Which DIS unit?

Tedor

Registered User
Hi I just brought a DIS unit that came from a 1990 SC and I have a 1991 SC, I replaced it with the one from the 1990 SC and the car runs normal. There are different numbers on them, I dont have them in front of me right now. Have yet to drive the car only idled for 5 minutes.

But my question is, what will happend over time, nothing?

Thanks
 
It should last a bit as long as you used heat sink compound. I prefer to be cautious. Fast Freddie made me a heat sink to place under mine to keep it cooler than stock. :)
 
Why will it not last as long as the right DIS? If it works now it will work as long as the right one? If i make it cooler of course
 
I can not predict the future and tell you how long a DIS will last. All I can tell you is that in the 90 they are exposed to heat that shortens their life. Some add heat sinks under the DIS. Others relocate it to the fender-well.
:)
 
I figure the heat sinks are CPU ones Zalman come to mind for me.

As for the part number difference I bet its just a revision number.
 
Thanks for the help guys!

I'm going to raise my DIS an inch so that it have less contact and in that way runs cooler, seems like a good idea
 
The base of the module need to be in direct contact to the chassis for ground and disperse the heat created by the ~30A form the module.
 
The heat sink I have is extruded aluminum. Aluminum is a good conductor/ ground. I currently do not plan to do it because I was told 1-2 screws ground the DIS but, you could add a grounding wire jumper from the bottom of the DIS to below the sink on the engine side.

The heat sink Fast Freddie made for me is extruded aluminum that is approximately 70mm wide x 100mm long x 17mm high. Cost $10 (2-3 years ago). Who knows, he may have some more lying around... It has four holes drilled in it to match the DIS mounting screw holes. The fifth hole was a oops. ;) Flat side will face the DIS and get a whole tube of heat sink compound.

The stock 5.5mm hex head screws with washer are not long enough. The stock 1990 XR7 DIS screws are M4 x .7 x 20mm long (5.5mm socket). 17 + 20 = 37 so 40 mm long should work. I ordered Ford PN N808155-S434, N808155S434, M4 X 0.7 X 40mm long. Cost $8.50. Expect to get them tomorrow. Wish me luck. :confused:

I will caution that I used an M6 x 45 mm long screw for my 90 Thunderbird. So confirm the diameter before committing.

Attached are pictures.
 

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don't raise it up and let it "float" on spacers it will burn up faster. the accessories bracket actually acts as a heat sink. it needs to be mounted. heat sinks are readily available of many varieties. use heat sink compound,use heat sink compound,use heat sink compound.
 
Kind of how I imagined it would be. Same sort of deal with the PMDs on the Chevy 6.5. Used to be under the intake behind the injector pump, and it would burn up due to heat. The fix was a heat sink similar to that located elsewhere. That, and the new style Stanadyne PMD.

Would you be interested in selling one of your spares? Dont mean to hyjack the thread....
 
Kind of how I imagined it would be. Same sort of deal with the PMDs on the Chevy 6.5. Used to be under the intake behind the injector pump, and it would burn up due to heat. The fix was a heat sink similar to that located elsewhere. That, and the new style Stanadyne PMD.

Would you be interested in selling one of your spares? Dont mean to hyjack the thread....

Fast Freddie made it and he is "ThunderRoad" here. He used to make raised tops and other things... Now he is a retired layabout. Send him a PM.
 
In the stock mounting location, I don't see how you can improve much upon the stock arrangement. The air there is hot anyway, so you can't cool the module much below the temperature of the engine (200-220?). If you extended the wires from each side of the harness, you could move the DIS somewhere else and mount it with a heat sink in some airflow. But then you would have issues such as water intrusion to deal with.

The stock piece seems to last 15 years in the stock location, so I think I will keep it as is. If aftermarket pieces prove to fail sooner, maybe I will reconsider.
 
IMO the aftermarket units are fine just get one with a lifetime warranty. I believe a lot of DIS claimed issues is either ECT or Balancer.
 
I have it so I will use it. In summer heat and stalled traffic a 180-200F temperature can be seen under the hood.

For a quickie... Assuming no air flow, DIS at air temperatures and using Fourier's Law:

ALUMINUM
Area 0.007 m2
Thermal cond 210 @ 220 F ALUMINUM (dart throw)
Temp eng 104 C @ 220 F
Temp air 93.3 C @ 200 F
delta T 10.7 C
Wall thick 0.02 m

q = k A dT / s = 925 Watts

STEEL
Area 0.007 m2
Thermal cond 43 @ 220 F STEEL
Temp eng 104 C @ 220 F
Temp air 93.3 C @ 200 F
delta T 10.7 C
Wall thick 0.02 m

q = k A dT / s = 189 Watts

DELTA ALUMINUM VS STEEL 736 Watts

Not much. But my DIS is old and I am too cheap to get a new one. :cool:
 
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As you can see in this thermal image of my '90, the DIS is cooler than the pedestal, which seems to be similar in heat to the pulleys.

The DIS is actually similar in temp to the fender.
D07.jpg


If you're looking to mod things, perhaps the plan should be to shield it from heat from the pedestal, and move away whatever heat it happens to generate on it's own...better airflow, maybe, but I'm not convinced it is a source of heat on it's own so much so that it needs help, etc.

I've seen aluminum heat fins stuck to the the top of a DIS, but I have no idea if they supplied any added benefit.
 
Tried to leave Fast Freddie a messege, but his box is full. Honestly havent ever had one fail on me, but i will be turning this engine a bit higher from time to time.
 
I have it so I will use it. In summer heat and stalled traffic a 180-200F temperature can be seen under the hood.

For a quickie... Assuming no air flow, DIS at air temperatures and using Fourier's Law:

ALUMINUM
Area 0.007 m2
Thermal cond 210 @ 220 F ALUMINUM (dart throw)
Temp eng 104 C @ 220 F
Temp air 93.3 C @ 200 F
delta T 10.7 C
Wall thick 0.02 m

q = k A dT / s = 925 Watts

STEEL
Area 0.007 m2
Thermal cond 43 @ 220 F STEEL
Temp eng 104 C @ 220 F
Temp air 93.3 C @ 200 F
delta T 10.7 C
Wall thick 0.02 m

q = k A dT / s = 189 Watts

DELTA ALUMINUM VS STEEL 736 Watts

Not much. But my DIS is old and I am too cheap to get a new one. :cool:

Where's the steel come in? I am pretty sure that both accessory brackets are aluminum.
 
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