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  #1  
Old 02-11-2011, 02:51 PM
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G-Brace???

I've been looking into different options for reinforcing the subframe on my '70 Nova and came across these "g-braces" (Hotchkis, one maker calls them "handle bars"). This particular design bolts to the firewall using the fender bolts and bolts to the upper control arm mount at the frame. In this case, the vehicle is a unibody construction (body + front subframe) 68-74' Nova or 67-69' Camaro.



I also found a home-brew varient that doesn't include a crossbar, but ties into a couple more points on the firewall.



My car is going to be multipurpose, probably 80-90% street cruising, 10-15% autocross, and 5% dragstrip. I currently don't plan on putting a cage in it, but it will have subframe connectors and solid body mounts. I'm also stiffening up the suspension (springs, swaybar shocks yet to be selected). I plan on notching my original subframe in a few places to clear LSx accessories and I was thinking something like this with a crossover bar might help compesate for the loss in strength.

Does anyone have experience with this type of brace? Does it make a significant impact on torsional stiffness? What are you thoughts?
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Last edited by TheBandit; 02-18-2011 at 01:04 PM.
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Old 02-13-2011, 03:07 PM
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I built a upper strut tower bar for my Celica, but it's a different beasty from your Nova.

From what I've read the idea is to stiffen up any flex in the unibody by triangulating body structures.

Being that the Nova is a body on frame, I would think that you would need to add braces to the frame and then attach the body parts to the bracing.

I would imagine that stiffening up the front clip as a whole would make it a better structure, but I doubt it would make a different with chassis stiffness.

Something for thought.....

-Jeff
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Old 02-13-2011, 04:15 PM
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I would definitely lean more toward the Hotchkis design then that homebrew design. The homebrew thing doesn't look like it would add enough stiffness to justify the added weight. The Hotchkis design with the crossover bar looks like it might give some extra stiffness and coupled with sub-frame connectors would make a difference in handling. I think that the problem is that without a cage of some sort to tie into the cowl/firewall flex will make this type of mod much less effective. But I could be wrong too.

I did a cage once on a Nova (65 if I remember right) with a back-half and sub-frame connectors and we tied the sub-frame into the cage in a similar manner but that was a drag car and honestly I never saw the car run or knew how much all the work we did helped. For that matter I think the car sits forlorn without engine and never finished.

Sorry to ramble. I hope it helped though.
Jaysin
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Old 02-14-2011, 08:42 AM
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The new Hot Rod has an article about putting a set of the Hotchkiss bars in a 2nd gen Camaro. I haven't read it yet, so I can't say where it falls in the spectrum of "Paid Advertisement" vs. "Tech Article".
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Old 02-14-2011, 01:19 PM
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Quote:
Originally Posted by Blind Studios View Post
I built a upper strut tower bar for my Celica, but it's a different beasty from your Nova.

From what I've read the idea is to stiffen up any flex in the unibody by triangulating body structures.

Being that the Nova is a body on frame, I would think that you would need to add braces to the frame and then attach the body parts to the bracing.

I would imagine that stiffening up the front clip as a whole would make it a better structure, but I doubt it would make a different with chassis stiffness.

Something for thought.....

-Jeff
The NOVA does not have a frame they are Unibody..





As for the hotchkins design yes it helps.. I make all the front end parts for BZ Rods, but this is to turn them into Gassers.. If you need any plates I have the upper firewall ones sitting on the shelf if you want to make up your own.
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Old 02-14-2011, 05:44 PM
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My bad.....

So pretty much just bracing the lower front of the sub frame to the upper firewall????

Meh....

-Jeff
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  #7  
Old 02-15-2011, 02:16 PM
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I've been looking at the hotchkis design recently. I came to it because we were looking at a similar situation. While I don't know your Nova at all, in general concept I think that there is a definite gain. The cowl of most vehicles has a fair amount of strength. With a cage and sub frame connectors I think that something like the "handlebar" design could be a HUGE gain in rigidity. Even without the cage I think it will make a significant gain. Tieing from the upper A-Frame mount to the cowl is a great idea. The cross brace will help even more.
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Old 02-18-2011, 05:47 PM
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i just got a 72 nova and am picking it up saturday its in real rough shape but no rust... gotta love so cal but anyway does anyone have pics of tying the subframe together or bracing im planning on a stroked ls1 going in it and am concerned about flexing the body chassis whatever
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Old 02-22-2011, 12:13 PM
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For those that don't know the 3rd gen Nova / 1st gen Camaro, they both are unibody cars with the same subframe under the front. The rear doesn't have a separate frame - it's built into the body.

Here is a good picture showing just the frame with the Hotchkis "handle bars".


Here is what I'm thinking for my Nova. The yellow shows where I'll be notching the frame for engine accessory clearance. The red shows where I would tie the bars into the frame on either side of the control arm mounts. Hotchkis ties their bars directly to the control arm mounts, but this requires tubular A-arms and I don't plan on those yet.


I'd like this thing to be bolt-in, so I'm thinking about welding some mounting plates onto the frame as placeholders, then tackling this project after more of the car is assembled.

Another idea I thought about is adding an additional set of bars like these shown in blue back to the center of the firewall, but I'm thinking this may be overboard (and overweight) for a car that isn't even caged.



If anyone has any good ideas for welding bolt-on points to the frame, I'd be very interested to hear them. I was thinking about tapping a thick plate, then welding that to the top of the frame. I don't have much access from inside/underneath. What is standard/good practice for this?
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Old 02-23-2011, 02:49 PM
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Id think the weak link with a setup like this is the strength of the firewall where it attaches as thats mainly what you are relying on here to keep the subframe from twisting.

I like the look of your red bars. It reminds me of what a front bar on a cage might look like. Its too bad the booster etc is in the way. The bars would be much stronger if they were straight without all those bends from the firewall. Which is prob why Hotchkiss put the other bar to the A arm and the large gusset (as well as the cross brace) in for.

I would try to minimize all the bends if you make a set. Maybe you'll have more room with the lsx? And if you do manual brakes that would clear up a ton of room on the drivers side as well.

Hotchkiss' design may not be the best but they were forced to 'package' it to fit most peoples needs.

Dan
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Old 02-23-2011, 02:54 PM
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as for attaching it.... what about welding on U brackets (or individual triagle frame tabs)and then use some non lubricated rod ends at each mouting point. It would be slightly adjustable (you could preload some if you wanted), all the hardware would be in double shear, and it would be easily removeable, and not require access from below, or bolts threaded into blind holes. Plus, I think it would look pretty badass.

Dan
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Old 02-23-2011, 05:06 PM
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i was hoping to hear better news im thinking about puting a front end from a el camino with power breaks and a better stering setup and brace it all in but it looks like a full cage is gonna be the only way to get the structural integrity im gonna need
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Old 02-23-2011, 05:20 PM
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Today I found a really good thread on how this type of brace changes torsional rigidity. The guy used a simple method of measuring and incrementally made modifications (including solid body bushings, subframe connectors, and a similar firewall-to-frame conector) and eventaully improved torsional stiffness by 40% on his first gen Camaro. VERY interesting read. I will have to repeat if I do anything like this.

http://www.pro-touring.com/showthrea...and-increasing
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Last edited by TheBandit; 02-23-2011 at 05:25 PM.
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Old 02-28-2011, 03:24 PM
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I kinda like this idea for the crossbar on top. Plate-arch rather than tube


I guess that would take a shrinker to make from one piece or you could cut all the sides and fully weld it. Or you could roll rectangular tube.
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Last edited by TheBandit; 02-28-2011 at 03:59 PM.
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  #15  
Old 02-28-2011, 06:13 PM
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What I do on the Gasser units is weld .375 plate on to the frame.. It is tapped 3/8x16 the the side bars have a plate welded on them that bolts to the front top frame horn the other just bolts up top at the Firewall.

This is the weld in model.. but picture what I descibed at the new frame


Crappy pic of Firewall tie in
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Old 02-28-2011, 06:39 PM
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Quote:
Originally Posted by TheBandit View Post
I kinda like this idea for the crossbar on top. Plate-arch rather than tube


I guess that would take a shrinker to make from one piece or you could cut all the sides and fully weld it. Or you could roll rectangular tube.
sold this is the design im leaning twards since the plan is to cage the whole thing because of the uni-body
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Old 03-01-2011, 12:32 AM
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sold this is the design im leaning twards since the plan is to cage the whole thing because of the uni-body
Based on that picture,... that is no unibody, that is a completely new tube chassis.
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Old 03-01-2011, 09:58 PM
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exactly thats why its the same idea im going for i just dont trust the unibody the car had a little cancer in the florboard i got rid of but im just sketchey bout the strength of it seeing as im gonna be puting my kids in it once in a while for cruse nights and car shows
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