Seat mounts/rear end

[Bababooey]

I'm building a 240Z into an ITS car and have a few questions before I go any further.

Do I use the stock seat mounts or should I order mounts for whatever seat I go with? (Also any recommendations on a seat?) I'm going to be using it for HPDE's for the first few times on the track so I'm going to have to put a passengers seat in also...should I just put in a stock seat with a 5 point?

Do I run a locked or limited slip rear end? I've heard running a locked (welded) rear end can break stub axles, which are impossible to find except on a parts car. I have a lead on a LSD, and while putting it in looks easy, putting it in right looks expensive.


I wish I would have just gone ahead and bought one finished looking back, but damn, I can tear a Z apart with my eyes closed now.

[spawpoet]

"I wish I would have just gone ahead and bought one finished looking back, but damn, I can tear a Z apart with my eyes closed now. "

Boy do we know that feeling. We just finished completely re-building ours about a year ago.

As for your questions, you can use the stock seat mounts if you can adapt whatever seat you are mounting to them. That said we welded in two pieces of 1" square-stock between the sill and the trans tunnel to mount our seat to. It's a bit lower than we would have been with the stock mount, and we feel it's safer. If you fabricate bottom mounts for your seat it's important to note that you cannot both weld the mounts to the car, and also weld them to the cage because of the limits on the number of cage attachment points (8). We just have a Kirkey seat, and we are fine with it. There are a ton of nicer seats out there, but this was a place where we had limit our budget to be able to do our car.
As for the passenger seat check with the club you run with as for what they require. We started with auto-x and HPDE's with our car as well, and we used a stock seat with a 5-pt for the instructor. That said if you have a race seat, technically your instructor is supposed to have a race seat by SCCA HPDE rules (last time I checked) which dictate that while stock seats and belts are ok, if the driver has upgraded to a harness or a race seat the passenger has to have the same level of equipment. Driving with the stock seat would be a slippery experience, but you could try going with two stock seats with race harnesses if you don't want to spring for two race seats to get you through your HPDE's.

As for the diff, the LSD is the way to go, but there really aren't any easy buttons out there on the r-180's. What units are out there for sale aren't cheap. $1200k and up. We ran with an open diff for a couple of years, and it's 100% fine to get started. The most important thing is that you get seat time. With or without an LSD it will probably take you a couple of years to get up to speed, and the guys that always run up front are always on fresh ($) rubber. As for welding a diff, it depends on what tracks you run, and your driving style. The car is going to struggle to turn in tight corners if you weld it up, and to get around this you have to really throw it around, but for years many z drivers ran with them. Most guys have LSD's now, but since we only have one LSD, we plan on welding another diff up with a taller ratio for Daytona.

Congrats on the build, and good luck finishing it. They are an absolutely joy to drive on the track. Very well behaved, and enough power to put a smile on your face. Post some pics up if you get the chance. I'll try to get some pics of our simple seat mount when I get home, and add them to the thread. The forum here is a great resource. A ton of z-pilots here with a lot more knowledge than I.

[Matt93SE]

As I recall, the seat mounts in the 240 are pretty whimpy at best. I'd be scared to put my life in the hands of 40 year old japanese sheet metal.

When I helped put the seat in a friend's Z, we took a sheet of 1/8" x 4" plate and welded it all the way across the floor about where the rear mounting tabs were. A suitable piece of square tubing would also work. Then you can weld mounting brackets onto the plate or tube.

I do not recommend bolting anything through the floor since the floor of the Z is pretty flat. My first off-course incident in that car involved a section of curbing, the addition of some air miles on my Southwest account, and then a rough landing in the grass.
The impact with the curb sheared off all of the seat bolts going through the floor. When the car stopped, I realized I was only held in place by the back brace and seat belt. Fortunately I was able to limp it back to the pits and I got out of the car. That was the last time I drove it. That coulda been real ugly. We learned the hard way, but at least I walked away from it.


Anyway, make sure whatever you do will survive simple off-course excursions as well as hold the seat in place while you're driving.

[Bababooey]

I guess I'll buy the seat and take it from there. I still have to replace the other floor pan so I've got some more work to do before I start on the cage and seat. I might even farm the safety work out to a shop that maintains Datsun race cars.

As far as the rear end, is there any ratio that is better than the rest? I've got a 70 and a 78 rear end. (Car is a 70) The car is going to see auto-x and hill climbs before the track, which will just be Watkins Glen for awhile. I'm assuming that I'd need two different set ups since the Glen has sweeping corners compared to a tight auto-x course.

I'll get some pics when it's out of the garage. I just finished up grinding the welds on the interior, now I need to get them under the floor pan and shoot some paint on it.

[spawpoet]

As far as ratios go, you are correct that it's track dependent. A 3.9 is probably most desirable, but not easy to come by. Nissan never sold it in any vehicle in great numbers stateside, and that ratio ring and pinion hasn't been available from Nismo for years. They did come in the front differential on 1981-1983.5 Datsun 4x4's and you can still find those at some salvage yards. Otherwise just keep an eye peeled for one on the various Datsun sites or ebay. They come up from time to time. Depending on model year some of the trucks came with R-180s in a 4:11 ratio. We bought one from a salvage yard a few years ago. The 4:11 great for auto-x and tighter courses. The other popular ratio is the 3.7, and it's again not super common. Most z's came with either 3.3 or 3.5 rearends. You really need one of the other 3 (4:11, 3.9, or 3.7) to be optimal. I don't know of anyone who races the 3.3. Some do use the 3.5.

Hopefully I attached some pics of our seat mount. Pretty simple and straightforward. It probably is a good idea to wait until you have your cage in to install your mounts. It just allows you to move things where you want relative to the cage. I look forward to seeing your build pics as we just went through all the same stuff. I never did get our build pics on here, so I might try to do that this weekend. Again good luck.

[Mike Mackaman]

the first gen Maxima came with a 3.7 R180.

Don't bolt anything to the floor, there is just not enough there to trust your life to it. Two bars across the seat area, tied to the door bars and then braced from the rear to the lateral bar on the main hoop is plenty strong and gives you belt attachement points that are all on the cage. You have to think of the worst case and decide who you want to go with, chassis or cage. And if your seat is on the floor and you belts are on the cage, or vice versa, you will be on the wrong end of a tug of war! My money is on the cage. If you are anywhere near Charlotte, NC, I can help you out. I have done 5 cars and they are all very safe and stable.

I can also hook you up with some good, cheap camber plates if you don't already have them, and you do need them.
Mike