SSI heater box inlets- OK to leave open?

[jbrinkley]

I've read that this air helps cool the heads. Is this fact? I get plenty of heat with just the footwell blowers and planned on putting screens on the intakes to keep debris out. But if I seriously need to push air through the heater boxes to help cool things off, I need to rethink my plan.
any good thoughts on this?

[Rot 911]

Not sure what it is you want to do, remove the engine blower? Even if all you use is the footwell blowers you still have to keep the hoses hooked up as the air has to go through the heat exchangers.

[jbrinkley]

what I mean is, can I leave these open? or will I damage the engine

[v9ff]

I would cap them off with something. Last thing you want in there is a critter cooking when you're driving!!

[david914]

I'd recommend connecting them up. I've experienced markedly higher temps with just a leaky hose from the fan housing to the heat exchanger.

[jbrinkley]

I want to screen them, but, if the heads benefits from air being pushed throught them with either the rear blower or a modified duct from the engine fan, then thats the route I want to take. Then again I know I've seen them capped off before on pelican. I was just going to use some expanded metal for screens.

[jwmc1]

I have a question....I am changing to headers...will this affect my engine cooling since I will not longer have exchangers...what mods do you guys suggest?

[aigel]

The point is that the air that goes into the heat exchangers is diverged from the engine fan. If you disconnect the hoses to the heat exchangers, there is little resistance in this air path. More air will come out this way and will not go over the engine.

It is no problem to leave the heat exchangers disconnected. However, you need to plug the connection on the fan side!. That way all the air that the fan blows has to go over the engine. And it isn't just the heads that are cooled by the air from the fan, it is also the cylinders and the engine oil cooler.

George

[jpahemi]

Don't you need air to pass through the heat exchangers to keep them from warping?
J.P.

[aigel]

Originally posted by jpahemi
Don't you need air to pass through the heat exchangers to keep them from warping?
J.P.

Why would they warp? The steel can take that without changing shape. Every car with headers would have that problem. Most cars with headers (like in other european cars and US cars) don't have heat exchangers.

What you'd say is that exhaust has to be actively cooled. I doubt that blowing air over the headers via heat exchangers will decrease header temperatures by any significant percentage.

Cheers, George

[GeorgeK]

My worry is that the exchangers if capped create a chamber in which the air heated by the exhaust tubes can not escape, thereby unduly increasing the temperatures around the exhaust.
I would go with headers if I removed the ducting that blows air into the exchangers.

[Willem Fick]

OK here's what I did: (sorry no pictures as yet)

I removed the cardboard-like tubing that connects the engine shroud to the SSI heater boxes, and replaced the ducts that they connect to on the shroud with blankoff plates (What George said!), so as to prevent any cooling air from leaking out. These plates are referred to in Wayne's book on engine mods. Mine are out of the car at the moment, so if you are interested in making a set, let me know then I'll send you some pictures and templates.

Having fitted these I then proceeded to merely putting blanking-off caps over the now open heating ducts (as shown in your picture) on the SSI heater box, so as to prevent water and debris from gathering and causing rust.

The nett result is no heater, but a much more uncluttered engine bay, as well as BETTER cooling efficiency, as there is no cooling air being bleeded off to power in car heating! I also think it is a safer option, as I am not too comfortable with having a carbon monoxide timebomb venting into the cabin!

Will make up for the loss of heating by fitting seat warmers later!

In further agreement with George, I simply cannot see why this would have any detrimental effect on the exhausts, as may free-flow performance exhausts come without heat exchangers in any case.

Cheers!

Willem Fick

[GeorgeK]

Wilem
That is the worry! you have created an "extra hot" chamber around the headers in the heat exchangers, which prevent air from circulating around the headers while moving. I fear the exhaust will be MUCH hotter than before without the forced ventilation it had while being connected to the engine turbine.

[Willem Fick]

Georgek,

(English is not my first language, so please pardon the formalness of this response, and also it's length!!!)

I understand the point you are making, and I think it is a very valid concern. It's in fact enough of a concern to have me now thinking about whether I did the right thing...

I however think that the question we need to answer first is: "does air always circulate through the heater boxes, or only when the heater flaps to the cabin are open?"

I honestly can't remember if the flapper boxes completely block off the path of the heated air, or if they merely redirect airflow away from the cabin. (anyone?)

If they were to block off airflow completely then there isn't an issue with manifold heat, as it is no different than what is proposed with the blankoff plates, as these would then effectively restrict airflow over the headers in much the same manner as the flappers do.

If however the flappers redirect air, thus still allowing for flow through the heater boxes at all times, we may have an entirely different kettle of fish, as it will then most definitely lead to an increase in header temperature...

My thoughts on header (and head) temperature; (and I could be wrong!)

Many folks wrap their headers and exhausts in thermal wrap. This is sometimes only to shield other delicate components from radiated heat, but other times because there is a school of thought that says a hotter pipe leads to higher exhaust gas velocity - since wrap prevents radiation, the pipe runs hotter.

Applying exhaust wrap isn't all that much different from the effect caused by having a enclosed volume of still air in a sealed off heater box around a header - except maybe that the latter is a bit more bulky. (and effective!)

In all truth, this could potentially lead to higher temperatures being experienced at the exhaust ports of a head or heads through conducted heat, but this should not be enough of a difference to cause damage (there is in any case still a proportion of the header not enclosed by the heater box, which can radiate away some of this heat.)

My thinking on this is that most of the additional heat now being absorbed into the heads, through physical contact with a hotter header should be compensated for through the additional flow of cooling air through the engine shroud...

To answer the original question though - I would still think of merely blocking off the heater boxes and fitting blanking off plates to the shroud, BUT to be on the safe side I'll go check what the flapper boxes do to airflow. If there is normally no airflow through the boxes when the heater is not in operation, great! If not, it's definitely time for new headers.

Mind you, this seems like a good excuse to fit some headers in any case then doesn't it?

Regards!

Willem Fick

[GeorgeK]

Willem,
The heater boxes under the car direct the warm air either into the cabin or out under the car. There is *always* forced air circulation in the exchanger around the headers.
For a few years exhaust temperatures caused all sort of miseries to 911 engines, as a result of devices that heated the exhaust even more (dreaded thermal reactors). IMO anything that risks heating the exhaust more is engine murder.

[jbrinkley]

I slept on it. May be I should have said I have a block off plate on the left side shroud and heater blower motor is gone, but my foortwell blowers work well.
I really wonder what kind of increase in temp inside the boxes would be seen if capped, or screened, or blowing air. I've driven around for a week or so with them open. Today I planned on doing something about it, except all the stores around here are closed

[Willem Fick]

Georgek,

If that's the case, you are entirely right! I do agree then that sealing the heater box will lead to additional heat in the headers, which may well be transferred to the heads.

I guess that leaves two options, the one being to buy new headers, and the other being to remove the heater boxes from the existing headers. I would think that, even though it is more expensive, option one would be best, as it is reversible, should a heater be required at some point later on!

Cheers!

Willem Fick

[aigel]

Come on now guys. I have personally wrapped headers on my V8 US car with HEAT INSULATION, to keep the heat in the headers, and not let it escape into the engine compartment where it would cook engine mounts, starter and get the intake air up in temp.

If you look at some 911 prepped cars, you will see that people do wrap those headers in insulation also. It is to keep the heat radiation from hitting the engine from the underside. If anything, naked headers will cook things from heat radiation. Surrounding the header with a heat exchanger will only help prevent radiation. There is still enough cooling to the outside that things won't melt, warp or do anything else that's problematic.

What you are basically saying is that the headers will get hot and then transfer enough heat by *conduction* into the heads. Now think about that: You have an area of a few square cm that is bolted to the heads with a lined gasket in between. How much heat is that going to transfer? Remember, this is exactly in the spot where there is hot exhaust flowing at high rate right out of the cylinders! I doubt there is a way to dump any significant heat into the heads via the exhaust port, even if you'd bolt a glowing header pipe on there.

I hope this helps. Sometimes you guys worry too much.

Take care,

George

[GeorgeK]

George, your argument seems to hold the road, but then why did we all remove the thermal reactors fearing all the uglies that the elevated resulting exhaust temps brought?

[aigel]

Originally posted by GeorgeK
George, your argument seems to hold the dorad, but then why did we all remove the thermal reactors fearing all the uglies that the elevated resulting exhaust temps brought?

The heat the reactors put back into the engine is transported mainly through radiation, not conduction. Those things are probaly acting like huge glowing radiators. If you'd wrap them in insulation, I bet they'd be acceptable.

George