We have the pleasure of continually developing Dirk’s 1973 Datsun 240z to help achieve his vision of a Z car that is adept on the street and track. Improving the driving experience are Z Car Garage Big-Brakes, Z Car Garage CV Axles, Silvia 6-speed transmission and a host of chassis and driveline upgrades. Dirk has been enjoying the Z at open-track days including Laguna Seca and most recently Sonoma Raceway.
Track Day Fun
Let’s hear from Dirk about his journey for optimal chassis settings enabling both spirited street and track driving…
DIRK: “Shortly after I first got my Z, I broke the factory open diff on a windy road, and started working on the suspension. It was on stock struts and lowering springs, and the car bottomed out badly under braking while going downhill. So, it went to its first track day with an R180 diff from a Subaru WRX (3.54 Torsen), the factory 4-speed, stock L24, rebuilt stock brakes with high-temp brake fluid, and a set of T3 coilovers with 200# front and 250# rear springs (see that roll)”
“After that, I went to 300# and 350# springs to reduce roll and improve overall handling, note much less body roll below”
Chassis and Driveline Upgrades
First, there was work to upgrade the steering geometry and suspension. With the car being lowered quite a bit, despite having 1″ RCAs installed, it had a ton of bump steer. Rob installed DP racing adjustable tie rods, removed the front springs, and completely eliminated the bump steer on the alignment rack while moving the suspension through its full range of motion.
New DP Racing tie-rods and in-house alignment:
We also refurbished Dirk’s steering rack with fresh parts from our stash:
With the Z back in the shop for bodywork we took the opportunity to make more suspension changes. New Koni Race shocks from T3 were installed, which were a much better match for the 300# and 350# spring rates than the Koni Sport shocks they replaced (as Dirk initially ordered the coil overs with lower spring rates, he never replaced the shocks after adjusting the spring rates, and the car always felt underdamped, particularly on the not-adjustable compression stroke):
ZCG Big-Brakes and CV Axles
Calipers: Stoptech ST42 4-piston front & rear race calipers (Alum 6061 mil-spec Type III anodized)
Rotors: 280mm x 20.6 with Alum 7075 hats
Pads: Stoptech 309 sport street pads
Blog posts documenting all of our customers running the ZCG Big-Brakes can be found HERE.
A few closer detail shots of the calipers, rotors and hardware:
We removed Dirk’s stock brakes and installed our ZCG Big-Brake kit.
At the rear, the factory drum brakes were replaced with our ZCG Big-Brakes. Factory handbrake functionality retained!
S15 6-speed transmission
After comparing the Z to his Subaru BRZ on the track, it was clear the Z was better at everything except for shifting gears. Since his engine made a healthy amount of torque, but not enough to warrant a CD009 (350z) transmission, Dirk kept looking for alternatives. He also wanted something with slightly closer gear ratios to better suit the engine’s power band. An S15 Silvia 6-speed seemed like the perfect fit and we installed it back in 2019.
The first S15 box had some weak synchros, so Dirk sourced another one that was installed with OE trans fluid, as well as a set of fresh OE motor and trans mounts to help with shifter feel and reduce vibrations in the car.
“The S15 transmission fit surprisingly well. ZCG built a custom crossmember to locate it, and the shifter lined up almost perfectly. No transmission tunnel mods were necessary. The modern shifter looked out of place, so ZCG built a custom unit that would look stock, and work with the Datsun competition shift knob. A small 6-speed shift pattern sticker modeled after the one used in the Silvia is the only clue there’s something different going on under this car. And of course the driving experience.”
Making the S15 shifter look factory, we are happy with the result and Dirk’s subtle shift pattern sticker:
Our Z Car Garage CV Axles help transmit power to the ground and ensure smoother operation compared to your standard half shafts. We have over 70 CV axle kits on customer cars and we are stoked with all of the positive feedback.
Also visible on Dirk’s Z are the excellent adjustable lower control arms from Techno Toy Tuning.
DIRK: “The Z has seen a few different tracks. Laguna Seca, Thunderhill in the dry, Sonoma in the dry and the wet. After quite a few street miles on the car with the ZCG big brakes, an 4.11 OS Giken diff, we sorted a few more things with the car. Most notably, we redid the front suspension, and installed a fresh set of Koni race shocks all around the car. These were a much better match for the 300/350 lb/in springs than the Koni sport shocks I originally bought with the coil overs.”
Finally, an opportunity to take the car to the track again came up, and Dirk with the S30, and his friend Joey with his E30 went to Sonoma Raceway:
DIRK: “The car was obviously a lot more capable than the last time it visited a track. The driver, however, was a little rusty, so with each session lap times started to come down but there is plenty more left on the table. The brakes were extremely consistent throughout the day, with not a sign of fade. And the whole car performed admirably. The temp gauge was steady right below the middle of the range all day long. I got fuel starvation in turn 11 once, which is somewhat expected with an unmodified set of Mikuni 44 PHHs, but other than that the Z didn’t skip a beat.”
We were stoked to see Dirk happy with our Z Car Garage Big-Brakes! Enjoy the video below showing in-car action from Sonoma Raceway, dyno run and more, volume up!
After many more tweaks, different induction setups, spring rate changes, rebuilt stock brakes, and 24K miles of driving including a few track days, Dirk’s Z was inching closer and closer to his vision. The next step in making the car faster would be to put in a more supportive driver’s seat.
3 Liter L-Series Power
Unfortunately, the Datsun Spirit engine developed rod knock which was the impetus for a big drivetrain upgrade. Several other parts of the car where refined as well.
The L28 engine was pulled, sent to Rebello, and built into a 3L powerhouse. Dave bored out the 44PHH venturis to a custom 38.5mm, to hit the perfect compromise between peak power and drivability. We also installed a fresh water pump, alternator, new fan blade, OEM fan clutch and fresh air filters. The beautiful DP Racing oil pan remained. More photos in the gallery below:
“The STR-3 already was able to slip the Exedy clutch and we were never fans of the Chromoly steel flywheel. A Jim Wolf Technologies clutch and flywheel combo was installed after first trying a newly developed Kameari single plate street clutch kit, which we both found too loud and racy for this street car. While the JWT pressure plate yielded a different pedal feel that took some getting used too, it was not too heavy and perfectly comfortable to drive in traffic. More importantly, it never slipped under any kind of abuse.”
The clutch hydraulics were replaced to work with new alumimum flywheel/JWT HD clutch combo:
We installed a ZCG-built 4.11 OS Giken limited-slip differential in the R180 along with a custom aluminum driveshaft:
Dyno Tuning
The previous L28 made 202hp/194tq at the wheels with Rob’s tuning. Now with the fresh 3L it baselined at 245hp/226tq with more area under the curve:
Rob tuned the car further on the chassis dyno, setting it up with a very lean idle at Dirk’s request (to minimize gasoline fumes at idle). With A/F optimized and Nismo Mikuni carbs massaged, Rob unlocked another 20hp yielding a stout 265hp/232tq to the wheels:
With gains of 62hp/37tq at the wheels over the L28, Dirk is very happy with the new 3L:
“While the Datsun Spirit engine had a very peppy mid-range and made more delicious induction noises, there’s no argument that the more powerful Rebello engine elevated the car to the next level of performance and fun. The entire setup worked incredibly well together, and we hit an impressive 265hp at the rear wheels, or 60hp more than the engine made in its previous iteration, putting it in the 100hp/liter ballpark at the crank. Not bad for a dinosaur engine on California pump gas!”
Datsun 510, 620 and Z car love
Dirk bought his first Datsun in 2014, a 1970 510, to learn how to work on cars himself. After learning more about the history of Datsun, and the significance of both the 510 and the 240Z in establishing Japanese cars in the American market, he knew he had to own a Z as well.
A year later, the right Z showed up on eBay in Texas, a 1973 in silver gray. After pouring over the photos and talking to the seller, Dirk bought the car sight unseen. The idea was to have a nice Z to enjoy and drive, while continuing to work on the (sometimes not) rolling restoration of his 510. The car was lovingly restored by a dad and his children and in mostly stock condition. Dirk also has Datsun 620 work truck complete with dual-Mikuni’s:
Dirk shares his experience working with us:
“Collaborating closely with Rob and ZCG has elevated the optimization process. Rob will frequently talk me out of a bad idea, or into a good one (like the OS Giken LSD). Sometimes I talk him into a bad idea and it turns out to work really well, like the S15 gearbox. The most fun is when we brainstorm stuff together like turning the catch can setup into an improvised simple PCV system, eliminating all hints of oil fumes from the car while running.”
Enjoying the Ride
Dirk’s been driving his Z-car pretty much every day since the latest upgrades, and it’s been working phenomenally well:
“The drivetrain + brakes make it as happy to accelerate as it is to stop, and with the quick, closely spaced shifts and eager engine, it’s fun to do a casual grocery run, and to drive quickly. With the electrical systems and all fumes well under control, it’s truly a car you can do anything with, and probably more reliable than my BMW.”
We loved to see Dirk driving his Z on rallies and fun runs this year. Most recently we joined fellow Japanese vintage car owners on the Tokyo Calling event hosted by Breakfast Club Rally:
Dirk also joined us for a New Year’s Day drive through our favorite Bay Area Backroads:
We enjoyed working with you Dirk and it was rewarding to help improve your Z.
“Some say good is the enemy of great, but that’s true if you think you’re done. I don’t see my Z car less as a “build” that’s done. I’m always developing it, just like continually developing a race car (e.g. my Lemons car, http://instagram.com/bittersc243) to stay competitive. In this case the competition is merely for making the Z into the most fun driving experience I can imagine, and the journey of continuous refinement and improvement is a big part of the fun for me.”
Farewell, Dirk!
We helped Dirk prepare both the 510 and Z for overseas shipment to the Netherlands. Stay tuned for a feature on Dirk’s Datsun 510, it’s a really neat little Dime with a screaming L-Series. Thanks for your support Dirk and LONG LIVE THE Z!
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- Mamiya 645E | Mamiya 45mm f/2.8 N | Lomography Color 100 100 Scanned with Epson V750 | Epson V850 120 Lab developed in | Dip and Dunk
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- Nikon F6 | Nikkor 24-70mm f/2.8G | Cinestill 50D 50 Scanned with Noritsu HS-1800 Lab developed in | Dip and Dunk
