brake venting and a few other questions (Page 1 of 2)

1. I don't see a lot of venting rear brakes.  It is the front that get really hot.
2. I see that fairly commonly if I understand what you are saying
3. If you are using the existing wiring from the stock fuel level sensor I don't see a problem with that.  I do that on my car as I threw away the dash years ago.  Do you know the resistances of full and empty?  You can also take a hole saw to the restrictor inside the fill neck so you can get a larger nozzle in it.
4. Small holes I ran a screw/bolt through with fender washers.  Big holes I riveted thin sheet metal with rtv.

1. Don't bother, the rear brakes getting overheated is not the problem you will have.  But you can cut body panels for ducting, just don't cut structure.

2. No problem

3. What's the point?  Leave the stock gauge.  The more you can leave OEM on the car, the more reliable it will probably be.  That being said, if you just change the gauge and not the sender itself, then it is fine.  Aftermarket senders are notoriously unreliable. 

4. I strongly suggest leaving the heater and vent system.  We took it out of our first few builds, but keep it now.  Having not had it in the past and having kept it in the latest car, the difference in driving the car in the rain is amazing to keep the defroster and venting.  It isn't worth the potential weight savings, and Pitt often has "seasonal" weather that is not sunny and clear.

Forget about cooling the rear brakes.  They only do about 10% of the work.

Removing the heater core is the WORST idea ever.  If you don't believe me, do it, and let me know what happens the first event that it rains.  All of us who still have our heater cores have BTDT.

Yeah, a lot of cars--VWs in particular, I think--have a kind of shelf that's above the firewall. That's fine to leave in place.

Agree with others on rear brake venting. If your rear brakes are hot enough to need venting, you're either driving the car WAY too hard (and your front brakes will be roughly surface-of-the-sun hot anyway) or something is mechanically wrong.

disagree. there are better ways to defog a windshield than to pump boiling water into the cabin to pass thru a heat exchanger.

Hey all, this is why I love this community, I really appreciate all the help and guidance!

here is my take away from all the questions with some more questions,

1. the idea of venting the rear brakes is dead, I will not waste my time and money doing that.

2. the vent for fresh air that I am referring to is on the passenger side just above the "shelf" of the firewalls there is that separation, I think for now we will use that with plan B being a nacho duct in the door or doors.

3. the reason for the after market fuel gage is that the stock cluster have been a bit hit and miss working but the intake sending unit has been fine, I checked the ohm range and got the correct one so I think I will switch to that being that using the stock wires is not a problem.

4. for the firewall I will rivet in some sheet metal and call it good.

a lot of you mentioned leaving the heater core/ climate controls for defrosting that's not really an option as it was already ripper out and damaged during removal and is already in the garbage. Chase mentioned a universal defroster grid, I am assuming you mean something like a rear window defroster, do you have a link to one? 

thanks again for all the help, I am sure I will have lots more questions and the build moves on

If you've already removed all the stock HVAC stuff then for sure get one of those electric defroster kits. Hell, even if you go through the effort to put back in the heater core and blower, install one of those as well. The difference it makes in the rain is monumental. Because you need to keep the windows down during the race your glass will want to fog like crazy, those kits make a world of difference.

The first time you get in the car with it installed you're going to find it weird to have the lines across the glass. After 5 minutes you'll forget they're even there. We've had them for a few years now and I don't even register them anymore.

The bimmerworld one is fine, they're sold through a number of places and all seem to be roughly the same kit.

I'm gonna have to disagree. We have two fresh air ducts to our driver... one "ball breeze 9000" that's 3" or 4" PVC that elbows forward (like a snorkel), then penetrates through our hood, cowl, and aims towards the man-region. We also have another one that's just a NACA duct riveted to our door. We did the NACA duct for fun, and thought the ball breeze would be the bees-knees but turns out it does nothing and the NACA duct made a huge difference. It's totally possible we just suck at making things, but we were really surprised by the NACA duct.

edit: Also +1 on always removing the heater core... even if it was needed for defrost (it might break fluid in driver compartment rules?) and at the age of all our shitboxes it's just a matter of hours until it fails. Out of all the ways to lose track time, bypassing a heater core seems like a really crappy way to be stuck in the paddock during a race.

In my experience, Lemons cars are ancient and the chance of a heater core leaking increases with age. Unless you replace it at build time, I wouldn't trust it to last.

Exactly, it's just an age thing and the fact that nobody likes to replace them because they're hard to get to. Not any less reliable than a radiator, but there's a lot more old heater cores out there than old radiators.

Most of the heater cores have failed on me at elevated coolant temps. High coolant temps = high coolant pressure and in these scenarios I guess the heater core decided to leak before the radiator cap relieved pressure. Racing=higher coolant temps=higher coolant pressure=more stress on heater core. I know I'm grasping here, but I'd rather my radiator cap vent inside the engine bay than my heater core "vent" on my leg. 

Maybe I'm just unlucky, and everyone's allowed to build how they want, but (at least on the west coast) I always pull heater cores out of my race cars.

We use something like that on all our cars now.

Regardless of the conditions that you see highest temps, you will see your highest vibrations on track.
While most heater cores aren't affected by heat cycling, vibrations can kill anything with enough amplitude
and/or frequency.

As far as brand failure, unless you have an encyclopedic knowledge of crapcan racer heater core failure
you gonna be guessing. Though, asking this august body of experience may yield positive results.