Fiat 131 abarth replica - hot under the bonnet

[miro-1980]

Dear Guy!

Thank you for nice comments.

I am facing a series of issues modifying the car for next season :

1/ keeping the coolant temperature down. I have two sensors one standard and one VDO placed in the three way metal connector to the rubber pipes in front of the engine. The reads I get from these sensors are very close , though the VDO sensor seems to indicate the temperature is higher when it raises than the standard sensor. In any case from these reads the normal operating temperature is between 100 and 110 degrees. (this is not during racing but just road driving). In hot weather and traffic jams the VDO goes as high as 120 degrees. The fan seems to switch when the readouts start going above 110 degrees. How do I get my water temp to 75 degrees? Are the sensors I use accurate enough? Are they placed in the right spot?

2/ keeping the oil temperature down. I have a VDO sensor build in the oil pan plug. The standard temperature readout is ca. 90 degrees ( not racing but road driving) but during racing conditions the oil temp goes well degree in access of 100 degrees.

I am using a standard thermostat with 84 degrees opening temperature and a standard fan switch (not sure of the rating). To control the coolant temperature I have installed a two standard Fiat 131 fans and a bigger radiator. I also have a manual override fan switch. The radiator fans work very well.

My plans are to :

1/ put an Abarth fan switch with a lower temperature activation of the fans ( what should be its temperature rating?)
2/ switch to original paraflu (50/50) instead of whatever I have now
3/maybe install a "water wetter" if all this does not help
4/ install a oil radiator (16 row) with a thermostat ( how do I test the thermostat rating ?)

I am also afraid that the temperature under the hood is too high. Any suggestions how to ventilate the under hood area better? There seems to be plenty of cool air inlet . but I am not sure the hot air gets from under the hood well enough.

Any suggestions ...

Miroslaw

Note: The engine has some 12 000 km of which ca. 500 in racing conditions. It was rebuilt in 2005/2006 with very low tolerances (0,03 mm) and we took care to breake it in slowly and without too much initial stress.

[Guy Croft]

1/ put an Abarth fan switch with a lower temperature activation of the fans ( what should be its temperature rating?)

The fans should not be operating over 20mph forward speed at all. You must not rely on them for cooling underway.

2/ switch to original paraflu (50/50) instead of whatever I have now
3/maybe install a "water wetter" if all this does not help

This is not a fundamental problem, either will be good.

4/ install a oil radiator (16 row) with a thermostat ( how do I test the thermostat rating ?)

Get an external thermostat form Think Automotive (Mocal brand) and it will do the job without worry. If the oil runs over 85 deg C either the air to the cooler is not getting in (easy to fix) or cannot get out the other side.


The problem of oil coolers and radiators is this: It's usual to be able to capture air from forward motion easily and shaped ducting of course helps to direct it to the cooling fins. However, the air cannot vent from the back of the units and carry away the heat if they are venting to a high pressure region, the air will simply stall and loss of cooling capacity will result. To make sure you don't arrive in this unhappy situation you ned to look very seriously at underbonnet venting. Going bigger on radiator is a waste of time until you have explored the absolute full capability of your current radiator, in other words got it to work.

The thermostat and rad do two totally different jobs, be clear: the stat controls the flow of water thru the engine, the rad cools it. So the stat should be such as to provide the correct running temperature, which should be 75 deg C under all load conditions and no higher, and the radiator must be of a sufficient size to disperse the heat in the coolant from that setting. If the choice of rad is too small the engine will just get hotter and hotter even with the stat fully open and if the rad is too small the engine will never warm up even with the stat not-fully-open. I have direct exp of over-large (esp ally) radiators and it's very bad news. Often you have to resort to shielding off large sections.

So begin with an in-head stat and get rid of the standard plumbing. You balnk off one side side of the T piece from the head and run the outlet to rad top and feed the pump from the bottom hose. No other mods. I sell in-head stats, see my list in GC Q&A. I supply a lot of oil system stuff too.

Now, venting. It is vital to vent and shield in the right places. Some facts, note carefully:

1. The region under the engine bay is turbulent and causes build up of pressure in the underbonnet region. It needs to be sealed off (ideally completely) with an undertray or well constructed sump guard.
2. The region below the windscreen is a high pressure region. This is why a fly can sit on your wipers at high speed. He can't get off due the pressure.
3. The low pressure regions are the wings of the car and frontal areas of the bonnet itself.

Finding the low pressure regions is best done with a U tube manometer survey but unless the open end of the manometer survey tube is presented perpendicular to the airstream you will pick up pitot pressure from the forard motion. What I mean is if you drilled thur the bonnet and glued the tube to the inside so that no part of the tube protruded into the airstream (in other words it was completely flush with the bonnet outer face) you would be able to gain an idea of the static pressure at that zone. The best kind of ducting is rear facing. Louvres are singularly ineffective and the more power the more venting you need.

The contribution of the oil cooler to engine cooling is measurable but modest. Naturally the hotter the engine the hotter the oil will become and you defintitely need to sustain the oil temp between 80-90 deg C or you're going to have no oil pressure at all on a wet-sump engine (the hot oil bleed-down rate from the bearings will be just too high for the pump to keep up). You should treat the oil cooler as a separate entity after you have solved the main engine coolant problem and the rear side of the cooler should definitely have a separate exit duct.

A word or two on contributory causes of high underhood temperature, here are the usual suspects:

1. Exhaust system. The radiant and convective heat is enormous and is worse if the ignition timing is retarded or the misture weak or if there is excessive baffling leading to high back-pressure. I don't go (AT ALL) for heat wrap because the thermal cycling on the metal is very, very degrading to the pipes. A really high powered engine will fracture the pipes in a matter of hours.
2. Braking system. The whole braking system from calliper, disc, lines, servo etc adds to the underhood heat and brake ducting is a very good thing.
3. Engine as a whole. Run it cool - 75 deg C (trust me) and the whole underbonnet region and power will benefit.


On a decent race engine installation it is vital to duct direct from atmosphere at the front of th car to the carbs or injection system. Ingesting from the underhood region will lead to density and power loss (high) and put you at risk from detonation.

The picture att is a model instalation.

GC

[miro-1980]

Dear Guy,

Thank you very much indeed for very exhaustive reply. You have put things in a very ordered perspective for me.

My order of priorities fundamentally changed after studying your reply in depth.


It appears that the first thing to do is to make sure the thermostat operates properly and provides proper flow of coolant from the engine to the radiator. I was thinking about installing the in head thermostat but really had no idea how to manage this. With your advise now I will get rig of the current stock thermostat and got for the in head stat you suggested ( where do I specifically put it in the engine head ? ) I will plug off one side of the T- piece , run a hose from the other (open side) of the T-piece to the top of radiator and run the bottom hose to the pump.

Once this is done I will I want to see the effects on the temperature to assess how effective this was. ( By the way I will try to note all results in simple and clear data so I can report it beck. Hopefully after the whole cooling program is done we will be able to see how much successive changes contributed to overall result. Might be useful to others).

Second in the order of business seems shielding and venting.

My concern is that the only bonnet out-vents are at far corners of the bonnet on left and right side near the windscreen. As you said there is plenty of area by which the cool air gets under the bonnet (front grill, under front grill opening and on the bonnet air opening for the carburetor) but not much by which the air can actually get out. I was thinking some time ago about getting a carbon fiber plates under the whole engine bay area but originally dismissed it thinking it would only make the engine bay hotter. Is this what you are saying : to seal off the bottom of the engine bay as much as possible? I have seen Walther Rohrl Audi Quattro and other rally vintage cars on display in Ingolstadt Audi museum and was amazed seeing engine bays totally covered with a steel plates. At the time I thought it was only to protect the bottom of the car (engine, transmission ,the works from damage when the car goes off the road or hit an obstacle on a dirt road. It did not occur to me this could help engine bay cooling !!!

It looks like I will revisit the carbon plates again, or if the cost is too high a 1 mm aluminum sheet under the engine bay.

I understand that sealing off the bottom of the engine bay is only the first stem and after this one must start building ducts to vent the hot air from the engine bay. With no oil cooler at this stage the two other great heat generators are the exhaust and breaks.

Re: Exhaust: If I understand you correctly you are suggesting no ducting of cool air onto the exhaust for fear of structural damage to the pipes and heir early wear. You are also suggesting NOT to wrap the pipes in any king of heat cover for the same.

I did have a problem with the Solex 34¢ž¢s delivering constantly too rich mixture and tear tuned them to deliver a poorer mixture. Checked the plugs and they looked just fine , but this is worth checking again. The engine trimming is correct, so this is not one of the issues to contribute to the heat in engine bay. However the 4-1 exhaust , plus a standard mid silencer plus a standard final silencer with standard (stock) diameter of the pipes are very likely a significant contributor.

This is exactly why I plan to change the whole thing according to your suggestions : Primaries: 1.5‚ x 25‚; Secondaries 1,75‚ x 7‚ than a run of 2.0‚ to the rear to connect to George Polley AX891 straight thru big bore oval silencer.

Re. Braking system. Initially I was planning to rebuild original Strada/Corsa air ducts for the breaks (front and rear). Than I saw on many original rally photos that the ducts were actually blocked off and finally decided not to do so, especially since the rear brakes are stock still drum brakes and I have put Zimmerman ventilated disk on front. Actually I used front spoiler duct openings to install a strong steel pipe to serve as an additional …œbumper‚ and provide a mounting for my driving lamps.

At this stage I will not yet go back to the shop to rebuild the break ducts, but will keep this as my next stage option ( to be dealt with when I work on increasing the breaking power: bigger disks and 14‚ or 15‚ wheels, etc.).

Hopefully with these changes I will manage to keep running it cool as you suggested 75 deg C and have resolved the hot under the bonnet problem.


Re: air ducting to carburetor: this definitely was and still is a problem. The way the air filter housing was constructed it was taking air from both near the carburetor area, from over the exhaust collector (how did I tolerate this at all) and from a short pipe directed towards the front grill. I intuitively knew something was wrong and took away the pipe from over the exhaust. But still the air was taking largely from under the hood (not from the outside). The first thing I will change is when I install the Weber 40 IDF¢ž¢s I will build a duct leading to the front of the grill so the air will be taken from outside of the underbonnet area. (Will four flexible 2‚ pipes leading from each carb barrel to the front of the car be OK or I should I build something like on the picture you presented (cover with filter and real large pipe to the front.)

Two more related questions:

1/ I plan to install original four Carello 20 cm diameter lights. If I do that two of the will be mounted over the black mounting pipe and two below. They will inadvertently block some of the air flow through the grill. Will this effect the cool air delivery to the underbonnet area ( especially the radiator)?

2/ Originally there was a flat plastic plate mounted on the left of the radiator, blocking fresh air flowing through the grill to the left of radiator.(I think it was the space provided for installation of the oil radiator any way I planne to place it there.) I removed it to improve fresh air flow to underbonner area. Now I think I may have made things worse by allowing air to …œescape‚ going through the radiator. As the radiator offers some resistance to airflow less air may be going through the radiator as the air encountering radiator¢ž¢s resistance might go towards the large opening to die side where the air flow is relatively unobstructed? Is my thinking correct or is this only a sign I am thinking about it too much?

Miroslaw

PS : My hot/cool problems are double as I have also a 124 2 liter with the same tendencies , but as the car is used for cruising it is less severe...