Hi
Have been asked to comment on the Hart Plenum.

It made 47bhp more Power on the Dyno than my 500 Plenum. Both used a 14mm Spacer & no other mods were done. I use it with a WRC 8 injector manifold & the pair cost £850 & has seen over 800bhp .
The casting was rough inside & Mark sent it to his head guy to be sorted.
Cant comment on gains at Lower Power levels but it certainly worked on mine. At £450 it seems a no brainer dont think anything else comes close for that money.