Project LSZ: Dropping Weight to Increase Speed

Sponsored by
Update by Tom Suddard to the Nissan 350Z project car
Aug 28, 2020

While converting our  Nissan 350Z from a cushy street car to a full-on time trial racer, we had erred on the side of caution and only removed metal when it was directly in our way. So we now had a fully caged, LS1-powered 350Z that, sadly, sat a bit on the heavy side.

There was only one thing left to do: Break out the power tools. We ran to the bottom drawer of our toolbox and grabbed the reciprocating saw, angle grinder, cutoff wheel and plasma cutter, set them all in a circle around our digital scale, and prayed to the race gods for a bountiful harvest of weight reductions for our car.

Face shield down, earplugs in, we channeled our inner Edward Scissorhands and went to work.

Law and Order

Or, well, we almost did. First we needed to read the rules, and read them well. We weren’t just swapping shift knobs or changing tires. We were going to start amputating huge chunks of our car, so there would be no going back without a spot welder and a donor car. Before we cut anything, we needed to be positive it wouldn’t cost us points, classing or even eligibility for our chosen venue.

So we went to work, downloading the NASA Time Trial rulebook and poring over it more closely than anything we’d ever been assigned by a professor. NASA’s Time Trial rules are tied to its Super Touring road racing rules, with class determined by the car’s power-to-weight ratio, which is then adjusted by a host of modifiers to level the playing field.

Modifications as large as moving the engine back in the chassis or as small as changing tires can bring unwanted modifiers with them, and our primary goal was to not incur any penalties due to careless removal of something required by the rulebook. Put simply, nothing in the interior of our 350Z weighed enough to offset a rulebook penalty for its removal.

Our target, at least starting out, was to build a competitive TT2-class car, which meant a power-to-weight ratio limit of 8 pounds per horsepower. That’s a race weight of 3200 pounds with 400 horsepower at the tires. How hard could it be?

As it turns out, not that hard–at least when it comes to interior weight reduction. Reading through the rules made it clear that we had basically free rein when it came to the interior. The 350Z’s dash and giant metal speaker box behind the front seats could be removed, as could all of the heavy bolt-in braces placed throughout the car that were made obsolete by the roll cage.

Heck, even the transmission tunnel, which we’d cut in a hurry at the LOJ Conversions shop to fit our Tremec Magnum’s shifter, was completely legal–as long as we were willing to call our car a “Non-Production Vehicle” and take the penalty for it.

We needed to patch the hole in our transmission tunnel in order to satisfy the folks at NASA (and create a safer race car). We started by making a cardboard template, then used a plasma cutter to cut a suitable steel patch. After some welding and grinding, our car was once again legal. The moral of the story? Be careful when you’re cutting holes in your race car. 

Breaking the Law

Whelp, there went the farm-we screwed up. The simple act of moving our shifter hole–or, well, swapping a completely different drivetrain into the car, which required moving our shifter hole–had just cost us a modification factor of −0.40.

What’s that mean in English? We’d just lost 20 allowed horsepower, and our 3200-pound target weight would only be allowed 380 maximum average horsepower. (That’s a NASA metric, and we’ll cover it in a future installment.)

No, 20 horsepower isn’t insurmountable, but we just couldn’t stomach the thought of taking that hit for something with no performance increase. We’re fine with modification factors, and we’ll end up with a few anyway, but we’d really prefer to not use them unless we’re actually going faster as a result.

So, what could we do? To meet the letter of the law, our car needed to “retain its unmodified transmission tunnel.” That’s pretty cut and dried, right? You’d think so, but later in the rules we found an exception: “The transmission tunnel may be modified for the purpose of installing a competition driver seat. The floor pan must remain in its original position.”

Maybe, just maybe, we’d found our loophole. This clause was obviously written for Miata drivers (the car’s tunnel prevents a race seat from mounting low enough in many cases), but we decided to see if we could shove our 350Z through the same opening.

Fortunately, NASA has a system to answer questions like this. After rewatching “My Cousin Vinny” a few times, we sat down to make our case. In our email to Greg Greenbaum, M.D., FACEP, who also happens to be the NASA National Time Trial & Super Touring director, we laid out our case under the subject line “ST/TT Rules Clarification.”

The gist of our argument: Though the rule is clear in its wording, it’s not clear in its intent. Is the intent to prevent wild transmission swaps and drivetrain relocations, or is it to prevent modifications as small as moving the shifter, as we’d done? And, if the answer is the latter, what would stop us from declaring that we’d swapped the Tremec Magnum into the car and moved the shifter to accommodate our competition driver’s seat? You see, we like to sit very far forward in the car, and the factory shifter location would be exceedingly dangerous in a wreck.

Did we smirk when we wrote that? Probably about as much as Greg did when he read our email. Part of racing competitively is creative rulebook interpretation, and this was as good a time as any for us to begin learning the craft.

Oh, and just in case our arguments weren’t persuasive enough, we closed the email with one more pitch: “Tremec does sell a special transmission that would put the shifter location in the OEM transmission tunnel hole on this car, but I’d prefer to not spend $3000 for no performance or durability change.”

Beating the Charges

We’re not sure how or why (maybe our prayers to the race gods had been heard?), but Greg’s reply brought good news, saying in part: “Your request to modify the top of the tunnel only for the new gear shifter location of your replacement transmission is approved.…and does not require the assessment of the Non-Production Vehicle Mod Factor.”

Somehow our gambit had worked, and we’d gotten away with murder (of our transmission tunnel). Will this decision ruffle feathers, prompt future rule changes, or cause all of our competitors to change course and push the envelope beyond where we had? Who knows? All outcomes are possible, and more than one can happen at once.

The most common LS-swapped 350ZTT formula right now is to keep the factory Nissan CD009 transmission, which doesn’t require tunnel modification. That’s also the preferred method of LOJ Conversions, our swap gurus. They say the factory Nissan transmission is plenty strong enough for what we’re doing. It’s for those reasons that we’re assuming this won’t be a big issue.

We’ll end the topic with this: Don’t be afraid to interpret rules creatively or even intentionally misread them. But if you do, tell the organizers and your competitors. There’s a fine line between pushing rules and cheating, and it’s mostly based on how many people you tell about your plan.

Next, we could tackle the factory sheet metal box that sits behind the seats. We removed it along with the factory bolt-in braces (you can see a black one still bolted onto the transmission tunnel) because the cage more than makes up for the loss in stiffness.

Back on the Streets

With Greg’s email safely stashed in the car’s notebook, we hurried to patch up the tunnel as requested before our luck ran out. First we tried to do things the easy way, ordering a hunk of 350Z tunnel from eBay for $100 in hopes of scoring the OEM metal we’d removed.

That didn’t pan out. Our car was originally an automatic and we ordered a tunnel from a manual-transmission car, so the metal didn’t match. We didn’t want to push the rules any further by swapping in a manual tunnel, so instead we grabbed some scrap sheet metal and the plasma cutter and made our own patch. After a few minutes with the welder, we’d patched the 350Z’s hacked-up tunnel and were back on track.

Next stop? Weight reduction. We grabbed an impact gun and an assortment of sockets and went to work removing every brace we could get our hands on. These hunks of thick, stamped steel are everywhere in a 350Z, placed by Nissan to stiffen the chassis. Won’t we miss that stiffness? Absolutely not. Our roll cage more than makes up for the loss in strength. Bonus points for the bucket of free nuts and bolts this yielded.

Once we’d tackled the bolt-on (bolt-off?) weight reduction, we could move on to more advanced techniques: Time to ditch that infamous speaker box. After a few hours with a plasma cutter and then a cutoff wheel, we’d reduced it to a pile of metal on the shop floor. Total weight? More than 25 pounds. We found more sound deadening hiding under it, too, which we then removed for more weight savings.

All this action left a much more open interior (nice feng shui), but we weren’t done yet: We’d left jagged shards of metal everywhere, and we could barely get in and out of the car without tearing our shirt. Every cut we’d made left behind a few inches of spot-welded metal with a rough edge, meaning the real work hadn’t even begun.

Yet again, we went to work. We estimate that we spent three times as long finishing rough edges as we did removing metal, but at the end of the day we’d cut about 50 spot welds and left behind clean, smooth sheet metal. This level of removal wasn’t completely necessary (it would have been fine to grind down the jagged edges with a flap wheel on an angle grinder), but we figured something worth doing was worth overdoing. Plus, all those strips of spot-welded sheet metal add up to free weight savings.

While we were cleaning up edges, we also cut off as many random studs and tabs as we could. These provided some weight reduction, yes, but our primary goal was eliminating things that could at best tear our suit and at worst cut our flesh in a crash.

The Future Looks Bright

After hours and hours of sweaty, dirty, dangerous work, we emerged from the 350Z’s interior victorious. Our hands were cut and our arms were bruised, but we’d removed 44 pounds of metal from our race car–not counting what we’d vaporized with the grinder.

Even better, our interior was now nearly complete. The only remaining step was a fun one: installing the rest of the odds and ends that separate a race car from a street car. We’ll cover that, along with more weight reduction courtesy of Shields plastics, in the next installment.

Success! We created a ton of additional room inside our cockpit, and shaved 44 pounds from our car.

Like what you're reading? We rely on your financial support. For as little as $3, you can support Grassroots Motorsports by becoming a Patron today. 

Become a Patron!

Join Free Join our community to easily find more project updates.
Appleseed MegaDork
8/27/20 8:59 p.m.

20hp hit? Time to find a 380hp cam that increases the area under the curve.

Tom Suddard
Tom Suddard GRM+ Memberand Director of Marketing & Digital Assets
8/28/20 8:34 a.m.

Actually, we don't have a 20hp hit–we covered in the article how we avoided that. 

Appleseed MegaDork
8/28/20 9:05 a.m.

I must have missed that. Time for a re-read.

DjGreggieP Reader
8/28/20 10:27 a.m.

I am always amazed at how much weight can be removed from a vehicle from the interior. One day I'll be at the point to read through a rule book and start cutting the interior to bits.  

8/29/20 7:21 p.m.

Adding lightness .

You'll need to log in to post.

Sponsored by

American Powertrain

Precision Transmission Center

LOJ Conversions

Our Preferred Partners