Round type and square type inlet manifolds

[DavidLaver]

I understand the very early inlets had exhaust heating.  Both types I have seem to connect to the same ports in the head with water heating.  Anyone tell me when each was used, pros, cons, gotchas.

Both have drain taps - the round type also has a take off of some sort on the top of an inlet passage.  Did Aprilias ever have a vacuum guage or a vacuum windscreen wiper?

Photos to follow...

David

[DavidLaver]

Photos per above.

David

[Sliding Pillar]

I think the difference is that the smaller square type was on the first series 1350cc car and the larger round type on the second series 1500cc car.  I had the later round one on my 1350cc car with a large Zenith carb and it was the fastest Aprilia I had driven, better than a car with a big carb but only the small manifold. Ade.

[DavidLaver]

I've a large and complicated looking Zenith VN and an adaptor plate to get me going but am concerned that its post war (I don't know for sure...) and the VSCC won't like it.  The next idea is a downdraught SU as its such a known quantity to get bits to set up just-so.

Any idea what that vacuum take off is for?

David

[JohnMillham]

The vacuum take off could have been for a windscreen washer. Such washers were popular years ago.

[ColinMarr]

The more rounded manifold (still fitted to the head in your photo) is more familiar as on a late Series 1 car.  I agree with Ade – best used with a big Zenith or better still a big Weber. I have never ever seen an Aprilia fitted with an SU! Did SU ever do a downdraft version?

There may have been a coolant duct through the manifold, but I don’t think any Aprilia had an EXHAUST heated manifold!

I suspect the connector fitting you have is for a vacuum econo-meter or as John says, for a screen-washer.

The photo below shows the early Aprilia from Italy that did the Sliding Pillar rally in 2006. It looks to have an early ‘square section’ manifold with the standard small Zenith carb. (Had I known David was going to ask all these questions, I would have taken more photos!) Note the very elegant cam actuated hand throttle linkage. What a fantastic car!

(Only I can’t post the photo because the bloody uploader is full again – s*d it!)

Colin

[DavidLaver]

One of my Viva cuttings said the very first cars had exhaust heating - maybe only prototypes that iced on the top of a mountain and they tumbled down the nearest ravine in disgust.  When I see it next I'll quote the referance.

Sounding like "square" is small and early - the academic debate as to quite when they made the change - for my purposes it sounds like its the one to use.  Also sounds like the tapping is not original, but might be handy to drive a vacuum wiper motor I have in hand.  Useless - but light and simple - and wipers can be quite a wee project in themselves as I learnt with the Aurelia and am struggling with on the Midget. 

The question this throws up is how much the 1500 and 1350 engines have in common.  Looking in LaLancia its 72 bore x 83 stroke for 1352cc against 74.61 x 85 => 1486cc.   

My engine numbers:

MOT97 *1383*, MOT97 *1637*, MOT97 *5* which is the dirty one - I struggle to believe it was 5th off the line...  Is that a code for "replacement spare" or something?   

David

[Scarpia]

Am I confused (don't all shout at once),

 but what is the purpose of the heating/cooling facility in the manifold. Is it to try and cool the charge on the way to the combustion chamber (to enhance in some respect the combustion process) or is it to warm the manifold as the engine heats up.Neither seems practical to me in terms of actually making a difference.Cold starting and icing of the carb will not be helped in the first few miles if the water jacket is still cool and conversely the small channels I see won't really cool the inlet manifold very much in my view when the whole thing is at running temperature.

I even less see the relationship in terms of preventing carb icing and I thought that didn't exist anyway in the good old days? (I understood this results from the use of modern petrol which is "thinner" and has different characteristics to older fuels;)
answers on a postcard please ...

[fay66]

Depends if your talking about a water heated manifold or not, my experiences of water heated manifolds is that the actual amount of coolant concerned is minimal, & as it is coming directly off the cylinder head & block water jacket, as soon as the engine is running it starts warming up quite quickly to aid mixing the fuel & air. try putting your fingers on a water heated manifold after a couple of minutes.
Thinking back to my old Vauxhall days the intake manifold was mounted siamese fashion directly above the exhaust manifold, with a thermostatically(coiled spring) controlled flap that directed the exhaust gases to the underside of the inlet manifold, which warmed things up pretty rapidly! downside was when the spring weaked it rattled like buggery
As for carb icing, it's always been around! certainly in my personal experience since my motoring days started back in the 1950's. 

[DavidLaver]

I measured up and both the same size for carb, all ports, and bolt holes.

The water passageways on the "round" inlet are SOLID with what looks like a soot and lime mixture.  Am knibbling away with a dental probe and have a satisfying pile of dirt to show for it for all still a way to go to clear it fully.

David

[ColinMarr]

I have to say I share Scarpia’s doubts about the wisdom of pumping coolant through the inlet manifold, but it seems to be common practice. I think my Aprilia’s late type manifold had passages for water, and the Fulvia’s thermostat housing is surely located where it is to warm the inlet tract.

All other things being equal (which they never are!) you might expect it to be best to cool the inlet so as to get the maximum amount (mass) of air + fuel into the cylinder. But, once the engine is up to temperature, I can only imagine that it’s heating rather than cooling that takes place. Perhaps this warming of the inlet is to counter any tendency for icing-up.

Icing-up can be a real problem. I had this with a Fiat Uno, which unknown to me was missing its flap-valve in the air box designed to take warm air from the exhaust manifold. The result was an occasional ice encrusted carburettor, which stopped everything, most notably on warm humid summer days – all very distressing. I have never encountered this problem with any other car.

Colin

[DavidLaver]

A turbo gets very hot - red hot - a note on the Phoenix Car Company page (engine woes with the car pictured inside the front cover of Viva Lancia each and every month) says 1090 degrees celcius.  On top of heat soak there is also the problem of air getting hot as its compressed.  Wrapping the exhaust and heat sheilds and having the correct spec intercooler and getting the cold air intake and who knows what else right are "details" that will make the differance between a championship winner and a car that does a couple of laps between repaints.

http://www.phoenixcarcompany.co.uk/latest_news.html

By contrast ambiant air temperature over 40 degrees is considered "hot".  What sort of temperature would an Aprilia's water run at?   I'd think the 70-90 range.   The exhaust will be more than warm but it is over the other side of a tall and wide block.  Maybe Scarpia can fix a max/min thermometer under his bonnet and enlighten us as to the range he sees.  In a normally aspirated engine there's also the issue of wind chill.   For a 1350cc Aprilia engine with a 32mm choke at 3000rpm I make it a 93mph breeze through the carb.  Hand out the window at 90mph and its chilly.

For sure if the carb is too hot vapourisation becomes the problem...

As discussed on another thread "cool fuel" can be a benefit...

For sure there's a small gain for getting cold air from infront of the radiator...

Then again a "clever" cold air intake system might be restrictive and sap more power than it gives back.  I remember a write up on a Fulvia in I think Classics Monthly were such a system fell off and they found it went much better.

David

[ColinMarr]

Let’s not get carried away by ‘wind chill’ and ‘hand out of the window at 90mph’. An engine drawing air through an otherwise dry carburettor will not chill the carb – it might even heat it up a tiny bit. The chilling effect comes from the vaporisation of the fuel. This change of state from liquid to vapour requires energy in the form of heat to be absorbed from the surroundings – just like the refrigerant in a fridge. It is this localised cooling around the venturi that can cause condensation and freezing of water vapour in the air that is drawn into the carb, and hence icing up.

I can’t remember anyone having icing-up problems with an Aprilia. Also I suspect that the water-ways into the inlet manifold were well and truly crudded-up many years ago and there wasn’t much warmth from that source.

At risk of another diversion… Remember that the Aprilia was designed to run on very low octane fuel. Modern higher octane fuels burn more slowly. An example that I know from a few years ago, was an Aprilia engine, running on what was probably 4 star, with the exhaust manifold glowing dull red because the exhaust valves were opening on still-burning fuel. I don’t suppose the exhaust valves liked this very much. How do Aprilia runners cope with this nowadays?

Colin

[Scarpia]

spot on Colin.
and the characteristics of modern fuel enhances this evaporation I understood. This is why I thought this was a recent phenomenon but Brian suggests it exists a long time already.To visualise it better think of a camping gas bottle that forms ice on the outside on a summers day.I have had this on holiday in spain at 35 degrees with thick white ice forming due to this cooling effect.

The octane argument becomes complicated but ironically octane retards ignition so "high" octane actually burns later as Colin correctly points out. Sounds the wrong way around of course.Incidentally , lead was introduced to perform the same retarding function and they only discovered later the protective qualities for the valve seats.

[DavidLaver]

Anyone help on this one:  "The question this throws up is how much the 1500 and 1350 engines have in common"

As for wind chill try this experiment: breath out - open lips - open teeth about 5mm - breath in quickly.  My teeth get very chilly.  How does that differ from air through a carb?   Am not saying its the whole story, but its a factor.

With the round manifold I dug as deep as I could.  Brushing I knocked out a plug the oposite side from the head but so far, for a fair bit of scraping, the blind hole goes nowhere.   Under the remains of the carb gasget is a date stamp 1940something and I think its 1945.   The square one is stamped 1939 on the side.

Am finding the variety of stampings facinating - no idea what they are or mean but an intreaging variety.

David