Heater backdate with a twist

[mkc1962]

I've ready many posts here on the topic. Along with the comments that go with them. Backdating the newer models does have some performance limitations namely air flow when idling. Many also remove the footwell blowers in a backdate, some leave them in. Some in colder regions have even commented that backdating doesnt work well for them as there is not enough air flow even when going down the road. One thing Ive alwasy liked about these forums is one can sure research just about every approach before trying their own.

My approach is just a little different than most I've seen. Figured I'd share it here as some might find it usefull. My car is a 87 911

I made all my own metal work out of HVAC grade galvanized sheet metal. The twist is the addition of a small blower to add extra air velocity to the fwd moving ducted warm air. Similar in operation to the original engine bay blower,but lots less bulky cleaing up the engine bays appearance, lots cheaper than a factory replacement. My first blower of choice was a conventional marine bilge blower. Rated at 145 CFM, 12v, 4a. Though it is the one I am using at present, IF I had to make any improvments at all on my approach it would be to maybe try and find a identical blower in the 400+ CFM range. The 145 CFM does make a diff particularily at idle as I now do have heat in the cab without having to rev the engine. But, a bit more would be nicer.

The blower is actuated using the existing switch wiring found beneath the Red heater levers betwewn the seats. Originally the levers did the actuation, but I wanted the feature of basic backdate plus added air only if desired. Pulling the levers up only opens the flapper boxes. Rotating the old footwell blower switch to "1" starts the add-on blower. In addition the blower is electricaly actuated using a basic 30a relay. The wiring to do all of this already exists both under the lever console and in the engine bay. Engine bay heater relay has been removed. The relay actuation wire is found in the Heater relay plug. 12vdc supply come from the spare fuse position found in the 3 fuse cluster adjacent to the engine bay relay panel

My plan is also to remove the footwell blowers, but at present they still exist but do not work.

The blower is obtained at most boat dealers for about $25. The main 3" ductwork I found at a local partshouse for $20.The main duct is some sort of flexible rubber/plastic that I did have some heat concerns about, but so far Ive used it this winter and no ill effects or melting. The smaller blower ducting is marine grade flex duct, 3' was about $5. All duct work could be done with the more common Sceet orange cloth type if desired. If heat ever poses a problem with the hoses I have, then the Sceet is the type I'll use.

Here are a few pictures showing my approach.

[Joe Bob]

Good job. I can't seem to find a place to put a stock blower in my engine bay......I have a pair of 4 inch blowers, too big as well....have to go smaller, the 3 inch looks like the ticket.

[mkc1962]

Joe Bob,

thanks and was hoping you'd see the post as we both commented on such ideas on another post. In my searches a few months back I did see a 3" that put out in the 450 range. Now I just need to go find it again. As you can see by the way I mounted mine, 4" would work if that is what it took to get the cfm. I started with the 3" bilge as it was extremely cheap, easy to obtain, and I could use it other places after I proved my point.

I'll probably paint the white blower if I leave it in to blend into the engine bay a bit better.

[Joe Bob]

I have an extra 4" bilge fan if you can't find one locally.

[Bill in OKC]

Good work!

[JeremyD]

Nice work - but you can probably eliminate the duct coming from the engine and just use the bilge blower to force air across the heat exchangers and into the cabin.

just a thought - but like the low cost approach. I plan on doing a version of this for cooling in the front...

[scarceller]

In my 84 3.2L I have SSI heat exchangers and went with 1974 style setup where air from both sides of the engine fan is diverted to each SSI.

I left my footwell blowers in place and they run just fine. This setup gives more heat than I ever could want with just the footwells and no rear blower.

The engine compartment looks very clean with this setup.

The real trick is that when you remove the rear blower this causes the Heat Control Relay to not allow the front footwell blowers to run, this is by design.

I had to modify the heat relay to by-pass a reed-switch so that the footwell blowers would run without the rear blower in place. There is a thread on this forum with the mod.

I suggest you try to get the footwell blowers working, you'll be amazed how much heat gets into the cabin with just the footwell blowers. Also, if the footwell blowers don't run they are a restriction in the airflow.

[scarceller]

My engine bay looks like this:

[Joe Bob]

Some of us don't have footwell blowers from the factory.....they started with Carreras in 84 IIRC.....

[911Jarle]

Originally Posted by scarceller

In my 84 3.2L I have SSI heat exchangers and went with 1974 style setup where air from both sides of the engine fan is diverted to each SSI.

I left my footwell blowers in place and they run just fine. This setup gives more heat than I ever could want with just the footwells and no rear blower.

The engine compartment looks very clean with this setup.

The real trick is that when you remove the rear blower this causes the Heat Control Relay to not allow the front footwell blowers to run, this is by design.

I had to modify the heat relay to by-pass a reed-switch so that the footwell blowers would run without the rear blower in place. There is a thread on this forum with the mod.

I suggest you try to get the footwell blowers working, you'll be amazed how much heat gets into the cabin with just the footwell blowers. Also, if the footwell blowers don't run they are a restriction in the airflow.

Interesting topic, running a backdated system om my 79 SC 3.0 ROW.
No blowers, just the cooling fan blowing.. It is not sufficient..
Before next winter, footwell blowers will be mounted.

How do you go about mouning footwell blowers on a car that hasn't had that at all? I can use the levers to activate, but how about the directing the hot air inside the cabin, and how do they fit on a car that hasn't had them?

Thanks!

Cheers, Jarle

[TRE Cup]

We've used those blowers in a variety of applications, and they are on the noisy side. They certainly move a lot of air

[mkc1962]

JOE BOB,

Thanks for the offer.My marine freinds also had a 4" but it was only 160 cfm, is yours any noticeable higher cfm value?

SCARCELLAR,

Well I agree as Ive done lots of reading on it, Keeping the footwell blowers going and doing the bypass on the relay is probably a better approach. But, my footwell blowers are toast as well, after 2 disassembly and greasings they just have given all they can give. Just like I did not want to spend big bucks on a new engine bay blower I dont want to spend big $'s on the footwell blowers. Though no where near as cluttered as factory, but yet no where near as clean as yours and others, I can remove my bilge blower and associated hose in under 2 minutes. My overall idea when I went for this approach was to make the heat system more like 95% of the cars on the road. 1 Blower, variable, providing all the needed heat flow to the cabin. Aside that I need to now find a large cfm source, I've pretty much achieved my goal. And though I know alot of folks remove the footwells just for weight loss, that was never and objecive of mine. I do plan to remove mine as they dont work and in playing around with 1 the other day noticed that just it being in place obstructed a fair amount of flow from reaching the top side.

JEREMYD,

Point well made and and idea that did enter my thoughts. IF I can get a 3 -4" blower that will provide sufficent flow, that is probabaly my exact next step. Afterall All I have to do is make another metal cover but this time with no 3" round duct, lots easier.

[Joe Bob]

It's an Attwood Turbo 4000. I've never been able to get a CFM rating for any of the bilge blowers OR the Porsche engine units.......

[scarceller]

Originally Posted by mkc1962

playing around with 1 the other day noticed that just it being in place obstructed a fair amount of flow from reaching the top side.

Yes they do restrict air flow, I think you could remove much of the inside of the blower like the squirrel cage and anything else you can do to clear the passage of air through it. Having the squirrel cage without it spinning certainly reduces air flow. Not sure if you could completely remove the front blowers and somehow pipe a by pass in the place of the blowers.

[Joe Bob]

Based on similar blowers, 3 inch are little under 200 and the 4 inch about 230 CFM. Don't know how robust they are as they mostly run for 3-4 minutes prior to an engine start.

[JeremyD]

They are robust - on a gas boat they should be run whenever the engine is running. I replaced a set that were date coded 1986 [Last year] soon my boat - I think they will last. And yes, as Dave said - they are a little on the noisy side.

mkc1962 - from my 993 HE on my old car - I just found that the fan delivered VERY little in the way of heat flow - most air was pushed out the bottom of the engine.

[mkc1962]

JOEBOB

Mine also was an ATWOOD. The cfm rating of 145 was actually stamped on my box. IF the 4" is only in the 230 range, I'll probably keep searching until I find that one I saw at around 450. IF I find one significantly higher I'll surely post the find here. I really woud like to find a higher CFM unit so I can go forward with my multi speed/resistor bank approach. As it stand right now I have 2 speeds, engine fan alone or this on on aiding.

SCARCELLAR,

If and when I remove them I'll probably just fab up some new metal transition pieces to take the place of what the blower and its duct does now.

As for fan robustness....I also have owned many boats, and like JEREMY stated, Ive alwasy had mine relayed to run the entire time the engine did. Though they normally come from the factory as switched run only. As for noise levels...I have found that if they are mounted to rubber standoffs as in my case with the avail factory mounts, or even mounted using a piece of rubber under a band collar it goes a long way in reducing their noise...( I do the same with electric fuel pumps)....For the record, on my application in the porsche. With the engine running, I cannot hear any increased noise in the cab with it running. With the engine off, if I turn it on it is somewhat noisier than the factory squirrel cage unit was with engine not running.

[scarceller]

The footwell blowers are very noisy in the 84-89 cars. My 84 heat system is much more noisy than my old 75 911. The footwell blowers are easily heard because they are right within the cabin. They do move tons of air though.

[mkc1962]

Hmmmm...wasnt thinking of those. I figured they were referring to the Bilge blower...what limited useage my footwells saw, I'd have to agree, those two were noisy even when freshly greased.

[Joe Bob]

Vash was nice enuff to send me a stock blower and I tripped over a plastic shrouded 914 model. Finding a place to mount it and plumb it into the existing flexible ducting is a challenge.

Of course the tubing is a mix of 2, 2.5 and 3 inch. Making it look nice and non Rube Goldbergish will most likely be the biggest issue.