I had one fitted by our man Phil, and yes it does indeed improve mid range, on the butt dyno at least. I wouldnt say it gives a massive increase, but its certainly feelable and one of the few mods the ECU doesnt cancel out
I have the Motordyne 5/16 spacer coupled with a Motordyne MREV2 Lower Collector. Both do improve mid range torque but I'm doubtful that you will see any gains in BHP as the ECU does negate any advertised power gains IMHO. The Lower Collector will further improve airflow to Nos. 1&2 cylinders on REVUP engines only. The only effective way to get full advantage of bolt-on mods is to get a ECU re-flash or send the ECU away.However do the moderate power gains to be had justify the costs involved in upgrading the ECU??
Kevin at Envy Performance was looking into offering a ECU reflash service some time back but not sure what the outcome was.
You can go to 1/2 spacer but this will require a modified strut bar to clear the plenum.
No gain from the 1/2'' over the 5/16th