boodlefoof

Around here (VA) I found that mail-order is much cheaper than buying from a local metal supply house... even after shipping. I have had good experiences with both of these guys: www.colemanracing.com www.lefthanderchassis.com

The original photo-chop of that car was the inspiration for me to chop and rake my roof as well. Looks slick and should help reduce drag significantly.

While it sounds like you guys do have some real problems with lack of rear pressure, just a word of caution... Whatever you do, don't adjust front/rear pressure such that the rear brakes will lock up before the fronts. That is a no fun situation.

Just to add to this thread, I have been doing some more studying up on this topic in the last week and have begun putting together a writeup on my webpage regarding brake component selection. http://www.geocities.com/boodlefoof/Project_Racer-Zbrakes.html Click "Next Page" at the bottom to continue. Sorry, no pictures yet and it doesn't yet have the info on master cylinder sizing/etc... but I'm still working on it.

For those who haven't visited before, you may also want to check this out: http://www.wheelweights.net/ Searchable by name, size and weight.

Let's just say I value my health.

Cool car! Economy and custom tube frame are hard to fit in the same sentence unless you are doing the design and fabrication yourself. If you are planning to autocross the car, you will at least need a cage, however. Also, if you have much sentimental value invested in the car the auto-x may not be the best choice as I would guess that thing is going to be easy to roll. What kind of shape is the unibody in?

As I calculate your front to rear percentages with the Wilwood 1.75'' 4-piston fronts and the 240sx rear (which you said has a 1 sq. in. piston area), your front to rear ratio comes in at about 82%. I went out and measured the factory '73 240-Z brake pedal and the ratio is right around 4:1. The ratio on my Coleman dual m/c setup is about 5.5:1. Regarding front to rear caliper sizing, I haven't found a lot of good data, nor any real formulae to calculate appropriate ratios. The general rule is, you want a big enough rear caliper to get maximum braking out of the rears without locking them up. The trouble calculating this is that the number is dynamic, changing as weight shifts in deceleration. Through a number of sources, it seems that many are using the following rule of thumb... Front to rear caliper area ratio should be somewhere between 1.3:1 and 2:1. With lots of rear weight bias, minimal weight transfer, low c/f conditions (wet pavement), or with lots of prop valve assistance you can use a ratio at the lower end of this spectrum. In situations with greater deceleration (sticky tires in dry conditions) or more weight transfer, you should err on the higher side of this spectrum. With that said, the 1.38'' 4-piston rears will give a 1.6:1 ratio, which is a little on the low side, but perhaps is do-able with the prop valve.

Hey Chris, As promised, for those who might have similar questions in the future, here is what I have found on the topics of piston area front to rear and master cylinder sizing given a particular piston area. This info comes from corner-carvers.com as well as discussions I've had with persons who know more about this stuff than I do. First, when calculating piston area one calculates only one side of the caliper (two pistons for a four piston caliper). For the fronts you listed above (1.75'' x 4 pistons) this gives a piston area for the front caliper of around 4.8 sq. in. You also indicated that you are using a single 15/16'' master cylinder. When selecting the appropriately sized master cylinder, here is what I have been able to find... To calculate an appropriate master cylinder size, you should calculate your front cylinder ratio. This is calculated as caliper piston area divided by master cylinder piston area. This defines the mechanical advantage of the master cylinder on the caliper. On a manual brake car, the front cylinder ratio multiplied by the pedal ratio is typically 40:1 or higher. On a power brake car, this will be lower (with a front cylinder ratios around 4.5:1, multiplied by pedal ratio should come to around 20:1). Increasing master cylinder bore will reduce the distance the pedal will need to move to actuate the brakes, but will increase the force required from your leg. Reducing bore will increase the pedal travel distance and reduce pedal effort. Reducing the bore too much can result in the piston pulling back into the caliper when you let off of the brake, which will mean that the next time you push the pedal you may have several inches of pedal travel before the brakes begin catching at all. Calculating your front cylinder ratio is as follows: A front caliper with four 1.75'' pistons has a piston area of 4.8 sq. in. A 15/16'' master has a piston area of .69 sq. in. This gives a front cylinder ratio of 6.95:1 I'm not sure the pedal ratio you are using, but assuming a fairly standard 6:1 ratio, your total pedal ratio comes out to 41.7:1. This sounds like it is in the ball park for a manual brake car, but very high for a power brake car. To reduce the ratio, you would have to increase master cylinder bore. Tilton has a helpful section on their website in which you input your car and brake system information and they will assist you in properly sizing the master cylinders if you're running a dual m/c setup. http://tiltonbrake.com/content.php?page=faq&view=9 If you properly size a tandem single master cylinder for the front brakes, it will operate appropriately sized smaller rear calipers. The question just becomes what is an appropriate rear caliper size. Depending on many variables, including the total vehicle weight and weight distribution, front you can determine front/rear caliper area ratio. For a heavier car with more front weight bias, use a ratio towards the higher end of the spectrum. If you're running dry pavement track tires and have lots of grip both front and rear, you may go with a ratio on the lower end of the spectrum. Once you're calipers are at the appropriate ratio, you can fine tune with a prop valve, a balance bar (dual m/c applications) and pad material. Additionally, rotor sizing front to rear should not be drastically different. A 1'' difference front to rear is acceptable. Increasing rotor diameter will minimally reduce the total pedal ratio required for the same brake performance. When rear piston area is too large in relation to front piston area, the result is that the rear brakes may lock up before the front brakes in a panic stop scenario. I'm out of time for now, but will try to add more info when I can.

Re: my post above... I am looking on a real monitor now and see that the watts link setup does make sense (it is attached to the tube)!

I'm out of town at present, but will try to go back and add some of my findings to the other post (re: brake balance and selection) when I'm back at home.

If you search google for "pinion mount" "emergency brake" you will find some kits. I think one site that has them is springfieldstreetrods.com. The piston area on your setup comes to 4.8 sq. in. front and 3 rear. This gives a 1.6:1 ratio, which is within the range I've seen cited as acceptable. However, I have seen people with heavier cars running similar front sizes and still say they have problems with rear calipers of that size. Wilwood has started selling 4-piston calipers with piston sizes of 1" and 1.12" that some have switched to. I am not an expert in this area, but am also researching it presently, which is why I mentioned it. Rotor size front to rear and pad material will also impact the f/r brake performance.

I'm reading on my blackberry, so the pic above isn't that clear, but it looks like the car has a de dion tube, but the watts link only attaches between the diff and the frame... That doesn't make any sense... The diff should be solidly mounted to the frame and any lateral location device should be attached to the tube. Some leaf spring cars do use a watts or panhard, but doing so will create two competing roll centers. I have no experience with how that would effect driveability. Despite the lack of camber gain, a straight axle can perform pretty well. The de dion tries to reduce unsprung weight, but it seems to me like more trouble than it is worth, and may be more prone to flexing than a typical straight axle setup.

There are several pinion mount E-brake kits for Ford and Chevy differentials. They are faiely popular with the hot rod crowd. They typically use a solid rotor and a single piston mechanical caliper that is cable actuated. It seems like you could modify one of these kits to fit pretty easily, provided that you have adequate clearance for the rotor. On a side note, what Wilwood rear kit are you planning on using? You should pay close attention to the piston diameter of the calipers. Some of their rear kits use very large piston diameters, which can cause the rears to lock up berofe the fronts. You typically will not see this problem until you are in an emergency stop scenario (when you least need a problem).

And for those who don't want to tackle fabbing their own, you can find everything you need at these fine establishments: www.colemanracing.com www.lefthanderchassis.com

I used to be a pretty avid runner... until I started at a job that that takes all of my time so that any free time I do have I want to spend with my son.

I had heard that QC went down after Comp bought out Pro Topline, but that sounds pretty extreme. So extreme that I'm almost inclined not to believe it. I have an older set of Pro Topline 180cc heads (pre Comp buy-out) and they were of excellent quality right out of the box.

Thank you Dave! I took a break from the body work to turn back to the suspension/chassis/drivetrain. So, the body looks about the same at this point. Now the suspension is basically done. The frame is also done except for the cage. I also have the engine and trans mounted. I've kind of stalled at the moment though. Since my son was born, I've spent most of my free time just enjoying his company.

I did nearly the entire 240 body with floral foam. Terry helped me out greatly with the how-to and to help others in the future I put a writeup on my website. http://www.geocities.com/boodlefoof/Project_Racer-Zfiberglass.html

Here is the plan for mine... when I ever find time to get working on it again... http://www.geocities.com/boodlefoof/Project_Racer-Zaerodynamics.html

How exactly does that work?

Without adding triangulation to the chassis, just sewing up the seams in the frame rails isn't going to do anything unless the chassis is inadequately put together to begin with (i.e., if you're worried it might come apart on you). I can't see any reason to use rivets to do this... except not having access to a welder...

Looking hot! Is that your '69 Camaro (or I suppose it could be a Firebird) in the background too?

Even if you didn't sign a specific assignment of IP or similar agreement, it is probable that a condition of attendance is that you assign IP created while enrolled and using the school's facilities. You may have signed something saying you agree to abide by school policies as outlined in the student handbook, or it may even just be stated in the policies that by paying tuition you are agreeing.

Very nice. Me likey.