tube80z

I'd only use metal of similar thickness to the frame rail, which I cannot remember off the top of my head. I can check today if needed as I have my race car cut up for a number of mods. You're spot on to why I'm doing all this. It isn't so much for stiffness, although that may benefit too. It's really protecting the passenger compartment from a wheel coming back in via this normally weak area. The main benefit I'm looking for is to add more crushable structure to this part of the car. I never gave much thought to any of this until I saw how badly the Falcon deformed in a fairly slow accident. Up to that point I was totally fine hurtling myself down the road at triple digit speeds thinking my cage and extreme skill would protect me. By making more of a box on the corner it connects the upper rail, inner rail, and top rail. The top rail now has a shorter span and should be stiffer. On my race car there's no cowl so I only have the firewall with no support. My cage will look overly complicated and heavy but only the required safety tubes need to be full thickness. The rest are of the same diameter but much thinner. The green line goes from the lower rail to the upper rail to the top strut mount. The yellow rail is tubing the sits on top of the normal engine frame rail, this is somewhat weird but based around some stupid SCCA rules that I'm working around. The tubes that connect the corner to the yellow tubes are what usually go to the TC pickup point. The idea behind all this is not only to make the car stiffer in torsion and bending but help protect the foot box in case I hit something hard enough to drive the wheel into this area. So it looks like you're well versed in all this. Nice work, BTW. Hope this helps, Cary

I don't think you need to go that large. I'd use the same tube as you would for a strut bar for the purely torsion stressed members unless you already have the material. It will just weigh a little more in the end. I think you have a couple options. You can do it in tube similar to what you have or was used on BJHines car. The other is to make a larger torsion box out of sheet in similar thickness as the rest of the car. Look at the convertible torque box mod for Ford mid-to-late 60s Mustangs and Falcons. They have a very similar unibody design to the Z. In those they build a box that goes straight down from the firewall and then back into the floor. This connects to the engine bay side. Here's a couple of links to give you the general idea https://ironhydroxide.blogspot.com/2017/04/boxes-of-torque.html and https://ironhydroxide.blogspot.com/2017/05/boxes-of-torque-part-dos.html. I've also seen this extended down to the level of the outer rocker lip and boxed into the inner rail. Many of the IMSA Zs boxed in the outer section from the upper rail to A pillar down to the rocker. This makes that more of a torque box out of that section and can tie in nicely with something similar to the convertible Mustang mods. Getting across the tranny tunnel is going to require a brace under the bellhousing area or you add internal rails that go from the front frame rail up and over the tranny tunnel and down to the next side. If you look at newer cars you'll see they have integrated a 8 to 12 point cage into the unibody design. They just do it with folded metal rather than DOM tube. For a street car that may do some track work I think meshing the torque boxes with the tubes in the image above would be a good way to go. The new Mazda RX8 is a very stiff unibody compared to all their previous cars. If you look at images of it and compare to older models all these little details start to pop out. However you go I really like what you've done. I need to get some projects out of the way so I can get back to cars myself and put this year behind me. Hope that helps, Cary

I love the level of work you're doing. The crash comment is one I've thought a lot about too. About 20+ years ago (vague) I witnessed the aftermath of a Ford Falcon leaving the road at not much speed and hit a tree. This was well below normal racing speeds (hillclimb event) as the road was wet. The driver suffered a broken leg, pelvis, and now walks with a limp. Why I bring this up is that the underside of a Ford Falcon is very similar to the Z cars. His car had a good cage and a racing seat. How he got hurt was the car rolled off the door bars when he went sideways into the tree and floor deformed as it was the weak element. And while he was held in his seat the car deformed and like a large lever broke his leg at the edge of the seat. To this day I can vividly recall his screams as the emergency crew removed him from the car. Making the floor stiffer is a good thing in my book. There are still a couple of areas to think about depending on how you intend to use your car (some could be handled by a cage). The main one I've seen where there's a problem is the engine compartment to passenger area. While you have the Bad Dog rail help there's no lateral protection in the front. I've heard that a few big crashes in Z cars have resulted in broken ankles as this area can fold in on your feet in a wreck. If you look at new cars they have structure that goes from the inner rail to the outer and this can be triangulated to the TC and upper strut mounts. Here's a picture of what I'm talking about. I have more ideas on fixing the firewall too based on newer cars.

I'm planning on using the BMW DCT in a street car build. I weighed the costs of it against a T56 and the heavy duty 5 speeds transmissions and it was comparable. With the right ECU you can automate downshifts with throttle blip and all. Amazing what parts are becoming available for our cars. Really cool to see a Z banging around Bathurst with GT3 and V8 Supercars in the mix. Go team Z! Cary

What are you planning for heater/defrost vents and will you use the Z heating assembly or the miata unit? Very curious for my street car project. Cary

The one advantage is that you know the parts are now solid and not relying on 40 to 50 year old spot welds. And if you do ever bend it you can pull it straight. With just the spot welds they often shear and you can't pull the complete part. I learned this from talking to a number of unibody racers and seeing first hand when they did pit repairs. Cary

One thing I've played with is using some of the late model car epoxy bonding. If the parts have good fit this seems to work, ideally probably needs some rivets too, which might be another problem that interferes with the sound deadening. Cary

As others have stated it's probably too low but it also somewhat depends. What are the diameter of your tires? And if your suspension arms point up towards the wheels then you are too low and will be in the nether regions of the suspension geometry.

There's a better way to do this but what you have will work too. If you mount the rod ends on the crossmember and then have the brackets on the control arm. This way you can change alignment but not cause changes to your camber curve or roll center. The third option is to let the inner end of the trailing arm float (no connection) and use a lateral locator behind the diff. I'll see if I can dig up some old pics and attach to this thready. Cary

Do keep in mind that the way the crossmember is bolted in is considered a safety feature. It's designed to shear in case of a heavy frontal impact and allow the engine to go under the car rather than through the firewall. The downside to all this as you mention is there isn't a lot of stiffness available for the strut tower or the front suspension points. When you look at newer cars it's interesting to see just how much additional structure they have put in place in these locations. Cary

It depends on what size chokes you plan to run. 45s with small chokes (aux venturis) flow less than 40s with similar size chokes. If I recall from memory that 33 mms is about the cutoff point where you'll find this difference. This will be an expensive and you want to think about what are future plans for your car. The other option would be EFI throttle bodies rather than carbs. This will be more expensive but probably offer better driveability.

Thanks for pointing this out. I removed the spam. I'll let Dan know there seems to be a reporting error.

As jobill stated you need deeper retainers. Nissan Comp used to sell ranges that had to be used for specific depth lash pads. A quick google search turned up many companies that seem to have the parts. You also need to make sure these don't alter the installed height of your springs or you may end up in coil bind or not have the correct seat pressure and then have valve float issues. Sorry to say that the wrong parts were used when you're engine was built. At least you didn't have the rocker fall off and get in their sideways and royally screw up the cam, which happened to me when I learned you couldn't mix and match parts. Hope that helps, Cary

The really nice thing about switching to aftermarket calipers is you can get almost any pad in any compound. I've had good luck with Performance Friction. They no longer sell the same material I used but it was a medium torque, good initial bite, great release, and long wearing while easy on the rotors. This was the 01 compound. They now have a new compound that is supposed to be even better, the 11 is what I'd try. Keep in mind when they say medium torque they are looking at braking in the 1.5g to low 2g range. Stay away from the high bite stuff unless you're packing a lot of downforce. Or it will be skid city.

I use a higher temp race pad on mine. You need to do some preheating to grid or warm things up some other way. It can make the first run rather dicey if you can't get heat into the brakes and pads. But having consistent braking with the rotors glowing red is really nice. Now only if the car was back together sometime this decade.