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MG MGA - 4inch inlet hoses..where to start?

I recollect seeing threads showing the hoses extended in front of the radiator and starting just behind the grill.The logic of this defeats me and I have tried to find what the original layout looked like.. and failed todate. My reasoning is as follows.
The air coming through the grill has three prime functions..
...a)cooling air supply for radiator.
...b)air to heater unit
...c) air for carbs
By far a) is the most important as reduction of air to b) is a comfort factor and reduction of cool air to c) is an efficiency factor.
It would seem to me that starting the hoses at the metal tubes in line with the radiator still gives non heated ram air to b) and c) but starting a lot forward and immediately behind the grill can drastically restrict ram air to the radiator. Am I missing something and what was the original design?

Neil Ferguson

The MG factory produced Special Tuning booklet for the MGA shows the air tubes extending in front of the radiator (image attached).


Mick

M F Anderson

Hi Neil,
Without the two pipes forward of the metal tubes, air will go through the openings instead of having to go throught the radiator. With the pipes forward, air is ducted to the heater and the carbs and the remaining ram air goes only through, not around, the radiator. Both pipes come forward to just behind, and follow the curve of, the grill slats.
regards
Colin

C Manley

Mick/Colin..thanks for your responses. The sketch does indeed show a tube coming forwards from the heater side ( carb side ? )...but where does it end?
I am an engineer by profession and used to do airflow and gas flow calculations in pipes, ducts etc etc at one stage of my my now past career ( got away from calcs as soon as I could but was good at it).
My comment ....
I look at the photo of the air ducts just behind the grill and by simple x-section it seems to be diverting up to about 15 to 20% of the air away from the radiator ( ignoring the friction in the hoses and the position of the heater butterfly valve etc!). The duct sizes are approx 12.5in2..total 25in2.
If the hoses are not started at this position then the air entering the space between the grill and radiator encounters no obstacles and is raised in pressure by ram effect and then is distributed into the hose inlets and the radiator. The air to the heater and the carbs stll has to go through sections of hose downstream of the radiator position so I do not understand Colin's comment that the air will just pass through the metal hoops and bypass the radiator.The sealing of the vol in front of the radiator from the downstream stays the same in both situations ( but see NB below )so this is not possible .
The differences between the two arrangements can be summarised in airflow dynamics as follows...

1)Ducts up front ..less air to radiator due to division just behind behind grill and less ram effect to radiator because of increased friction/restriction due to the presence of the hoses in the plenum ( the plenum being the vol between grill and radiator )
Air to heater probably increased marginally due to ram and slightly impeded by friction of longer hose.
Air to carbs ....probably the same .
2) Ducts starting in line with radiator....increased air into plenum and increased air through radiator due ram effect of this increased air vol rate . Heater and carb vols..little effect!
I keep reading about cooling problems with MGAs and here we can restrict the air going to the radiator with the hoses just behind the grill. Possibly this is a climate thing..in Oz I want as much air as possible ...in the uk maybe the heater air is more important and when the heater is required there is no radiator overheating problem.
However to me it is plain directionally that positioning ducts up front must lead to less air passing through the grill into the plenum

I have operated as per the latter for a year and find plently of air to the car via air hose.

NB One thing does occur to me irrespective of where you start the hoses..we bother to put some basic hairy plug strip between bonnet( hood?) and radiator to restrict bypass air but there are big gaps between the air hose hoops and the bonnet.


Neil Ferguson

Neil,

Could you please explain what you mean by "big gaps between the air hose hoops and the bonnet"?
I can't follow what you mean.
Do you mean the gap above the vertical panel through which the air hoses pass?

Mick
M F Anderson

Mick ..sorry i was not more precise..you are correct..there is a large v shaped gap between the hose panels each side of the radiator and the bonnet that is not sealed ..see attached pic of my underbonnet area ..is it the same on all MGAs or just mine ?

Neil Ferguson

You raise interesting questions, Neil, ones I've pondered in passing. The general relationships you draw between placement of duct openings and the diversion of the air stream to various thermal and carburetion functions are all intuitively obvious, although you put a finer point on them than this. Optimization of the duct placement in the plenum space should probably be empirically determined in light of ambient temperature range, as you note. This would be a good project for a retired engineer with a bundle of thermocouples.

The other matter, the felt pad between radiator and bonnet, has long puzzled me. I imagined this to be a jury-rigged solution to the tendency to overheat, since it's so incomplete a barrier to air flow around the radiator. LIke many jury-rigged solutions, it's effectiveness is pretty marginal. It seems much the same kind of back-of-the-envelope engineering that gave us the roadster door latch.
Ken Korey


And how do you determine the exact positioning of the felt pad in the bonnet? My new felt pad (yet to be installed) is a 2 layered piece. The top layer can be seen to obviously fit between the steel strengthening fore/aft runners in the bonnet, but determining the exact positioning can't be seen with the bonnet up (and away from the radiator).

I assume a typical spray adhesive is to be used to attach the felt pad to the bonnet.
JM Morris

The aerofoil profile of the MGA front end creates a lower pressure over the radiator grill and bonnet than that passing under the car. The air pressure over the bonnet would also then slightly lower than the static air pressure inside the engine compartment. Therefore, without the aid of a radiator fan sucking air into the engine compartment very little dynamic air would enter the engine bay, even with ram effect. If there were no pipes attached to the front end of the 4" holes in the radiator bulkhead hardly any air would enter these holes (the pressure within the engine bay would be too high). In fact reverse air flow could even be experienced. The only way to get the air into the heater duct system is to have a pipe well out in front of the radiator so that it benefits from the airflow being drawn through the grill by the fan. This air is then ducted through the high pressure engine bay and exhausts into the slightly lower pressure cockpit.

Steve
Steve Gyles

PS. If you don't believe me about the high pressure engine bay try this little experiment: tape back the gearbox oil filler carpet flap; remover the rubber bung; get the car up to speed; apart from engine fumes in the cockpit witness the blast of air through this hole; also watch the water temperature gauge drop as a result of improved airflow through the engine bay.

Steve
Steve Gyles

Neil, -- You are overlooking a key feature of the cooling system, the engine driven fan. As you are an experienced air flow guy, I'm sure you will know that this creates a high pressure zone aft and low pressure zone ahead of the fan. This is what pulls air through the radiator when the car is standing still. If the 4" air hoses are not in place, the same pressure differential will push hot air aft of the radiator forward through the 4" steel ducts, and the heated air will recirculate through the radiator to reduce cooling. This is the same reason for installing the felt pad under the bonnet, to prevent forward recirculation of hot air above the radiator.

With the fan working, absolute pressure just ahead of the radiator is lower than pressure just inside the grille. This is what moves air from the grill area back toward the radiator. Installing the 4" air hoses on both sides places the 4" inlets in the higher pressure zone farther forward. In the case of the carburetor side with hose open aft of the radiator, the forward hose may prevent back to front recirculation of hot air with the car standing still or moving slowly. On the heater side, the forward hose will allow inlet of cool air for comfort of the passengers in hot weather, rather than taking in warm air from the face of radiator.

When the car may have no heater, the 4" port on heater side of the radiator should be plugged. There is an original factory supplied blanking cover for this purpose. There is alternately a (rare) factory accessory fresh air system. This is essentially a heater setup without the hot water core inside the box. This allows inlet of fresh air from the front for comfort of the passengers in hot weather as well as outside forced air for demisting the windscreen.

The photo above provided by Colin Manley shows incorrect positioning of the air hoses. The hoses should be positioned farther outboard, tucked away into the outer corners of the inlet plenum, and not intruding so much into the aperture area immediately inside the grille. The bolt for the 4" P-clip securing the front ends of the hoses goes through a hole in the air pan immediately in front of the body to frame mounting bracket. Some people may move the hoses inboard for easier installation, and for easier access to wiring harness and connectors in the same corner. I position my hoses in the original intended (outboard) location, but flip the P-clip around to put the bolt inboard for easier installation.

The "V" shape openings above the 4" ports are relatively small compared the opening above the radiator. As such, the pad closing the space above the radiator makes a noticeable improvement in engine cooling. Closing the "V" spaces as well could be good, but the difference might be so minimal as to be uncertain for improvement.
Barney Gaylord

I don't doubt that you're right about the pad above the radiator serving to reduce forward circulation of heated air, Barney, and I'm certain that was the intent of its designers. Thus I expected some observable reward after installing it after my first year of ownership, getting noticeably lower radiator temperatures for my effort. I can only say that without rigging the car for a systematic testing I haven't been able to see much difference. So I'm sure that my disappointment with the design is simply the result of my lousy testing and not the unseen and apparently unappreciated improvement I've achieved.
Ken Korey

Barney....
Two particulars about my car...
.....a)I have the hoses in place from the hoops adjacent to the radiator ..the heater hose and the carb hose..the latter goes as close to the airfilters as possible. This nearly eliminates recirc back to front.
.....b)I have dual electric fans so the ram effect is the only effect most of the time ( the fans only come on in about 1 min bursts ) and I get a plentiful of air via the heater hose to cool my feet when moving and, when still, I put the heater fan on.

Even without b) ...and I ran with the engine driven fan for many moons before I went electric....I still had plentiful air coming into the car via the heater hose.

Steve...agree that there must be some aerofoil effect but have not yet managed to get airborn..in fact the front of my car tends to squat down a little at speed....In any case I have no engine fan and the engine stays cool without the electric fans most of the time so plentiful ram air must be coming in and when moving I find no need to use the heater fan to draw cool air in for my tootsies...
( will try your plug hole experiment though..but given above it may be increasing airflow slightly by creating an even bigger DeltaP over the radiator to assist the ram efeect ..but maybe I'll put a butterfly valve on the hole and when the water gets up to 185 and before the fans cut in I'll just open the valve and need no fans at all....but the lungs may suffer over time...)
Neil Ferguson

Here's a look at it without the grille...

David Breneman

Hoses are in the wrong location. They belong more outboard, stuffed up against the body mount brackets on the sides, then turning back inboard to point toward the grill opening with maybe 1/3 of the hose end hidden behind the body shell. Look for a bolt hole in the air pan farther outboard in front of the body mount, where you cannot see the bolt from the front opening.

I can't find the right picture at the moment, but someone recently posted pictures with the same viewpoint. They had moved their oil cooler below the air pan and pushed the 4" hoses outboard to leave a huge clear opening through the plenum. Their final hose position was spot on. Perhaps someone can dig up the photo again.
Barney Gaylord

I'd be interested in seeing the actual location, because the fellow who did this work on my car is our area's leading expert. Barney, are you saying that the brackets are attached through the wrong holes? It's late now, but I'll look for the outer holes tomorrow. Are the brackets in the proper orientation, or should they be turned 180 degrees? I've never had any cooling issues with my car until I put the "50th Anniversary" grille badge on and tried to drive in 85-90 degree weather. Needless to say, the grille badge is now off the car and on a display shelf.
David Breneman

I can see where Barney is coming from. Just had a look at mine. From the 4" bulkhead hole the trunking hugs close to the inner fender wall, then curves inwards and downwards to the front. It certainly looks like the bracket hole you are using is too far inboard. That said, all of the trunking hole on mine is just within the open aperture space, but angled at say 15 degrees. Maybe I cut/stretched it too far forward. Cooling is not my problem either. I cannot get it up to 160. I have the trunking bracket the same way round as yours Dave.

Steve
Steve Gyles

To JM Morris,

Fitting the felt pad.

I found it best with the grill removed. Simply use a pencil to trace the line onto the bonnet directly above the radiator. I masked off the area and used a brush to apply contact adhesive. Spray adhesive seems to go everywhere for me.

Good luck.
Lmazoway


Thanks, Lmazoway. I am learning that with the A, anywhere from 1 to 2 items must be removed to get to the area or piece that needs work. A vastly different experience from that of working on midgets, B's and TR6s.
JM Morris

Picture of inside where 4" hose loop mounts.
This is a original unrestored 60 1600. The hole places the tube right on the edge of the grill opening. This is the only hole I know of.

R J Brown

This is a 58 1500 coupe. The radiator shelf has been replaced with a Moss unit. The sinlge hole appears to be in the same location.

R J Brown

But as I think Barney is suggesting the bracket should be turned 180 degrees so the pipe is tight to the inner wing. I have my original 4" pipes and will look at them over the weekend.
John Francis

Just how many of these “P” clips are used to hold the hose in place? Is it just the circular clip securing the hose to the bulkhead flange and then the single clip as shown on RJ Brown’s image? As someone with neither of these hose in place (OK truth be told I hadn’t noticed they were missing until this thread started) this is of real practical interest to me. It will be interesting to see if I notice any difference in engine temperature after fitting.


Kevin
K Garner

If your car has a heater there are three hoses, four band clamps, and three P-clips. One of the P-clips goes on the inner fender to support the long hose midway.
Barney Gaylord

Thanks for all the information, another job to get sorted.


Kevin
K Garner

If you have the correct hoses, you don't need the third P clip to support the hose to the heater. the hose supports itself just fine without it, and it's just another thing to get in the way when you want to remove the hose to do anything that side of the engine.
dominic clancy

Somewhat related - but wanted to bring it up since cooling and running temps are mentioned.

I am convinced that the majority of As are being run with grilles that feature slats that have been reproduced to tan incorrect specification/profile. The slats simply close off too much of the grille opening.

If you look at contemporary photos of original cars, you can clearly see right through the grille and into the radiator fins when standing in front of a car.

This does not seem to be the case with the reproduction slats. We have the same problem with the T Series slats and correcting this solves many overheating/or high temp issues.

Just mount your grille without the slats and you should see a big difference - though possibly not as much as we see on the T Series cars (due to the pressure issues mentioned above).

I would suggest twisting the slats to alter (reduce) the forward facing surface - this will, at least, allow more air to enter.

Jeff Delk


Years and years ago, I vaguely recall reading an article written by a radiator manufacturer's engineer. In it he stated at one point that the ideal situation for a fan/radiator combination was for the fan to be pulling air through the radiator in front of which was a zero pressure plenum--ie, neither negative nor positive.

Perhaps the slanted fins create a negative pressure in the plenum and opening them up creates a more nearly zero pressure.
JM Morris

JM Morris..
I believe the engineer was right.. but only
in the sense that if the fan was pulling the air through the radiator and there was no pressure in the plenum then the fan itself was ideally matched for the vol of air coming into the plenum via the grill without any ram pressure building up to generate a bigger deltaP to assist i.e. the fan is correctly sized for that operating condition.
Somewhere between low and top speed this probably exists but the rest of the time...not a chance!!
When stationary or at low speeds the always-on fan draws a slight vac in the plenum to draw air through the grill to match the fan characteritic.
Neil Ferguson

Jeff,

I think you are on the right track about the grill slats, but it appears that even the original grill was an impediment to air flow. Both factory racers and vintage racers have been run with every other slat removed. Scroll down this web page for an early article on MGA air flow:

http://rutgerbooy.nl/mga-z-magnette-specials/blog/pagina-4

Ken
k v morton

It would be really interesting to find out what exactly happens to the airflow through the radiator at different driving speeds.

Obviously when the car isnt moving, the only airflow through it is created by the engine fan.

1 Does the airflow through the grill into the engine compartment increase in a linear fashion with increasing road speed?

2 Or does the restriction to air escaping out underneath and through the oval vents cause the engine compartment to pressurise and "stall" the airflow?

The latter could mean that the standard engine cooling fan would still be the main provider of airflow through the rad at above certain road speeds.

It could also explain why some owners (Not Neil in Oz) still feel the need to leave the standard fan in place when they have fitted an additional electric fan.

Really interesting!

Colyn
Colyn Firth

Is this the correct position of the 4" hoses?
The hose is completely behind the sheet metal nose. Cannot be seen from directly in front.

R J Brown

Colyn,

According to the testing cited on Rutger Booy's web site, air actually flows INTO the oval vents instead of out.

Ken
k v morton

RJ

My opinion for what it is worth is that the P clip is now the wrong way round. I think that your original routing was not that far out, may be a bit straight and needed to be curved a bit more. But I am by no means an expert on this one, just my thought and interested to see what others say.

Steve
Steve Gyles

I alway put them in this way, see picture.
The question I have is which is correct?
Without information to the contrary this is how I believed they are to be installed. Just like David's car.

R J Brown

I can see the logic of moving the hoses away from the grill a little since they don't need a prime position but would not want to take the grill out for this. I find that I can just reach in and get hold of the hoses and its possible to bend and rotate the p clip away from the grill. I think this leaves the hose slightly lifted off the duct panel but not quite sure at the moment if I want to do it.
J H Cole

RJ

Not sure if this helps, but this is what mine looks like. Sorry no frontal view.

Steve

Steve Gyles

Every MGA that I have seen that had the hoses in front of the radiator had them mounted like Dave, Steve and I. The only reference to that being "wrong" was Barneys earlier post. I respect what you've got to say but don't see any other way to mount them.
R J Brown

You really do post some great pictures Steve!
How the h*ll did you get into that position to take the photo, but even more worrying, did you ever manage to get out?
Colyn

PS. really interesting subject too.
Colyn Firth

Nice photo Steve. Small digital cameras are great. I've been using mine to "see" places in my cars where I can't otherwise get, such as finding the hidden studs under my TR's exhaust manifold and above the transfer case in my Jeep. Sort of like a colonoscopy, Colyn!

Ken
k v morton

I do not know if we will ever determine the way the factory fitted the clips, and knowing the factory methods for other items it could depend on whether they were fitted before or after lunch.
To confuse the issue further, the factory Service Parts List shows one hose fitted Barney's way and one fitted RJ's way.
One more item for those trivia nights at the MG Car Clubs.

Mick


M F Anderson

Item 62(shown as item 47 on R.42 1500 SPL) is the forward air hose for the heater side and it seems to show the fixing bolt inboard. Illustration D.7(1500 SPL) shows the air hose for the carburetor side, also with the fixing bolt inboard. I believe this is consistent with what Barney says.

John DeWolf

I think that we just have to leave it to personal preference.
The 1500 SPL shows it fitted in both ways.
See image this posting and the next one.

Mick

M F Anderson

Second image from the 1500 SPL.

Mick

M F Anderson

On the basis of all that good stuff I have just purchased more 4 in hose and will install hoses toward of the radiator and as far outboard as practical to minimise x section in grill area...and will wait until next radiator removal to install...
Neil Ferguson

I think the SPL only shows them one way; with the fixing bolts inboard.
John DeWolf

Mick, I beg to differ - the sketchs in the SPL support Barney's position.

Plate RS shows the heater inlet pipe "Clip - large" Illus No. 30 with the bolt hole on the inside (fitted to the right hand side of the car - looking forward).

Plate DC shows the "Clip for air intake hose" Illus No. 11 with the bolt hole on the inside (fitted to the left hand side of the car).
(second image wouln't open for me).
Regards
Mike
Mike Ellsmore

Don't get too carried away using the hand drawn book illustrations for spatial relationships. The illustrations are often drawn wrong as a matter of convenience for the illustrator. In the SPL the primary use of the drawings is to illustrate the parts being listed for service replacement, but position in the drawing may be otherwise irrelevant.

Location of holes and bolts in the air pan for fixing the forward P-clips is a good example. The original holes are so far outboard as to make it impractical (nearly impossible) to orient the P-clip and hose outboard from the bolt location. The bolt is also rather difficult to access when the hose is inboard from the bolt location (as normal). I have cheated in my car by drilling new holes inboard from the hose location for easier access to the bolts. If you make a new hole you can position the hose wherever you like.
Barney Gaylord

I put my original tubes in position which I determined from the dent in the tube where the cross member for the hood/bonnet latch goes. This is how they look. Neither would be easy to mount with the clips to the holes in the new front pan. However, I don't think they were very tight up against the inner wing. Also, what is noticeable is that they are both much shorter than the replacement tubes. The tubes finish just a bit longer than the position for the clips so quite a distance from the grill.

John Francis

John, you have to stretch the pipes!!

CP
Colin Parkinson

This thread was discussed between 15/05/2010 and 25/05/2010

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