Intake ducting, Yes or No

[wildthings]

I have noticed that when I have run my 411 with the intake ducting remove and the fan drawing its air from the engine compartment that items in the engine compartment are noticeably cooler. I have never noticed any increase in the engine temperature itself when running without the ducting.

Vans run without the ducting just fine and are under a much higher load than a light T4.

Is the ducting really a plus? or is it just something that is in your way.

Yesterday it was 107 in the shade at my house, today it barely cracked 100. What a relief

[raygreenwood]

The ducting is a must! Yes...you are 100% correct that all of the surrounding tin and components inside of the engine compartment stay remarkably cooler. This is because......the air passing ovr them and into the intake....is pulling that heat from the components and putting it in the engine! .

If you have instruments...you can see the rise in engine oil temperature and head temps. Ray

[wildthings]

As much for the sake of argument as anything else I am going to debate this point.

Whether the ducting is installed or not I am going to assume that the engine puts out the same amount of total heat. The relatively small amount of heat that enters the engine compartment has to eventually go somewhere. It either has to pass through the body of the car or go out with the cooling air. As I have never noticed that the body of my 411 is unusually hot I think that the largest part must go out with the cooling air.

(I guess that if the engine compartment with the ducting installed is actually slightly pressurized then some hot air would leak out through the cracks and holes in the tin, firewall, etc.. I am guessing that this would be a very small amount of the overall heat flow so I will ignore it.)

If all the heat (or nearly all the heat) goes out with the main cooling air flow over the heads, jugs, and oil cooler there should be little if any measurable difference in any of the engine vital signs. The CHT's should be nearly the same and the oil temps should be nearly same ducting or no. Any increase in CHT's should be offset by cooler temps in the oil and cylinder or vice versa.

If there actually is a measurable difference in CHT's, cylinder temps, and/or oil temps when running the ducting instead of running without it I would guess that it would have to be from improved air flow due to the shape of the ductwork and not much at all due an change in the number of calories being carried by the cooling air.

Fire away!

[raygreenwood]

Yes, a some of the heat just leaks away because there is positove pressure in the engine compartment due to the alternator blow through system and the lack of a perfect seal at the fan itself.. But..some of it....in a time metered manner...soaks into the intake runners and slowly gets sucked through the engine. Since the heat leaching from the intake runners never adds more than a couple degrees to the intake charge zipping through it...its negligable. Most of the heat actually radiates into the sheet metal and gets carried away by the cooling air that is being pushed around underneath it. The sheet metal being black also aids in radiated heat goingto those parts the most efficiently. All of this together is why ...though it gets damn hot under the hood......it does not get damn, damn, damn hot!
Thats still an awful lot of heat. Most of the cooler times of the year....it would probably not be a big deal to draw warmed air from the enegine compartment. But in the summer...especially around here......you get street level ambient air temps in the 100+F range. Any heat you pick up going through the enginecompartment is ugly. It shows up in the ambient air temp sensor and your fuel milage....as well as head temps. Ray

[Lars S]

My opinion is that running without ducting could possibly be be harmful in an extremely hot climate, the bus/vans are the evindence for that.
This is if the seal surrounding the engine is in perfect condition, any leaks, especially in the rear above the muffler could give free way for hot air to be sucked in to the fan. Even the black sheet metal joints has to be tight. I found that the sheet metal joint under the pulley (above the muffler) was factory sealed with some type of glue on my 412.
Another reason for running ducted and keeping the seals in good condition is that the engine compartment stays clean of dust since rather little air passes through.
/Lars

[Wally]

Since I run twin IDF40's on my otherwise stock 1,8S engine, I needed to remove the engine tin around the bell-housing for some neccesary fresh air for the carbs. I also haven't renewed the engine sealing strip for a good two years now.. It does use the original ducting for ccooling air tho.
Nevertheless, the engine runs with about the same operating temps as before it seems.
Totally original engine otherwise and ran 40.000km since it stood still for 7 years and it runs on propane (LPG) on a daily basis. And yes, we have 32 degree C outside temperature here as well. More and more so with the planet warming up...
Sealing it up like orignal seems best indeed, but I haven't seen much difference so far I must admit.

[raygreenwood]

Wally 32C is only 89 F. No big deal. We are at 95 F (95% RH) in dallas today (about 35C)...and its actually still cool here. 89 F should not be a big deal.

But, if you have cut a forward side inlet into the engine compartment(unheated by exhaust)...and have your seals off, you would have a very cool compartment and probably negate the need for the actual foam seal as your fabricated forward duct would probably pump air through from the front and out the missing seal area. You now have plenty of cool air for your carbs. Also having your original hood ducting/bellow in place......gets rid of "most" potential issues as your cooling system then draws air from above.

In my climate...your engine compartment would be filthy in a week. Also...as noted this problem is different in different areas in in different driving conditions. In Dallas by August.....and this goes for most of the southern.western and southwestern states......the ambient air temp will be 100-105 F average or worse (37.7 C to 40 C). The air temps above the black top and concrete streets ....I have personnally measured in Dallas...range to 150F+. The air temp right above the streets sitting in traffic is commonly 115 to 125F. Any air coming up through missing seals by the exhaust is even hotter.

Whenever I drove in the summer in Oklahoma city, Dallas or Atlanta...without a proper seal...which has happened before as they used to be hard to get......everything inside of the engine compartment was very hot...well over 225 F. Burn yourself on any piece of metal you touch. It put a lot of radiated heat into the cooling manifold. It made a noticable difference in oil and engine temp.
When it gets over a certain temp and the metal around your engine starts banking heat....you cannot get rid of the heat if hot air is circulating over it. Of course a missing seal is one thing. Leave out that rear piece of sheet metal...and it gets ungodly hot in the engine compartment.

Also...running without outside intake air for the TB...essentially turns the inlet through the alternator into a much higher volume intake. That much circulating cool air would do a great job of taking radiated heat out of the engine compartment.....into the engine though.

But still......the most essential seal/trunking of all on a 411/412 is the bellows feeding the cooling manifold. VW went to a lot of trouble to make sure that the TB had a feeder pipe from this cool inlet air on all type 4 models. Having seen how much radiated heat is inside of the engine compartment on a hot day in dallas.....why would I leave the TB trunking off to suck all of that through the engine? Ray

[Steve Arndt]

40C here, and look at all the precip.
http://www.weather.com/outlook/health/a ... _topnav_aq

[Lars S]

Looking back at the different designs:

Type1: Sealed engine compartment, no ducting.
Type2: Sealed engine compartment, no ducting (even with Type4 engine).
Type3: Not sealed engine compartment but ducting.
Type4: Sealed engine compartment AND ducting.
The Porsches from that time all have the Type1 design(?)

No model had no sealing and no ducting, probably because of overheating risk.
Type4 combined the both methods (seal and duct) wich ment wider margin for overheating, and/or it could be used for to reduce the air flow=fan size=power loss.
Does all Type4 engines (1,7, 1,8 and 2,0) have the same size fan or does it, as the cooling fins on the cylinder heads, grow with bigger displacement?

/Lars

[raygreenwood]

Lars...interesting correlation. In my experience(s)....it also seems that 411 and 412's seemed to have the lowest rate of horribly overheated engines and dropped valves....as compared to 914's and busses. Ray

[wildthings]

Looking back at the different designs:

Type1: Sealed engine compartment, no ducting.
Type2: Sealed engine compartment, no ducting (even with Type4 engine).
Type3: Not sealed engine compartment but ducting.
Type4: Sealed engine compartment AND ducting.
The Porsches from that time all have the Type1 design(?)Lars

I find it interesting that the 411/412's preceded the T4 powered vans by several years and yet had an "improved" cooling system. You would think that if ducting was measurably better then VW would have used it on the vans as well, surely VW made a prototype van with ducting. Would have been pretty easy and cheap to design it in I would think, and would have prevented a lot of engine failures due to bad foam engine compartment gaskets over the years. Note: VW didn't use any ducting on the Vanagons either so they must have been pretty satisfied with not having used it.

I have wondered what would happen if you at least installed the lower boot of the T4 ducting onto a van fan shroud. Would this tend to channel more and maybe slightly cooler air into the fan? or would it just be one more thing in the way.

[Lars S]

Yes, I admit, it's a bit strange that VW did not use ducting on the Type4 engined bus/vans but they did on the 411/412's.
One thing that differs the Bus from the other VW's with Type4 engine are the air intakes, shaped like "scoops" and heading forward making a lot of air stream through the engine compartment (just like raygreenwood suggested earlier).

I guess that fitting the lower boot would make the air colder (especially if your sealing is bad) but also reducing the airflow a bit since the part is angeled, so telling if the engine runs cooler or not is hard.

/Lars

[raygreenwood]

Its worth it to remember....that the type 4 cars and engine came into being in 1968. That means they were probably working on them by late 1966. At this point, the van was not their major seller. In fact....if I remember my history correctly, the van was an "accident". Its creation was the offshoot of a factory floor parts transporter that was simply a ladder chassis with a drivers seat and a type 1 engine.
My bet is that since the buses were doing OK with the type 1 engine...and they were not the major sales maker.....the type 4 engine was not even being targeted at the bus.
The type 4 car was mainly being targeted at the US and other luxury oriented markets. Markets that were flooded with power hungrry drivers who needed a better engine.

VW actually did make changes to the ducting on the type 1 versus type 4 vans. In the earlier type 1 vans...the grating at the rear for intake was flat to the sides. Pretty useless. Later right before changing to a type 4 engine, the grates became higher and more 3-D...standing off the body into the windstream.

The problem I have found....with the bus air intakes....is much the same (in theory) as Jake found with the cooling air in the type 4 as it enters the sheet metal on the engine. It needs something to direct it. Yes...the engine fan is sucking a lot of air....but the air coming in the intakes up high must change direction twice...and just gets lost and undirected inside the engine compartment. I would bet that a big "Y" at the fan mount and a pair of 8" ducts going straight to the grates would make a huge difference.

I always remind people that the type 4 enegine...is just that. It was built for and came in....type 4 vehicles starting in 1968. A lot of design work went into the whole car. It is not a bus engine or a 914 engine. It only later....was "improvised" into those vehicles. Ray

[Lars S]

Yes, the Bus (second generation) was not designed for the Type4 engine, the engine compartment was made bigger just before the introduction of the Type4 engine. Still it is a wery compact installation, from the rear end of the pulley to the inside of the body it is only about 5" wich is less then on the 411.

Just saw a picture of a Type2 "truck" it has no "scoope" at the air intakes, but the intake grills are bigger probably to do the same effect as the scoopes.


/Lars

[raygreenwood]

Lars.....I have a friend sitting across the table from me who spent time in Finland and Sweden. He wants to know how the drive along the coast is toward Stockholm from where you are. He said he may be coming back to spend some recreation time at some point. Says the map makes it look like a lovely drive in the right season. Ray