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  #91  
Old 02-13-2007, 07:04 PM
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Quote:
Originally Posted by Jazzbass View Post
Ideas regarding safety (kill switches, warning lights, etc from people who have BTDT (or have even just thought about it) are welcome.
I haven't actually executed this myself.....YET....(soon!)......but it is my understanding that you can easily wire the secondary switch of the common 6 pole kill switch to the pin 86 of the DME relay and effectively kill both ignition and fuel pump in one flip. This can be done otherwise also, but it is less wiring and cleaner overall I think if you go the dme-relay route. Of course...this also illustrates why the DME relay (and its failure) is so crucial to the car operating at all.
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  #92  
Old 02-13-2007, 07:05 PM
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Originally Posted by Lucky View Post
Seems like you could apply the same tricks to a '44 and free up 5+ HP.
Might be an issue unless you are running in a GT class...
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  #93  
Old 02-13-2007, 07:22 PM
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Originally Posted by BlackTalon View Post
Might be an issue unless you are running in a GT class...
that would be an issue. we are doing nothing more than repairing wiring and installing new gauges . . . which is permissible. I read the rules AND talked to the director . . .
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  #94  
Old 02-13-2007, 07:50 PM
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Originally Posted by TD in DC View Post

With respect to the DME Relay, it would be great to delete if it is easy and does not delay the completion of the project. If it does, just forget it because I always carry a spare DME Relay in the Sequoia.
You should Velcro it to the roll bar so you could change it mid race if need be.



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Originally Posted by Lucky View Post
. Turns out they have some nifty ideas to free up HP the engine is already making -- two of the biggest are underdrive pulleys (so the accessories like AC, alternator, and water pump spin a bit slower) and electric water pumps (which eliminate the friction lost to yet another belt and pulley). Seems like you could apply the same tricks to a '44 and free up 5+ HP.
Wouldn't an electric waterpump essentially negate the effects of the lightened load on the belts?

FWIW on a 944, the water pump is driven by the oh so important timing belt anyhow. I'm not sure there's enough black arts around coming up with a different size belt and the related tension to make such a swap.
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  #95  
Old 02-13-2007, 09:34 PM
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Update:

RE: the DME relay. In the picture I posted before I show part of the wiring for the 944, with the DME relay and the DME shown. I stated I wasn't sure what the DME pins were doing, or exactly what the relay was doing. Well, the Clarks Garage stuff Andy posted helped, and I also remembered that I just happened to have the complete schematics for the 911/944 DME. Convenient, huh?

OK, so in this picture:

Name:  dmerelay.jpg
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Pins 18 and 35 into the DME are the +12V power supply to the DME. So, power is supplied to the DME (and the fuel injectors) through the right half of the DME relay, which is turned on when the ignition switch is on. If the right half of the relay fails, no DME power for you! The EE side of me tells me that's bad.

Pin 20 of the DME is connected to a high current relay driver (darlington) transistor, which is controlled directly by the 8051 Microcontroller that runs the DME. When this driver circuit is turned on, the right DME relay coil is grounded, turning that side of the relay on and thus turning on the fuel pump.

Some searching revealed what the microprocessor is doing here. From Steve Wong's site:

Quote:
When starting the car, power is supplied to the main DME relay, powering the DME computer. As long as the DME sees the engine turning a minimum of 200 rpms, it switches on the fuel pump relay, powering the fuel pump and allowing the car to start and run. This is designed as a saftey precaution, shutting off the fuel pump in the event of an accident where the fuel system ruptured.
IOW, not a good idea to replace the fuel pump relay with a switch. The main relay could be replaced however. Stay tuned, I'm revising TDs wiring diagram as we speak...
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  #96  
Old 02-13-2007, 09:50 PM
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I just remembered the accessory that I had forgotten . . . the yet to be purchased but probably at some point will be purchased race radio . . . .
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  #97  
Old 02-13-2007, 10:36 PM
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Impact fuel pump kill switch.
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  #98  
Old 02-14-2007, 02:25 AM
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Is the alternator completely free under the regulations? Travis has a very good solution for an aftermarket newer style altenator that is much more efficient.
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  #99  
Old 02-14-2007, 06:38 AM
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I just remembered the accessory that I had forgotten . . . the yet to be purchased but probably at some point will be purchased race radio . . . .
You meant CB right instead of race radio, right? 10-4 good buddy.
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  #100  
Old 02-15-2007, 11:49 AM
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Very interesting thread. I should have found it sooner as it's near and dear to my heart. I'm in the middle of re-doing Don Ruschmans car as we speak.

FWIW, and your consideration, my thoughts after a long time pondering the 44 wiring (924s share almost identical wiring with early 44 chassis).

I think track cars need a balance between simplicity and function. For the cooling fans I favor eliminating the relays entirely. The reuse of the AC switching relays and cooling fan is very clever (wish I was that sharp); but needlessly complex. After much consideration I have opted to split the 2 stock fans both for redundency and reliablity.

The 'main' fan I wire directly as oem except without the bigass ceramic resistor (which lowers fan speed with key off) and without the fan relay which normally bypassed said resistor with key to 'run'. This leaves a single fan operating as per oem but without 2 failure points (relay and resistor). The fact that it runs on high speed when stopped has not been an issue.

The 'secondary' fan I wire through a simle toggle switch. My drivers are directed to turn the secondary fan 'ON' when entering pit lane and 'OFF' when leaving pit lane. I find even drivers can be trusted to follow such simple instructions. Best of all, even if they don't the cars are not really in need of the secondary fan and/or the temp guage serves as a reminder.

So only a single fan is running at at time but you do have the second fan to use in case of a failure or need. I do not think it smart to disable the fans. At the other side, I have considered a toggle around the main fan temp switch to cover that failure mode. However, assuming that's probably something that would be found in the paddock I can just as easily jumper the temp switch upon diagnosis to the additional toggle and wiring is a needless complexity.

Early 44s use the same fuse board as 24s and I have the same revulsion to them as you. I installed ATP holders on the inside right side and so have short runs from the stock battery location to the fuse panels. The power distribution is then moved from the engine side of the firewall the behind the dash. More protected and it doesn't have to go in and out and in and out ...

As you have already determined there is good reason to keep the DME/Fuel pump relays. (Jim Pasha has covered this a couple of times in Excellence). I believe that after the full modifications rewiring the car as you are the relays should fail much less frequently. As signficant amount of the failure (I'm guessing) was occasioned by the combination of interanl relay contact heating and external relay plug to receptical heating. Especially early cars tend to have much corrosion in the relay board and contacts which then heats the relay which then cooks the contacts ... Also, a couple of items can with good effect be left off the current load: some cold start stuff, and the O2 sensor heat.

I'm curious what you think of my approach. And also, would love to find the site with the DME circuits. I've dabbled with sorting out the schematic of the relay on the 924Turbo (especially as it appears to have a rpm limit built in) but gave up did without -exactly as I shouldn't do.
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