Carrera heater vs SC heater vs backdated heater
 

Can someone give me firsthand comparison's of the actual performance for each? I know the component differences and engine idle speed differences of each already.

Curious if the Carrera system is by far the best over the others or is it just a marginal difference.

Asking because I like the heat output my stock Carrera offers BUT all three heater blowers (engine and both footwells) shriek and squeal at various times. I could pull them apart and fix but I also like the simplicity of the backdated system (not to mention three less electrical items to catch on fire!)

With my 88 I find that I only need to run, REQUIRE, the footwell blowers, other than initial defrost, to remove interior windshield fogging. Further windshield fogging can usually be prevented via lowering the windows slightly.

In my 78 getting the windshield defogged once it formed was a difficult task, even with the windows lowered more than a crack.

Just recently I took the footwell blowers apart enough to re-lub (30w) the sleeve bearings and oil soak cotton wadding, still noisy, but wind turbulence, not bearing sqeal.

Fire...My 88 has individual inline fuses at/for each footwell blower.

For all the extra blowers and relays involved, I'm not really convinced that my 84 or 87 911 Carreras heated or defrosted all that much better than my old 75 911 Targa once I converted to the SSI heat exchangers. Used to be you just chose a lower gear to increase the revs and thus provide more air through the system. That still works great on my 914-6s, though I will admit that once it really frosts up, it does take a while for them to defog.

Heating and defrost, defrost especially, depends on how quickly the engine rises to operation temperature, MADDINGLY SLOW with UNLIMITED COLD air for cooling the engine, COLD roadbed to help COOL the exhaust/heat exchanger, plus the efficiency of the heat excharger.

As I said, the only real gain between the two, 78 Targa vs 88 Carrera, is the ability to use the footwell blowers to QUICKLY (high speed) defog/demist the interior surface of the windshield, and keep it defogged (low speed).

I can't add to the comparison because I only have a '74, which is the backdated version.

However, I would make one comment....I wouldn't mind adding the engine compartment electric blower because it (I think) gives you some fresh air blowing thru the heat exchangers vs now, if I have an oil leak, I tend to get some oil smell in the cabin. This is one reason I always wipe down my engine and clean from the bottom whenever I wash the car.

I have an 87 with the d/s footwell blower working and p/s footwell blower gutted but in place with the place the motor used to be blocked off. When i have both red handles pulled up, i get about the same airflow to the windshield on both sides. Once i turn the footwell blowers up to 2 or 3 on my manual heat 3 pos switch, the d/s clearly has more flow. I havent had any rain to test the defogging in yet. Agree that quantity if heat is never an issue, and at least on my car i get very nice temps no more than 2 minutes into a drive even in the 20 degree weather we have in ct now. If you dont drive in a lot of rain id say ditch the footwells for sure. Cant comment on rear blower, mine works quietly.