tube80z

You have subframe connectors, cage diagonals, etc. all welded in that help keep the floor from moving. Those are all going to help keep this from moving. Take a look at the top of the tunnel, I don't think you need a lot more than that to strengthen the bottom. From personal experience I can tell you that I've broke that crossmember (diff mount issue) and never noticed any handling issues. I even ran one race with just the caps and couldn't tell. I have broken cracked and broken the rear transverse mounts, which I can feel. So I'd say you're safe and I'd spend the effort at the back and leave this area alone. Cary

Or if you really think you need it weld a tab along the bottom of the RT mount for a bolt in crossmember. This would be more in line with the lower control arm mounts than a piece further up where the seat belt anchors are. I don't think you need much to strengthen this area given the rest of what you have done. Cary

Magnafluxed and all bearings are standard. Maybe a fluke but still impressive to see. Even more impressive when you think it was still revving to about 6K for a bit after this.

A friend has my old race motor and it started getting what sounded like a nasty rod knock. He took it apart expecting to find a broken crank. I've never seen one break like this and it was very close to coming all the way apart. This engine had one season under me 7500 RPM limit and a few events for him at a lower 7K limit. Just goes to show that these parts are getting older and racing is hard on things. Cary

If you have the large front damper it won't hack 7K very well. The first signs of a problem are bits of rubber that look like they came from the fan belt on the bottom of the hood and up the inner fenders. That's the sign of a damper dieing, and you better take notice. You also need to throw away the flywheel bolts and install new ones. When you lose one end of the crank the other takes all the beating. It may seem like overkill but you won't be very happy when the flywheel comes loose and wipes the end of the crank. Don't ask how I know this. Cary

You may want to take a look at http://www.jakelatham.com/radical/info/brake_calculators.shtml and see what your current system looks like before making changes. C

There's a group of us that are racing in XP, which has basically turned into our own little rivalry between a 89 vette and the rest of the Zs. If I look at the vette in pictures you can see the suspension on it does a much better job of keeping the tires flat to the ground. Currently the vette is quicker but if I look back at times against my old car they are closely matched. So like many things there are other variables at play that make a direct comparison difficult. I had the opportunity to race a 510 on struts and then run the same car converted to double a-arms. What I mostly noticed was the car had much better steering feel. The odd thing was that it didn't have a lot better front grip. It was very similar to the lexus setup discussed in a different thread. As Ron points out above the Z has a lot of SIA and this is what I think is more of an issue than the scrub. If you look at the tire contact patch you'll see the SIA has a tendency to roll it from edge to edge. There are a number of other effects too but I wonder if that is one that causes the front end to be harder on tires. My gut feel is that double a-arms will better for a car that's going to do much longer runs on the tires. I also think it's better under brakes especially if you are generating large longitudinal loads. I asked a similar question in the motec seminar because I knew they had experience with the V8 supercars and got a more thorough but similar reply. Cary

In the past I used delrin and a router to do what you described. You can make different length spacers to mount those on if you want. I saw a really cool set made from aluminum and figured this was worth a shot. Cary

I was curious how you'd do the X given where the bend is in your current bar. That's what all my question was really. Cary

So my only question is how will the other bar fit in? Cary

I'm all about easy

When you put in the tube between the cage legs I would add a tube underneath (say 5/8 ID) that allows you to slip in a remote jack point. You'll need to notch the rocker and you can then back this up with plates on the inside of the rocker to the tube and on top of the rocker. If this isn't clear I'll attempt some Cary CAD to make a visual version. Just an idea. I'm going to a go a little farther and do this at the ends too so I can put the car on stands with nothing under it very much like a rally car. Cary

I would rethink that. I've seen a couple bad accidents and in each case how the driver was hurt was from the rocker crushing between the X and getting to him. While these weren't Z cars they had similar weak rocker areas. If you look at newer cars you'll see these areas have been really strengthened. This is also a good location to create an external jack point, which at some point you'll wish you had. That's one area where the nascar door bars are a little better. For my XP car I'm probably going to do the X too, but I will have a bolt-in nascar type structure for when the car is hillclimbed. If you happen to look at one of the recent race car engineering mags you'll see this is the type of thing the FIA has been testing for rally car side impact protection. Having one tube try and crush through another has been shown to dissipate a fair amount of energy. Cary

Good work on those compound tube junctions. They aren't easy and never look right. Cary

Bridge reamer taper equals ford tie-rod taper. That's what my local hotrod guys do instead of rod ends for their more streetable cars. I'm not sure of the taper. I do know you can get the reamer for about $100 for these, which makes my bridge reamer look like a super bargain. Cary

As Ron points out you have a lot of options. I gave some basics to get started earlier in this thread. Using Ron's pics and Terry's idea you get what similar to the front end of a Aussie touring car (at least under a Falcon). They are setup with rear steer and a upper arm that goes into pockets welded on top of the frame rail. The upper arm is splayed with equal angles, unlike Ron's arm. This keeps the forces more equal on it and allow room for the coilover assembly. In the Falcon the pics I have show that they use an extender on the shock to tie it into the strut tower that's no longer used. This is the direction I think I'll eventually take with my XP car. Cary

If you stay with struts that would be one option. You could move the top mount back towards the firewall to increase caster and not have the fender well interference. If you had power steering you could use large caster angles to overcome the large SIA of the stock strut. Ideally you need to run one-half the SIA as caster to cancel the camber loss from steering. You could fab a new cross member to allower you to move the rack towards the axle centerline to help with ackerman. And while you were at it you could put in some vertical adjustment for the lower control arm to play with RC height. A lot of what you want to do is going to depend on your engine and what you have room to do. Cary

The simple answer for rear steer is that it will probably be the only option for getting 100% ackerman steering. To get it in front steer would probably require that you raise the rack to the stop of the a-arm attachment point and that's probably going to be going right through a frame rail. I don't know how much ackerman is used on the R&S trans-am cars that have a low mounted rack but I can tell you that they have an interesting tie rod. It's sorta S-shaped to allow the wheel to get full lock. For a car that sees track or autox use 100% ackerman would be a good goal to shoot for. The tires that most of us have access to (slicks, etc.) are all designed to respond well to this. Cary

I have susprog3 and that can be used to model these. Really all it spits out are the coordinates and then there are easily graphed in excel or something similar. I have a lot of thoughts on what matters but little in the way of answers. Unfortunately you're going to find that once you nail down the constraints you're not left with a lot of options. I think one of the first things to do is to start with the tires and intended use of the car because these will have influence when you get to item 6 below. Here's a basic list of what to look at to get started. 1. Lower arm should be close to horizontal (when in use) 2. Longer arms are better than shorter arms 3. Don't get carried away with antis (things should move free and easy) 4. Decide on spindles/knuckles/struts. 5. Decide on halfshafts (for RWD) 6. Now decide on camber gain, roll center height, aim for zero bump steer, and don't forget to the ARB. Now that you have "designed" a suspension you must learn to "tune" it. I guess that will a different topic altogether. Cary

I've used something similar and it was fine. I have a smart camber now that I'm very happy with. Cary

There's a good book you need to get by John Dalton called DIY gas porting. Search Amazon and you should find it. It may have a different title now but I believe it's back in print. He has DIY ways to make molds and a flow bench. When I used to do this I made a few molds to port heads I didn't want to destroy. Then I made a number of guages up that you inserted a certain depth down the port to get the shape I was after. These could be based off molds but are a more realistic way to do this work. And these days if you do one cylinder and get it to where you like there are companies that can put this into CNC and do the rest of the head for a reasonable cost. Hope this helps, Cary

You need more of a throat section. Think of a carb venturi sliced in half. The diffuser acts to speed the underbody flow, which results in lower air pressure. Cary

Maybe rediscovered but if you go back in history you can find these on some of the old landspeed cars. I seem to recall seeing a mercedes or auto union in one of my books. Just like a really old pic of a car with a wing. Cary

Just putting a ramp in the back of the car isn't really building a diffuser. Sure it's a crude one at best. But a real diffuser has a throat section that leads to the ramp and often a aero plug as well. If you look at how these work they are really to accelerate air under the flat section ahead of the diffuser and that's what creates your low pressure zone. If you don't have a copy of Mcbeath's new book (he writes aerobytes in RCE) then you will want to get it. Cary

I won't argue with your results but I wonder if it's really the diffuser that's helping or the fact that you don't have a parachute in the back of the car creating a high pressure zone? Cary