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Meeting 90dB Noise with GT350/R

I do have some concerns about running with the flaps closed and the engine thinking they are wide open. I either have this right or wrong but it might make the engine run richer and if that's the case it won't be a major issue.

@CSL yes closed in all modes. We'll call it the Laguna Seca Mode or LSM. ;)
Would be nice if there was a module to just keep the damn things open. I don't suppose these can be calibrated to accomplish the reverse?

Did you happen to do any research on concerns about keeping the flap closed with extended WOT?
Geez guys, that was quick :) I'm glad to help out. They're still a bit more of a hassle to install than the McMaster-Carr solution... but they're the same cost.


2017 GT350R
Does the stock valve system only open/close the two inner pipes (the outer pipes are permanently open)? If the defeat plugs only defeat the inner pipes, the outer pipes should allow enough exhaust gases to come out without massively increasing back pressure.
I finally tested my GrimmSpeed modules and they worked as advertised. Car is quiet under full acceleration and I'm confident it will pass 90db at Laguna Seca. LSM works well and allows you to use Track driving mode.

What took me so long to test them was as I was trying to install the modules I was having a tough time getting the connector to separate. What I didn't realize was not only do you have to slide the bar back you need to depress a part in order for them to separate. Regardless I thought it was a PITA reaching up on top of the muffler. While I was under the car I noticed there is a pigtail with heat shielding on it. The other end of the connector is very easy access and should make the job much easier. I sourced the pigtails from my local dealer and it worked beautifully. They were $42 for the both of them. Maybe a bit expensive for some added convenience but I think it's going to work well.

Note there are two different part numbers for passenger and drivers side. You could order two of either and it would work just as effectively. But you might as well order one of each in case the existing ones fail then you have a backup. The difference is one is about 2' longer than the other. Otherwise they are identical. The orange tag is for the drivers side and the green is for the passenger side.

The part numbers are:

FR3Z 14A411 H Drivers Side
FR3Z 14A411 J Passenger Side

Parts and packaging

Passenger side


Drivers Side

Nice work- a must have for LS. Creeping up the hill blows. I had two black flags when forgetting and leaving in 3rd. Trick was 4th and pedal up the left , then once under bridge at 6 hitting it again.


Lord knows I'm a Voodoo Child
Exp. Type
Time Attack
Exp. Level
10-20 Years
Cookeville TN
Steve did you order the pigtails? They will make it much easier using them.

Did not. Is it that bad if the car is jacked up? Figured to put them in when changing to track wheels and remove when switching back to street. I only have one or two sound restriction tracks.

Sent from my iPhone using Tapatalk
Exp. Type
W2W Racing
Exp. Level
20+ Years
Snowy North
Does the 2018 GT have the rear undertray/ diffuser?

If so...would be a b#tch to get up inside the bumper cover.

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