Boost restrictor pill

[user842]

Hi folks!
I have just completed my second club track day.
Very enjoyable!
I may actually buy some sticky rubber instead of my streeters for the next one! The stock EVO is quite a weapon on the more technical and tighter tracks. Once you get to the long straights etc. it's still good at the entry but not really a match for a "warm" GTR further along! A very different deisgn philosophy highlighted there!

I thought I might include a couple of dyno graphs taken before and after I removed the boost restrictor pill (orifice) which I accidentally discovered was cleverly fitted to the boost solenoid inlet port. It was a tiny little toroid-shaped metal device with an approx 1mm aperture.

I reckon the graphs demonstrate just how well the stock setup is sorted for good reliable horsepower and how this simple mod adds around 10ATWKW (and a massive slab of extra torque right where you can get at it!) with no apparent side effects!

The rather linear increased torque is very subtle but definately noticeable.

This is a 2002 Jap-spec EVOVII with no other mods (apart from a K&N cotton drop-in filter element) operating in Australia with 98 RON pump fuel.

All passes were completed in 4th gear on a 4 wheel rolling road dyno.

[user842]

And as I was over the filesize limit and couldn't add the last one, here it is.

This graph shows an overlay of the 2 runs (before and after)
"Before" is red and "After" is blue. I believe the boost curve is generally mirrored by the torque curve although the displayed torque curve is not too useful here, as it is graphed as a result of torque mutiplication(gearbox, drivetrain etc.).

There may be very slight differences in the RPM to curve mapping as the RPM was taken from wheelspeed both times on separate occasions by 2 different people. All runs were performed on the same dyno.