Kudos for the design change. Maybe my car is back in the running to get one of these? Without the side braces, I don't believe there'd be contact issues with my exhaust tubing. (Plus, it was hard for me to see the benefit of those parallel-to-frame pieces.)

As for Diz's idea on side contact points (welding), the side exhaust I have required drilling the frame rails. If you even went down that road, I think it makes more sense to do the same. Everyone can drill, but not everyone can weld. Plus, it's more easily removable.

 

Still making slight adjustments before the first prototype. I took a detailed look under the car today. I think tying the system into the c-brace will work well. I will look into making the system fit well for attaching to the c-brace. I also want to split up the mounting points so welding or bolting will work well.

The rest of my day was spent working on the single gauge pod, rear lip spoiler, front ground effects and a battery relocation kit to go behind the passenger seat.

Thanks,
Brandon
www.riceperformanceproducts.com

 

tying to the C-brace?

you're referring to the C-shaped rail that locks the diff to the trans? both the diff and the engine/trans are rubber-isolated from the chassis. so this chassis-reinforcement would need to be, or, should be rubber-isolated from the C-rail. or polyurethane.

just my $0.02.

 

I think if you were to tie the x brace to the c beam (at the diff side), you would fix a major problem with diff snout.

The diff snout wants to rotate (and will snap due to the weak alum d44 case),

Tieing the diff snout into this design is a great idea.

If one was to replace the batwing and motor mount with solid bushings, now the trans, engine, c beam, and diff become a totally structurl member.

I've aslo heard that cars w/ solid motor mounts seem more responsive to throttle input, etc.

The million dollar question then becomes if noise vibration harshness becomes an issue..

I bet its not as bad as people think.

User churchkey is the member to talk to here about this. I think he made some solid motor mounts for c4.

 

Just posting so people don't think I have forgotton about this project. Currently I am finishing up the drawings to get the first prototype built. I am making changes because I want to be able to weld or bolt the main brackets. For any C-brace tie in, I will probably work on urethane mounts. They would only be necessary for reducing any vibration.

I am also working on a battery mount and new cargo cover to move the battery behind the passenger seat. It is a fairly simple project compared to the other projects so I should be done in a couple weeks. I am thinking carbon fiber for at least the cover plates.

Thanks,
Brandon
rppcorvette2@gmail.com
www.riceperformanceproducts.com

 

Nice, always great to hear updates. Keeps the interest high!

 

That's a good idea for a c brace tie in.

That way if someone wants to solidly mount it, they stll have the option to do that (via solid bushings vs, urethane)

 

Urethane would work but solid, eh, that C-beam has to float and twist a little under torque. Not much, but it does move.

 

I would like to be on the list too if your final version ties in to the C-brace near the transmission. I just snapped the front of my Dana 44 hitting 2nd gear last weekend at the drag strip. I am thinking of redesigning the front of my c-brace (Cut the front and bolt down possibly with an L bracket) so it doesn't bolt and hug around my trans and thus twist with engine torque. It would bolt down to a transverse bar (hopefully your final version) cushioned with a poly bushing so the c-brace only has vertical only travel capability. If your brace can allow for a trans cross member and the customer can choose to separate the twisting motion of the c-brace you will also have a HUGE drag racing crowd that will consider purchase. I think the design is great, but with a small tweak, I think this can appeal to an even larger group. I was just looking at how to design something when I came across this thread.
Thanks
Sal

 

That really sucks about the broken differential. I have some bends in my C-brace, but luckily no catastrophic failures yet. It only has about 3000 miles with all of the engine upgrades and hasn't seen drag slicks yet.

I am trying to optimize the design still so I am not sure how I will tie in the C-brace. I am considering making a additional chromoly or aluminum plate that can be bolted to the C-brace in several points to prevent creating a new weak point. I have also considered making a chromoly C-brace, but I'm not sure how many people need that level of support. Do you know the differences between C-braces for different years and transmission combinations. I would like to make my designs as universal as possible.

Thanks,
Brandon
www.riceperformanceproducts.com
rppcorvette2@gmail.com

 

Guy, those you you thinking of tying the frame to the C-beam...ya need to read this:
http://forums.corvetteforum.com/c4-t...al-member.html

You can't do it with out major re-engineering of the whole car, solid motor mounts and solid dif mounts. The C beam (along with the motor and diff) need to be able to "float" w'in the frame.

 

Interesting read and pictures. So just to summarize, you are in agreeance with previous posters that the C-beam should remain isolated because:

1) the idea of reinforcing the frame by tying into the C-beam would create a new weakpoint;

2) the C-beam in OEM configuration does not (and therefore is not designed to) provide structural reinforcement as it is isolated by rubber mounts from the frame; and

3) the C-beam is furthermore not designed for resisting torsional forces and is only for the longitudinal direction along its axis

Is that correct?

 

Tom,

Thats great information, but I disagree that it cant be fixed without major modifications. I dont ever want a c5/ c6 so getting into a car with a better design isnt an option for me.

If someone needs to put in solid motor/batwing mounts then so be it. Not a big deal (i think member: churchkey even makes solid motor mounts for our cars). However I think that polyurethane, heck even rubbber mounts might restrict movement enough to make it all still work (ie. prevent pinion snout from rotating far enough to snap under drag use).

This is a better idea than cutting a hole in the floor for a pinion snubber - off the roll cage.

The key to making this idea work is to make the connection points at the strongest point possible. I would assume thats the diff snout bolt area. The diff snout needs the reinforcement.

We will have to let RPP speak for his design, but thats where I thought he wanted to connect at (the diff snout).

The c-beam isnt strong enough to prevent the diff snout from rotating. Though I think that a connection to it is still better than nothing as it will spread the torque force to the frame (via the brace).

Something can be done at least to prevent diff snout from rotating and snapping (a major problem with drag racing on this IRS).

I love drag racing, but I dont want to give up road course/ AutoX for a solid axle quite yet.

 

Yep. That is precisely correct. The C beam is only strong in one (meaningful) direction and that is bending on the vertical plane. It's purpose is to support the rear end of the trans (as a z member normally would) and the diff (as a "snubber" normally would).

The C beam in no way, adds meaningful strength to the car's frame, and it can't.

 

You're misunderstanding how the c-beam and diff work. The Diff doesn't move (in response to the tq it imparts on the C-beam). ESPECIALLY compared to other cars (that don't use a C-beam). And even if it did move, movement of the diff doesn't cause breakage. In fact, it might add some "cushion" to a launch that may potentially save the diff. Anyway, the problem with diff housing breakage lies 100% in the housing design itself. The thing wants to rotate rearward...that needs to be prevented. It can be either w/a snubber, or a lever-arm. The 'Vette uses a lever arm (the c-beam), but EITHER WAY, the forces exerted on the nose of the diff house are the same.

This is correct. If you want to prevent diff housing breakage, the HOUSING needs reinforcement. Bolting more crap on the front of an un-modified housing won't prevent the housing from breaking. What MAY help is a device that encapsulates the entire housing, THEN attaches to the device that resists rotating tq (the c-beam, in this case). That way, you'd be spreading the load throughout the housing rather than focusing it on the nose, like a snubber or the C-beam does. Think DTC brace for the C-5/6's, but for a C4.

HOWEVER, NONE of this will help frame stiffness, which is what is being covered in this thread.



Again, the C-beam IS plenty strong enough to prevent rotating of the diff housing...and does so better than most cars' control their diffs. You should see the amount of movement of the diff in my CTS-V!! The C-beam "spreads the torque force to the frame" through the engine mounts (which, incidentally, makes it way easier for the frame to deal with those forces, than a snubber/rear point.

 

Ok. im following you better, but the stock c-beam design isnt without problems.

If the c-beam is 'absorbing' the tendency of the diff snout to rotate its probably also picking up the right (passenger) rear tire and allowing that to spin.

 

No, it's not doing that either.

You are right, that since the C-beam can't manage and rotational tq along the centerline of the car (tq parallel w/the driveshaft) that if the car were a solid axle, it would do as you say. Since it's IRS though, the axle shaft U-joints guarantee that no tq imparted on the diff housing makes it to the wheels.

So what manages tq along the centerline of the car? The batwing mounts. The tq is spread or "resolved" in the frame of the car. So why doesn't the whole car tilt to one side? This tq travels down the frame rails and and into the motor mounts where it counters the opposing forces that are created by the engine/trans unit.

Under a WOT launch (clutch engaged), a ZR-1 (for example) is creating up to 375 lb ft. It's bolted to the trans; they're a single unit. Trans has a 2.68 first gear ratio, so total tq produced by the engine/trans assy during a WOT, 1st gear event is going to be 375x2.68=1005 ft-lbs being sent down the drive shaft, and into the rear diff. If the engine trans, DS and diff were sitting on a shop floor, and you replicated this "event", the engine would fall (roll) over one way, and the diff would spin the other. However, bolted into the frame of the car, the opposing forces are managed by the frame. The engine/trans exerts 1005 ft-lbs of tq into the frame in the clockwise direction (as viewed from the drivers' seat) and the diff exerts 1005 ft lbs on the CCW direction. The frame deals with that. The wheels see none of it.

Note that in a C5^, the tq is dealt with by the tq tube; the frame doesn't see any of the engine/trans and opposing diff tq b/c engineers took the powertrain assy one step further (than a C-beam) and used a cylindrical tq tube, that CAN deal with the tq. loads. So, in the case of the C5^, the loads imparted on the frame under a WOT event are in one direction only; lifting of the front end, through the engine mounts.

Clear as...mud?

 

This is helpful as Ive learned from this. Its interesting.

So what would solid motor and batwing mounts do for you?

What about a steel c-beam?

Make it all more likely to snap a diff snout?

Or provide a whole bunch better engine response/ stiffer car altogether?

How would you make this frame brace design?

 

I think this design is great. My 85 is terrible with the top off and ok at best with it on.

Count me in for a setup when it is ready.

I run a 3inch exhaust as well so clearance will be the same as yours.

 

I've never tried solid mounts but all I've ever heard is that they improve "throttle response". I have no doubt that they would make the car feel more immediate, and responsive. I also have no doubt that they transmit a lot more vibes, hummmms and buzzz's into the cabin. (You'd have metal-to-metal from the trans/diff&motor, to frame). As far as increasing chassis stiffness, I don't see any meaningful benefit there, as the C-beam can bend sideways, and twist like a wet noodle (relatively speaking). Longitudinally, the mounts on both ends of the car are stamped tin and would themselves, flex easily when faced with loads that matter, that the frame deals with now. Then there is the issue of expansion. The diff/c-beam, and trans are made of aluminum and heated by friction and exhaust. The slower expanding steel frame rails stay pretty much at ambient temp. So if trying to make the drive train a stressed/functioning frame member...there is that issue.



I wouldn't spend much time on this particular frame brace...especially without a mechanical engineering degree and software -neither of which I have. I personally feel that the BIGGEST (though not the only) problem w/the C4 is the torsional rigidity w/the top off. Affixing something to the bottom of the car that is itself, on a single plane, I don't see helping much. I would focus on areas or methods that allowed 3D structures to be added to the car. For ME, my criteria would be:
*"Invisible" -i.e. targa bars don't do it for me b/c ya want the roof OFF...but there is a thing there.
*Bolt-on. It's a Corvette, not a stang or f-bod, so I don't want (and I believe many don't want) weld-in pieces. Car should be able to go back to stock.
*Needs to be able to make an objectively measurable difference. No SOTP claims here.

I have day dreamt about installing 3" round tube INSIDE the rocker rails. I feel that would dramatically increase torsional stiffness. BUT, it would have to be a weld in piece. I doubt many 'Vette owners would go for that.