2001 Toyota 100 series 4500 petrol

Yep that about right. Mines without the K&N and Hiclone. But I do have extractors.

Unichip will give you more power low down and more torque, it also
might impove a fuel economy.

Link

Unichip makes a big difference to this motor...know someone who had one fitted...makes motor run more efficient with trmming of fuel and ignition maps....get extracters fitted first then a unichip....or....put it on gas and start saving big time....
Andrew

Extractors improve it noticeably, and whilst you're at it, get a larger diameter mandrel bent exhaust.
I took off my hiclones and economy has improved slightly.. I got 367km on the full main tank thru to first signs of the empty warning light with hiclones in, and 398km with them out, driving the same patch of road, a calm day and same speeds both ways. Read that how you like.

After seeing improved air flow and air filtering results for the cheap AC delco paper air filters, my finer filter will be the next thing to go. Althought K&N is markedly better than the finer filters, the AC Delco still came out ontop of it in the particular results I saw. Certainly something to check into.

If you are looking to mod the actual engine, not just ECU, Look into mods for the straight 6 Toyota/Lexus Soarers- they have the same block setup as cruisers, with the exception that theirs is alloy. Of course, if you do find something, share and share alike.

If you get a chip, make all adjustments to draw and air flow first- snorkel, filter, hiclones, exhaust etc. then get it done. If you do go down this path, let us know the outcome- I am keen to find if it is worth the cost.