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   73 MKIII GT6 Big Red 
         Heater Boxes and Fresh air in a GT6

   Big Red - 1973 GT6 MKIII Specific Tasks and Procedures

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    Over the years, Triumph apparently used what ever was available to them at the time to assemble their cars. For one reason or another, much of these slight variations, even within model years, in un-documented.  Well here's another one.

    GT6 models have air vents in the dash. Some also had a pair of these 'eyeball' vents under the dash right next to the center radio console/support.  These were originally designed to put out 'fresh air' not heated air. It's the consensus, that the GT6 didn't need any extra heat as they are already infamous for being 'hot boxes'.

   Later model MKIII GT6's were built with many of the same components used to assemble Spitfire's of the same era. Why? Cost! Even though the latest model GT6 was a big hit in the U.K. the bulk of sales were in the U.S. Emission laws all but killed the sales in the U.S.  Hence, the end of the GT6's production run in November of 1973.

   This GT6, built November 1972, has/had what is apparently, a Spitfire air box in it. What's the difference? The stock Spitfire heater box, has the 'footwell vents' on the sides of the box, and only two 'tube' outlets on the box for the defroster vents. The older GT6 heater boxes, had four tube vents on the box. Two in the same places as the Spitfire box, but two additional tube vents bottom center of the box. On the GT6 the two bottom center tubes fed the eyeball vents. These two bottom tube vents are 'inside' the heater cores, while the stock Spitfire tube vents, as well as the floor vents, are 'outside' the heater core as compared to the fresh air intake from in front of the windshield.

heaterSpit.jpg (17820 bytes)


   This is the 'stock' air box as removed from Big Red. It's virtually identical to the all my other Spitfire heater boxes. In  these photo's, the heater cores have been removed to simplify the visual differences in the vent outlets. The yellowish foam, glued to the boxes, is where the heater cores would have been. The cores would have been between the fan and the outlet tube vents signified by the green asterisks (*)

heaterGT6.jpg (19000 bytes)


   In this shot you can see the two extra tube vent outlets on the bottom of the heater box. (top of the box in this photo as the boxes are upside down on the table in these photos)
    Since these vent outlets are 'inside' the heater cores, they would/should send un-heated air to the eyeball vents.

   Then again, this all depends on how your under-dash vent pipes are hooked up.

      So, on Big Red,  I've re-installed the older GT6 air box with the extra vents, rather than re-install the Spitfire type box I had pulled out.   I'll need to acquire another set of eyeball vents to put under the dash to hook it all up the way the older GT6's would have had it.

   On one of the email lists I'm on .... a couple of comments returned to me concerning the various hook ups other GT6 owners have follows. The names have been removed for privacy sake. (They were willing to answer MY questions... doesn't mean they are willing to be bugged by you  :-D )

....my original email question/comment....
OK...so the GT6...at one time anyway....
had 'eye ball' vents under the dash as well as in it.
The heater box on a Spit and the late MKIII GT6 has only
2 vent 'pipe' outlets. I have a GT6 heater box in hand
with 4 vent 'pipe' outlets (as well as the two long vertical
vents on the sides of the box)

After opening up both heater boxes (1 with 2 and 1 with 4 vent pipes)
From what I can figure... the 'under dash and dash mounted'
eye ball vents on the 4 pipe box would have been 'fresh air only'
vents? The two extra 'pipe' outlets in the heater box are on the fan
side of the heater cores...so no heat would have come out of these
vents in this configuration. Right? Anyone have this setup that can

On late MKIII GT6's the heater box has only two 'pipe' vents
on the heater box. So if a 'Y' is in the line...one goes to the defroster
vents and the other the dash mounted eyeball vents...you'd at least
get heat out of the eyeball vents. Right?

Has anyone ever re-arranged the vent plumbing so ALL 4 eyeball vents
would output heat?
...or is this a case where a GT6 runs hot enough inside that winter
time driving, doesn't need the extra heat? Just fresh air (cool air)
for summer driving?
...am I yammering on or do I have all this right?


.... and a couple of returned comments........

I have all four eyeballs hooked up im my GT6 - late and the only thing that comes from any of them is hot air - even though two are supposed to be fresh air!  After all, there is NO cool air under the bonnet of a GT6!
Seriously, my eyeballs have the twi in the dash hooked up tp the fresh air side, and the two leads from the heat side split to feed the footwell eyes as well as the defroster vents.  As far as I know, they came out of the factory with that set-up.

Hi, Paul.

this is all news to me, I guess I'll have to run out to the shop and look
at my swing-spring parts car (made in Aug., I believe)  and see how many
outlets there are.  You are right about the eyballs only for unheated
air.  The paradox here is that if you insulate the gearbox tunnel
sufficiently to avoid driver/passenger overheating in the summer,  It
negates the 'natural' heating in the winter.  I suspect with the
asthmatic blower (not to mention all the bends in that wonderfully
turbulent ribbed plastic pipe), by the time you hooked up everything to
the heated outlets, you wouldn't detect much  flow.  The heater in my
green '69 benefits a little from a motor and impeller from some 70s Dodge
product, but its so big that maximum airflow is probably restricted by
the hole in the bulkhead.  Besides, it blows so much air anyway that it
pulls all the heat out of the core (not much in it anyway with that
rinky-dink manifold nonsense) in a minute.  I'm planning (at some point)
to redesign the heater entirely, with a more efficient core, and perhaps
some replumbing under the bonnet.  The housing will be easy, I work in a
sheet metal shop.  The thing about blowing heated air out the eyballs is
that the only time heated air comes out the outlets is when it's set on
defrost.  Two large flaps are used for 'heating' the car.  I don't think
you'd want to rob those already woefully inadequate fishtails of what
little they do.


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last edited 03/18/10

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