Quote Originally Posted by matt5112 View Post
This makes zero sense. Wouldn't it shorten the intake runners? The piece you remove is an extension of the intake runner which makes them VERY long runners. Long runners are better for mid and low end power but piss poor for high end power. The shorter runners are better for high end power.

ZZP found the right length and shape to maintain low end power and increase high end power.
Right from the horse's mouth (EP describing ZZP's HV insert during the original development):
"Their solution increases the lower intake manifold runners by an additional 1/2". This insert also has the entrances to each runner rounded to improve entrance flows into each runner."

Yes, the stock runner cage was supposed to be a faux-extension for the runners, that provided minimal low-end help, but anyone who's driven an N/A car before & after installing an HV3 (or even HVII), knows there's plenty gained overall.

For those who haven't looked, here's their results in early 2003 from the testing on a GP GT with minimal mods:

Stock UIM dyno chart
HV Insert dyno chart

Even the torque numbers improve when removing the restrictive stock runners, shifting peak 200rpm higher wit a 2ft-lb gain, and remaining 25ft-lbs higher at redline. Not to mention the peak and redline HP gains.

I've even heard that removing the cage alone, will start you on the path to these gains (possible proof in old CGP threads). The HV insert would then reduce the turbulence, add a little runner length, and smoothly direct air to the ports. I plan on monitoring airflow gains from this with another local's L36 I've started tuning, while they save up for an HV3 to install.

- Dave