SSI Backdate and Heat

[ROW911SC]

I'm a bit confused. Does an SSI backdate (2 in/1 out) on an '81 SC mean I automatically lose my heat? Dos the heating system then need to be backdated? Thanks.

[Josh D]

Originally Posted by LenS

I'm a bit confused. Does an SSI backdate (2 in/1 out) on an '81 SC mean I automatically lose my heat? Dos the heating system then need to be backdated? Thanks.

No, SSI's are heat exchangers. It's just a matter of reconnecting the heater hoses to the SSI heat exchangers once installed.

Heat backdate is when you remove the heater blower and ducting in the engine compartment and use early heater ducts to direct engine fan air to the heat exchangers.

[lsf911]

Len, no you do not lose your heat with SSI's. I do not believe you need to backdate the heat either but I would recommend it.

[ROW911SC]

Thanks guys. So the SSIs have the heater ducts then. The hoses just run up through the rear engine tin and connect as they would in the factory setup?

[lsf911]

That is correct.

[ROW911SC]

Great. Out of curiosity, what is the advantage of also backdating the heat?

[SilberUrS6]

Originally Posted by LenS

Great. Out of curiosity, what is the advantage of also backdating the heat?

That's exactly what I want to know.

IIRC, one of the benefits is that it cleans up the engine bay.

I had an idea where it is a semi-backdate - the aux blower and its relay and all the stuff that goes with it is removed. Instead, an inline blower (like a bilge blower) is added to the hose, and that is controlled with the switch between the seats.

[timmy2]

Removing the blower motor and ducting is the advantage of backdating the heat system.
Weight savings and really cleans up the engine bay.



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[hydrocrust]

Is the heating less efficient with back dating? I would like clean up the engine bay, but like the heat in some days. Thanks.

[McLaren-TAG]

IMO the heating is better with the backdating. Almost like the heat you get from a fireplace. No foot well blowers no fans, just direct heat being pumped into the cabin from the alternator fan.

Only drawback is that you do not get a lot of heat while idling since there's less air flow. At cruising speeds however the heat could roast a turkey if you cranked it up all the way.

[timmy2]

My heat is as described above.
In about 3 minutes of driving I am turning it down.

The only drawback is as mentioned, at idle there is less flow. I rev the motor if I need more heat when idling.




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[Josh D]

Backdating works well with auto heat if you have it. It will continuously adjust with the various output due to varying engine speed.

[bigred23]

timmy2,
what did you do for the left heater duct to clear the distributor? I know approximately 10 years ago, there were members that were attempting fabricate left ducts for SCs and Carreras...

[Craig_D]

Originally Posted by McLaren-TAG

IMO the heating is better with the backdating. Almost like the heat you get from a fireplace. No foot well blowers no fans, just direct heat being pumped into the cabin from the alternator fan.

Only drawback is that you do not get a lot of heat while idling since there's less air flow. At cruising speeds however the heat could roast a turkey if you cranked it up all the way.

Ditto here, with my SSI and heater backdate. You can make popcorn at your feet! It works way better than my stock exhaust/heat exchangers and the old fan system ever did.

[Craig_D]

Originally Posted by bigred23

timmy2,
what did you do for the left heater duct to clear the distributor? I know approximately 10 years ago, there were members that were attempting fabricate left ducts for SCs and Carreras...

I found tin that was already notched, and had to do a very slight amount of bending with a rubber mallet. Works great, and looks great.

[will hung]

Originally Posted by bigred23

timmy2,
what did you do for the left heater duct to clear the distributor? I know approximately 10 years ago, there were members that were attempting fabricate left ducts for SCs and Carreras...

For mine, I used a hammer to massage the duct to fit behind my distributor. Then I found out about part number 930-106-321-02. It already has a groove in it to clear the distributor. Looks like it has come down in price too.

Link from our host:
Pelican Parts - Product Information: 930-106-321-02-OEM

[lsf911]

I took my left side engine heater duct to a local welding shop. They cut and welded it to look like the turbo version for $30.00, then I repainted it. Fits well and looks good.

[911pcars]

Here's a layout of the engine sheet metal prior to powder coating for a "period-correct" cabin air backdate - that is, with air hoses routed through early sheet metal into the heat exchangers below it.

The pieces with an X are the parts needed from an early (pre-'74) 911. The remaining sheet metal is from a 3.2:


Note:
Later versions of the rear, engine width sheet metal route hot air through a large hole on the left side into a shared hot air distribution tube.

Another view of the left/right side hose ducts that attach to the engine shroud.


A backdate project from DarrylD's Porsche 911 Restoration Project Journal shows the left side hose duct ('70, 2.2) modified to clear later distributor caps (template via John Walker).


Another backdate heat link: Why you should backdate your heat on a 3.2

Hope this helps,
Sherwood