[Roadsters] Was there ever a stiffer isolator solution for our stock motor mounting?

[Walter.Peterson]

I searched back through my email ring archives and only found a few
discussions on this subject. (2010)
I'm hoping someone else has done all of the work already and can just email
me the link to success.

A few years back I started researching & finding a suitable replacements for
the stock isolators. I tried an isolator that was made by one of our Datsun
Parts vendors but unfortunately they ripped apart and were also
discontinued. So I went back to the stock super soft isolators.

This became a priority again when I recently bought a new set of sticky
tires (Falken Azenis rt-615k 14") and the motor/Mikuni air cleaner started
twisting up and hitting the brake master again. This doesn't happen as much
when your tires suck and BTW, no tire slippage makes you feel like the car
lost Horsepower!

I recently installed a modified set of those Prothane Jeep CJ5 mounts &
brackets to get it all to fit.  Its tight, but it works all too well. Still
using the stock trans mount. 

Wow, the car works so much better! The shifting is so much tighter. It's
almost imposable to miss a shift going up or down. High speed drifting &
setup into the corners is far more predictable. Next thing I noticed was
that the Solexes needed that neglected second round of rebalancing due to
the replacement of the broken throttle linkage 6 months ago.

Now the downside. It's got severe chassis & dash area vibrations from idle
~1000 RPM up to 2700 RPM, then it goes away. Its vibration free from 2800 to
8000 RPM. Another round of tuning/syncing on the carbs will likely help some
more on the bottom end, but the basic physics of a 4 cylinder engine is why
there are isolation dampers on motor mounts. It also turns out that the
specifications for most of the isolators I've looked at have absorption
(resonate damping) values around  2500 Hz.

Another upside was discovering that the outside fresh air cowl vent cover is
one of the vibrating culprits, as well as the SS vent level interior plate
on the heater console. The door wing wings are also taking notable exception
to getting vibe tested and something under the instrument panel is
complaining. It's not the wiper arm or anything else I can reach on the
driver side either.

A few more options.
I can go get the stock Jeep rubber mount, now that the trick one was fitted.
Probably too stiff as well but maybe fine.
Find & use the Chevy mount mentioned back in the 2010 archive.

The 510 mounts were actually pretty good back when I raced. Now that I've
modified a set of brackets for a center single bolt, I could try them &
maybe even put some travel limiting set screws in their little built-in stop
brackets.

**** Making a new isolator. ****
I started a dialog with a custom Urethane vendor in LA who has agreed to
make us something. I say us, because making just a few sets for just me, may
be cost prohibitive.

I'm hoping someone else has done all of the work already and can just email
me the link to success.

Walt Peterson
Santa Barbara
20R Street Racer
"Datsa 67"