Ok, I now have all the new parts installed on my GSR: DC 4-1 header, AEM cold air intake, Greddy Evo2 cat-back, and Carsound cat. The other night my friend pointed out that it sounds like Vtec is engaging at 4,500rpms. I don't have a VAFC so theres no way I could have changed it. I mean @ 4500rpms my engine really opens up. Anyone have an answer for me on whats going on with my car?

 

The sound you're hearing at 4500rpm± is that of the secondary intake runner valves opening.. just before the VTEC switchover.

The CAI has eliminated the baffles and resonators that otherwise mask that change in the intake note.

 

The cam changeover occurs at around 4500 and the butterflies open up around 5700 rpms, so what he is experiencing is normal vtec engagement.

 

:thinking: I could have sworn it was the other way 'round. h:
Whoops.

 

on my GSR, at 4400 (actual RPM for engagment) you could hear the pins lock the rocker arms. the increase in engine sound is due to the valves now opening longer and with more lift.

now at 5600 you'll hear the secondary butterflies open thus allowing you to hear more engine noise through the intake.

 

Hmm. My butterflies are wired open at the vacuum, even I hear a different note at 5700 RPMs..

It's weird because I feel like I'm starting a whole new powerband. Like one burst of power, of course is at 750, the next at 4400, the next at 5700.. But my butterflies are always open..

Is it all in my head?

 

with the engine at operating temperature. pull the vacuum hose that connects to the dashpot. the arm should drop. this will tell you if they are working properly.

 

I know how VTEC works but some terms ive never heard. What are the butterflies?

 

the butterflies are the plates that open and close the secondary intake runners.

 

mmm..i did away with my butterflies, got a skunk2 IM and bumped my vtec up to 5200