Heater backdate with a twist

[BK911]

How are your engine temps when running the fan? It looks like this arrangment may suck some air from what would blow across the engine. Sort of like a sand blaster sucks up the sand. May be better to block off the connecion to the alt fan??

[mkc1962]

As per an Atwood web page. Their 3" blower provides 145 cfm and their 4" provides 245 cfm. Both of these are figured as open suction. In-line applications are roughly 1/2.

I Know that no one has been able to find the actual CFM specs of the OEM factory fan. And though my efforts are not exact, atleast they are at best so close, who would ever care. I work for a large chemical Co in which I do quite a bit of purchasing. I just called a manufacturer that we commonly use for fans and blowers. Based on technical specs of 12vdc ,4" x 2", and squirrel cage, (which is what I remember measuring on the OEM). They stated that the most he has ever sold any similar such unit was in the 250 CFM range. Based on some air curve chart he referred to, he stated that the most a 4" any size blade would ever do was at best maybe 275 cfm. SO...this being said the 4" bilge approach, rated at 245 cfm is probably the cheapest, closest to OEM spec approach available. That is, based on my approach.

[mkc1962]

BK,

Ive been running the setup a few weeks now, and I have not noticed any differences in my engine temps at all. I do plan to also try a complete blocking of the engine fan as well to see if the inline alone will provide sufficient air flow to the cab. If that works, I'll probably go with that approach and leave the ALT fan flow to provide the engine cooling all alone.

The way I see it.....the factory approach for an 87 with its inline squirrel cage, probably robbed more from the engine than my approach.

[Joe Bob]

I would keep the alternator fan assist. One reason is that I have a dual dizzy vent. The other is that it assists the CFM.

[Wavey]

I guess I don't understand this mod... you removed the original fan, did the backdate, then added a fan? Why?

[Joe Bob]

Well, in my case I did a 3.6 engine transplant. I did not need heat until I moved to the freezemyassoff State of Nevada.

[mkc1962]

All my fans were toast, Engine bay and both footwells.

Traditional backdate relies soley on alt fan for air flow for most. Some do choose to still use the footwell blowers if they even exist.Base backdate with no footwells, As many will tell you, is little to no air excpet maybe when going down the road. Even then, in extreme cold situations not enough.

I wanted to repair my system and leave it stock but could not stomach the price of all the new fans. However at the same time I Liked the cleaned up engine bay look. One cannot have both.

I figured...as so many have complained about how the stock system has pitfalls, and the backdate has pitfalls, Why not improve on the entire situation if possible.

My idea....1 Blower, variable speed if possible. Also, less clutter in engine bay.

95% of all vehicle on the road rely on a heat source, and "1" variable speed blower. Why cant a porsche be similar? Right now I have heat at 2 speeds. Speed 1 is just the alt fan as in a traditonal back date. Speed 2 is with the assist fan. Then I have greatly reduced the clutter in my engine bay and made it where if it needs removal can be done in under 5 minutes.

[Wavey]

OK, got it! Makes perfect sense now.

[Joe Bob]

I put the 4 inch bilge blower and the stock blower side by side. The stock blower is quieter but my seat of the pants/hand found the CFM to be more on the Bilge blower side.

I've mounted/plumbed one in on the driver side and one is going in on the passenger at half time. I'm watching the Seahawks and the Bears slide around on the TV.....it ain't pretty. 14 zip and Da Bears B driving for anudder....

[mkc1962]

Joe Bob,

Thanks for the update. I havent had the opportunity to get back at mine since last post. But, so far its working ok. May follow suit with the 4" to get that extra cfm...afterall whats another $23 for another blower. I can always use the 3" in my boat.

[Joe Bob]

Well, the Seahawks stunk it up, turned them off at the beginning of the 4th......went out to the garage and finished it up.




Next cold snap I'll test it out. My guess is that I won't need foot well blowers. I wired it to a fused ignition side connection. It's on all the time but has a simple quick disconnect when not needed.

My goal is to be able to drive with the top down and heat cranked full on. After a snack, I'll clean up the wiring....

[mkc1962]

JOE,

I can see what you mean when you say you have not much room...didnt realize a 3.6 was that much bigger...of course I'm still kinda new to the P cars and havent actually been in the presence of one

let us know how the flow at the vents go.

[theoldfonz]

Hi, I have an 89 Carrera and want to backdate my heater. I was woundering if I have to do both sides or can I just do the side where the blower is fitted. What happens if I leave the right hand side as it is?

[scarceller]

You really need to do both sides, you can't just remove the rear blower. The rear blower feeds into a 'Y' pipe that then splits left and right. The idea of the backdate is to remove the blower and the 'Y' pipe. Look closely at the pictures in this thread and you'll see how the left side is feed from the duct near the distributor and the RHS feed from the duck under the AC Compressor.

Originally Posted by theoldfonz

Hi, I have an 89 Carrera and want to backdate my heater. I was woundering if I have to do both sides or can I just do the side where the blower is fitted. What happens if I leave the right hand side as it is?

[Gerry van]

l just backdated my heater system on my 89 3.2 and only replaced the left side ducting, l took it for a quick run and l it seemed to run a little warmer is this normal? Thanks for any info as l live in a very warm climate and don't need to be making it run any hotter. Cheers Gerry

[scarceller]

Gerry,

The stock system has the ability to turn on the rear blower if engine temps get very hot. This is done to run fresh/cool air through the heat exchangers. This air is then dumped out the heat flapper boxes near the front of the transmission. Usually this function is only enabled when running in very hot climate and most likely stop and go traffic. It is very possible an engine could run warmer than usual under these conditions if you backdate it.

So how hat a climate are we talking about? and what type of driving?

Originally Posted by Gerry van

l just backdated my heater system on my 89 3.2 and only replaced the left side ducting, l took it for a quick run and l it seemed to run a little warmer is this normal? Thanks for any info as l live in a very warm climate and don't need to be making it run any hotter. Cheers Gerry

[Gerry van]

Hi Sal,
ln summer very warm here but we are just at the tailend of nice winter at the moment, last night it was about 24deg and l was just cruising around town.lt didn't get hotter than the first mark on the gauge but it just seemed to get up there quicker than usual.l am missing the front thermofan l amgoing to fit one and someone also suggested fitting a 210deg oil thermostat.Cheers Gerry