g6civcx

A bunch of members requested me to do this so don't flame me if the information already exists and/or not interesting.
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The stock S13 has 37.8" of headroom (source:Edmunds.com): 1990 Nissan 240SX specs, auto safety at Edmunds

I measured the bottom of the seat to the headliner on my seafam green fastback with no sunroof and it appears to be about 37.5":



The first thing you'll need to do is remove the seat. There are two (2) bolts on the front. Use a 14mm socket.



And two (2) more in the back. Also 14mm. Pop out the plastic trim pieces to expose the bolt and nut.



Tips: if you have problems with the bolts/nut, dab them with a little bit of PB Blaster and let soak. Use a breaker bar and apply gentle pressure.

It's easy to strip the threads here so be careful. Install and remove bolts slowly. Try to hold the seat up to take the pressure of the bolts so you don't shear them on the seat rail.

Remember to unplug the seatbelt sensor.

Then bolt up the aftermarket rails using the stock bolts and nut. This is a Bride FG. Note the extra hole on the left rail. Apparently it's to fit the Skyline.



This is the crucial part. I measured everything myself so dimensions are approximate.

The rails come with brackets to bolt on to the side of the seat. They do have some adjustment.

The biggest seat they can fit is about 16" outside width.

You can also move the brackets in to accomodate a smaller seat. I have them set at the thinnest position possible and they appear to fit a seat with 15" outside width.

Anything smaller or larger than 15-16" and you'll have to fabricate your own mounting brackets.

I also measured the maximum height possible.

The seat can go as low as possible until it hits the catalytic converter hump. The seat goes between the rails so there's nothing on the bottom of the rails to stop the seat (as stated by some of the members here). Basically you can go as low as you want until you hit the floor.

I measured from the highest point of the floor, the cat hump, straight up to the headliner. It's about 36.5".

As far as length goes, I suppose that anything that can fit between the steering wheel and the rear seat would work.

So let's say using a Bride FG sidemount rail on a stock S13:

15-16" outside diameter. other sizes need custom brackets. You can squeeze something up to 17" but you'll lose about 1-2" of helmet clearance because the seat has to go over the rails and not between.

Anything over 17" you'll have to start modding the brackets to extend and move the locking handles out so the handles don't get trapped under the seat. Look at the picture and think about how you need to mount the seat to ride on the rails.

Obviously anything that's too wide to fit between the transmission hump and the door panel won't work. Use common sense here.

I went ahead and measured between the door panel and the transmission hump. A seat that is wider than 21.5" at the base will not physically fit unless you start hacking up stuff. So keep that in mind while trying to fit some of the bigger seats.

Let's say 36" max height. Anything higher than this won't physically fit between the cat hump and the headliner.

Length let's say be reasonable. If it can't fit between the steering wheel and the rear seat then obviously it won't fit at all.

I also have another solution for people who want maximum lowness. The Dent Sport Garage car gave me some inspiration. Stay tuned.

g6civcx

For reference, I use a Kirkey Roadrace Intermediate 15". It measures 16.5" width, 35" height, and 24" long. It fits perfectly on these rails, with about 2-3" of clerance between the seat and the headliner.

3AM

the extra hole is so the rails will also fit skylines.

g6civcx

Thanks for the info. I updated the post with the info.

We don't have Skylines here so the vendor couldn't tell me.

Do you know if it fits all R32-R34, or only certain models?


More tips:

Use antiseize compound on the treads of the nut and bolts. Torque the bolts to 32-41 and the nut to 19-24 ft-lbs. Be very careful threading the bolts in since the weird angle can strip the threads easily.

lbkid180sx

if you use kirkey seats why not use the kirkey seat rails that they sell that use your stock rails ?

g6civcx

Who sells?

I'm using custom floor mounts for more clearance.

Tearlessj

Thanks for putting in the effort to make this article. I'm sure many will find it handy.

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punxva

good information, this should go into the FAQ

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Ruff Ryder 6

I have a Kirkey Intermediate Roadrace seat as well that i want to try to fit to my car this winter so this post is a great help to know that i can use a set of rails and not have to completely engineer my own brackets. Thank you
Can't wait for more info

g6civcx

I got the idea from the Dent Sport Garage car.

I drilled out all the spot welds that held the bar that elevated the seat up from the floor.

Then the floor where the hump is was cut as much as possible without hitting the cat. Then the floor is rewelded in flat.



I'm using a universal Summit bottom mount sliders shown mounted and next to the Bride for comparison.





When mounted in the car, headroom becomes a whopping 43". The seat is actually too low. I have to order a pair of seat brackets to raise the seat off the floor and adjust the title a little bit.

boske

Do you think some sledge hammer work would give similar results without cut/welding the hump? Maybe some hammer/dolly if I can find someone to hold up a dolly under my car...

Ruff Ryder 6

So using one of the aftermarket rails with that seat was not an option? how close to the headliner would you be if you used some of those rails without removing the cat hump. looking for a quick option if there is one here.

g6civcx

I don't have a measure of headroom of the Kirkey on the Bride rails.

What option would there be? You put the seat on the rail. You mount the rail in the car. If it doesn't fit, you bend or trim the aluminium seat. Done.

mattro

this is awesome i also have a kirkey, but i tried useing the stock rails....

it hits the sun roof, and the car is stripped, no headliner.

gotta get me some rails.

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21Nemesis

Do you have a part # to the slider? I am in need of a new one for my aftermarket seat.

Thanks

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g6civcx

Go to SummitRacing.com. Drill down to Interior & Accessories, Seats, and Seat Brackets.

They care a bunch of universal bottom mount sliders. The one I have is the summit Racing brand part # SUM-G1153.

Ruff Ryder 6

I ask because when i decide to put a cage in the car, my head will have to be lower than the forward bars when i am sitting down with a helmet on. That is why i was asking if one could "get by" by using some low max rails or something.

g6civcx

it all depends on the design of your cage.

Otto347

Just an fyi you can beat down that hump on the drivers side (custom exhaust, no cat of course) for people not wanting to cut/weld.

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boske

cool, I was going to just bolt my seat down no slider but I might have to give this a try.

lbkid180sx

kirkey sells them u bolt them to your stock rails and u can lean the seat back as far as you want there like $45

g6civcx

Link, please.

lbkid180sx

Kirkey Racing 99204 - Kirkey Universal Seat Brackets - Overview - SummitRacing.com here you go

lbkid180sx

Kirkey Racing 99204 - Kirkey Universal Seat Brackets - Overview - SummitRacing.comthey say to bolt to your roll bar but u can bolt them right to your seat rail the to the side of the seat

g6civcx

So you have to unbolt the stock rail from the stock seat and then use these on top of your stock rail?

lbkid180sx

thats how it was explained to me yes i have not yet done this but i am planning to with my pro drag kirkey in hard top s13 hatch

niSm095

Does anyone know if these summit sliders will fit most aftermarket seats? If so, how do they mount with that hump taken out? I assume flat on the floor, with holes made through the floor?

g6civcx

There is a stud that comes up from the bottom to mount to the seat. If the bottom of the seat shell is not accessible, then you have to find a way to fab a mounting bracket.

They bolt to a piece of metal to raise the seat height or can be mounted straight to the floor.

It's just nuts a bolts. Nothing special.

240z4u

Found a source for those rails for even cheaper; Universal Seat Sliders

g6civcx

Thanks for the link. That's pretty much all you need. The sliders bolt straight to the bottom of the seat. Then you can buy a spacer/riser to raise the seat up if it's too low, or fab your own .