on otherwise similar engines.

Dan Jones