1MeanZ

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96LT4c4

Man that brings back memories.....

CaliChevyLover

this is one hell of a project. keep it up, subscribing

screeminchicken

iTrader: (2)

Newbie to this thread question.......

So with this rear swap did you completley eliminate the need for a Torque arm as required in 3rd and 4th gen fbodies ?

What does corvettes use for a torque arm ? or does the Torque tube server dual purpose in a corvetter drivetrain ?

Or
are you going a fabricate something on the rear diff to attach a stock torq arm ?

Thanks

ericjon262

an IRS rear would need either a pinion support, a "C" beam, a pinion mount, or some type of torque tube to keep the geometry correct, and not have the diff twist with the tires, I don't think a torque arm like our cars have would hold up very well, maybe an aftermarket piece would. I believe he is going to use a pinion mount in the drive-shaft tunnel.

I drew a diagram of what I think he said he was going to run, everything black is the differential/batwing, the red are the mounting points to the frame/body, and the blue is the halfshafts.

Hope that helps-

Eric

ericjon262

any updates?

subroc

iTrader: (2)

Ive been quietly following this progress from the start to now. I must say this is just unreal and awesome. Your doing a great job. With that said...any more pics or news?

speedo

As an owner of two C4 corvettes, My 91 is a stock 245hp l98 automatic, And my 94 is an LT4 355, crane 222/230 cam, AFR ported heads, 30# injectors, TPIS long tube headers, GMPP 1.6 roller rockers, 58mm throttle body, etc Dyno tuned on a dynojet 364rwhp @ 349ftlbs. In the 1/4 mile it ran a 12.9 @ 111mph. With 315-35-17 street tires.

It is a ZF6 6-speed with the dana 44 8.5" ring gear, 3:45 ratio. Ive NEVER had wheel hop, and traction has always been good.

Ive seen many other corvettes run much better times with the stock IRS. The day I ran my 94, their was another guy with an 86 corvette, running a supercharged LSx/t56 combo he ran high 10's all day long with the stock IRS running slicks.

It looks like the swap is going good! Im thinking of doing the same in the future. Check out www.suicidedoors.com They sell many random brackets and 4-link bars. They will custom make anything you need. Their work is quality. Ive used their parts many times for random things. They built the adjustable rear link bars and tq-arm for my 94 Firehawk for under $250.

ericjon262

It's looking awesome, but we want to see more!!

1MeanZ

iTrader: (9)

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lowflyr

A-freaking-1.

I was all set to do this last year. I was at the junkyard measuring up the C4 rear, about to buy one, and I came over all funny feeling, like maybe I shouldn't. I've already got a 10point in the car, and I still need to upgrade the rear axle and brakes, it still in fabrication stages, so it seems like the time to do it, and I haven't done much to the car yet with working on other projects and all. My car is in perfect condition with zero rust, I hesitated, most likely because I didn't want to risk it, or admittedly I just plain wimped out.

You have no idea how much you've got me thinking of this again. I do drag race with the car, but its not important to be the quickest at the dragstrip to me, I just want a wicked fun street car, and IRS is the way to go for handling, especially on the *imperfect* roads here in Canada. I really, really didn't want to put a heavier rear solid axle under the car either, good call.

Awesome work, I can't wait to hear how it performs. I won't be far behind you if this works as good as I think it will.

1MeanZ

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RED_DRAGON_85

make me one?
the roll cage looks great so far.
not the "roll of dimes" you can get with tig, but will work fine

1MeanZ

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iTrader: (15)

the welds look to have good penetration, so i would be fine with them, dont think they will just break apart. Just keep practicing and they will get better looking

racing geek

iTrader: (5)

Yup, you're going to die from the roll bar breaking apart and spearing you.

1MeanZ

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iTrader: (15)

you can do it, you just have to be very flexible and have a steady hand

articwhiteZ

iTrader: (56)

welds Look Good.
is that welded together, out side of the car?

//<86TA>\\

iTrader: (15)

sure looks like it, but i would think that you could get it in the door with the seats out of the car. I would assume he tacked it together int he car, took it out somehow, then finish welded it. Hopefully it didnt warp

1MeanZ

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RED_DRAGON_85

agreed 110%

articwhiteZ

iTrader: (56)

i know mine slips in with the Back opend up..
you then stand it up.

welding with parts inside the car is a pain.. but nothing you cant Fix with lots of alum foil.. ya want the insides to look fantastic when done..
This will protect the interior from the heat and ultraviolet / infrared radiation that will be created when we MIG weld in the anchor plates.
nothing like washed out plastics (keep them coverd..or take them out)

Omega

iTrader: (1)

Very nice install, I'm impressed with your welds considering you are new at it.

Does the cage need to be checked and then certified after your done to be legal? I thought all cages needed to be welded by a certified welder to be NHRA compliant?

1MeanZ

iTrader: (9)

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rapid rods

cut out the corvette rear end and then it is very easy to mount everything,plus you get a complete frame to.

1MeanZ

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iTrader: (15)

sorry, but nothing about doing that would be "easy"

iroc a 86 berli

lmao!!

nice work so far 1meanz, welds look damn good for a novice!

lowflyr

Not to bring up the obvious guys, but rapid rods has already done this swap. Check his sig and his album......

rapid rods,

Do you have any pictures of the installation? A little illustration of what you are talking about would be helpful.

-Brad.

//<86TA>\\

iTrader: (15)

nobody said it cant be done, but just that its far from something that could be called easy

1MeanZ

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lowflyr

Good work 1MeanZ. There is alot of strength being added to the car with the cage, I like the tie in you have done for the rear diff. You may already be doing so, but I do have a suggestion to dramatically reduce strain on the body and stiffen that diff connection even more. You could take two lengths of roll cage tubing and run them from your main hoop on each side where your crossbar ties in, and run them to the diff mount. This would definitely triangulate the the mount better and reduce the spreading forces on the body over the rear suspension greatly. It would also transfer the load forward via the cage so that you would get the force being applied more directly where you want it. A small run of tie-bars from the main hoop to the rear cage where it ties to the floor would indeed make it rock solid back there, but could be unnecessary weight for current power levels. Keep up the good work, you're doing awesome.

-Brad.

RED_DRAGON_85

how are you going to seal that off?
i would have used a single vertical bar and used a shift boot to seal it off, then triangulated out from there...

lowflyr

With the way he is mounting it, it is simply a matter of welding the removed floor section back in (cut to fit of course). There is no movement at this point by design, so it will simply look like a mounting point welded to the body from underneath, when it really is connected to the roll cage for strength.

As I mentioned before I am rather seriously tossing around the idea of doing a similar swap myself, but with a c5 or c6 rear. In my case, I'd be placing a mount for the entire transaxle at the point where the roll cage meets my tunnel. (see picture) Of course there will be alot of fab work required. For reference, the underside picture does not show the welded pads for the cage, but they are welded immediatey above the e-brake reinforcement, sliders seen in the tunnel. This will not be significantly different in concept from what 1MeanZ is doing now, other than the mount being further forward in mine to accomodate the rear mounted trans.

dimented24x7

iTrader: (2)

The diff mount looks a bit dodgy. There will be a tremendous amount of force there. Up to, and possibly exceeding 8000 lbs if you launch on slicks. For reference, just imagine suspending something like a large pickup, or tow truck from it. Would you stand underneath it and trust your life to it? I would be inclined to say no. If possible, you would be better using a large C beam up to the trans to secure it, but it looks like there may not be enough space in the tunnel.

1MeanZ

iTrader: (9)

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lowflyr

Dimented is right about the loading, and uses a good analogy to give you the concept.

I'll explain why his numbers are reasonable (We know that you are not building a drag car, so this is a little over the top)...

As you could probably expect even with a great street clutch it could transmit no more than about 800ft-lbs under a launch condition at lets say peak torque, clutch dumped (I know the engine does not generate this much, don't forget about impact of the rotational inertia). Your first gear in the TKO600 is 2.87:1, and you rear axle ratio (assuming) is likely 3.45:1. Also assuming you dead hooked on slicks under these conditions and the dana 44 did not explode, you could simply multiply through. 800ftlb x 2.87 1st gear x 3.45 axle ratio = 7921ft-lbs. Even doubling this condition again for an impact factor (no way the dana 44, or your driveshaft, or halfshafts survive this, one of them will let go under this circumstance) we arrive at approx 16000ftlbs, for an instantaneous moment during launch, but can only hold 8000ftlbs until the clutch stops slipping as revs are matched, then drops to a peak of say 4950ftlbs as you hit peak torque of say 500 ftlbs at the motor.

Great, what does this mean at the diff mounts? Well assuming (I believe accurately) the distance from the rear mounts of the diff to the front mounts (speaking strictly in the direction from front to rear) is 10.5" that would mean tha actual maximum anticipated force you would see at the front diff mount would be 8000 x 12/10.5 = 9143lbs. If you do not expect to dead hook a max rpm launch, then you will not see these loads. The impact factor of 2 is not necessary for such an extreme theoretical condition. Your clutch, tire traction, tire sidewall flex (wrinkling), tire slippage in the rim, driveline flex will ensure you do not get that stupid high value mentioned earlier (16000ftlbs).

Yes the loads are very big, but you not lifting the titanic from its watery grave either. The suggestions I have listed above for additional bracing should handle what the expected loads on street tires will be. Add a little more bracing if you want to be extra sure. The long and the short of it, when you get the car together, if you do a relatively hard launch (work up to it), and you see any flex happening at your mount, then you could use more bracing. But the only immediate and complete failures are those due to broken welds and fatigue failures. Good welds are key, and eliminating flex will keep the fatigue failures at bay for a long time.

In answer to your question about where the failure would likely happen now, its the twisting of the sheetmetal for your trunk floor relative to the sides of the car. The addition of bracing to the cage will give it a much better anchor point to stiffen it up. Additional bracing from the rear cage to floor mounts run up to the main hoop will also improve stiffness. I should also mention, the loads placed on your trailing arm mounts may also warrant a little bracing. You could tie these areas into the lower main hoop mounts on the floor. Again, no flex is good. You should also be aware that the loading conditions are the rear diff mounts, although different, are still very significant and this is why the concerns were brough up over strength earlier by a few others. Don't give up, you just need to ensure adequate bracing is in place.

Cheers,
-Brad.

lowflyr

I did some digging and came across some pictures I took back on 2008 when I was first looking at this type of setup. I will attach a few pictures that may be helpful to you. I do not have one of the front mount, but the trailing arms mount directly to the frame, as does the wing mounts, no surprise. Its the sizing of the wing mounts that may interest you. I do have pictures of the front mount for a c5, but it does not apply to your case.

Cheers,
-Brad.

dimented24x7

iTrader: (2)

Another point worth mentioning is that, in a stock t-top car, the trans tunnel is primarily what resists the engine torque. There is very little structure in the floor pan, and the roof doesnt help much. Due to all the loads imposed on it from body flex, and more importantly, engine torque, its prone to failure around where the tunnel joins the rear of the car. My trans tunnel and rear subframe rails are completely wrinkled up from all the engine torque (car has SFCs now). Since you have cut yours to allow for the pinion mount, you will also need to make provisions to tie the floorpan to the rear of the car. If this is not done properly, you run the risk of having the tunnel rip completely open around the cut.

Make sure that your cage ties not only into the floorpan, but also into the area where the rear spring seats are as well as the rear subframe rails, or what currently remains of them. The strongest part of the floorpan seems to be where the rocker panels/pinchwelds are. Try to anchor to as much of that as possible. I would say beam or tubular SFCs running the length of the floorpan on each side would be a good way to tie everything together and provide a solid foundation to mount the roll cage/bracing to. I did something similar with my tubular spohn SFCs. Basically I welded all three layers of the pinchweld to teh SFCs at 6" intervals the whole way down on each side, and fully welded the base of the SFCs to the LCA mounts and also into the front subframe. This really did wonders to stiffen the car, and solve, or at least band-aid, the wrinkled subframe rails and tunnel.

Corner Worker

wow....you have a whole lot of critics still about this setup. Your system will work perfectly. Im sure if some strange way it breaks or fails, you simply fix the car. Its a race car people.....have any of you actually been to the track or built a car of your own? It seems like a ton of theory based opinions, not so many real world experiences....

89ROC-Z

iTrader: (7)

How about the hole for the shifter on a manual?

imo i think you'd have to have 1000's of hp to actually tare the trans tunnel apart. There's people making 6-700 hp and i'm sure there car is cut up more than his

lowflyr

1MeanZ,

If you would like to talk theory and forces, or what to do about them, pm me. I'm here to help if you have questions.

Cheers,
-Brad.

dimented24x7

iTrader: (2)

Im not being critical of it. I think its awsome what he is doing. But, there are some areas of the thirdgens that are not that strong in my actual experience here in reality. Id personally rather have a little more structure than not enough, and a failure.


Thats what I thought too, but the rear of my tunnel is wrinkled, along with the subframe rails there. Keep in mind that the front area around the trans has subframe rails on either side for additional support. Its not unheard of to hear people splitting the tunnel in half in that area at teh rear. Have a look at mine. The wrinkles are in the direction of engine torque. This was done with a mere 300 HP engine, sticky tires, and my old 700-R4 w/ a shift kit.

lowflyr

Dimented,
Just so I understand, you're talking about the 'wrinkling' around the bends in the car? If your talking about what I think you are, I can show you loads and loads of pictures that show simliar creasing in the cars I've had.

The metal when stamped at the factory shows alot of these waves where the metal was stretching in some areas, while being compressed in others. Sometimes the creases take all kinds of funny shapes. I actually worked in the BIW (Body-in-white, where they car bodies are assembled) shop in GM's Oshawa plant a number of years back. The small creasing is absolutely normal, and it is there from when the piece was originally stamped. I'll attach a few examples from two different cars. I have seen very strong ridging happen as well. Unless you can say with absolute certainty that it was not there before, I'm inclined to think it is the results of the stamping process you're seeing, not a 300hp motor. Just check out the difference in the left and right wheelwells of the IROC. Its not as bad as the 84 Z28 I had years ago either. That car had what looked like rippled sand dunes in a few places on the sides of the subframes. The care and attention to making perfect stamped parts only applies to the visible exterior panels on a car. I for one, have only seen a tunnel torn up when the driveshaft decided to have a wayward stroll, or trans mounts break, or something along those lines.

dimented24x7

iTrader: (2)

I can say with 110% certanty that it did NOT come from the factory like that. The rear subframe rails show teh same sort of wrinkling deformation, as well as kinks and fatigue fractures in the metal, all in teh direction of applied torque. Before the SFCs, the car literally felt like it was going to come apart under power. I could also see a lot of body twist under power as well. The front would be at an angle, and the rear of the car would still be level. Its pretty tweaked, and wasn't like that before I got it.

I can understand the waving in the metal from the stamping process, as it inherently involves deforming the metal into the desired shape. But the kinking and cracks that formed are what really worried me. The car also does not sit level anymore. The rear end is twisted with respect to the front.

lowflyr

I do not doubt that what you say is true, I've just never personally seen it result on wrinkles in the tunnel. Do you have any pictures of the wrinkles in your subframe area? It would be beneficial to know if there is another area I should reinforce when it comes to making my sfc's.

iroc a 86 berli

damn 1meanz, shlt's looking good! you are inspiring me to get out in the garage and do some fab work! problem is my funds put a damper on all plans.

BTW, your pinion support looks fine imo. the bars are anchored by the rear, upper shock mounts, witch is beefed up from the factory.

considering how the pinion support on the "chassis builders" setups are. i see no need for doing a bunch of equations,lol. fit your pieces together tight and burn it home, you can always add some gussets if you detect any deflection after she's back on the road.

but anyways, keep up the good work, and take what some of these guys are saying with a grain of salt, this forum seems to be on its period lately. way too much negativity in whats seems to be every thread!

dimented24x7

iTrader: (2)

I can get some pics of the wrinkles and cracks. No cracks on the tunnel, but mainly on the rear subframe rails.

1MeanZ

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