Have you given thought to trying other mounts? Such as but limited to Nismo, energy suspension, etc? It would be interesting to see this comparison.

Thanks for your clarity.

I thought you were revving the car to 4500 and beyond... Just thinking oil should help it a bit and I do like the idea of trying different mounts, maybe with lower durometer like driftfreaq mounts.

This is very interesting as I have been trying to figure out a resonance vibration on my KA for years. Contrary to your experiences, the vibration in my car is felt anytime the engine is revving around 2200 rpms (free-rev clutch in/out or driving in any gear) which means the source is the engine itself. Replacing the harder Nismo engine mounts with softer, liquid-filled motor mounts perhaps off an older BMW 5 series is what I'm going to try.

Positive rep for the very methodical and technical approach to testing and updating this thread with findings!

I won't be building and selling these as I don't want the headache that goes with all that. I will however provide the plans for whatever I build so anyone else can replicate it, or at least have a fabricator build it for them.

I have already done this. I've tried:
- OEM s14 mount
- OEM s14 nismo mount
- OEM 350z mount
- OEM 370z mount
- Generic energy suspension bushing

The 350z mount with the damper bolt was the best, but only marginally better than an OEM s14 mount. Frankly none work well as they are all not designed to work in this application.

This is probably normal. The second order vibration moves lower in the rev range as the 4 cylinder gets bigger. As the KA is a bigger engine this would make some sense. You can use an app like Vibrations! on your phone to determine the frequency of the vibration. If you have a vibration of ~70Hz at that RPM it's a second order vibration and your plan for the 5 series mounts would probably help.

I figured this would be the results. It only makes sense, since they are sold as a higher durometer rubber. Thanks for confirming!

Did you ever make those plans? I get the same vibration with a cd009 and turbo K24A2. After 4k rpm the chassis is vibrating pretty intensely, but flat out I cant notice it feel it.

Trying it without the damper does not eliminate the damper - it simulates a really-bad-case (I only don't say worst because half a damper could be even worse... but worst possible, right?) damper damage scenario - it's highly inadvisable to rev it like that without a damper, even briefly.

Yeah that makes sense. Under full throttle the time you spend at that rpm is limited so the chassis has trouble getting into resonance, as well as the gear lash stays tighter inside the trans.

I did make the mount but it also wasn't a huge help (though it worked great free revving the engine). Under cruising load the vibrations are being transferred from the trans through the driveshaft to the rear end. I have solid subframe mounts so that probably isn't helping. Guessing most of the people on here have solid subframe mounts as well. Anyways, here's my design:

https://i.imgur.com/blV3lDI.jpeg

The rubber mounts on the side mount to aluminum L-brackets that bolt to the stock location. Like I said, works great with no load on the engine, just free-revving. Inspired by this jaguar mount design:

https://i.imgur.com/tVHcZGL.png

Since this still doesn't work under load I'm gonna try switching my subframe mounts from solid aluminum back to nismo rubber bushes. If that doesn't work I may try a carbon fiber driveshaft. I'd like to throw a dual mass flywheel on or a guibo on the driveshaft but both of those options would require crazy custom machining. Honestly I may say fuck it and go back to a 5 speed.

I have no idea what you are talking about. There is no damper that is integral to the CD009.

I think swapping the solid subframe bushings out is a good plan. I have solid aluminum bushings on my subframe and I get noticeable vibrations from the rear of the car right around 2200rpms in lower gears. 2200 rpms is also where I get resonance on my KA 5 speed. I just ordered Nismo subframe bushings because it is bothering me so much.

I fixed the vibrant on accident... I redid the rear most hanger on my exhaust hoping it would make the drone less intense on the highway, as it had one of these cheap "hangers" welded to the the frame rail. It worked, it was a bit quiter at highways speeds, I could hear the 525LPH walbro at idle, and my 4k vibration was gone. I do still have a mild vibrant between 3500 -3750rpm but that's probably from using poly leaf spring bushings as custom motor mounts.
https://images-na.ssl-images-amazon...._AC_SX355_.jpg

So interesting development on this, Taylor Ray built a similar mount for his K24 BMW trans combo. Seemed to solve his problem mostly.

https://www.youtube.com/watch?v=dSZSMsZ604Q

I think he is on zilvia, because he mentions something about someone doing a similar thing lol.... I wonder if we can use a mount with a low durometer? Might be better? SR with CD009 and valve springs is a easy solution.... I wonder if safe?