sommmatt

iTrader: (2)

I don't really contribute to this forum, but the information and resources in this forum have helped me so much since I bought my RX7 I was hoping that I can give back to this community a little bit.

This information might never help anyone, and it really only pertains to those who are contemplating building an FB from bottom to top.

I loved my stock rotary car a lot, but it had two problems, those being the steering and the lack of power. I know not everyone here will agree with how I dealt with the power, but if you want a steering solution that, in my opinion, is better than any of the kits proposed so far, please read along.

I now have about 1000kms on this setup and can say that it works well enough for me to want to tell other people about it. Your mileage my vary.

Information I found on this forum from a build that I don't think ever got completed or I never kept up with showed that by ovalling the mounting holes of a 240SX subframe, it would bolt straight into an FB. This is something I quickly found to be true after ordering a subframe and rack+pinion from an S13 240SX from ebay (but any 240SX 89-98 should work).





Here you can see how little ovalling was required and how close it fits against the lip of the FB frame rail. Perfect.

NOTE THAT THE 240SX SUBFRAME HANGS ABOUT AN INCH LOWER THAN THE STOCK ONE.

This is mounted using the original subframe bolts without modifying the chassis of the car, just the subframe itself. When I realized this would work, I ordered a pair of 240SX spindles from ebay (again any year 89-98), along with new inner/outer tie rods from rock auto for the rack and pinion, and new lower control arms from rock auto or ebay or something, which all costed about 6 pennies. I don't remember how much but it wasn't expensive.



Okay we're starting to get somewhere. I then emailed BC Racing coilovers, as they have a local distribution center in my city, and asked if it would be possible to order 2 240SX front coilovers with RX7 FC top hats. They said hells yes and sent them my way. The coilovers of course bolt to the knuckle.




And FC top hats work if you oval the FB strut tower mounts just slightly.

sommmatt

iTrader: (2)

So now all we need is a tension strut. We don't have the location to mount the 240SX tension struts but we do have the location to mount RX7 tension struts, but the orientation and angle is all wrong.

I ordered Techno Toy Tuning FB tension struts, which lose the front bushing so they pivot easier. Turn them upside down and expanded 1 of the 2 mounting bolts just slightly and it bolts up to the 240SX lower control arm.




Okay with that figured out we have everything we need for a functional front suspension.

I ordered 2 front 240SX wheel bearings, and 240SX brake calipers, pads and rotors.



These are the smallest brakes you can mount to a 240SX, they only get bigger from here with a ton of OEM and aftermarket options. You have to find a new solution for the brake hoses as they are a bit of a different shape.

The suspension has adjustable camber from the plates, adjustable caster thanks to the T3 arms, and easy steering rack toe adjustment. IO adjusted the T3 arms so they would put the wheel in the middle of the wheel well.

I will note that an RX7 FB sway bar WILL work, but looks to be about half an inch too wide on either side, but I do still think it would be fine to use the FB sway bar with 240SX sway bar end links. I can't use it on my set up because my lower radiator hose outlet blocks the FB sway bar. I will use a 240SX sway bar at some point in the future, I just need to fabricate a reasonable way for it to mount directly to the FB frame rails.

The steering column is where all of this goes to ****.

I believe the best way to do this is to find a factory 2 piece power steering column. I never found one but I'm still pretty sure that's the best way to do this without hacking up your car. Then pretty much all you need to make is this!



I tried modifying the RX7 steering column to do what I want. The real problem with the RX7 steering column is that your steering wheel is bolted to a 4 foot long spear coming out of the steering box, and the outer shell does not mount to the car in enough places to support a modified version. Lots of cutting and welding and I came up with this.



I was trying to retain the RX7 collapsible steering column. Also reusing that column allows you to retain your switch gear. I had an idea for how it had to work, but I didn't have the tools or the skills to make it happen. That design ended up having too much play in it, so I scrapped it.

I didn't take a lot of pictures while doing it, because it was the bane of my existence, but I ended up buying an NA miata steering column, modifying it to bolt to the Rx7 pedal box and dashboard, and then creating a 2 piece steering shaft to go through it. The miata column I was hoping would allow me to retain the RX7 switch gear, which of course it didn't fit, so I converted my entire steering column to Miata junk and rewired everything so it would work. Nightmare. No room to work under the dash and it's the part of my car I hate the most. This is how it looks now. All of my custom steering column parts come from Borgeson. I probably have like 2500 dollars wrapped up in this stupid column. Pretty much all because I could never find a 2 piece power column.





I figured out everything in the engine bay in about a month. To get the steering column to be acceptable took 2 years.

As far as track width goes, the fitment of wheels on my car appears to be REAL CLOSE to a GSL-SE. I haven't measured and I don't know anyone with a complete GSL-SE I could compare to.

As my car was a GSL, and I have no converted the front axle to 4x114.3, I bought GSL-SE axles from a forum member here, bought some ruined GSL SE brakes out of a junkyard, rebuilt and swapped that stuff over. It all bolted up fine but had to re-use the GSL ebrake cable brackets. Replaced all of the bearings and seals while I was in there. I give that information to mention that my car's brake set up is as follows,

1981 Mazda RX7 GSL master cylinder
1989 Nissan 240SX non-abs front brakes
1985 Mazda RX7 GSL-SE rear brakes

The brake pedal feels absolutely the same as it did when it was running stock 1981 brakes all the way around. I mean it feels GOOD. The 240SX brake calipers are not appreciably bigger than the RX7 ones and the rear calipers are identical hydraulically with different castings. (I had to use my GSL pistons in the GSL SE calipers).

This was the car after I put it on the road. As you can see the front wheels look natural, not like it has bastardized suspension.



I had to add put more negative camber into the front than I wanted for these wheels to fit, which were set up for an aggressive GSL-SE fitment by Love20Bee.




CONCLUSION AND DRIVING IMPRESSIONS

When I put the vehicle on the alignment rack, I was comparing my numbers to what a 240SX should be. Of course I had more camber than I wanted, but caster was within specification and toe was easy to adjust.
I have not depowered the rack, nor have I hooked up the power steering pump. Steering effort is about the same as a stock no power steering car. Parking is meh and that's about it.

The steering is about a million times sharper. The front coilovers work a lot better than the techno toy tuning coilovers I previously had did, but I think the springs are too heavy. Because of the heavy springs I don't notice that I don't have a sway bar.

But wow does it ever steer fast and precise. You might have noticed that I changed the engine, but the steering is more noticeable to people who know what an FB drives like. People who have never driven my car don't comment on the sloppy steering, because now it feels like a car from the 80s instead of a car from the 60s.

So it was fricken hard. But it works. The biggest hurdle is the steering column for sure. It was incredibly frustrating and expensive to find something that works, and if I could go back in time, I'd spend 2 years looking for a power column before doing what I did again.

I hope this helps anyone looking into a steering conversion, but it's not for the faint of heart.

JOE68

good stuff .... besides the engine swap.. lol

Mivroum

Very interesting and well documented.

mazdaverx713b

iTrader: (91)

This is a really good writeup! Its definitely not for everyone but the fitment is excellent and the car looks fantastic once it was finished! No more steering slop!

t_g_farrell

iTrader: (1)

I was excited about the undercarriage swap from a 240. Too bad about the column tho. Nice writeup.

yeti

iTrader: (1)

Inspirational!

sommmatt

iTrader: (2)

Like I said if you really wanted to do this without being a hack like me, a power column is probably what you want, as you can see in this guy's photos.

1st gen RX7 factory power steering setup - AusRotary

tommyeflight89

iTrader: (4)

That is a great write up!!

Almost seems like a but more of a natural "FC Front Subframe" swap. And the parts might be a bit easier to come by...

But, what about the engine mount? I am sure you are running a custom setup for your 4 cylinder, but would OEM front cover style 12A or 13B GLS-SE mounts work without much trouble?

The FC Subframe swap is great but it takes away the front cover mount... and is obviously no issue of you swap in a later 13B...

KansasCityREPU

iTrader: (9)

The rotary oil pan will not work with this left hand drive S13 mount. I wonder if a right hand drive S13 would work for a rotary engine? Just flip the mount around so the rack is in the front. I like the idea of parts availability for the S13 suspension.

Can the left hand rack itself be flipped?

sommmatt

iTrader: (2)

I can't definitively answer any questions as to how the rotary would mount back into the engine bay but I think if you were going this far it would be silly to think it would bolt in place without cutting and hacking something.

What I can say is that the rotary mounting location with stock subframe and with 240SX subframe will be very similar, likely that the front cover style engine mounts would have to be used.

Any existing rotary in S13 swap information would have to largely be ignored, as the subframe and shock towers in a 240SX are much closer to the rear of the engine bay, while in the RX7 engine bay they are closer to the center. In my own situation, I used an SR20DET motor, and had to modify the engine mounts to push it about 3 inches rearward for the engine to be placed correctly in the bay (and for the shifter to pop out of the hole in the right spot).

A 240SX is set up for a front sump oil pan, however the subframe can be easily modified. The only parts of it you want to stay in the same spot are the steering rack mounts and lower control arm mounts. Anything else can be cut up or what have you.

If I was fitting a 12a rotary into an S13 subframe swapped RX7, Id lower it down on the subframe without the oil pan in place to see if it will fit around the rack and pinion. If it does, you're probably in pretty good shape. An oil pan is easy to fabricate, it's a tin box. The pick up tube is a little tough. You might have to find a way to slide the engine backwards or forwards about an inch for correct positioning, you'd want to use your transmission mount to know you're in the right spot. I suspect because of how short a rotary engine is, you would need to cut the center of the subframe out and brace it to have room for any kind of sump.

This is by no means an easy solution or something for everyone. This might not be anything for anyone. The FB market is too small to make a kit to sell that would be fairly expensive. This is strictly for the madman with a grinder and a welder. You can't ask the forum to help with this stuff, you just need to hope you can solve each problem that comes up before you've spent thousands of dollars on something that doesn't work. I started down this road because I had an idea of what kind of car I wanted to build, not to be fast, not to be unique, but because I knew how I wanted the car to make me feel.

KansasCityREPU, you can bolt it in backwards and I think the lower control arm positions are still similar, enough that it is workable. My initial thought there is that the S13 rack will now be pointed at the engine mount location. You can work around that by laying the rack down and passing the steering shaft through it, or modifying the engine mount location. Either way you're in for a bit of a fight. You would than have to figure out if the steering geometry would be correct since you would now have to use knuckles with the tie rod attachment points at the front, which probably puts you into FC stuff, so you then have to make sure you can build control arms that will attach to the FC knuckle's lower ball joint and have a way to make a tension strut. If the relationship between the rack location and the tie rod mount location on the steering knuckle is different from how a manufacturer set it up, you can have unforeseen steering behavior. The advantage of using the subframe as is, was that I didn't have to figure out if it would work or not, because Nissan already did that for me.

Diezel97

What size u joint was it for the steering rack?