Project LSZ: Suspension Upgrades

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Update by Tom Suddard to the Nissan 350Z project car
Sep 6, 2019

It's no secret that our 350Z was tired–after all, the car had more than 210,000 miles on it when we bought it. We ignored the chassis' age, though, and LS-swapped the car without upgrading anything else. Time to play catch up.

First on the list? The factory suspension bushings. A quick inspection revealed that the stock rubber pieces were trashed, and even in perfect shape we prefer stiffer polyurethane bushings on a track car. Stiffer bushings create more predictable handling and suspension tuning by removing compliance from the chassis.

So we called Prothane and ordered a complete set of polyurethane suspension bushings for our car.

And, since that kit included rear differential bushings, too, this was a natural opportunity to upgrade from our car's factory open differential. We ordered an OS Giken Super Lock LSD to install while we had everything apart, then grabbed an extra 350Z differential off of Facebook Marketplace for $100.

Why not install the LSD in the differential that came with the car? Because our 350Z originally came with an automatic, its factory final drive ratio is 3.357:1. Manual cars, like the one we purchased the new differential from, use a 3.538:1 final drive, giving the car shorter gearing and effectively bringing each gear closer together. With a theoretical top speed of more than 200 mph with either ratio, we decided (along with a healthy dose of anecdotal evidence from fellow racers) to switch to the numerically higher ratio. We dropped our replacement differential, along with our OS Giken limited slip, off at our friendly local transmission shop: Precision Transmission Center. Setting up a differential is a precise science, so we'd rather pay the professionals than risk destroying expensive parts because we set a tolerance slightly wrong. Plus, Precision is staffed by experienced road racers, and they were able to help us decide which ratio to choose from their own experience. Is it a little bit ironic that we built our own engine but didn't install our own limited slip? Probably, but setting up differentials is a skill we'll have to learn next time.

While the LSD was getting installed, we started tearing apart the suspension. Installing bushings isn't rocket surgery, it's just grunt work and a lot of time with the press. The most remarkable part was seeing just how bad the bushings we'd been driving on had gotten. The new polyurethane bushings from Prothane went in without a hitch. Removing the old bushings wasn't even too difficult–we only had to burn out a few of them. We cleaned everything as much as possible while we were in there, too, since nobody likes working on a dirty race car.

After a day in the shop, our 350Z no longer had ruined factory bushings, but stiffer polyurethane pieces instead. And its open differential was now a sturdy limited slip.

Next up: an alignment, and for that we headed over to Very Cool Parts. And, well, then we screwed up our story's timeline a little bit. While we had the suspension apart, we got ahead of ourselves and installed the set of Motion Control Suspension 2 Way Non-Remote dampers. Retailing for $3350 for the set, these shocks aren't cheap, but they're good. Really, really good, as we learned after we installed a set on our Project Mustang. Why would we spend so much on fancy shocks for a street car? Simple: The street-legal phase of our 350Z's life is quickly coming to a close, and we didn't want to hamstring our 350Z with sub-par shocks when it does. We didn't want to buy shocks twice, either, so we'll be rocking the way-overkill MCS pieces while we cross a few more things off of our 350Z's street-legal to-do list. 

Up front, we paired the MCS dampers with springs from Eibach, while out back we kept our soft stock springs for now. Why? Simple: Our 350Z's next event is a drag race, and stiff road-course spring rates would hurt our launch significantly.

We'll cover the reasons we chose these MCS shocks–as well as the process we'll use to pick appropriate spring rates and adjust the shocks–in future updates. For now, though, we aligned and corner-balanced the car.

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