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  • race car wiring

    hello

    im currently making a wiring harness for a race car from scratch, and have a few questions if any one can help so ill post them here in this thread any input is appreciated

    im locating the battery in the passenger side rear footwell and need to re route a main positive cable to the engine bay for power distribution, my plan is to have two cut off switches that also kill the engine on this line, one in the dash for the driver and one on the scuttle panel under the windscreen passenger side as per regulations.

    my questions are:

    what is the thickness of the standard battery cable from rear to front?

    what sort of thickness cable should i be using? the standard stuff that runs from the rear is really thick, i was thinking of using either 25 mm2 (2 awg) which can carry 170amps but is this enough for the starter motor what amps does that draw? also be sufficiant for the circuits that maybe running ie engine, fuel pump, lights, wipers? i think the safe bet is 40mm2 (approx 1 awg) which carries 300 amp? any input?

    Also where would you route this? the easiest place would be up the side of the tunnel to the first switch in the dash panel (where the heater controls where) then from there to one on the scuttle panel then to the distrubution block, this way if theres an accident and the driver is consious he can kill the power before outside help arrives, or if the driver is unable all the power can be cut from the scuttle.

    only problem with that is there will be big ugly cables running up the tunnel and clogging up behind the dash switch panel, any one got any better ideas or pictures of cars?

  • #2
    Bab:

    Can't tell you for sure what the gauge of the stock battery cable is, but I'd guess maybe 00? It's really irrelevant for a race car since your current carrying capacity should be remarkably less than a street car. I wired my race car to handle the sum of the current that every device could draw, and came up with something like 60A. (I don't recall exactly since it was 6 yrs ago now). I researched on the web the proper gauge size for my load and came up with I believe 4 Ga. I haven't had a single electrical issue with the car since I built it. As far as routing the battery cable, I chose to route it in the same place as stock, along the right side rocker panel, under the factory retainers. My battery is located in the passenger rear foot well too. My exterior Cut-Off SW is in the right cowl (scuttle) where the panel is drillled for a windshield wiper in RHD cars. My interior Cut-off SW is mounted on the battery box proper which I can easily reach from the drivers seat.
    Ron ///Man

    • '91 Gr-A Former CiBiEmme / Ravaglia - Sold
    • '90 M3 Faux EVOII Alpineweiss 36K Orig Owner - The Queen
    • '91 M3 Faux EVO III Brilliantrot Euro Driveline - The Rocket
    • '91 M3 Faux Gr-A Club Racer DM - The Alter EGO
    • '89 M3 M3T / ITR Club Racer
    • '94 Spec E36 - Eh....
    • '09 M3 - Tarmac Terrorist
    • '04 330Xi Sport 6 Speed - Snowmobile
    • '07 530 Xi - Highway Star
    • http://www.imwcarparts.com/e30-m3-parts.htm


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    • #3
      I am about to rewire the battery as well. I decided to go with Ron's spec of 4 gauge cable.

      The starter is rated at 1.4kW according to this:

      http://bmwfans.info/parts/catalog/E3...ystem/starter/

      At 13 volts, that corresponds to peak current draw of ~110 amps (assuming starter operates at peak rated power).

      According to this table, 4 gauge wire is rated for 60 amps for power transmission, but I assume that is for sustained transmission, and is a conservative rating.

      http://www.powerstream.com/Wire_Size.htm

      IIRC, Brendan might be running 4 gauge wire as well without issues.
      sigpic

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      • #4
        I used #2 welding cable, Its fairly light, and easily available.
        I basically wired my silver car just like my Grp A car.
        Battery still in the stock location, up the trans tunnel to a replica Grp A breaker panel on the tunnel, then power distribution from there.



        My main reason for wiring was consistency, that whenever I sat in each car, everything fell to hand exactly where it is in the other car so everything is "automatic" in my head.

        I also liked moving the battery cable inboard away from the door sill, I had visions of in a severe side impact the cable could get smashed / pinched / cut by a side intrusion. Moving it inboard to the tunnel lessened that chance.

        Cheers
        jimmy
        jimmy p.
        87 E30 M3 Prodrive British Touring Car
        88 E30 M3 Zinnoberot - Street
        88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
        92 E30 M Technic Cabrio - S14 POWERED!
        98 318Ti M44, Base - Morea Green
        04 Ford F350 - V10

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        • #5
          That looks great! I'll try to move the cable to the tunnel later on...
          sigpic

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          • #6
            Length of the cable is also a factor. The closer you are to your main power drainer, the thinner you can go.


            Goodbye M3, you served me well.

            Comment


            • #7
              Right, resistance will increase with length. There are some rough estimate guidelines on that on the page I referenced.
              sigpic

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              • #8
                I'm running 4 gauge from the passenger seat area, without issue.

                I tried running 8 gauge from the firewall to the starter and it went up in smoke.
                sigpic

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                • #9
                  Originally posted by lucid View Post
                  IIRC, Brendan might be running 4 gauge wire as well without issues.
                  Yep. 4GA from the trunk along the passenger side like stock. No issues at all yet.

                  I did add an extra layer of heat shrink to the outside of the cable, and then added cable wrap in certain areas for abrasion protection. Also made sure to route the wire around the inside of my cage bars so there was no chance of the wire getting "pinched" between the cage in an accident.
                  sigpic
                  Track Car Build | COM Sports Car Club

                  Comment


                  • #10
                    I just pulled the battery cable and oem terminals/power distribution block from a e36 coupe 20 at the breakers.

                    Jason

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                    • #11
                      I replaced the OEM cable with 4 gauge cable, and ran it against the tunnel on the inside in the mid section. I installed two kill switches: one on the dash and the other under the wiper. It works fine.

                      Has anyone installed a fuse on the main power cable? I am thinking about a 150amp ANL fuse right after the battery.
                      sigpic

                      Comment


                      • #12
                        Just so you know, if you need any wiring/connectors we carry a fully line of Deutsch parts and mil-spec wire, plus crimp tools!

                        store.apexspeedtech.com

                        Thanks,

                        Neel
                        Neel Vasavada
                        Apex Speed Technology
                        2931 S. Sepulveda Blvd Suite F
                        Los Angeles, CA 90064
                        310.314.2005
                        [email protected]
                        www.apexspeedtech.com

                        Comment


                        • #13
                          Nobody makes a Grp A replica harness for those of us planning on full race/track cars?
                          1988 BMW M3 Alpine/Black
                          1988 BMW M3 DS/Grey
                          1989 BMW M3 Zinno/Tan
                          1989 BMW M3 Brilliant/Track
                          1990 BMW M3 Alpine/Black

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                          • #14
                            Ton Vink had a few NOS Grp A wiring harnesses for sale but I cant see why you would tie yourself into that. Even if I had to rewire my BTCC car I would start from scratch not buy a replica or NOS Grp A harness.

                            You are best to have someone like Neel at Apex make you one if you dont have the tools and the skills to make one. Just work with him on exactly what you need, sort out the lengths and they can make it. Or, Painless Wiring makes a few 6 or 8 circuit race harnesses that you can self terminate.

                            Geoff Atkinson had a few of those Grp A replica breaker panels left I think like mine in the photo above if you wanted to retain the period look.
                            HTH
                            jimmy
                            jimmy p.
                            87 E30 M3 Prodrive British Touring Car
                            88 E30 M3 Zinnoberot - Street
                            88 E30 M3 Lachsilber - Race (#98 SCCA SPU)
                            92 E30 M Technic Cabrio - S14 POWERED!
                            98 318Ti M44, Base - Morea Green
                            04 Ford F350 - V10

                            Comment


                            • #15
                              Thanks for the insight I am relocating my battery and kill switch to the dash.

                              Comment

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