I spent the first 15 years of my life in a suburb of Chicago, IL, fairly close to MN and so I remember the winters and the salt damage - and watching the fenders flappin' in the wind on the cars on the highway because everything has rusted to pieces, I remember that stuff.

Why that 68-72 vintage? My first car when I was your age 1979-ish was a 1970 Mustang fastback.

~~

By this and your profile, I see you're a 16 yo kid with his first car (truck(s))... welcome to FTE, I'm Chris.

We've had more than a handful of kids like you show up here over the years, and I think you're the youngest we have right now (who posts regularly, anyway). And it's kinda cool to see guys your age sometimes (especially if you write well and not in Text-ese), you offer an entirely different perspective than the old pharts which is increasingly including myself who are talking about how this stuff was designed 30+ years ago, and we sometimes need that here as a break.
But please be respectful of the people you encounter here...

There is nothing wrong with disagreeing, but disagreeing + asking questions is encouraged rather than just outright accusing somebody of lying. If you don't agree, fine, then state your case and ask intelligent questions about exactly WHY you disagree, and there's a better chance you'll be included in the discussion and you will be treated lots better than when you act like that... OK?

Making accusatory comments like you did without any substantiating text is likely going to get you ignored... just sayin'.

 

Chris - I would never ignore him! I read what he posted and chose to ...... decline to comment.

 

I was only joking. I had made my points in earlier posts. A 68-72 cutlass because their are so many things I like about them like the OAI hood scoops, rear bumper/taillights, interior, 350 rocket and 455, the ss3 rally wheels, and the hump over the rear wheel for starters.

 

1) '51 ****** wagon with a '52 Mercury 255 (sadly gone from the fleet)

2) '48 ****** CJ-2A with the stock L134 (will have to pry this from my cold, dead hands)

3) '02 Snapper mower with the stock Briggs & Stratton

 

It wouldn't surprise me if that plate had that side effect (look at how leaves & debris accumulate there), but I kinda doubt it was designed with that intention in mind as one would need to drive through a LOT of debris to clog the thing, dontchyathink?

Ha!!!! Nah, not this time, only sometimes.

 

Maybe this post will help this thread qualify......

 

You can't deny Ford sold millions of cars and trucks from the early 60's(my 65 mustang aircleaner has the 2 inch hole) till they came out with efi in the late 80's, and they all ran fine with that 2 inch hole. I realize in theory it doesn't seem right but in practice it works fine.


I was talking about the vacuum from the engine that operates the flapper. If the throttle is opened wide in the carb, the vacuum will drop to zero, this is the vacuum that is holding the flapper closed. I am not sure if the flapper would open under these conditions.

 

I was thinking they were similar devices - either you had one or the other. So, some vehicles will have BOTH of these devices? If you had high underhood temperatures, wouldn't you also have high coolant temperatures?

From your explanation, the distributor ported vacuum switch uses manifold vacuum to lower coolant temperatures (from high coolant temperatures) by advancing the timing to raise the idle speed.

If the hot idle compensator lets in air to lean out the fuel mix when fuel evaporation in the carburetor is high (from high underhood temperatures), wouldn't that also raise the idle speed?

If the hot idle compensator is open, when would the distributor ported vacuum switch ever have to work?

Some Autolite and Motorcraft carburetors have the hot idle compensators on the carburetor itself, and other vehicles (like the Bullnose trucks) have it inserted in the PCV hose instead. If it is inserted in the PCV hose, wouldn't the "intentional air leak" be unfiltered?

 

And they do not run fine through that hole not by a long shot especially on larger V8's. It richens the mixture significantly and can cut hyway fuel mileage in half and this is where the issues of the flap not opening will occur, been there done that in more one vehicle this is not just limited to Ford. It wont be an issue puttering around town but at 60 or 70MPH at -25C or colder it likely will be. Convection heat loss squares with wind speed.


The engine always has a vacuum except when going immediately from idle to WOT or near WOT that is why the accelerator pump is there. No manifold vacuum=no air flow, no air flow=no fuel flow. Even at WOT there is still manifold vacuum. And air flow is not just dependent on throttle position but also manifold vacuum/engine speed. As engine speed increases at WOT manifold vacuum increases and in turn air flow.

 

Yes vehicles can have both devices.

And no high under hood temps do not mean the vehicle will have high (above normal operating) coolant temps.

You have to look at these as two separate and independent items.

The boiling temperature of gasoline is quite a bit a lower than the operating temp of the coolant in the engine. In the right conditions it very possible to get under hood temps high enough to boil the fuel in the carb and still have the coolant at normal operating temp. This is especially true if it is a particularly warm day out or a tight engine compartment.

Yes when the hot idle compensator opens it increases engine RPM this helps increase air flow in the engine compartment also helping to lower under hood temps.

Some hot air idle compensators are not filtered, is this an issue?
No... for 2 reasons, the vehicle is generally at rest when it is open and not really being exposed road generated debris, dust dirt etc.
the other reason is it is flowing very little air so there is about zero risk of ingesting debris especially at rest.


No the ported vacuum spark advance is still needed.

For example you are blasting down the hyway maybe pulling a trailer or what ever, but working the engine hard regardless, then you either pull off for a leak or come to a stop light or what ever, the vehicle has now gone from working hard to idling.

The cooling system has now gone from high GPM flow to a much lower GPM flow but the engine will still retain the latent heat from when it was working hard just a couple mins ago, since the cooling system's effectiveness has been reduced and the engine still retains this latent heat form working hard coolant temps will rise and may get high enough for the vac spark advance to kick in thus increasing cooling flow though increased engine speed and reduce combustion temps with advanced spark timing thus lowering the engines coolant temp.

The under hood temps in this case will be acceptable as you have just been on the hyway keeping things under hood cool with air flow.

Now lets say it's a really hot day and you sit there for a bit the engine is hotter than normal the vac spark advance has kicked in and lets say under hood temps start to rise if they continue to rise the hot idle may open further increasing engine speed and leaning out the fuel air mix to prevent staling. Eventually the Vac spark advance is going to close as the coolant reduces in temp but the hot idle compensator may stay open if underhood temps stay high.

Most engines that had the under carb heated spacer also had hot idle compensators on the carb (makes sense of course), so you should not add heated spacer plates to carbs with out hot idle compensators.

Hot idle compensators could be located on the carb, added in to the PCV inlet line or integral to the steel PCV inlet line, or even on the intake (Pre WWII). I know you are thinking how would it work on the intake as the intake vacuum would hold it closed and yes it does but as soon as the engine hot idle stumbles the manifold vacuum drops and it will then open increasing engine RPM.

The vac ignition advance was also used in applications that had AC , when the AC was on and was dumping all that extra heat right in front of the rad coolant temps would quickly rise.

 

Ok,we are getting on the edge again. Tell the old timers this. The ones that used to drive the old cars and trucks that had vacuum operated wipers. Each time they pulled a long hill their wipers would stop.

There is a complete system on all these trucks(all cars and trucks) with a vacuum reservoir and a check valve. It's purpose is to maintain vacuum to the HVAC controls when you do not have vacuum when pulling a hill or accelerating.

If you want to split hairs, yes with the factory air cleaner you probably would have a couple inches of vacuum at WOT. But with your chrome aircleaner you would have almost none, especially with a properly sized 4bbl and all 4bbl's are open. There will always be a slight pressure reduction in the engine, of course that is why the air is flowing in. But it's not enough for us to harness and do anything with as far as vacuum hoses and vacuum components.

 

Bwahahahahahahahahaha!!!!!!!

But first....

OK, Matthew, you've passed the acid test. Why don't you tell us something about yourself? What you know, what you're good at, what your experience is, and how you know this stuff? A fair number of guys here could really pick your brain....

I remember you mentioned a bit a few months ago during some emissions discussion but life was busy and I forgot by now.

 

I'll second that - the "tell us something about yourself" bit.

 

This looks cool...no sensors, doors or diaphragms but looks cool

About Ram Air Box

 

But you said

Yes there is vac reservoir for the HVAC but you stated the obvious it is for the HVAC and the cruise if equipped ......


The vacuum in the intake manifold will ALWAYS be higher than in than the air cleaner because well it's well the intake and needs to have air flow to generate fuel flow..


As for the flapper the force of the incoming air trying to open it increases the negative pressure in the air cleaner (Vacuum) thus increasing manifold vacuum by a like amount, there by increasing the the inHG holding flapper closed by the diaphragm, multiplied by it's square area. This will continue to compound as engine RPM increases and the demand for combustion air increases.

So in short NO you may not open the stove flapper as you increased engine speed. This is not splitting hairs it is a quantifiable fact.

If the air cleaner flapper used a spring like they used to. Engine vacuum has no affect on it all and it could pull the flapper open and may not increase the fuel mix at all. (Explained later)



The carb and it's inlet is designed to operate at atmospheric or near it a couple of inHg vacuum in the air cleaner is significant and could drastically throw off AFR. Increasing vacuum in the air cleaner reduces air flow into the engine but can have drastic increases in the the fuel flow in to the engine (There are exceptions to this, more on this later) This is exactly how the choke works.

The fuel is delivered to the engine by the venturi's the air moving through them speeds up thus creating a low pressure area allowing for the air pressure in the float bowl to push fuel from the fuel bowl to the venturi and into the engine..

Increase the air speed and you increase the venturi vacuum therefor increasing the amount of fuel being delivered. To increase the vacuum in the venturi you have to either reduce the pressure surrounding the venturi (Provided the fuel supply is at a constant pressure IE atmosphere) or increase the volume of air going through it. Since the fuel in the fuel bowl is at the pressure of the surrounding atmosphere it pushes the fuel through the venturi's

Now here is where external float bowl vents can screw things up and why they were blocked off in later non emmsions applications and why they are NOT a good idea over all.

We all know that the pressure in the air cleaner is not static it is affected by the heat stove, filter restriction (how plugged it is etc) and air cleaner design and of course the total air flow that will affect the pressure drop imparted by the former.

The pressure drop across a venturi is fixed. And only increases with air speed.

But Fuel flow is through the venturi may not be fixed to air speed like venturi pressure drop it.

And here is why.....

Example:
Lets say you have a 5 inHG drop in the venturi at a given air speed. You will in turn then have 5 inHG of pressure pushing the fuel through the venturi and into the engine.


Ok so now lets say you have air cleaner that is developing 2 inHG vacuum above the carb compared to atmosphere at that air speed.

Lets say the carb's has externally vented fuel bowls. So you now have a 5 inhg drop in the venturi and you also have a 2 inHG drop in the air cleaner. So in total you have a 7 inHG drop over atmosphere, you now have 7 inGH of pressure pushing fuel through the jets.

Flow through a restriction roughly squares with pressure. So now you have increased flow through the jets by roughly 80%

Now lets say you have the same situation but the fuel bowl is only vented in to the air cleaner.

You still have a 5 inHG drop in the venturi and still have a 2 inHG vacuum in the air cleaner compared to atmosphere. But the fuel bowls are no longer at atmosphere they are at air cleaner pressure. So they are are also at 2 inHG vacuum compared to atmosphere, so now the total pressure drop in the venturi over the pressure in the fuel bowl is 5 inHG. Your fuel metering is now locked to venturi vacuum, regardless of air cleaner vacuum. Plugged up messed up filters air cleaner design etc will then have a much smaller affect on fuel metering. You will never have the fuel bowls at exactly the same pressure as the air cleaner but it will be much closer.

Now with this is, it begs the question if this is the case how does the choke then work to deliver more fuel. The carb vents are always OUTSIDE the choke flap so you are still increasing the pressure forcing the fuel through the jets as you have increased the vacuum around the venturi's and not reduced the pressure in the fuel bowl a like amount

Now in many many Evap emissions vehicles the fuel bowls are not fixed to air cleaner vacuum this can and will drastically throw off AFR. This is in part why I advocate plugging external fuel bowl vents.
This is also why early external mechanical bowl vents closed above idle.

If you absolutely have to have evap due to a personal environmental creedo run the purge line to a small metered orifice hooked to the intake and plug off the external bowl vents. This will slowly purge the canisters as you drive .

So no this is not splitting hairs at all by any means. On externally atmosphere vented carbs an open air filter will help make fuel metering way more accurate by making sure that you are pulling as little vacuum as possible in the air cleaner and keeping fuel metering as accurate as possible.


This may be splitting hairs but accurate fuel metering in an internal combustion engine is all about splitting hairs.