'89 Carrera - Back-dating heater?

[JMA-RUF]

Can someone please confirm what diameter heater ducting is required from the engine fan tinware (back-dated duct) to the heat exchangers?

Is it 2.5" throughout?

I'm about to order some SCAT-10 AeroDuct, and want to make sure I order the right diameter for the whole system.

Thanks in advance.

[mb911]

yup 2.5

[JMA-RUF]

Thanks, Ben.

I heard with the back-date ducting which secures to the fan housing, there are issues wirth the right hand side duct and the A/C compressor. Care to elaborate?

[Talewinds]

Originally Posted by JMA-RUF

Thanks, Ben.

I heard with the back-date ducting which secures to the fan housing, there are issues wirth the right hand side duct and the A/C compressor. Care to elaborate?

Yes, I'll elaborate, it doesn't fit. Choose one or the other, right side duct OR air conditioner, but not both. Please someone prove me wrong WITH pictures, but I don't see how it would fit.
The good news, you can use just the drivers side duct tin and there's plenty of airflow, the passenger side duct is just not necessary, so save your $$ and keep your A/C too.
You'll find that you need to do a bit of customizing eg, cutting and bending to make the drivers side tin fit correctly so don't expect to go out to the garage and just slap it on when you get the tin, take your time and make it right. Also, using that Sceet is the only way to fly, it can make the very tight radius bends that the OEM style cardboard/ alum duct cannot.

[Talewinds]

[JMA-RUF]

Great pic! Thanks!

BTW, what happens if one uses a 964/993 twin distributor? Does that interfere with the duct routing at all?

[fxeditor]

Okay, I'll bite on the stupid noob question. What are the advantages, other then more engine access, to backdating the heat?

Thanks in advance,
Michael

[Talewinds]

Ooooooh, now you had to go throw a wrench in it didn't ya? Eeesh, Although that duct has the large dent in it to accommodate the distributor, the stock style distributor cap BARELY fits, the plug wire boot is squarely up against the duct. I would think a dist. that's ANY larger diameter wouldn't fit without significant mods to the duct tin. Are you currently using a twin dist. or just planning for the future?
Having said all that I haven't laid eyes on the 964/993 twin distributor so I'm just guessing out my a$$.

[Talewinds]

Originally Posted by fxeditor

Okay, I'll bite on the stupid noob question. What are the advantages, other then more engine access, to backdating the heat?

Thanks in advance,
Michael

I think that's a fair question. In my opinion it comes down to design and necessity from an engineering standpoint. True, doing the backdate makes the engine look much nicer and greatly improves access back there, but when trying to make improvements to the car I think of it as making improvements to designs that were somewhat of an oversight from the factory. Bottom line, the heating system in the car is a debacle, and anyone who's assessed the OEM system's merits, well, it's eyebrow raising at best. The engine bay's electric blower is just NOT necessary. Chuck it, save some weight, improve access, improve aesthetics and move forward. Make the necessary changes to the control relay so that the footwell blowers still work and overall it's a nice improvement to the car.
It's kind of like adding the relays to the headlight circuit. It's just plain better.

[JMA-RUF]

Originally Posted by fxeditor

Okay, I'll bite on the stupid noob question. What are the advantages, other then more engine access, to backdating the heat?

Thanks in advance,
Michael

I had no choice - I have to back-date because I removed the engine bay heater blower motor to accommodate the Intercooler.

Talewinds, I'm currently running the factory single distributor, but plan to remove it very soon to slip in a 964/993 twin distributor

I'm not exactly sure which direction the 2nd distributor points to... I'd need to look at a pic of a 964/993 motor.

[Talewinds]

Of the twin dists. that I've seen, and I must admit I'm just guessing out my rear again, the twin style dists. are either a larger diameter circle with the 12 jacks around the circumference, OR, the other style where there's 6 jacks around a normal-ish diameter dist. with another 6 jacks around another circular section, but from any pics I've seen that second offset dist. cap is attached to and faces toward the rear of the car, therefore not limiting space around the heating duct tin.

[Talewinds]

I think I remember your car, got some pics as a reminder?

[Wavey]

Just a point of interest - I *think* that fan is wired to engagewhen the AC is on to provide extra cooling to the engine, and also when the oil temp reaches a certain point for the same reason. Not that it's going to do much to cool a hot engine, in fact I can't imagine it helping at all. But someone correct me if I'm wrong - I'm too lazy to look it up.

[Talewinds]

I think you are correct about it acting as a supplemental cooler when the oil temp rises...
About the A/C, I dunno.

[Pazuzu]

Originally Posted by Talewinds

Yes, I'll elaborate, it doesn't fit. Choose one or the other, right side duct OR air conditioner, but not both. Please someone prove me wrong WITH pictures, but I don't see how it would fit.

I put 2.5 inch SCEET out of both ducts WITH the A/C in my SC

I built the right duct out of the metal block off plate and PVC plumbing parts and JB weld. It took some playing around, but it can be done. The SCEET is exceptionally flexible, and will take the bends required to get under the AC bracket.

heater backdate with AC still installed questions

I do not know if the 3.2L is so different in that area that you cannot make this work.