Quick question regarding front subframe replacement

[AkumaNoZeta]

It's been a while since I've posted on here. My car is gutted and the passenger side floor board was removed, next month I'm getting a Miller MIG and I'll be fabbing up my own connectors and floors. After I get that done I'm planning on cutting out the old front subframes and replacing them with 2X3 0.063" tubing.

 

My question regards to the fact that a lot of you with lowered Zs have drilled out a hole 1" above the original on the crossmember to raise the roll-center and I was thinking since I'm replacing the whole sha-bang anyways if it would be a bad idea to raise both the frame rails 1"? I figure by doing that then the TC bucket would also raise an inch so the anti-squat stays the same and the sway bar mounts being higher would prevent any chance of it binding.

 

It's an early 260Z by the way. Would 0.063" tubing be thick enough too? I know most people here use 0.085" but I can't find it locally.

Edited December 22, 2011 by Grim

[redneck1545]

find a good metal dealer/steel yard. Most suppliers will carry or can at least order .085 walled 2x3 square tubing. I ordered a full 20' stick for my subframe connectors.

Don't know what your plans are really but I tied mine from the rear control arm mounts all the way up to the T/C box. I can give you pics if needed.

 

Lets tackle the first problem with the floors and 2x3 tubing though. 1" stays below the floor boards and 1" comes into the cabin area. I made custom floors in two sections per side because of this.

The left outer and inner as well the right side outer and inner. I came across my measurements, as far as the bends in the outer pieces go, the other day and as soon as I find them i'll post em up for you.

 

I made my floors from 16ga steel and connected them to the trans tunnel, aft and fore floors as well as the side of the subframe connecter with 1"x1" angle out of 16ga as well.

It helps if you have access to sheet metal brakes and shears.

 

Now the second problem of relocating your front frame rails 1" higher...Dont do it...It will cause an unforeseen amount of fitment issues with everything else that attaches to them.

 

And I think your confusing subframe connectors with frame rails. They are not the same. If your just replacing your floors and subframe connectors your NOT replacing the whole sha-bang as you call it. Merely from the T/C mount back is getting worked.

 

We drill the hole 1" higher for a reason. If you were to move the entire front frame 1" higher in an effort to not drill the hole your creating alot more work than needed.

It's much easier to drill four holes for proper suspension geometry than it is to fabricate a whole new front end. Your steering rack and more importantly, your engine will all be one inch higher if you were move all that stuff upwards too.

Your CG would be WAY higher, which completly negates any advantage you just tried to create by lowering your car in the first place.

 

I think you need to do a little more reading, your thoughts about roll center/suspension geometry and such are skewed.

 

Get through the floor and subframe replacement first and then decide what else you want to tackle.

[AkumaNoZeta]

I know the difference between subframe connectors and frame rails. I was going to use 2X2 tubing for my connectors from TC to the rear crossmember and 16g for the floors like you mentioned. But my front frame rails are in bad shape as well with small rust holes above the crossmember and the driver side sway bar mount is crumbled. You did bring up a point that I forgot to think about, the engine is attached to the crossmember. I've spent so many years looking at other people's swaps and I forgot about that since most swaps result in people making a separate crossmember for their engines.

 

That's why I asked it here. I knew there was something I wasn't thinking about. I guess I'll just replace the front frame rails with 2X3s like other's have on here before, in the stock location and then after I have the final ride height established I can measure the pick-ups points, find the instant center, and map it out so I can play with a string computer like Carroll Smith and see where the best spot would be for my particular car.

[redneck1545]

I would use 2x3 for the subframe connectors and 2x2 for the front frame rails.

 

And thats why I love this place, so much information on here. I've been building my car in my head since back in 2004 and then I found this website and have been sifting through the massive amount of information ever since.