[NOS2Go4Me]

I've done some fairly in-depth testing with the SPI's IMRC motor, or Intake Manifold Runner Control.

What this system does is give you half of your intake volume capacity below 3200 RPMs. Once the engine's revolutions surpass that threshold, the motor activates and turns the butterflies in the secondary intake tracts (or runners) so that the runners are completely open and available.

What does this mean? You get great gas mileage around town, and when you're wheeling and dealing at the track or on the highway, you get the full performance capability of the engine.

"Can I mod my intake manifold so that the secondaries are always open?" Yes, I've just finished doing that mod. "Does it make a difference?" Yes, it does. It allows you to have a much more seamless power delivery experience and a flatter powerband, but at the expense of a decent amount of gas mileage. The engine was never meant to be run in this fashion for any period of time, especially without a performance tune in the ECU. It doesn't run rough, but the gains don't outweigh the detriments and there's no real benefit to doing this unless the car is a dedicated track car.

I'll be modding mine back to the factory configuration this weekend, as the decrease in city/highway mileage is much greater than I anticipated or calculated earlier. I went from 40-42 MPG (approx 6.15L/100KMs) to 32 MPG (7.1L/100KMs).

ICK.

I sure as hell didn't gain 30-40WHP to offset that chunk of range being lost. :angry:

[smith21]

ouch! sounds like your forking out alot more money now adam. Especially with the gas prices the way they are! WOW!!! Sounds like a cool mod if you have the money to fork out for more gas

[NOS2Go4Me]

It IS a cool mod, but really in my mind you'd have to be turbo'ed or massively N/A modded to make use of it. I felt an immediate difference driving it with the mod done, but not in the terms of big numbers at the wheels or anything.

With that said, I'm happy to put the SPI back the way it was (at least in that context) because it really does sap the fuel economy. Had I tuned it with an X-Cal or something, it might have been manageable. Same for having the 50% UDP I want installed. Neither of those things were at hand, so I have to revert it for now.

EDIT - well, my impressions after driving the SPI for about 2 weeks with the IMRC mod. I need a HECK of a lot more mods or a really good clean-up tune to make that worthwhile.

They make mention of the fact you lose some bottom end when you do the mod... make that you lose a LOT of bottom end. I was driving just to the mall last night with Sara, and DAMN. I can actually move off the line and not have to wait for 3000+ RPMs for acceleration.

What's more, in retrospect, I don't really notice the IMRC.