** Z
Tech Tips
Z Intakes **

The size of the intake runners varied over the years but not the port size on Z heads.

The typical Z intake port is 34mm in diameter.

The cross sectional area is 908mm˛

The typical runner diameter on an early Z carbed intake manifold is 34.5mm. It matches the port in the head.

The cross sectional area is 935mm˛. (This combines to a total cross sectional area of 5905mm˛ for all 6 intake ports.)

The typical runner diameter on a later Z EFI intake manifold is 30.5mm. Obviously, it is narrower than the head port!

The cross sectional area is 731mm˛. (This combines to a total cross sectional area of 4384mm˛ for all 6 intake ports.)

The EFI manifold runner is a restriction when you compare it to carbed intake manifold and when you think about its interface with the head.

The typical carbed Z intake manifold mouth diameter is 47.2mm. Since there are two, the equivalent cross sectional area is 3499mm˛.

This equates to 582mm˛ per port cross sectional flow.

Since the combined cross sectional area of the same manifold's runners is 5905mm˛, the smaller mouth is a 40.7% restriction.

The correct mouth and throttle body diameter needed to match output cross section is 61.3mm.

The carb manifold runner is a restriction when you compare its input cross sectional area to its total output cross sectional area.

The typical EFI Z intake manifold mouth diameter is 52mm. The cross sectional area is 2124mm˛.

This equates to 354mm˛ per port cross sectional flow.

Since the combined cross sectional area of the same manifold's runners is 4384mm˛, the smaller mouth is a 51.6% restriction.

The correct mouth and throttle body diameter to match output cross section is 74.7mm.

The EFI manifold runner is a restriction when you compare its input cross sectional area to its total output cross sectional area.

Bottom Line

EFI manifold runners are a restriction and do not match head ports

Carb manifold's runners match head ports and flow better than EFI manifolds

Both EFI and carb manifold mouths flow less than the sum of their runners. ( However, the intake duration for each port is only 1 stroke of a 4 stroke motor AND it is proportionate to how far open the valve is so it is can only draw up to 25% of its maximum draw. Thus comparing input and output cross sectional areas is not significant).

Suggestions

acid port EFI runners

use bigger throttle bodies and port the manifold mouths

two 52mm TB's on a carb manifold would make a nice "poor-man's" setup to maximize stock parts performance (of course EFI bungs would need to be fabricated).

RacnJsn95 of Zcar.Com's EFI injector flange welded to carb runners and dual TB.

1 fast Z of ZCar.com and BMC discovered that manifolds from maxima LD28 motors have larger runner's and mouth.

The LD28 runner dia is 35mm (same as the Z head and Z carb manifold runner) The LD28 runners are longer too. They just need a TB plate and injector bungs attached.

BMC make custom intakes for Z's

Lone Wolf Performance make a highly recommended high-flowing custom intake.