Early vs. Late VH45DE Head comparo.

[WizardBlack]

Aside from the early head's dual circle intake ports versus the late head's oval intake ports, are there any dimensional differences in the heads themselves? Any links to threads? I searched quite a bit, but only came up with comments about differences in torque vs horsepower without any of the referenced images, measurements, tests, etc. The only test I saw was the flowbench numbers for the oval port heads.

[T45]

Mettler posted a side by side pic-fest a long time ago when he visited a local racing shop. Search for Mettler and maybe pics in the title, can't remember the name of the thread.

[Q45tech]

The primary reason for port redesign was to correct an emission spike problem caused by fuel puddling after a sudden high rpm closure of throttle.

Flow changes were insignificant, but the two HP peaks [5500 and 6,000] did merge into just one at 5750- 5850 rpm depending on air temperature and density.They realized these emission problems but 32,000 heads were already being built and they decided to wait until model update to make change.Same problem occured on I4 except thay reduced cam duration as part of fix.

When you calculate the speed of sound vs temeprature you will see 45F>145F is 9.5% thus the tuning of runner changes by that amount roughly 400 rpm at torque peak.So assuming 77F ambient [SAE spec] 4,000 +- 250 rpm would be expected same with Horsepower.From a 1995 converstion with Nissan designers in Japan. My JP coffee partner's brother was on engine original design team.

[Carl H]

huh mebey that explains the 'rich smell' when doing high rpm work that ive noticed with the car when going to closed to part to wot and anywhere in between.