Mustang II Swap Knowledge Base

[mav1970]

Originally Posted by stockhatch

At this point, I'm debating on a cage. I think it would be nice to have if I did take it to the strip and something happened... Even so, the back seat would become pretty useless, and I think that detracts from what makes it a street car

I'm putting a cage in mine and have designed it to be able to still use the back seat. I attached the rear kickers to the main hoop with electrical tape until I can get them welded in. I'm also doing the Mustang II deal and will completely remove the inner spring towers. I'm going to do front down tubes from the front of the frame rails and through the firewall to the front cage uprights. Then a Monte Carlo bar between them.

[stockhatch]

So are you not going to put a harness bar in? I guess NHRA certs are not your priority, and you are just after a little added chassis stiffening? Not that that is a problem, I am contemplating the same for my car. Or maybe even a removable harness bar that I can put in at the track. I know its not legal, but I am sure a removable harness bar is better than no harness bar, right?

[mav1970]

Originally Posted by stockhatch

So are you not going to put a harness bar in? I guess NHRA certs are not your priority, and you are just after a little added chassis stiffening? Not that that is a problem, I am contemplating the same for my car. Or maybe even a removable harness bar that I can put in at the track. I know its not legal, but I am sure a removable harness bar is better than no harness bar, right?

I already blew the NHRA certs by choosing tubing that might not be exactly what their spec book would want. There will be a harness bar but it will start out level right behind the driver's seat and then "S" shape it's way down towards sill plate level at the passenger side. That way the rear seat can still be used but only entered from the passenger side. I still may decide to pin a removable bar in there somewhere. I always wanted a car with a cage so this was going to get one regardless if it got the MII front suspension or not but now that I am getting rid of the inner spring towers, the cage will serve a more important function to re-stiffen the front frame rails. I've built many stock car cages and the design always worked well on circle tracks so this one should work OK on a street car. Additionally, the stock sheet metal front rails are getting replaced with 2 x 3 x .125 steel tubing. Then the MII cradle gets welded between them.

[stockhatch]

Sounds good. I like the idea of tying the cage to the frame rails up front especially. I agree that it would restore some of the structural integrity lost by losing the towers. Be sure to post some pics of that MII swap Hopefully mine will be posted up here very soon.

[mav1970]

Originally Posted by stockhatch

Sounds good. I like the idea of tying the cage to the frame rails up front especially. I agree that it would restore some of the structural integrity lost by losing the towers. Be sure to post some pics of that MII swap Hopefully mine will be posted up here very soon.

If you look at the Heidt MII front frame sold for the 66-67 Chevy II/Nova's, you can see how the front down tubes come up and bolt to the firewall with plates (this is also a car that had inner spring towers that are removed with the MII kit). I saw 2 of these setups on Novas at shows this past year and that is all there is to it. I can't believe that they would just flat plate it to the thin sheet metal firewall plus one of the Novas had a 500+ big block in it. Mine will look similar to the Heidt kit but inside the firewall will also be identical plates with short tubes welded between the interior plates and the front cage uprights. Once bolted together it will be solid to the cage with the firewall sandwiched in between. I think this might be easier than trying to do multiple tubing bends to try to get the tubes from the front of the frame to the cage all in one piece.

I can't start my MII conversion until my shell is off the roll overs and blocked up level on the floor. If I started sawing the towers apart, I'm sure I would fold the car up on the roll overs. I'll have pictures in the future for sure.

[stockhatch]

Looking at that Chevy II setup, I cant believe the ditches aren't full of Novas without front ends. That is some crazy stuff. Maybe they could save money on hardware and just bungee it on there.

[jayman]

Consider that on a stock lower control arm, the arm is held in place bya single bolt passing through a sheet metal bracket, the lower controlarm, another sheet metal bracket. The total thickness of the two sheetmetal brackets is about 1/8 on either side. When was the last time yousaw a failure at the mount point of the stock lower control arm mount?

The tubes serve several functions for the lower control arm. The firstis A-arm positioning (making sure the arm is in the proper planes X Y and Z). The second it to helpspread the load on the bolt that is the real support for the a-arm. Here, we have a frame with about 2" of bolt sticking out in front and about 3" in back. This gives the lower control arm more leverage to bend the bolt when under load. The tubes actually provide quite a bit of support as they are, effectively increasing the diameter of the bolt and the amount of force required to bend it. Tubing is stronger than a bolt when it comes to resisting bending. (There was a real nice article in Street Rodder magazine explaining the relative strength of various tubing sizes compared to solid rod. interesting reading.) As shipped from a reputable manufacturer, extra gusseting is not required if you are using a kit designed for your vehicle.

On that note, gusseting of the lower A-arm mounts tube never hurts as long as you don't deform the tube when welding. Makes it hard to get the bolt through if the tube bends from too much heat. Most cars do not "need" the gusseting, though, as they almost never get driven hard enough to bend the tube. Dropping a wheel into a really big hole would do it.

[mav1970]

Originally Posted by jayman

When was the last time yousaw a failure at the mount point of the stock lower control arm mount?

Jayman, I have not heard of any failures at the lower A-frame mounting bolt tube but I have read where the long bolt that runs through the tube has sheared off and the car dropped to the ground.

Initially I wasn't going to invest in the aftermarket wide tubular lower A-frames because I have 2 NOS stock Mustang lowers that I want to use first. They will be installed inside the cradle and will be using a much shorter bolt to attach them. I have aftermarket front support bars to use with the stock ones also. Later on, I can always weld in the bolt tubes and change over to the tubluar arms. Maybe instead of using such a long single bolt through the mounting tube, I could weld in 2 threaded bungs into each end of the tubing and then be able to use 2 grade 8 short bolts.

[stockhatch]

Originally Posted by jayman

Consider that on a stock lower control arm, the arm is held in place bya single bolt passing through a sheet metal bracket, the lower controlarm, another sheet metal bracket. The total thickness of the two sheetmetal brackets is about 1/8 on either side. When was the last time yousaw a failure at the mount point of the stock lower control arm mount?

That is true, however on a stock car the strut rods transfer the majority of braking and impact loads to the frame(via a beefy rod, large bushings, and a thick crossmember). With nothing to transfer all that energy to the frame but a tube thats hanging a few inches out into space on either side of the crossmember and a long bolt, I still think the stock setup would be stronger. Again, I am no engineer, just making some observations based on pics of failures that I have seen, and the notes and opinions of those much more learned then I.

I do still plan on an MII swap. I think in my case it will be plenty strong. Again, I wont have the wheel tire package for cornering, or high braking loads. I think a skinny aluminum front runner will bend before the suspension in the case of a pot hole or jumping train tracks. Hopefully, most of the time the car will be in weight transfer mode and the front tires will just be kinda dangling there lol.

I dont know that I would put an MII setup on a road race car UNLESS it was a stock strut rod type setup. And even then I would want through-the-floor subframes, and a nice cage to triangulate and brace the frame.

[ModMav71]

Originally Posted by stockhatch

Oh, I meant to ask about gusseting on the rear section of the lower a-arm mount tube. It seems like some of the crossmembers I have seen pics of have NO gusseting on this section, and some do. The strange thing is that crossmembers from the same companies can be found with and without this gusseting. I wonder if the gussets were added in a revision?

I do know that if I run a setup that does away with the strut rod, it will have gusseting, and most likely and extra bracket like the one added to the car in that first failure link I posted.

I'm no engineer, but I agree that it makes sense to have as much reinforcement in that area as possible. That lower a-arm tube gets hammered under braking especially, and it does not take a genious to see that.

Like JayMan said. That is some thick wall tubing used for the lower mount and it goes all the way through the lower crossmember. With the being said I know my cross member was ordered out of the old R&C catalog (as the new one was not yet out) and no one bothered telling me when I order the setup for tubular arms the they just changed the config of the lower mount for their NEW LCA's. I already had my LCA so I had to modify my mount by cutting off the front section of the tubing and welding it to the rear. After that I did add gussets just to be on the safe side.

If I could make one suggestion to anyone thinking about doing the swap is to go ahead and buy the whole complete kit and be done with it. Manufactures change their setups every so often and what fits today may not fit tomorrow. So at least buy the crossmember and a-arms from the same place. It will save you alot of headaches trust me!