Originally Posted by stlwagon
Welcome to the boards Dave. How do you like the CMRC deletes?
Thanks, I've been lurking for a while, but figured I'd jump in on this thread. Anywho... the CMRC deletes are a pretty decent mod for the $95 or so I gave for them.
I've seen spreadsheet from a pull of a more highly-modified car than mine (think the difference was long tubes and O/R H) that shows a peak-to-peak gain of 11.4 RWHP and 17.5 RWTQ. I'm sure I didn't get that much, but SOTP feel is noticeable and if I only got 50-60% of the gain logged by that other car, it's still somewhere around 6-7 RWHP and 9-11 RWTQ. For less than a Benjamin, that's OK in my book.
Interestingly, I have not experienced any loss of grunt down low, as has been speculated in some other threads. I think it's stronger across the board, which is supported by the spreadsheet also.
My only potential regret with this mod is that I seem to get a bit less less engine braking under low-rpm + closed throttle situations. I suspect the CMRC's being shut completely in that scenario really cut off the intake charge, increasing effective engine braking. I can't say for sure it's the CMRC deletes though, as I changed several items over that weekend and didn't really notice it until afterward. So, that assumption would have to be cross-checked with someone else who's done this mod too.
AFStang, Ricesmoker already hit the essentials of the CMRC deletes. In the factory setup, the CMRC controls the intake charge at various RPMs with a set of butterfly valves located in the plenum runners. The position of the valves is controlled by the computer, and it's original function is still not entirely clear to me even after studying many posts. The best read I can get is that it's intended to control low-speed emissions - but totally possible I'm wrong on that.
The computer apparently fully opens the valves once the throttle is cracked open a bit, but even at the fully-open position, the mass of the butterfly and the actuator rod running through the intake runner obstructs some of the flow.
By replacing the plates that house the CMRC's with the delete plates (one per head), this obstruction is removed, gaining a small amount of flow volume back. Of course, since this increases the flow over the factory configuration, the computer's air/fuel tables have to be adjusted. And as well, the computer (finicky piece of junk
) doesn't seem to like it when the CMRC actuator motor stops sending a signal on its wire. So, for both of those reasons a tuner is MANDATORY if you're doing CMRC deletes.