cylinder jug air deflectors-use or not?

[caracal76]

The air temps are getting up there this summer and so are my temps-close to 250 oil temp on a 97-deg sunny day in Nashville. I just sent my heads off and, looking at the bare jugs, wondered why the air-deflecting tins that clip under the jugs aren't there. I then looked at my spare (from a different builder) and it has them. So is this a some do-some don't thing? Is there any drawback to using them? The only thing I can think of is more drag created by forcing the air between the cooling fins, but if that in turn keeps my temps down, won't I see better HP from the engine? Who does and doesn't use them and why?

[hardingfv32-1]

I vote for the use of deflectors IF you supply all of your cooling air from above. As has been the case in every instance, the VW engineers knew what they were doing. The goal is even expansion, perfect cylinder roundness and, the main goal, good ring sealing.

Brian

[Dietmar]

From what I understand, the purpose of the deflectors is to force the air around the bottom of the cylinders, and as Brian has stated- the engineers knew what they were doing.
I have seen "bluing" around cylinders that do not have the deflectors installed.

I use them in all my engines.
Dietmar

[Veefan]

I do not use the deflectors, the main cooling is from the bottom, and the top duct forces warm air out of the engine cover.

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[RacerGeek]

John,

Even with the bottom cooling duct, Ed Womer has said he would like to experiment with a deflector at the top of the cylinders to improve the cooling. While we used it as a First with no cooling issues, our races were run in early April, October and November, so with higher ambient temps we might have had issues. Of course, with the dual port head I didn't use the top duct like you do, but some type of deflector would still even out the air flow over the cylinders.

[Veefan]

I spoke to Ed and Dave, pulled them from the bottom and was going to put them on top if I had a problem. I ran at Limerock, 80 degrees out, oil my temps were really low almost too low 170's. Thats even with a smaller oil cooler installed. Not sure how even the air is flowing, but its running cool.

If I put them on top, better flow & higher temps?

[hardingfv32-1]

You do not push air out from the cooling fins, it is drawn out with a low pressure source. Unless you have some kind of venturi in that top duct, all you are doing is pressurizing the top of the engine. One of the two ducts needs to be turned around. Now sure the engine is stay alive, BUT could it be better? The ducts also have to be sealed well. This all takes a lot of work IF you want to get it right.

Brian

[Veefan]

It's hard to see in the pictures, but the top duct is not typical. It's open in the front and back, so the air travels straight across the top of the cylinders. The bottom duct is sealed well, and is basically the same as most vees.

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[RacerGeek]

I spoke to Ed and Dave,...

If I put them on top, better flow & higher temps?

John,

There isn't anything I can add that's better advice than you got from Ed and Dave. I do agree that Ed does a very good job at sealing the duct work. As I noted before, the black body looks great in person, but it's really difficult to show its details in photos.

[remmers]

Correct me if I'm wrong, but doesn't all air have to make a "right angle" inside the bodywork? I know the interpretation usually means obstructed line of sight through to where it's going, but that does look as though it's straight through. Does that rule only apply to within the minimum frontal area dimensions?

[hardingfv32-1]

With air entering the TOP at the front, what is the incentive for the air flow to go UP through the fins? At best you have zero pressure at the top of the cylinders when you need a negative pressure zone to help pull the air out the top of the cylinders.

I would say "right angle" air flow inside the body is legal. The rule only applies to the specified min frontal area.

Brian

[remmers]

Ah. Thank you for the clarification.

[cendiv37]

A close look at 9.1.1.C.9.L and 9.1.1.C.12 indicates that the intake manifold defines the "profile" area in this region. Thus any air ducted from inside the "profile" of the manifold is required to make a 90 degree turn (somewhere before it exits). Air ducted from outside the manifold (and head/fan shroud) profile can go straight through.

Hmmmmm

[Veefan]

GCR 9.1.1.C.9.L "Forward facing air ducts may be installed for the purpose of delivering cool air directly to the engine, cylinder heads oil cooler and/or carburetor." If these ducts are within the profile area defined in section c.12, then the ducted air must make a 90 degree bend within the body work. "

No part of the body/duct is within the " profile area" again, hard to see in the pictures, it's not enclosed.

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off on a tangent...

caracal76... I think we agree on one thing... use the cylinder jug air deflectors! It's best to install them when you're putting the engine together. They can be installed and removed later with the engine built... but it's not fun...

[FV80]

A close look at 9.1.1.C.9.L and 9.1.1.C.12 indicates that the intake manifold defines the "profile" area in this region. Thus any air ducted from inside the "profile" of the manifold is required to make a 90 degree turn (somewhere before it exits). Air ducted from outside the manifold (and head/fan shroud) profile can go straight through.

Hmmmmm

Nope - anything within the fan shroud area (that INCLUDES any part of the manifold area) MUST turn 90 degrees.
Steve

[remmers]

How would that 90* bend be checked though? I know a lot of people that NACA duct air in for their oil coolers and it makes more of a 45* bend, then a -45* bend to get to the cooler, then straight out the back of the car. Is that okay because there's no straight path for the air to go through?

[caracal76]

Thanks for the opinions-I'm going to look for a set of deflectors.

On the ducting: seems to me that the bodywork above the heads is just that-bodywork. Its purpose, while giving the air a place to exit, isn't functioning as a "duct". The duct is underneath and does bend 90 deg.

As to the two 45 deg bends equaling 90: yes, it adds up to 90, but the rule is "A(Meaning one) 90 degree turn, right?

[brian]

the one thing I have learned after nearly 50 years of working on VWs is that the Germans did not do anything without a purpose, and usually a well tested purpose. These engines are designed to receive air from the top and flow out the bottom. The deflectors are designed to force the air across the bottoms of the cylinders to aid their cooling. I would never run a motor without deflectors.

Generally speaking, engines that run hot are suffering from a lack of air flow. Monster oil coolers only mask the problem. There are tons of studies that show that cylinder head temperatures over 350f will cost horsepower. Air derived from the lower parts of our cars is very dirty and subject to turbulence and separation from the ductwork. The higher you receive cooling air the more effective it will be. Air will travel the path of least resistance. Making a lot of turns, changes in duct cross section; traveling inside long ducts and sloppy fitting duct work will reduce flow. Another problem with many cars is that the front exhaust pipe travels too close to the heads and pushrod tubes. This turns the pipe into a heat exchanger, certainly something we don't need. An aluminum plate between the pipe and engine can help if your pipe is too close. Just don't make it so large that it blocks the air flow out of the cylinders.

As to the GCR and ducts, anytime you can look inside a body and see out the back of the car, you're asking for trouble.