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RiggetyWrecked

Subframe Connectors to handle 300lb/ft

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Hello, my name is Ian. I'm new here. Long story short, I have a 280Z 2+2 that will be receiving a supercharged Buick 3800, which should be making around 300lb/ft of torque with basic bolt-ons. I'm trying to get the frame more or less situated before I commence the swap. The floors and under floor rails are completely trashed, but the rest of the structure appears to be sound after ripping out all the interior.

 

I'm getting ready to order materials to build SFCs and new floors, and I'm torn between getting 1x3 .065 tubing or 2x3 .083. My natural tendency is to overbuild, but will 2x3 .083 be serious overkill for a primarily street driven car? I don't mind a tad bit of extra weight if it's worth the added stiffness.

 

Sorry if this has been discussed already. I've been browsing searching and browsing the fab forum, but haven't seen any definitive answers one way or the other.

 

Regards,

 

Ian

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The Z cars are a monococque, or unibody, chassis.  Essentially just steel boxes with stiffening elements, either extra "rails" or bends, strategically placed around the box.  And the stiffening is done to specific purposes.  You're implying that you'll be drag-racing since you're talking about high power.  Thicker subframe connectors might be oversimplifying your situation.

 

Generally, people recommend a full cage if you really want to stiffen things up.  SunnyZ and RebekahsZ do drag-racing.  Read through their past threads.

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Thanks for pointing me in the right direction. I don't intend to drag race. It's going to be a street car that I may end up auto-crossing with. I chose the 3800 V6 because of its potency given that it is dimensionally smaller than just about any V8, so I can keep the mass low and center (not to mention they're cheap and plentiful where I live). My focus is to have a car that will corner and accelerate well.

 

Ian

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I'm not going to cage it (again, street car). I may do stitch welding in conjunction with the SFCs if it turns out to be necessary. To be as explicit as possible, I want the frame to not wonk itself up under the torque it will have or from the stiffer springs which it will get at some point. That's my end game for the chassis -- avoid self destruction and hopefully let the suspension actually do its job.

Edited by RiggetyWrecked

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The Z cars are a monococque, or unibody, chassis.  Essentially just steel boxes with stiffening elements, either extra "rails" or bends, strategically placed around the box.  And the stiffening is done to specific purposes.  You're implying that you'll be drag-racing since you're talking about high power.  Thicker subframe connectors might be oversimplifying your situation.

 

Generally, people recommend a full cage if you really want to stiffen things up.  SunnyZ and RebekahsZ do drag-racing.  Read through their past threads.

300hp isn't really "high power." It's plenty in a Z, but not really that much. 500hp+ is a different story. SunnyZ and Keith both have a good deal more than 300hp.

 

These are John Coffey's suggestions for a street car.

 

1. Seam Weld (every sheet metal seam overlap.)

2. Bad Dog Subframe Connectors

3. Weld-In Roll Bar.

4. Welded In Rear STB.

5. Triangulated Front STB.

6. Radiator Core Support Reinforcement.

7. Transverse Link Bracing Reinforcement.

8. RT Diff Mount.

9. Tubular Seat Mounts.

10. Box Upper Frame Horns to Firewall/Cowl.

11. Reinforce Pedal Box/Brake MC Mount.

12. Reinforce Front ARB Mount.

13. Reinforce Front Strut Tower to Frame Rail Junction.

 

All that should be sufficient if you only plan on 300hp.

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I don't think they do nearly as much as a roll bar, and triangulated strut tower bars do. I believe (don't quote me) John had the Z chassis analyzed at one point and found that the chassis flexed like a hinge at the front and rear bulk heads, which are roughly at the firewall, and at the rear door jamb.

 

I'm just a reader here, so take that with a grain of salt. Unfortunately John is no longer with us to answer these questions himself. This is my best understanding of what he has said.

 

To answer your question, I would go with SFCs from http://baddogparts.com/ although you have a 2+2 which complicates things slightly.

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Generally, for a long beam you want to avoid stress risers, areas that will do all of the bending as loads concentrate there.  So you'd want them to be the same gauge and size as the frame rails, with smooth welds and few discontinuities (bumps, crinkles, bends, etc.).  Nothing is completely rigid so you want the loads and subsequent bending to be distributed smoothly down the length of the beam. 

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Just drive it as it is. The year or two you spend stiffing the chassis for 1% improvement could be better realized without any chassis improvements, but with a 50% improvement in driver experience. I don't know if you really realize how much work you are signing up for....

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I know it's going to be a bit of work, but I have a lot of free time to throw at this right now. My floors are at full Flintstone status and the rails are totally rotted out, so those things are definitely getting rebuilt. I just thought it would be silly to do that much and not connect the subframes while I'm down there. I can do the other items incrementally as I please. While it is a street car, I'll be running a stripped interior because I'm already half deaf and just generally predisposed to be "that guy", so going back in on it won't be much more than grinding off some primer/spray paint, welding and then repainting the afflicted area.

 

Cheers.

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Ditch the 3800 and go with the 3500V6, it makes the same power as a stock 3800SC, with NO boost. 2004-2006 malibu/impala, dirt cheap. Lighter, stronger, smaller, better cylinder heads, and if you just need blower whine:

 

KIMG0217_zpsaaisee8v.jpg

 

SixShooter here has one in his Z, plus a GT3582R IIRC, and it scoots. I'm putting the one above into my pickup truck in a few weeks.

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As long as the car isn't rusted out, you will be fine with what your putting down. I don't even have strut braces and my car seems to be just fine. My engine is 325hp/340tq at the flywheel. I don't drag it at the track or road course either.

Like most everyone else here, if you just building a street car with some "spirited" drive time, a cage is going to be nothing more than something that will get in the way. 

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Well... after some more extensive digging into the chassis, I do believe mine is rusted past the point of no return. At least past the point that my budget and skill set could return it, anyhow. After cutting out the passenger floor pan, I found rust all the way up the tilted pan the goes under the rear seat hump, as well as a good portion of the underside of hump part. 2/3 rocker vertical members and the bottom of the quarter were also completely rotted from the wheel well to almost a foot forward. The driver's side isn't looking a whole lot better.

 

New plan: Sell of anything salvageable (suspension, diff, subframes, body panels), and start fresh with a ZX platform, as I understand they are sturdier and less prone to rust. My interest and skills are definitely more on the mechanical side of the spectrum VS body and fab work. Chock this up as a learning experience, I guess.

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I will confirm with my meager experience that the front hinges pretty much right at the firewall with rotten rails/floors. Not much there to hold it up. The rear will deform as well, can't close my hatch when the car is slanted. 

 

I did 2x3 0.083, the 2x3 is harder to do as if you stay with the stock rails you end up with a beam coming up through the floor. 1x3 is better in that regard, 0.065 is 16ish gauge so thicker then the floor. I wanted to be able to jack the car up by the rail so I added additional plates and went for the thicker material. 

 

As others have mentioned 300ft/lb isn't a whole lot of torque, I would say replacing what you have lost should be adequate for that power level.

 

If you are worrying about power affecting the frame rail that would imply launches and such, then you have to combat the twisting motion of the car which means heavier rated springs which in turn means reinforced suspension mounting points which would best be accomplished via a cage as NewZed mentions.

 

I would say a triangulated STB for the front is high on the list as well as stitch welding seams that are coming loose or can come loose. The engine bay frames are C-channels and prone to rust so that should be looked at. If the floors are gone then the rockers will not be far behind. That list RT listed is really golden, there used to be an album associated with that list. Quite overkill for street, but it would definitely address the weak points in the chassis. Keep in mind that it is more of a package, you reinforce one part of the box then other parts can fold. Either let the box flex, or make the box unbreakable, try not to compromise there or you will get some weird stress points.

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