RMM and false knock?

[Chuckable]

Not sure if this should go in another subforum or not, but in speaking with a Mountune rep he mentioned that some RMMs cause vibrations which in turn cause the engine to interpret them as knock. This results in retarded timing as well as a whole bunch of other countermeasures beyond my knowledge. This then reduces power. Anyone have any experience or insight into this issue for our particular car?

I know that many tuners chasing down an unknown knock tend to look at mechanical items after checking all the usual suspects, so it seems plausible. But again, does anyone have any real world experience with the popular RMMs and popular tunes?

 

[Sourskittle]

I think this is happening. I have no proof.

 

[johnlopez624]

This is just what i wanted to read seeing how i was going to go get Cobbs RMM today.. dammit.. Anyone else think this is true? :/

 

[Ghostwhite]

It's true. Every tuner has to work around false knock with stiffer mounts

 

[Olddave]

Interesting --- would like to know if anyone has experienced any problems. I'm still trying to find the time to fit my Cobb RMM

 

[Sourskittle]

I think the higher end motor mounts have a much lower chance of causing false knock. The race inserts like a lot of us run, are prob fairly likely to see it from time to time.

Also wondered about shifter noise. My shifting linkage/arms are really loud.

 

[BRGT350]

One reason I went with Cobb over any of the others was that they used rubber in the bushing with voids, instead of urethane. This would be the least likely to cause issues with the knock sensor. I don't have any actual data to support the rubber vs urethane, but my experience has always pointed to rubber being better for absorbing NVH than urethane. It stands to reason that a rubber would transmit less vibration back to the engine that could be detected as knocking. The fault in this logic comes from rubber can be as hard as a hockey puck and urethane can be soft as a pencil eraser.

 

[Butterybunz]

Hmmm so I shouldn't install my Boomba RMM until I'm tuned for it? or can at least monitor the KR with a Cobb AP?

 

[Sourskittle]

Like... How does this happen? 3psi, barely any mass air moving. 87* outside ( cooler for Florida this time of year ).

Ironically, I have 1.5* of global timing being pulled at all times via the tune. Pretty obvious to me its not real knock... I have the 2J race insert

 

[baldtaco]

You are correct Brian, and I witnessed it happen on every mount but stock.

 

[iso100]

I wonder if the CP-E mount avoids false knock...

 

[Sourskittle]

Last time I went to the track, it was pull timing when I shifted, so I kept dialing the timing back around that rpm... Ot really made the car fall on its ass though, when it should have been really pulling its best. Odd enough, my friends 1992 syclone is chasing the same issue.

 

[Ghostwhite]

Like... How does this happen? 3psi, barely any mass air moving. 87* outside ( cooler for Florida this time of year ).

Ironically, I have 1.5* of global timing being pulled at all times via the tune. Pretty obvious to me its not real knock... I have the 2J race insert

Yep I'd guess that's false knock. I get that exact same thing rarely while not driving hard at all

 

[me32]

Can the knock sense be tuned down some?

 

[dyn085]

I have the Cobb RMM and have yet to see any false knock through any of my data-logging throughout my tuning process. I wouldn't be concerned at all unless the negative corrections were large or happening a lot-that's part of the benefit of having dynamic timing.

 

[Sourskittle]

Can the knock sense be tuned down some?

Yes. But then it sorta stops it from doing its job. I'm not willing to except that.
I think we need help from other mounts as well as a slightly stiff rrm instead of a crazy stiff rmm and 2 garbage can mounts.

 

[iso100]

A sensitive knock sensor is a good thing. If you disable it and don't detect the knock yourself while driving you can end up with a blown head gasket, burned piston or worse... a ventilated block.

 

[a10thunder]

I have the CP-E RMM and an Accessport. How do I detect whether engine timing is being affected, just datalog Ign. Corr. on all cylinders? I went back to the stock factory map and I'm not getting the gas mileage I used to get. This thread is making me wonder if gas mileage is down due to the engine timing being retarded. Or I may just be paranoid.

 

[Sourskittle]

Doubt it will effect total fuel mileage very much. But yes,
Watch the ign correction for all 4 cylinders.

 

[RAAMaudio]

SS, Those sections of aluminum I sent to you are to piece together the drivers side mount(transaxle mount actually) as it has a ton of fore, aft and verticle play in it. Just take off the cover and fit in the right parts, I taped them together for test fitting then would of welded them up for final fitment but I had moved the battery to the rear so made a much lower weight and tight fitting cover for the rubber part, works great!

I found out my Cobb RMM(REM, my car has an engine, not a motor hits my subframe brace/rear undertray mount I made so I have to notch it a bit, I might be getting a bit of timing retard from that if it can touch under full boost, it hits when shifting a bit aggressively, did not think it would move that far as I tested the flex with a bit crow bar while designing the part.