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Discussion Starter #1
First off I tried the search function but came up with nothing.
I currently have MM full length XL sub frame connectors welded on but still feel like the car is flexing and twisting under heavy cornering and loads in general. What would be the next step be to stiffen up the stang. It is a 1990 coupe. Also I can still feel the car bow front to back if i hit a divit in the asphault mid turn, and can still see stress marks appearing paint/body. (I know the sub frames won't stop flex but expected it to help more)
Also should add, the car is street driven.

Anyone have any input/ideas on how to help with the flex?
 

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addition throught the floor pan subframes connecting the front subframe to just ahead of the rear control arm mount ( step by step in a forum on here somewhere ) also a six point tied into the subframes. i had this done on my 88 vert couldnt open the doors when i was in the air before flex problem gone.
 

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i went frm hpm welded subframe connectors to through the floor units and an 8 point roll bar... difference was night and day!
 

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+1 on through-the-floor subframes tied into a decent roll bar. If the car is a daily driver get a bar with the low slung door bars so that climbing over the door bar doesn't become a PITA.
 

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Discussion Starter #5 (Edited)
would a 6-pt with low slug door bars work with the mm sub frames or will i need to go to a through-floor set up.

Also is the only way left to stiffen her up through a 6-pt / bar or ...?
 

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Plenty of threads about subframes/infloors. Use different search terms.

What else is done to the car? When I drive a friend's car (91 coupe, subrames, Bilsteins, H&R springs, 5 lugs, everything else stock) it feels sloppy like to you describe, when compared to my car. I think (between my car and his) it's I'm used to my much more located rear axle vs his that sways like a partier on their 21 bday
 

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Discussion Starter #7 (Edited)
right now it is a 4banger with prokit springs (4 banger springs), stock fox V8 shocks and struts. Car is stick with a cam and some other stuff, making about 100 hp at the wheels (dynoed). It will be getting a 331 and an almost full mm suspension. I'm worried about the body flexing and cracking. The car is mint currently, no rust..... and want to keep it like that if I can. And it feels sloppy like the body is taking up what the suspension should be.
 

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Also I can still feel the car bow front to back if i hit a divit in the asphault mid turn, and can still see stress marks appearing paint/body.
Where on the body are you seeing stress marks?

Not exactly a Fox body, but this might give you some ideas...Chassis Reinforcement
 

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Discussion Starter #9 (Edited)
Where on the body are you seeing stress marks?

Not exactly a Fox body, but this might give you some ideas...Chassis Reinforcement
on the roof, along the the top of the door/quater window. Along the quarter pillar between the quarter window and rear window. Along the edge of the trunk on the quarter panel piece. And a couple of other spots.
 

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On the qtr are you possibly seeing the seam where the roof/body joint is?
I have been driving foxes since 1988 and have not had this issue. I have only seen body flex issues on pretty hardcore mustangs.
 

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I wouldn't recommend a full roll cage if you are street driving your car. Unless you like to strap on a five point harness and wear a helmet when you go to the grocery store, of course.
 

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On the qtr are you possibly seeing the seam where the roof/body joint is?
I have been driving foxes since 1988 and have not had this issue. I have only seen body flex issues on pretty hardcore mustangs.
A buddy of mine in college (this is around 1995) had an early '90s Fox coupe with heads, cam, intake, headers, etc. as well as a pair of old school style traction bars. He beat the holy hell out of that thing and you could see that the traction bars not only hit the rear subframe as they were supposed to, but they'd also sometimes hit the unibody. His car had stress marks in the quarter/roof area as the OP described. I can't say I see a ton of Fox notchbacks but I have never seen or heard of another one with stress marks before or since until this post.

As far as roll bars go (I also would not recommend a full cage if it's at all used on the street), of course you don't have to have one with through-the-floor subframes, but they really do tie the front and rear subframes and the roll bar all together and form a pretty stiff setup. Going with a bar that doesn't have through-the-floors will definately (as long as the bar is decently designed) add stiffness to the car and will help distribute some of that load that's going into the roof away and into the bar, how well the system works depends on the setup and what compromises you make in it.
 

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The Stifflers setup seems nice. I'm running the MM XL welded braces, MM 4-point strut brace, and MM 4-point K-member brace. Also had a steel bar/brace welded along the floor between the rear shock towers (essentially tying them together) after the welds on one shock tower broke along the trunk floor.

It's a 92 vert so different from yours but all these additions really tightened up the car.
 

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Was looking into it. like the idea of a custom 6pt more than through the floor sub frames.
What I'm saying is that some 6 or more point bars do include the through-the-floors as part of the design. Not all do, and again, it's not a requirement, just a good design as it mates the front and rear subframe at the same plane instead of an offset plane like external SFCs do.

That being said, you'll be just fine with a well thought out 6 point and your existing SFCs, just make sure whoever designs the bar knows what they're doing.
 

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Does welding up the seams in the floorpan and other areas provide any worthwhile improvement on foxbody cars?
 

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Does welding up the seams in the floorpan and other areas provide any worthwhile improvement on foxbody cars?
That's a good question. I know it's universally known as a good idea on just about any car with racing intentions but I've never heard any before and after impressions on doing this. Anyone?
 

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Not a fox but I did it on my '00 mustang race car. I spot welded along the top and bottom of all the seams that join the front subframe to the floor pan and the floor pan to the rear subframe, including the front beam that the seat bolts are anchored to, the rear cross beam and the pinch welds. I also spot welded the subframes to the floor pan under the car. Full cage and I also tied the cage to the A pillars with some flat strapping that I punched holes in.

Tack weld 20+ pounds of additional bracing to shore up a limp noodle or try to fix the wet noodle? I chose to fix the noodle.

Can I tell the difference, I dunno I never drove the car before I did all the welding. So is it stiffer? I think Im headed in the right direction with not alot of added weight.

Car has the short Kenny Brown SFCs.

IRS DOHC car thats 2800 lbs empty.

 

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Griggsracing recommends the through the floor subframes in addition to the ones under the rails, quoting something like "a thousand percent stiffer than stock", and being "stronger in a vertical plane". Look it up on his website. I did his kit on my 84 hatch, and now my other foxes feel like flexible flyers.
 
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