Pretty good stuff. Since you're documenting this and it might be useful to others in the future, maybe look into submitting this to be uploaded in our tech article directory. Info below. Good luck!

Enthusiast Tech Article Submissions - Pelican Parts

Thanks Luccia. When and if I get that far, I'll reorganize it all for an article.

Since I started this thread I've been deeply occupied with rebuilding my 3.0 engine, but now I'm at a point where I've got everything pretty well figured out regarding how to backdate the heat in a 911 SC. I've got access to my car (1983) and my brother's car (1979) so it covers a pretty good range over the life of the SC. In reality, the cars aren't that much different. We did remove the air injection system on the '79, which does affect the ductwork to an extent, and I'll show how that affected the process on the '79. I'll be using photos gleaned from the forum, as well as my own photos of my '83 (both with engine in and out of the car) and the '79 as we backdated the heat on both cars. I started this thread mostly to do my own research and get some help from this community along the way. I felt moved to post this, to consolidate the info I learned earlier in the thread, and to give something back here since I've learned so much in the past year. I should add that I don't know much about 911's. I've owned one for less than a year, but hopefully this will be helpful to another novice like me. I'm simply sharing my experience. Experts and experienced folks are more than welcome to chime in and correct any errors. I welcome it in fact. Here goes....

First off let's define what backdated heat is. I learned that a lot of the time "backdated heat" and "backdated exhaust" can be confusing terms, especially since both the heat system and exhaust system are linked through the heat exchangers. For the SC, the stock heat system includes an electric blower placed in the engine compartment that turns on when you raise the heat levers between the seats inside the cabin. The levers close off the heater boxes under the car and allow hot air to enter the cabin by means of the engine cooling fan blowing through the fiberglass fan shroud, out the hot air duct, up a long air duct, through the electric blower, down through two hoses which passes through the engine tin (and the right one takes a long route to get there), then into the heat exchangers and over the hot exhaust pipes, out the heat exchangers, through more hose, then finally into the cabin. Once you pull up on the levers to the maximum, a switch turns on the electric blower which gives a boost to the air coming into the cabin from the cooling fan. So why would you want to backdate the heat? Two reasons I've found. The first is: easier access to the engine. Without the electric blower and its extra ducting, one can work on the left side of the engine much easier. Second, I've read that because of the extra ducting and circuitous route the air from the cooling fan has to take with the stock setup, the effectiveness of the hot air is lessened, even though you'd think the electric blower would compensate for that. Backdating the heat system on an SC does away with the electric blower and its maze of hoses and ducts and replaces it with two older-style hot air ducts that flank the cooling fan.

So what is backdated exhaust? It doesn't have much to do with backdated heat. Instead, it means using heat exchangers and a muffler from the earlier cars, 1974 and earlier (or something close to that.) Whether you backdate your heat or not, the heat system connects to stock or earlier heat exchangers pretty much the same way: via two hoses at the rear of the engine. You can backdate the heat and exhaust independently from each other.

How the systems work:

Stock:
Here you can see the route the air has to take to get from the cooling fan to the warm pipes in the heat exchangers. Lots of twists and turns, not to mention getting through the very restricted passage of the squirrel-cage-style electric blower (yellow arrow). All heated air must pass through this blower. This is a '79 with the air-injection pump still in place in the lower left hand corner and the mounting bracket for the A/C compressor still in place at the lower right. We'll be removing both of these on the '79, but leaving the A/C in the '83.

http://forums.pelicanparts.com/uploa...1490754248.jpg

Here's the same car with backdated heat.

http://forums.pelicanparts.com/uploa...1490754320.jpg

To get the job started, first remove everything highlighted below.

http://forums.pelicanparts.com/uploa...1490754411.jpg

I removed the large plastic duct at the left first. It connects to the hot air duct directly behind the distributor, and at the left side of the electric blower. Below I've removed the plastic duct.

http://forums.pelicanparts.com/uploa...1490754444.jpg

Loosening the various hose clamps is next. I was careful to not damage too much of the ducting. If its in good shape it can be reused.

Now I remove the duct that goes to the right heat exchanger. I also removed the two hose mounting brackets on top of the shroud. They are not needed with the backdated heat.

http://forums.pelicanparts.com/uploa...1490754498.jpg

It may be difficult to remove the hose out from underneath the A/C bracket. I remove the bracket anyway since I'll need to access the shroud behind it. I remove five fasteners (yellow arrows). The left most arrow points to a bolt that joins a bent steel bracket from the engine case to the compressor mount. It's a little tricky to get to. The two lower bolts are pretty easy to access. The top two arrows point to two smaller nuts that hold this aluminum bracket to the top of the cam housing. I use a small 10mm swivel socket and some extensions to get to the front one.

http://forums.pelicanparts.com/uploa...1490754529.jpg

With the A/C bracket out of the way, I remove the hose. The yellow arrow points to a coupler that joins the two sections of hose. It's got to come off. We thought we could reuse this section, but we ended up up removing the entire hose down to the heat exchanger.

http://forums.pelicanparts.com/uploa...1490754557.jpg

Next I remove the block off plate from the right side of the cooling fan. Arrows point to the three screws/bolts that need to come off. I was careful not to loose the wire retaining tab on the top most screw.

http://forums.pelicanparts.com/uploa...1490754615.jpg

http://forums.pelicanparts.com/uploa...1490754648.jpg

Next I disconnected the electric connector for the electric blower and then removed the blower motor itself. It'd held onto its mounting bracket with a metal strap thats pretty easy to remove. You'll have to use some clever movements to get the blower past the fuel lines without damaging them, but it will come out. The bracket has some of the CIS components mounted to it, so it has to stay (yellow arrow.) I've also taken the air-injection pump off in the '79 in the pic below. I also removed the bracket later on.

http://forums.pelicanparts.com/uploa...1490754687.jpg

Next I take off the distributor cap and coil to gain access to the plastic left hot air duct. There are four screws to remove. Two up top, one into the left side of the fan housing, and one hidden down below just above the chain cover.

http://forums.pelicanparts.com/uploa...1490755127.jpg

Here's the bottom one:

http://forums.pelicanparts.com/uploa...1490755148.jpg

We pulled the duct out from the back. The back side is pretty well clogged up with plug wires. Arrow shows bottom bolt.

http://forums.pelicanparts.com/uploa...1490755177.jpg

Duct removed.

http://forums.pelicanparts.com/uploa...1490755198.jpg

That finishes up the removal of all the stock heater components. There are a few different ways of handling the actual backdating of the heater ducts and hoses. The earlier rear most tin did not have a built-in duct at the left corner, like the stock SC tin. A is the SC rear tin, and you can see the built-in duct to the left of the A. B is the side tin piece that joins A to C that runs along the left side of the engine and attached to the cam housing.

http://forums.pelicanparts.com/uploa...1490755272.jpg

Here's a picture of an earlier rear tin "E" with no duct. On the earlier cars tin "F" had a hole and was used to route the heater hose from the left hot air duct down to the heat exchanger.

http://forums.pelicanparts.com/uploa...1490755344.jpg

The right side engine tins are the same on the SC as the earlier cars, at least for the purpose of backdating. In other words, the short tin that joins the rear tin and the right side tin has a hole in it for the hose. Below is the right side tin from the '83 SC.

http://forums.pelicanparts.com/uploa...1490755369.jpg

A couple approaches here work. First, the hose from the left hot air duct can be routed directly to the stock SC tin and its built-in duct. That looks like this:

http://forums.pelicanparts.com/uploa...1490755392.jpg

Versus routing the hose to the earlier small tin, which looks like this:

http://forums.pelicanparts.com/uploa...1490755452.jpg

The advantage of using the SC tin is, you don't have to replace the tin. Just leave it in place. You also don't have to find/buy the short tin with the hole in it. The advantage of using the short tin with hole is a straighter shot for the hose from the hot air duct to the tin and down to the heat exchanger. It's a cleaner look, and might give a little better hot air flow to the cabin, but I'd bet that's splitting hairs. Here's what the hose routing looks like from the side using the stock SC tin. Yes, this is a 3.2 Carrera engine and SSI heat exchangers, but the results are just about the same.


http://forums.pelicanparts.com/uploa...1490755475.jpg

I opted to keep the SC tin on both the '79 and the '83 because it meant less work, less hassle, less money.

Now lets talk about what hot air ducts to buy. For the left, I bought part # 901.106.321.02. This is the stock left hot air duct for the earlier cars. When fitting this duct to an SC, the distributor, and more precisely, the distributor cap and wires may end up too close to the duct. I had to heat up the duct to make it more pliable and "massage" as they say the metal with hammers and various implements to get everything to fit. It took me a while, but I eventually got it to fit and look pretty good. Here's some pics of that process.

http://forums.pelicanparts.com/uploa...1490755703.jpg

Here I'm test fitting the duct against the plug wire. It's just barely kissing the sheet metal.

http://forums.pelicanparts.com/uploa...1490755730.jpg

Here's what the duct looks like on the front side. I tried to shape the metal so it conformed closely to the shape of the surrounding parts.

http://forums.pelicanparts.com/uploa...1490755750.jpg

Once I was happy with the fit I painted the duct then screwed the duct in place. There's a screw on the underside that's easy to forget.


http://forums.pelicanparts.com/uploa...1490755784.jpg

The upper front screw also holds the adele clamp for the wiring harness.

http://forums.pelicanparts.com/uploa...1490755801.jpg

The other screw that attaches to the fan housing had a rather large hole. I didn't fill this, but maybe I should have?


http://forums.pelicanparts.com/uploa...1490755833.jpg


http://forums.pelicanparts.com/uploa...1490755846.jpg

In order to avoid the hassle of fitting this early duct to the SC distributor, the duct from a later Turbo 911 can be used. Part # is 930.106.321.02. This part however is quite expensive, and costs about $100 more than what I paid for BOTH parts listed above. I felt an hour with the hammer and some engine paint was work the cost savings. The turbo duct has a deeper concavity where it meets the distributor cap, so there are no clearance issues.

On the '79 we used the same early duct, hammered away, and got it fit and installed. The original hose was still connected to the rear tin, so we simply started cutting it back until it would slip over the hot air duct.

http://forums.pelicanparts.com/uploa...1490755880.jpg

This hose does not like to cooperate! I can see why some folks are using the orange aircraft hose. That stuff looks a lot more manageable. But we got it eventually.

http://forums.pelicanparts.com/uploa...1490755908.jpg

The duct comes with two tapped holes on top. These aren't used on the SC that I can tell, so we plugged them with two tin screws. Underneath the car there are no changes to be made. The hose from the stock setup can remain since its not connected to the upper section of hose. It's a separate piece.

http://forums.pelicanparts.com/uploa...1490755949.jpg

The right side of the engine is a bit easier, especially if you're not running A/C. But again we've got both here, so that's what I'll show. On the '83 I bought hot air duct # 911.106.327.00. I'd read that these don't really work on cars with the A/C bracket, but I was pleasantly surprised when my bracket fit really nicely over the duct.

Here's the opening without any duct.

http://forums.pelicanparts.com/uploa...1490756027.jpg

Here's the duct in place. It attaches with three screws. The two on top of the fiberglass shroud...

http://forums.pelicanparts.com/uploa...1490756067.jpg

and one underneath that screws into the chain housing. You can see the duct doesn't fit perfectly against the top of the chain housing (cylinder fins are peeking through.) This can be tweaked with some manipulation.

http://forums.pelicanparts.com/uploa...1490756095.jpg


And here's the installation on the '79.


http://forums.pelicanparts.com/uploa...1490756221.jpg


We ended up using some of the hose that we removed to route to the heat exchangers. Arrows point to the fasteners, plus the one below (shown above on the '83)


http://forums.pelicanparts.com/uploa...1490756242.jpg

The hose on the right side is one piece, and goes from the hot air duct, through the short tin with the hole, terminating at the heat exchanger below.

http://forums.pelicanparts.com/uploa...1490756274.jpg


http://forums.pelicanparts.com/uploa...1490756297.jpg

And here's some pics of the right side duct under the A/C bracket on the '83. I don't have pics of that engine in the car yet, since it's still in my woodworking shop, but I think you get the gist, it will look nearly identical to the '79 when complete.


http://forums.pelicanparts.com/uploa...1490756355.jpg

http://forums.pelicanparts.com/uploa...1490756331.jpg

http://forums.pelicanparts.com/uploa...1490756344.jpg

One thing I haven't figured out yet and that's how to disable the electrics for the blower motor that gets removed. I do recommend taping off that lead from the engine harness, but I'd also like to disable the call for power to that lead when lifting the heater levers inside the cabin. If anyone would like to complete this thread with that info, that'd be great.

So that's it. I hope this info is helpful and that I haven't shared a bunch of bad instruction here. Like I said before, I'm pretty new to all this, just sharing my experience.

One more shot of the completed backdated heat on the '79

http://forums.pelicanparts.com/uploa...1490756560.jpg



Here's another backdated heat from the forum...a much nicer looking engine!



http://forums.pelicanparts.com/uploa...1490756676.jpg



And finally (yeah, showing off a little here!) my '83 3.0, just about ready to go back in the car just as soon as I sort out my CIS.



http://forums.pelicanparts.com/uploa...1490756750.jpg

Sorry to wake up this thread but im about to order all my parts and im wondering what diameter hose you used. From the "backdate ducts", is it 60mm? Or is it 75mm?

Very useful thread, thanks for all the pics and instructions

If you are talking about these hoses, 2.5" (63.5 mm).

Not cheap but they are the best, remember buy cheap by twice...

$11 US per feet SCEET AIRCRAFT DUCTING - CUT TO LENGTH from Aircraft Spruce

$14.50 Can Per feet SCEET AIRCRAFT DUCTING - CUT TO LENGTH from Aircraft Spruce Canada

http://forums.pelicanparts.com/uploa...1480174822.jpg[/QUOTE]

Backdated Heat Tech Article
 

I bought all new oem looking hoses last winter, but now my fan let go. Doing the backdate now and wanted to keep my black hoses, but they're 60mm. Is it going to fit on the backdate ducts?

I guess my question is, are those openings circled in red 60mm?


https://uploads.tapatalk-cdn.com/201...22f2d8f2e5.jpg

https://uploads.tapatalk-cdn.com/201...0d6a975ea7.jpg

They should be a perfect fit as the 2.5" was good after I flip in some skin at the ends.

This is a great thread. Thanks, OP, for putting it together. Unfortunately it looks like a fairly time-consuming job on my 82 SC. Especially since the engine is in the car. It seems like our host would put together a package with all the required pieces to it straightforward. I’ll continue my research and add it to the task list. Thanks again!

I'm doing this in conjunction with an exhaust backdate on my 82 SC now. It's quite easy thanks to this thread and others. I ordered everything needed from Pelican except for the small engine tin with the hole for the drivers side, I found that used for $15.

Just go for it, its cheap, easy, only requires a few tools and is totally reversible. The engine bay looks much better and you lose a couple pounds. What's not to like?

Just wanted to say that I am using this thread currently as I move through backdating my own heat. Right side is done in about 20 mins thanks to this thread and hopefully will get to the left side tomorrow. Thanks so much for documenting this for us - its been a huge help!

On a related note, OP how long did it take you to do the whole backdate?

Quoting another thread (http://forums.pelicanparts.com/porsche-911-technical-forum/997426-79-sc-thoughts-ac-delete.html) because I'm trying to keep the info in one place for easy reference:

TheFaculty, did you ever revise your list or is this list exactly what is needed? Seems like the part that makes the whole thing much more expensive is the left-side turbo duct that clears the distributor. If you wanted to just "massage" the non-turbo one it would be much cheaper. I'm with you though, I'd rather just buy the part that fits well. EDIT: One thing I am confused about is that in the walkthrough/tutorial, it looks like there is just one duct on each side. On the parts list below, there are 4 separate parts for the right side?

Also, regarding the SCEET ducting, is the correct size 2.5"? How much did you order for each side? I have an 82SC (SCEET AIRCRAFT DUCTING - CUT TO LENGTH from Aircraft Spruce)

Got most of my backdate done today. I didn’t button up the right side because I need to replace my oil pressure sender and it’ll be easier with that side disassembled. A few takeaways:

- The right side plate, which is a non-Porsche part, was not made to very high specifications. I had to do quite a bit of metal bending around the edges to get everything to look correct. The gap on the bottom is still similar to some of the photos in this thread.

- The left side plate, which is a Porsche part and is the turbo plate, is better made but still needed some work on the side that met the fan housing to get everything flush.

- I found that on my car, which is an 82 SC, with metal fuel lines, it was easier to disassemble the blower and remove it in two pieces than try to figure out how to remove it as one.

If this job had simply been removing the blower and hoses and then installing the plates with no reworking of the metal and then installing the tubing, it would’ve been a pretty quick job. Because I am somewhat detail oriented and wanted everything to look nice and flush, it took probably an hour and a half longer than I would have expected.

One question: after removing the blower I did leave the mounting bracket. Previously it was mentioned that some of the CIS components were attached to the bracket and so the bracket had to stay. Take a look at the photo below. It looks to me like I can remove that bracket as nothing is attached to it. Thoughts?

http://forums.pelicanparts.com/uploa...1532835389.jpg

My 83 has the thermo valve monted on a short metal arm off that bracket.


http://forums.pelicanparts.com/uploa...1532858847.jpg

Interesting. You can see where my bracket had an attachment for that at one time. Must have been relocated. I guess I'll take a look and see where it is.

Anyone know if it is required/best for it to be there? If it's been relocated, any issues with removing the bracket?

The thermo hold off vacuum for several seconds at startup. I believe if you have a US model 1982, the system doesnt use a thermo. Its only on euro models and the 78/79 US. The connecting vacuum hose comes from the wur so you should be able to see it if your model has it. I would think the thermo could find a different home as the btacket is much larger than needed once the blower is gone. I was too lazy to take mine off...