New Experiment for Engine Compartment Seals on VS Cars

This material appears to be pipe insulation. It will burn where near the J-tubes.

@Jim Gilbert - Madison, Mississippi posted:

This material appears to be pipe insulation. It will burn where near the J-tubes.

I don’t mean to sound nasty but I tried to be as clear and thorough as possible in my post.  I suggest you read through it; and no, this seal will not come in contact with the J tubes.

Did say in contact? I said NEAR. The stuff melts and burns.

Your car

Thanks for clarifying but it seems you did not read my detailed post. This is a VW Bus H seal, not pipe insulation.

I do not think either of you should come to Carlyle.  We don't need any fights on the dance floor!  How to you winky-wink on this platform?

Marshall

@Marshall posted:

I do not think either of you should come to Carlyle.  We don't need any fights on the dance floor!  How to you winky-wink on this platform?

Marshall

No one is fighting; I am just pointing something out. I believe in order to contribute with an input it is of utmost importance to first understand thoroughly the original post. That is all.

@Marshall posted:

I do not think either of you should come to Carlyle.  We don't need any fights on the dance floor!  How to you winky-wink on this platform?

Marshall

I think they live a lot closer to reach other as it is. @Impala aren't you in NOLA?

@DannyP posted:

I think they live a lot closer to reach other as it is. @Impala aren't you in NOLA?

I was until 2017; now I’m in the Miami/Ft Lauderdale area.

i made a template where the H foam gasket sits and took it to a metal fabricator and am having a piece of aluminum sheet cut to size and mount to the body and overlap the tins without out fastening to the tins leaving a small gap. Any thoughts as to how it will work in relation to cooling.

@Phisaac posted:

i made a template where the H foam gasket sits and took it to a metal fabricator and am having a piece of aluminum sheet cut to size and mount to the body and overlap the tins without out fastening to the tins leaving a small gap. Any thoughts as to how it will work in relation to cooling.

My feeling is that you want something flexible that will seal the gap as airtight as possible. I am thinking that maybe you could add some sort of a seal/gasket to those aluminum pieces so that you can achieve the airtightness. Otherwise you run the risk of hot air being recirculated into your engine compartment.

The H-seal has been the "SOC approved" way to seal the engine an surround tin for years-- but as @Jim Gilbert - Madison, Mississippi points out, it's really just a "pipe-insulation" type of foam. As @Impala noted in his first post, it doesn't last very long before it becomes crumbly from the heat. It isn't the heat in the engine compartment that is the issue, it's the heat from the exhaust (not the j-tubes , as noted- but from the number 2 and 4 cylinder pipes, and from the header collector).

There needn't be a fight here, because you are both right. That H-seal is convenient and does an OK job (until it doesn't), but it certainly isn't the final solution. I'm personally not a fan of how it looks, either (it's bunchy and thick where it needn't be).

I got tired of changing mine all the time, and got a roll of 1/2 thick felt weatherstripping. I glue this to the engine tin. Then i remade all of the surround tin (in 3 pieces), following the radius of the engine tin, but held way from it by apx 1/2". I then adding a lip pointing down in a manner similar to what is on the engine tin (this requires welding or some crazy-skilled metal work on the curved piece at the back). It creates a nice, tight seal, without using a heat-sensitive material.

Exactly; I’ve seen some different solutions used by different folks. In my case I feel that the H seal fits nice and is fairly trouble free to replace and I don’t feel like getting into fabrication, etc since I don’t really have the skills. That’s the reason of this experiment; to see if by coating the whole thing with Flex Seal, (thus rubberizing it), I can extend its life and for how long.

Thank you, I will work on that once I have pieces back.

Never have really understood why an airtight compartment is best. With Cool air drawn in by the vents and fan. You would think it needs a place to exit freely to keep a good flow of cool air?

I believe it is drawn through the fan and exits below the tins and cools the underside of the motor as it exits out the back openings? A carefully thought out and executed system.

Marshall

@Phisaac posted:

Thank you, I will work on that once I have pieces back.

Never have really understood why an airtight compartment is best. With Cool air drawn in by the vents and fan. You would think it needs a place to exit freely to keep a good flow of cool air?

As Marshall said above the theory is that the motor sucks up cool fresh air from above into the engine compartment which then gets blown through the fan housing into the heads and cylinders and gets expelled as hot air at the bottom of the engine compartment and back of the car. If the engine compartment is not sealed up hot air from the bottom can get recirculated back to the engine, effectively overheating it.

Clean air is introduced the the engine by the the fan intake, the air then passes over the heads and directed to each cylinder via the lower cylinder deflector tins then ejected via the sled tins.  What I do on the speedsters is to utilize the 8" opening in the firewall as the clean air intake and affix a screen to the fan shroud intake to keep road debris from being ingested into the fan and becoming lodged ion the cylinder head. I also leave a 1" gap at the base of the engine firewall ( L to R) as this allows a lot of cool air into the engine bay which then exits the deck lid grill. The engine bus seal gets installed with the coated surface of the foam facing down. The area directly above the exhaust must be sealed to keep the exhaust heated air from being sucked back into the engine cooling .On speedsters with larger cc engines I also cut two holes on the Left and Right of the engine bay (below the carbs) and also screen them for additional clean air. Works for me , your mileage may vary ~

All

Thank you for the explanations.

Paul

The air cooling system is not simple.  Being surrounded by lots of air we can't see doesn't help us understand it.  It helps if we think of air as a very thin (extremely low viscosity, low density) liquid, because that's exactly how it behaves.  

We need A LOT more volume to cool an engine with air than water.  Air is has much less mass to absorb heat, so an air cooled system is sensitive to issues that negatively impact the supply of cool air or its distribution.  This results in one very important engineering principle: When using air to cool an engine, only use the air once.

Because of this principle, the VW/Porsche system is designed like this:

1 - A fan is run off the crankshaft and to provide airflow for cooling.  The fan is run at very high speed to provide high volume and to pressurize the air.  At 3400 rpm a stock VW fan in a doghouse fan shroud will supply about 1700 cfm @5psi.  That's a lot of air and the pressure is an important part of the system's ability to get the air onto the hot parts and then carry the heat away from them.  (Our water cooled systems run at pressure, too, partly for the same reason.)

2 - The fan is above the engine so the flow is from the top down, or from inside the engine compartment to outside the engine compartment.  This flow direction has nothing to do with the top or bottom requiring more cooling, it's just a real estate thing.

3 - The fan moves LOTS of air to get the job done, so the air pressure in the engine compartment is lower than outside the engine compartment.  Fresh cool air will be continually supplied to the engine compartment for the fan if we manage the flow properly.

4 - The seal between the tins and the engine compartment prevents air that has already been used to cool the engine from being sucked into the engine compartment and passed over the engine a second time.  This is critical to our prime engineering principle of only use the air once.

5 - The tins, and seals help complete the management of the airflow.  Without them the used, unmanaged hot air will recycle though the system.  This is a little like bypassing the radiator in a water cooled car.  Eventually the recycled hot water can't absorb any more heat from the engine.  An air-cooled engine without a complete flow management system will recycle heated air until the engine fails.

There are lots of other very complicated things going on that we could get into, like maintaining the air pressure gradient across the system (ask our HVAC expert @Stan Galat about that), the effect from the oiling system, and more.  But I hope this gets at the heart of air cooling and helps explain why us old codgers with lots of air-cooled miles get all persnickety when a discussion of tins and seals comes up.  (It also partially explains why I went Suby this time )

Thank you for that great explanation

Paul ISAAC

Michael; that is a beautiful and clear explanation. Thank you.

What an elegant explanation, @JMM (Michael)!

The pressure and volume of air is hard to wrap our heads around, it may help if we think of it like this: The furnace blower in a modestly sized home moves about 1200 cfm of air at a 1" water column static pressure. 1" of water column is equal to .036 psi. That's enough to push air everyplace in your house, and enough that you can feel the air moving across the room when the blower is on.

A fan curve is not linear (performance drops in a dramatic and non-linear manner as static pressure increases)-- but if that VW fan is operating at 5 psi of pressure (and I'd like to confirm that), that's about 140x the pressure of your home's furnace, and 500 cfm more air volume as well.

That's 140x the pressure and 1.4x the volume - that is a freakishly powerful fan cooling your engine. It's powerful enough to overcome the low pressure area behind the car, and powerful enough to blow into the high-pressure area under the car. It's powerful enough to go into all the nooks and crannies of your heads and cylinders and carry a truck-load of heat away.

The marvel isn't that it doesn't work better- the marvel is that it works at all. That it works well enough to support 200 hp of ragin' lawn-mower power is nearly miraculous, and one of the reasons I love the air-cooled oddity of these engines so much more than I should.

I don't remember an EXACT source, but I think I read about the fan on thesamba.com:

The VW fan consumes 8hp(or it may be 12) at 5000(engine) rpm.

EDIT: I poked around a bit. I saw 15hp at 6500, I also saw 5-10hp. The average though is 10hp at 5000rpm engine speed, plus 1 for the alt/gen. I had forgot to think about the power consumed by the electrical load also.

I'm guessing the 30 amp generator draws the 1 hp, and a 55 amp draws more at full load. END EDIT.

The 911 fan consumes 20hp(source: Jake Raby), which makes sense to me for two extra cylinders.

8hp may not seem like much, but it's enough power to run my wife's roto-tiller or my snowblower. My zero-turn is 23hp(and aircooled at that!).

Just thought you guys would like this info.

@Stan Galat posted:

What an elegant explanation, @JMM (Michael)!

...

A fan curve is not linear (performance drops in a dramatic and non-linear manner as static pressure increases)-- but if that VW fan is operating at 5 psi of pressure (and I'd like to confirm that), that's about 140x the pressure of your home's furnace, and 500 cfm more air volume as well.

Thanks, Stan. Long ago I did some technical writing for money.  If I pay attention I can still approximate fluency.

I saw flow figures from 1500 to 1900 cfm repeated on enough forums (shoptalkforums, samba, etc.) that I figured splitting the difference was accurate enough.  It also seemed to jive with figures of 8+ hp being used to drive the fan.  The 5psi number was so consistent on various sources that it's either true or a lie so well an entrenched that it probably has a placebo effect on the cooling.

Our air cooling is truly a marvel of 1930's engineering and I love it. But...

As much as our engines are air cooled, they are oil cooled. There's a lot of discussion in the dune buggy forums about what engine tin they need. Since there's usually not much of an engine compartment, no one/hardly anyone worries about the perimeter tins. Almost everyone say the rest of the tins are desirable.

So, I suspect that perimeter tins are helpful for our enclosed engines, but they're probably not as important as the rest of the tins AND the effectiveness of the oil cooling system. You can measure the oil and head temperatures to see how your particular engine is doing with your setup. I don't want to see my oil temperatures going over the thermostat setting. I over design the oil cooling and keep track of the air cooling. Your mileage may vary.

The Spyder guys are caught in the middle between Speedsters(tiny sealed compartment) and dune buggies(wide open). I totally agree with JMM Michael about using the air to cool ONCE though. We are wide-open but covered with a clamshell. Unless you're Ed, with a complete and functional undertray.

My home-made sled tins directing hot, used air rearwards while intaking cool air from the firewall with my 911 fan seems to work just fine. Sled tins on a Speedster are not a bad idea, keeps the air moving AWAY from the motor.

I also agree with Mike Pickett about making sure you've got enough oil cooling. Keeping the oil temperature controlled and non-aerated is key to engine longevity. But not too cool, there is a Goldilocks zone. The oil MUST warm to the point of burning off water and impurities. Too cold is just as bad as too hot.

I did some more poking around, and found this interesting:

https://www.pelonistechnologie...vs.-centrifugal-fans

The VW squirrel cage, or centrifugal fan, is high pressure, but low volume. The high pressure ensures that the air is directed everywhere, i.e. no hot spots. They won't stall the engine if airflow is interrupted, like when the flaps are closed. They do consume more power to turn them than an axial fan.

The axial fan(911) works on low pressure but high volume. I believe that this is why it doesn't work well unless ducted properly on a 4 cylinder instead of a 6. The only advantage is that it consumes less power to turn it compared to the centrifugal fan.

Cheers.

The 8hp needed to run a VW fan (regardless of the hp produced by the engine) is especially noticeable if you throw a fan belt on a 40-ish hp dune buggy under a hard pull ("hard" being relative, here - No VW under 65hp pulled very hard).  

INSTANTLY it seems like you almost double the HP while the noise drops by 1/3.  It's enough to make you instantly think, WTF just happened?

Don't ask me how I know, but I stopped within seconds to see what the hell just happened.....

@DannyP posted:

My home-made sled tins directing hot, used air rearwards while intaking cool air from the firewall with my 911 fan seems to work just fine. Sled tins on a Speedster are not a bad idea, keeps the air moving AWAY from the motor.

Keeping the oil temperature controlled and non-aerated is key to engine longevity. But not too cool, there is a Goldilocks zone. The oil MUST warm to the point of burning off water and impurities. Too cold is just as bad as too hot.

I totally agree. While I debate the relative contribution of the perimeter tins, I have sled tins under my cylinders.

As some of you know, I also did the Hoover mods on the oiling system to move as much oil around the internals as possible. I run a 180F oil thermostat on the oil cooler in the driver's side wheel well (thanks, @Gordon Nichols). With the sleds and the cooler I try to keep as much engine heat outside of the compartment as possible.

@DannyP, I chose the 180F oil thermostat because it was easily available. I can't remember what temperature thermostat I was running on the old 911 (except I remember thinking that it was really expensive...).

What do you think about keeping the oil at 180F? Hot enough? Also thanks for the link on axial vs centrifugal fans. Nice explanation.

I think 180 degrees is fine for Hawaii, Mike.

I tried to do the Hoover oil mod with the 12" drill on the motor I'm building, but there isn't enough material on the inside of the case. It has Berg 1.45 lifters which have grooved washers/shims to let oil spray in the valve covers. The only Hoover thing I can do is groove the lifters between the two circumferential grooves already there.

I found a 190 degree Derale (I think on etrailer.com or something like that). With the 911 fan overcooling the cylinders I wanted to make sure my oil got hot enough. It seems to work.

Thread drift alert.

I spent some time about 15 years ago studying fluid dynamics when thinking about building my own (legally) silencer for .22 long rifle.

I was contemplating a stainless steel monolithic baffle stack inside a threaded aluminum tube.  The idea was a one-pice baffle stack that is removable from the tube to simplify periodic cleaning of carbon fouling.  The baffle stack would be a series of millings through a solid billet of stainless steel round stock.  The best silencer designs use fluid dynamics to 1) allow the gasses to expand inside the tube rather than outside the muzzle, and 2) to divert gas flows to be used against itself, further slowing them to subsonic speeds before exiting through the muzzle.

Robert Silvers and Kevin Brittingham of AAC beat me to it.

I should have patented the idea of a monolithic core while I was thinking about it.

I remember the guy who said that we should put 20oz  bottles of water in vending machines back in the late 60's.

Re 5 psi: One time I left my spare tire strap unbuckled before starting the engine. The fan sucked the brass buckle in immediately, from a foot-plus away, up and over the "seat" the spare would be resting on.

Sounded like one of those 30mm gatling guns they put in the nose of A-10s.

That little squirrel cage fan is no joke.