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How To: Reinforced Frame Rails

Old 08-16-15, 01:00 AM
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How To: Reinforced Frame Rails

This guide is a How-To install the V8 Roadsters' Mazda Miata frame rail reinforcement frame rails onto a FC3S RX-7.
They can be found here: NA/B 90-2005 - Suspension and Drive Train - Frame Rails - V8 Roadsters

It is best to perform this with 2 people as it will go a lot quicker. I am legally not responsible if you screw up your car or hurt yourself or your friend. Thanks!

Note:
Flying Miata does make reinforcement frame rails for the mazda miata. However, we did not test these for fitment and chose the V8 Raodsters one as it is thicker and cheaper. Also the design for the Flying miata kit is different in that it has cut out sections for weight savings. We did not know if the holes that were cut from the rails would match up for the exhaust hangers and if it didn't match up then we would have felt scared to cut an already cut up design, possibly ruining the integrity of the reinforcement frame rails. For these reasons, we decided to go with the V8 Roadsters' kit.

I would like to say a quick thank you to Jim at "Built by JIMMMMM Motorsports" for being the tester for the first set that he and I installed on his LS1 swapped FC and for the help of doing it on my car as well!

Review:
I definitely feel like there is reduced flex on hard launches and heavy braking, I feel this is due to the frame rails being linear in reference to the body. Definitely improved ride quality over bumpy roads and bumps. The car just feels more solid and stiff as a whole. But who knows, it may be confirmation bias. Another benefit to these is that if you are to use a rack on your car, the rack is placed under the frame rails. These will prevent the frame rails from being further damaged and further pressing up the floor board. The rail reinforcements can support the car and not bend.

To Address some criticism on this mod:
Why did we chose to go with miata ones instead of fabricating ones?:
The reason that we chose to go with these is because they were cheap. If I were to fab my own that would of been fine but I still would of had to buy the bolts, small and large washers and nuts. Grade 10.9 bolts from fastanel cost 3 dollars each. 22 bolts would of been 66 dollars, for the bolts alone. That is not including grade 10.9 nylon locking nuts and the large and small washers. Not to mention cost of the metal and coating them. It was just cheaper to buy these as they are a great quality and fit.

Why we don't care that they do not fit the entire length of the frame rail?:
We do not care that they do not cover the front section of the frame rail because the front section is reinforced and does not need any more reinforcement. Only the latter half is weak and frail. This reinforced frame rail covers the entire weaker half and works for our purposes.

Aren't these only good for verts? The coupes are stronger than the verts.:
These work on strengthening coupes and verts. Honestly all FC3S frame rails are super freaking weak. I would do this on any FC!

Why we didn't weld them in?:
This is to support of INTERCHANGEABILITY. If these frame rails were ever to get damaged because they are bolted in ordering and replacing these would be fairly simple.


Tools used:
Jack
4x Jack stands
Phillips and flat head screw drivers
Socket wrench
Drill
Vice Grips
Circular Saw (If you decide to go with the box method mentioned below)
7/16 Drill Bit
16mm wrench/socket for the bolts for the frame rails
14mm wrench and shallow socket for seat bolts
10mm wrench for fuel rail bolts and socket for the self drilling bolts
12mm socket for exhaust hangers
A nice Hammer!

Parts you will need to get at the store:
Four M8x1.25 bolts for the exhaust hanger bolts (Can be picked up at Lowes)
A box of #14x3/4inch Self Drilling Hex Bolts (Should be 10mm hex head, again can be picked up at Lowes and look like the picture below)

Ensure there are 22 large washers, small washers, nuts and bolts that come with the kit

Picture of the kit as I got it

Last edited by astrum; 08-16-15 at 01:35 PM.
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Old 08-16-15, 01:01 AM
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Steps to take:
  1. Jack up the front and rear of the car.
  2. Place jack stands under the lower control arms in the front and under the rear subframe bushings (or somewhere else as long as it is out of way of the frame rail).

  3. Using a 14mm socket/wrench remove the seat bolts from the rails.
  4. Remove the seats.
  5. Using a Phillips screw driver remove the door sills and place them in the rear out of the way.
  6. Go underneath the car and place the first frame rail behind the reinforced section, I started with my drivers side (USA passenger side) as it does not have fuel rails going along them. For my drivers side I used the passengers side rail but on a USA car, the passenger side rail would go with the passenger side. To make sure you have it correctly the V8 Roadsters logo should face the outside. The picture below shows the reinforced section. The rail should be placed behind the reinforced section. This is so that it extends all the way to the very end of the rail towards the rear. The reason for this is because these rails were made for a miata so sadly they do not extend over the entire frame rail.
  7. After you are holding it in place, have a friend jack up the jack underneath the frame rail to hold it in place. This picture is of the USA drivers side and my passenger side, however it is the same process on the opposite side. REMEMBER TO PLACE THE RAIL BEHIND THE REINFORCED SECTION!
  8. Mark with a pen or the drill where the 2 holes are for the exhaust hanger on the inside of the frame rail
  9. Have your friend lower the jack and take the rail out from underneath the car
  10. Drill 2 holes or cut out a box for the exhaust hanger. This may take some re-measuring. We decided to go with a box as it was easier. To cut the box I used a circular saw.
  11. Once you have the box/holes place the frame rail back in place and then have your friend jack up the jack to hold it in place.
  12. Return to the top of the car and remove the gas and trunk latch plastic pieces by removing BOTH Phillips screws and removing the plastic tab with a flat head screw driver.
  13. Remove the carpet by lifting up on the white plastic pieces that the carpet is attached too. The carpet also needs to be pulled out from the plastics by the pillars.


    [IMG]https://cimg0.ibsrv.net/gimg/www.rx7club.com-vbulletin/2000x1124/80-20150813_024650_8479d5c4c8540856f8a56b44b992d60250 099d5c.jpg[/IMG
  14. Once you are at this step it is time for you and your friend to take their places inside the car and underneath it.
  15. You or your friend will sit in the car and hold the carpet up while you go underneath it and drill up into the cabin. The person holding the carpet should place their feet out of harms way by putting them onto the center reinforced section. I do not take responsibility if they hurt themselves.
  16. The person underneath SHOULD drill 1 hole on the outside towards the rear of the car.
  17. The person on the top will drop in a bolt and large washer through the hole.
  18. You should tighten the bolt first before continuing. To do this you will use 2 16mm socket wrenches or a 16mm socket and a 16mm wrench. I recommend the person on top use a 16mm wrench to fit between the carpet/padding.
  19. IF you cannot put the small washer and nut on the bolt from underneath, meaning now enough threads are exposed, then the chances are that your floor is bent upwards. To fix this issue have your friend inside the car hammer down on the bolt and washer while it is in the hole. This will hammer the floor back into place and give you more thread to place the washer and nut on from underneath.
  20. The reason for bolting in the frame rail before continuing is that it likes to move around and you don't want the frame rail to move around a lot and screw up your positioning. So tighten the bolt before continuing.
  21. After you have created about 3 holes and bolted them down all the way you can remove the jack to give yourself more room.
  22. Continue doing this until you have done all 11 holes for the (JDM Driver's side) USA passenger's side rail.
  23. A quick tip for the front bolt holes being drilled, it is hard to hold the front carpet up without removing it all the way, use your feet to hold up the carpet for the front holes to be drilled, like so:

Last edited by astrum; 08-16-15 at 01:33 AM.
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Old 08-16-15, 01:02 AM
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  • By the time you are done with all 11 holes it should look like this:

  • Once you are done tightening all the bolts it's time to go underneath the car and install the exhaust hanger.
  • Install the exhaust hanger as shown using the bolts that you have purchased at Lowes/Insert-Random-Hardware-Store



  • Now for the harder side, the one with the fuel lines aka the USA driver's side and JDM passenger's side.
  • Get underneath the car and use a 10mm to remove the fuel line bolts.
  • Pull the fuel line out of the way, don't put too much pressure on the fuel lines but keep them to the side out of the way.
  • Align the frame rail behind the reinforced section and then mark where you will have to cut a box/drill holes for the exhaust hangers.
  • Remove the frame rail and drill the holes/cut the box for the exhaust hanger
  • Get underneath the car again and pull the fuel lines out of the way and put the frame rail in place. Once it is in place have your friend use the jack to hold the frame rail in place.
  • Start drilling 2 outside holes through the frame rail.
  • Place the bolts inside these 2 holes and tighten them down.
  • Now for the tricky part drilling the 1st inside hole next to the fuel lines. Carefully pull the fuel lines out of the way and drill 1 hole. Have your helper drop the bolt in and tighten it down.
  • You can now remove the jack.
  • Continue doing the outside as it is easier. Once you have done the outside continue on to the inside carefully drilling the holes while holding the fuel lines out of the way.
  • Once you have finished tightening everything down reinstall the exhaust hanger with the new bolts you purchased.
  • Now we have to readjust the fuel line holder's to fit the frame rails.
  • Here is how the fuel line holders look stock:
  • Carefully bend the tab using pliers or a vice grip. I found a vice grip worked really well.
  • Holding the bent tab onto the rail drill in the self-tapping bolts using a 10mm socket and a drill to socket converter. The finished product should look like this:
  • Once this is done continue doing it for the other 2 fuel line holders.
  • After you have connected the fuel line holders to the reinforcement frame rail, you are going to gently press back the fuel line tab to give it a kind of bend. The purpose of this is to offset the fuel rail so that it is slightly below the frame rail. This is for protection of the fuel lines and to prevent someone from accidentally puncturing the fuel rail if they were to jack it up from there. The finished product should look like this:
  • After this you are pretty much done. Reinstall the carpet, door sills, seats and then lower the car and you are good to go.

Last edited by astrum; 08-16-15 at 01:12 AM.
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Old 08-16-15, 08:30 AM
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Great review, I feel like these would make a massive difference in a vert actually. I think Im going to give them a shot. On a side note though, I would highly recommend slathering those washers and hardware with some kind of silicone so you seal up those holes in the floorboard. Water will inevitably work its way in there, and I dont think any of us want rusty frame rails.
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Old 08-16-15, 01:37 PM
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Originally Posted by NoMorePoison View Post
Great review, I feel like these would make a massive difference in a vert actually. I think Im going to give them a shot. On a side note though, I would highly recommend slathering those washers and hardware with some kind of silicone so you seal up those holes in the floorboard. Water will inevitably work its way in there, and I dont think any of us want rusty frame rails.
Thank you for the recommendation. You are definitely right on the silicone. It would definitely help. I have already purchased silicone to place around the washers of my cusco cage's bolts so I will just use that. I will add that to the guide as well.

Last edited by astrum; 08-16-15 at 08:32 PM.
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Old 08-16-15, 02:27 PM
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Originally Posted by NoMorePoison View Post
Great review, I feel like these would make a massive difference in a vert actually. I think Im going to give them a shot. On a side note though, I would highly recommend slathering those washers and hardware with some kind of silicone so you seal up those holes in the floorboard. Water will inevitably work its way in there, and I dont think any of us want rusty frame rails.
As a turbo vert owner who may be losing his front strutbar to make room for a Taurus alt, this thread is very interesting to me.
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Old 08-17-15, 09:26 AM
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Hey guys ended up spraying it with this product from home depot.



3M also makes some which you can get at NAPA.
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Old 08-17-15, 11:14 AM
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How does it handle the floor jack now?
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Old 08-17-15, 11:41 PM
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Originally Posted by JustJeff View Post
As a turbo vert owner who may be losing his front strutbar to make room for a Taurus alt, this thread is very interesting to me.
The strut bar would be for the flex between the 2 strut tops. You still might want to fabricate the front bar to fit
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Old 08-18-15, 07:16 AM
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Originally Posted by Rob XX 7 View Post
How does it handle the floor jack now?
^THIS!

I wish I could blame the first owners of my FC, but in a pinch, I too have managed to dimp the OEM rails with a floor jack
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Old 08-18-15, 12:31 PM
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Lowered the car with these on and they were fine. I haven't raised the car with them yet but assume it would be fine as well.
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Old 12-25-15, 11:28 AM
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Has anyone thought about welding these on?
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Old 12-25-15, 11:43 AM
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If you are going to weld, I would just pull up the carpet cut the floor above the frame rails, and drop square tubing INTO the frame rails and weld them in place.

Through the floor subframe connectors are much stronger. Mustang guys have done this for decades.


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Old 12-26-15, 10:41 AM
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Seems like laminating frame reinforcement sleeves over the existing rails would create a massive layered rust pocket.

Some drain holes should be drilled.
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Old 12-29-15, 10:21 PM
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The rails are open at the front and the rear. I would expect them to drain decently well. But, we all know rust never sleeps, so probably holes drilled at the 1/4, 1/2, and 3/4 lengths should work.
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Old 12-30-15, 10:48 AM
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depends where you live, western US it wouldn't be an issue, most of the rest of the world it should probably be addressed.

my car was pristine until i moved to florida, now anything that can rust is rusting even under a covered carport.
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Old 12-31-15, 12:09 AM
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Up here in Washington, it's hit and miss on what will rust and when. It rains here in the Seattle area. A lot. There is a reason this area is the depression capital, just from nonstop rain, anyways, since it doesn't really freeze or snow up here, it's mostly just regular rain. Most of the vehicles that are rusted out are from the midwest, or somewhere where they use salt on the roads. This will likely change around here though. A few years ago, the Seattle mayor was trying to do the "green" thing and mandated that roads be cleared of snow with sand instead. This was a particularly bad snow storm we had, so there was pandemonium just from the snow. Now we had dump trucks dumping tons and tons of sand, which promptly clogged the sewers once the snow melted. Caused flooding in the streets and huge amounts of cleanup. The city doesn't want to make that mistake again. The sand did more damage to the local ecosystem than salt would have.
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Old 01-03-16, 07:10 PM
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Rather than open the floor and drop the bars in, could you open the back of the frame rail and run the reenforcement in from there then weld it?
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Old 01-03-16, 07:52 PM
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Originally Posted by iamsisyphus View Post
Rather than open the floor and drop the bars in, could you open the back of the frame rail and run the reenforcement in from there then weld it?
No because the height of the frame rails changes slightly, and you will want to tie the bars into the floor. The through the floor style subframe connectors are the most work, but yield the best result.
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Old 02-13-16, 08:38 PM
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Originally Posted by ACR_RX-7 View Post
Up here in Washington, it's hit and miss on what will rust and when. It rains here in the Seattle area. A lot. There is a reason this area is the depression capital, just from nonstop rain, anyways, since it doesn't really freeze or snow up here, it's mostly just regular rain. Most of the vehicles that are rusted out are from the midwest, or somewhere where they use salt on the roads. This will likely change around here though. A few years ago, the Seattle mayor was trying to do the "green" thing and mandated that roads be cleared of snow with sand instead. This was a particularly bad snow storm we had, so there was pandemonium just from the snow. Now we had dump trucks dumping tons and tons of sand, which promptly clogged the sewers once the snow melted. Caused flooding in the streets and huge amounts of cleanup. The city doesn't want to make that mistake again. The sand did more damage to the local ecosystem than salt would have.
Hmmm, I think you guys need a governator!

Hmmm, now I'm getting ideas on how to strengthen the chassis without a roll cage. Damn those new cars! You lift one corner and the whole car comes up. Must be magic. You think i can use 3 jack stands to hold the whole car up?
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Old 02-14-16, 11:20 PM
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haha nice. Luckily I live in AZ. No real rust issues here.
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Old 08-14-16, 12:58 PM
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Great thead!
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Old 05-19-17, 09:01 PM
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I been looking at doing the through the floor style subframe connectors. but I had thought, instead of cutting the floor up and dropping in a square tubes, how about cutting off the stock frame rail and use a thicker gauge metal like how the OP used in his mod. mine on certain spots has collapse. it seems to be the same amount of work to do either.
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Old 05-19-17, 09:55 PM
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Way more work and risk doing it that way. You can pound out the damage in the factory framerails very easily from the top when the floor is cut.
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Old 11-15-17, 08:44 AM
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Great thread!
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