Race Engine Forum UK

Installation work delayed till Monday.

The new clutch arrived !

Looks to be very very strong.
The thickness of the plate is an impressive 2 mm.
The spring s to soften the blow of a quick clutch release are also very impressive.
Metallic friction plates are 8 mm thick.
The pressure plate appears to be also very strong...

This will make the clutch stick to the pressure plate with incredible force, eliminating slipping while gear changing and at hard start.

Miro

Ok, this is time to deal with the heat!

I have been trying to deal with it as long as I have been using this car for sports.

Initially, when I bought my 124 spider I noticed it had an additional switch on the dash panel. This proved to be a manual override switch which allowed to turn on the radiator fan at will/ When I read more about it on the internet this was one of the first pieces of advice to all new 124 spider owners : INSTALL FAN OVERRIDE SWITCH.

The switch quickly proved to be very useful . When idling for long time in rush hour traffic the coolant temperature would go quite high (to 110 - 110 deg C) getting dangerously close to the red zone on the temp gauge indicating overheating.

The car was not really used for sports but I did few race track races on the car . Again the coolant temperature would go quite high and it had to be drought down by turning on the fan. Later I started using more heat resistant oil, put in a lower temperature fan switch and for most of my driving the engine would be kept at ca. 90 deg C.

When 131 came along the same problem appeared. I sought advise but until i asked Guy I was hearing :
1/ put in a lower temp fan switch
2/ put in a lower temp thermostat
2/ install additional fan
3/ install a bigger radiator.

I did put in a a lower temp fan switch (75 /82) , a lower temp thermostat and installed a second fan. This worked fine for civilian driving but did not help much when I pushed the engine into high RPM, racing it for extended period of time.

When I asked Guy , his approach was totally different. Sure you need a proper temp fan switch, proper temp thermostat and a proper size radiator with goof flow through but you should consider that hot air is trapped under the hood by combination of over the hood air flow , under hood air flow and no where to escape. His key suggestion was to block off the under engine area with an air shield first.

I did not do it (initially) relying on the conventional wisdom which told me that if the engine is getting too hot and you tried all you know to decrease the coolant temperature , you need to make sure the oil will not lose its viscosity in such high temperatures ( I started using Castrol Edge Sport 10 w 60 ). This actually decreased the oil temp from as much as 130 deg C to 110 deg C. The coolant though would still be running high on temp during the events.

When I decided to bet a new GC engine I had to accept that whatever he says goes. With the in GC installed in-head low temp thermostat and my low temp fan switch , twin fans the temperature would normally stay at 85 deg C. But GC said it is 10 deg over the temperature he recommends and I should get it down and to do it I must follow his recommendation . What was I to do. I have learned a lot since I started dealing with Fiat DOHC engines , but trying to argue technical issues with an experienced engineer and my engine builder is like shooting yourself in a foot. Makes little sense. Also his recommendations never failed me in the past. what is more what he says makes sense to an engineering layman/amateur like myself.

So the story is this.

First you needed to understand what are the sources of heat under the bonnet:

1/ internal combustion engine (this is the key heat source)
2/ the exhaust manifold ( who touched it once on a running engine will remember for life)
3/ the cooling system generating high volume of hot air when radiating it into the engine bay

But these are obvious sources and they are part and parcel of the engine operating under the hood. Well here the hood is what appears to be a key. What happens under the hood as regards heat is not only related to normal engine operation but also engine cooling. DOHC is a "water " cooled engine , but cooling the engine is not only in the coolant. It is also in the air that flows around the engine. It should be preferably cold. The air temperature in this part of Europe during summer racing season gets sometimes as high as well over 30 deg C. Certainly the engine would keep lower temperature if the outside air were 20 deg lower. But the external air temperature is beyond anybody's control.

The 20 deg lower air temp can be partially substituted by a 10 deg lower temperature and significantly increased volume of air flowing around the engine. ( It was well known to the Chinese prior to middle ages that you can cool yourself by using a simple fan. The temperature of air the fan delivers is exactly the same as the air around you , but your 36.6 deg C can be brought down by blowing a stream of air of any temperature below your body temperature. it will be more effective as the temperature gets lower and volume of air gets higher. Best known as windchill factor this phenomenon is key to any cooling system.

Now what does it have to do with my engine running 10m deg too hot. It seems everything. The bonnet / hood encloses the engine into a semi closed compartment . It is closed ion the top on the sides and in the rear and semi open on the front and on the bottom. Such closing off air circulation around the engine was a result of a body design not a choice of the engine builder.

Now in normal daily use of a car the grill was sufficient to cool the engine. But under such normal use you drive the car at 3500 over 4500 , rarely allowing it to go over 5500 rpm. You do not keep it at top speed all the time pushing not to the limit of traction.

When you do simple existence of a grill does not suffice. You8 need to increase the airflow around the engine , if you want to keep it at 75 deg C all the time. ( even driving it at almost constant 8K RPM). So how do you achieve this increased air flow around a running engine with the car in high speed.

Apparently the answer is by understanding what blocks the airflow. Certainly if you start blowing the air into the semi closed compartment trough the front (the grill) and from underneath car (under the engine bay area) and allow such elements as hot brakes to contribute to the heat generated by the engine without making sure there is sufficient hot air outflow you are operating a thermos ( keeping the heat in instead of blowing it out).

Look a the the simplified schematic drawing below.
The hot air is pressurized under the bonnet with no way to escape, by several fractors :

1/ over the hood air stream: the two small openings ( air vents) located on the sides of the bonnet near the windshield do not really vent the engine bay. The high air pressure created by the air stream flowing over the bonnet effectively prevents hot air from escaping

2/ under car air stream : The fresh air flowing through the grill is prevented from easily escaping under the car , as strong air stream of fresh air under the car keeps the hot air under the bonnet.

In addition brakes that ( under rally and track event conditions) release large volume of heat largely rel;ease it to under hood area.

Once we realize this the remedy seems to be straight forward:

1. vent the hood,
2. vent the brakes and wheel arches
3. close off the under engine air flow

Look at the schematic drawing below:
- REAR FACING HOOD VENT : Putting a rear facing vent on the bonnet (hood) : allows hot air to escape (arrow A) from engine bay and increases cold air flow through the grill (arrow 1). [Shape of the rear facing vent induces low pressure area past the vent and prevents air flowing over the hood ( arrow 2) from blocking hot air under the hood (arrow B).

- AIR SHIELD UNDER THE ENGINE : Putting an air shield under the engine bay decreases air pressure under hood by severely limiting the volume of air pushed into engine bay from under the car ( arrow 3) and allows more cold air to flow through the grill (arrow 1).; it also severely decreases turbulence under the hood inducing air flow and heat exchange between cold air coming through the grill and the radiator, engine block, and exhaust manifold.

- BRAKES COOLING AIR FLOW INTAKE (TUBE) and WHEEL ARCH SIDE VENT : installation of these allows cold air to cool the brakes (arrow C) and release the brake generated heat to escape through the side vent (arrow D) . (Instead of releasing much of the heat the brakes generate to engine bay).

This is exactly the plan .

Miro

Implementation (documented by photos and data on effects) will follow.

For those with advanced technical knowledge : Sorry for oversimplifying what really is a quite complex technical issue of heat dispersion , gas flow , aerodynamics and few other branches of physics, but I lack formal technical training and my formal physics training ended in high school.

For those amateurs like myself : this was the simplest way I could understand the issue and believe that some you you might benefit from it as well.

For GC: Hope I have not made a major technical mistake. Like in the case of port flowing I have never expected to be exposed to so much serious scientific concepts fine tuning the car. Thanks for awakening my technical inclinations I never followed in my education but always fancied.

M

Thanks very much for taking the time to post that Miro. Having read the section in Guy's book (with the annotated Yellow Lada rally car pic) I was about to start sketching out a very similar diagram in an attempt to understand what I need to do regarding venting my Spider hood (not that it is actually producing any heat yet!). I was going to follow the Abarth strategy of venting the rear corners but wanted to understand what is actually going on. Looking forward to the seeing the results you get.

Thanks Simon,

I just shared the process of conceptualizing the problem and the solution.

Glad to be on the same wavelength with you.

Once I started thinking about it I had to draw it to keep all the basic dependencies straight.

I am still awaiting a one potential hood vent. Once in my hand the hood will to my body shop. They will either use one of the three vents I have collected or build their own ...

Miro

PS: pitting side vents on my spider is a future project . I believe replicas of these Gr.2/ Gr 4 side vents may be bought. If I find them will let you know

PS PS: Soon I will also post pictures of my own design air box.

Hello Miro

there are some mistakes in your understanding, especially about the flow underneath the car.

First some basics: high flow velocity= low pressure and vice versa.
Flow, i.e. mass transport between 2 areas will always go in the direction of lower pressure.
Example: driving with a closed car,
around the cars outer shape there is high air flow velocity,
inside the cabin there is relative low flow velocity.
If you open the side window slightly, you allow the pressure difference to work,
and the air flow direction will be towards the outside (where the pressure is lower).
Due to this effect the hood top vents and sidevents, as you mentioned correctly, do work.
The top hood vents will clearly help removing otherwise trapped hot air in the upper region (heating the carbs).

The same physics is true for underneath the car (provided clean bypassing flow).
The pressure underneath the car will be lower than inside the engine bay,
repectively lower than in the low speed/high pressure region before the radiator.
That makes the air flow go from the front of the car, through the radiator
into the engine compartment and exit underneath the car.

The air flow from underneath into the engine compartment, as you scetched it,
would only be possible if there would be a "spoiler/airdam at the end of the engine compartment towards the passenger compartment.
Therefore I would not advice to block the engine compartment underneath as you scetched.
Make an airdam at the front and then some plate to reduce turbulence and provide clean flow,
but let the plate end early enough to allow the air flow through the radiator escape.


Thomas

Thomas,

regarding 'The pressure underneath the car will be lower than inside the engine bay'

this is only true if the underside of the vehicle is 'clean' in aerodynamic terms which few production cars are. Intrusion of vehicle architecure into the airstream under the vehicle causes significant turbulence and build up of pressure in the underhood region, the reason for using undertrays and spoilers.

G

Miro, excellent post.

re: "REAR FACING HOOD VENT : Putting a rear facing vent on the bonnet (hood) : allows hot air to escape (arrow A) from engine bay and increases cold air flow through the grill (arrow 1). [Shape of the rear facing vent induces low pressure area past the vent and prevents air flowing over the hood ( arrow 2) from blocking hot air under the hood (arrow B)."

Nice work with the annotated diagram and how nice it would be if more folk here took the time you do.

Don't put the rear facing vent too close to the windshield which is a high pressure zone. There we have the heater intakes for that reason and it's also why a fly can sit on your windshield wipers at speed..

How close, dunno. As I indicated in my book there is no reason at all why you could not 'map' the pressure zones under the hood with simpl water manometers. All you need is windscreen washer tubing fixed in a U shpae to a piece of wood and water with a bit of antifreeze for color. One drives, one 'maps. You will soon establish the trends.

G

Guy,

I absolutely agree, thats why I gave the above advice.

My main point was to show Miro the fact that the airshield underneath the engine should not close it off, as indicated on his scetch.
The mayority of the air going through the cooler needs to exit towards the underneath of the car. (unless one severly changes the hood design, as its possible with some midengined cars (as Ford GT40, Lotus Elise) where a large portion of the cooler air exits to the top).

Thomas

Yes and no Thomas with respect.

The hot air from the radiator (and potentially oil cooler too) concentrates at the top of the engine bay and it is better to either stop it reaching the engine altogether (see 90s NHRA car below) or vent it at the top and upper sides of the bay. to get it out at the bottom it has to be 'evacuated' by a depression. But to be honest anything under a stage rally car is likely to get smashed to bits - if you are fast in forest - so the last thing you want is a bit of thin gauge alloy undertray exposed below - behind - or level with - the sump guard.

QUITE FRANKLY - I have little time for cosmetics and authenticity when it comes to competition cars and I see no reason why the bonnet (hood) on well-sorted 131 should not look like the NHRA one.

G

Guy ,


Technical issues aside...

With all due respect, but how do you put a ugly bonnet like that on my beautiful 131Abarth?

I would rather race at half throttle and 1/4 speed than "beautify" my great looking car with a bonnet like the nose of a flipped over, dead hammer fish.

I believe that 51 % of a Fiat value (and fun to drive) is in the looks and style. Performance is actually second with 49 %.

There has to be a compromise allowing for proper looks and improved engine bay cooling at the same time.

If this is what it takes we will actually do the under bonnet temperature and air pressure tests but I would have no fun driving a NHRA monster like this.

Miro

We will work on this all week starting Monday, including tack tests during the weekend .

how could I possibly take issue with you when you put it so eloquently, Miro?!

G

Well Guy ,

I wanted to get you into this discussion , but you are far too sharp and know me all too well. (LOL)

Miro

PS: My new bonnet ...
looks as if fat person with one buttock set on it for a while during molding.
I do not think it is much better than one on NHRA car.

Oh, well maybe what it takes to race ( anyway , I will not see it very well from the drivers seat.) And when they ask me why is it reversed I will play surprised and say it was my body shop mechanic was drunk and put it the new hood vent backwards.

M

PS PS :

1/ New side vents selected :
The new clutch is installed :

We also started putting heat shielding mat over the exhaust ( just under the co pilot's feet - last time the pilot was complaining his feet are burning ) , in few other places where the exhaust is very near the chassis and near the spare wheel bay (where we have the tank).
We will also try to put some over the gearbox tunnel which typically disperses a lot of heat into the the cabin. The mat is used for industrial applications and has heat resistance up to 1000 degrees. It is also quite thin ( ca 1 cm ). Got it from a friend who drives a Porsche 911 RS Turbo Carrera GT ( or whatever ) and manages a company which sells this to steel mills and forgeries for heat shielding. Quite inexpensive too. For a sheet 160 cm x 100 cm I have paid 35 euros (with courier delivery!)

M

Nice work. It only looks weird because it's black. Once it's painted it will look just fine.

You could develop a duct/scoop from the rear of the rad to that underhood vent too, ie: fitted under the hood. I keep these ideas (concepts?) coming because they matter, readers, they really do.

More engines break due to high temp and its overall effects than any other cause.

As for the clutch I should be happier if I could see a red paint mark on one of the bolts indicating that the set has been torqued-up to 14-16lbf ft. I trust that new spring washers were used? My Schnorr ones can't be..

G

Hi

The body shop is working on the bonnet . The space has been cut out and the vent permanently attached. It is supposed to be ready Friday at 5 pm.

( we are starting off at 6 pm)

Re Clutch: The torque is correct.

What new spring washers do you mean ?

M

Bonnet Vent Progress

The body shop owner promised to get it all done by Friday , only if I do the cutting – so I did !
The shape was cut out in a manner to avoid cutting reinforcements of the bonnt.