Power!

[robin]

I prefer two person days, but I've done a few by now so ready to do some of the more complicated stuff, which works better with two people - that said, 4 person days are great for getting started and Victor is probably right - you'll absorb more over 2x 4-people days back to back than 1x 2-people day IYSWIM.

If you've got a group of people wanting to go, he can tailor the day to suit, but there are limits of what is practical beyond which you'll spend a lot of time kicking your heals and not learning anything.

Campbell Ford's car is probably the best source of data - we have back-to-back charts of his car on the same dastek rolling road before and after fitting the head you're talking about.

comparison

The blue lines are after, the red lines before. As you can see, tiny loss of torque at low RPM and a modest gain at high RPM. His car wasn't bad to start with, of course. Between 2,500 and 3,500 RPM is the K-series characteristic torque hiccup and it's here that you normally find that tuned heads perform a bit worse; to some extent it can be returned to normal with custom mapping, but not big enough issue to warrant the expense.

Niz's setup is a bit different so not directly comparable.

Cheers,
Robin