additional engine cooling at firewall

You're asking some good questions; I don't know what the inside of a 356's engine compartment looks like (or in the pushrod cars if there's any more air intake than the grille, or if there's a difference in the 4cam cars, other than the louvers in the lid), but I do know that to keep an aircooled motor alive it needs air, and lots of it. Carl's discovery of the large amount of air leaving through the grille, and holes in the engine compartment sides dropping oil temps at highway speeds is important. With the shape of these cars, it's easy (just like in a beetle) to have enough negative pressure in the engine compartment (at highway speeds) that the fan, which is designed for high volume (and doesn't develop a lot of pressure) is literally being robbed of air. A cht gauge will tell you if the "heat management" is under control. 

Gordon- Do you have a cht gauge? It will tell you definitively what's going on...

Yeah, I know that, but I'm just to cheap and lazy to put one in.  If I've been on a turnpike for a while in moderate 70° temps and stop to check the dipstick I can put my hand on the fan shroud for a few seconds before I have to let go and I've always figured that if the heads were really hot then the rest of the engine would be really hot, too.  You don't want to touch anything near the dipstick, but the shroud is OK for a short test.

Plus, the engineer in me compels me to have as much cooling input air as I can muster directly into the cooling fan inlet.  I've also trimmed the underside of the engine cover to get a bit more open area there, too - not much, but I figure it helps.

Besides, if I had CHT readouts I would start to feeling like Jack Crosby flying his plane...

Interestingly enough, my head temps have always been in the 300 to 325 F degree range, even when my oil temps hit 240 F.

When Henry, at Intermeccanica, rebuilt the car for me (including a new rear clip) we discussed installing a deck lid with extra louvers.  Henry didn't recommend it, saying that the extra louvers didn't improve the cooling.  He said they were more for looks.

I am not convinced that deck lid louvers were made to let hot engine air out.  The fan is designed to pull air in, and the carbs need air.  If propping open the deck lid makes the engine run cooler (and more efficiently), then it would seem that the engine is starving for air, at least under certain conditions.

One of the problems I see is that the deck lid configuration used by VS and other makers is taken from the 57 model, which has a solid "engine protector" or inner skin that cancels out almost all of the square footage of the grill opening in the outer skin.  On deck lids without louvers, the only opening in the deck lid is the oval or rectangular vent holes at the bottom or rear of the deck lid.

The engineering challenge would seem to include increasing the air passages through the interior and exterior skins or panels of the deck lid while maintaining a dry environment for the engine.  At a minimum, most of the rain would need to be diverted away from the engine.

Propping open the deck lid accomplishes the above, but not in a very elegant way.  In my opinion, it's letting more air in to the engine, not letting more air out.  This equates to more cool air for the fan and the carbs.  Later deck lids changed the configuartion of air openings dramatically.  The inside of the deck lid on the Super 90 GT looks like something from a more modern 993/996, with greatly enlarged openings and cowls to separate fan air from carb air.  If anyone else has the Johnson "Restorer's Guide . . .", look on page 42 for a comparison of the inside of deck lids.

A few years ago I put a new roof on my house, and with the type of roof I was putting on, I needed venting at the peaks of the house. I found these round aluminum louvered vents so all I needed to do was cut a 4" hole with a hole saw and these things popped right in . They have screens built right in to keep the bees and hornets out, and the louvers keep the rain out . A little silicone and it seals right up. I used a 2" one in the bulkhead behind the seats as a heat vent into the car. 

I'm thinking 2 of these side by side in the fire wall might do the trick. You can paint them any color you like and turn the louvers in any direction you want. I guess you could even make some kind of scoop on the other side to direct more air.

Yep, it's madness

I also have the port holes in the wheel wells to get at #1 & #3 plugs, but I think there might be more crap flying around in the wheel wells , and they might be too close to the hot parts, heater boxes and stuff. 

Jim- I agree with you; if the engine lid louvers were put there specifically to let hot air out then there would have to be a dedicated air intake from another source (you would think..). And you're right, when popping the lid makes the engine run cooler, it's definitely starving for air. This (for most cars) isn't an issue when toodling around town (different engine and vehicle speeds and never really going that fast for a sustained period) but is more prevalent at faster highway speeds; as the rpm's climb, the carbs and fan simply demand more air. Combine this with the physics of the air travelling at said speeds, trying to turn the corner (on the grille) and enter the engine compartment (the faster you go the more difficult it is, and the progression isn't linear; those of you more edjumacated than I will know the formula) and at some combination of road and engine speed (usually somewhere above 3,000rpm, depending on the heat of the day) it becomes incapable of cooing itself properly. You can see why another source (or 2) of air intake is so beneficial.

 Are you talking about an engine lid that looks like this? And thanks for the compliment earlier, btw. I'm really not that smart, but I do pay attention, and sooner or later it sinks in, sometimes just by osmosis.... Al

"I also have the port holes in the wheel wells to get at #1 & #3 plugs, but I think there might be more crap flying around in the wheel wells , and they might be too close to the hot parts, heater boxes and stuff."

Al- K&N has all sorts of flat panel filters (round and rectangular) that I think would work to keep road debris out of the engine compartment. You might have to resize the holes a little bigger to find something to fit. IIrc, there's even some flat round units big enough (6 or 7") to use on the firewall if this is a problem.   

Al, my Spyder is the exact opposite. Runs cool no matter the outside temp or load as long as I'm doing 30-40 or better. In traffic, hot 90 plus days, hot air from the cylinders bounces off the road and gets recirculated into the fan intake, not a good situation. Of course, you don't really know what is going on unless you have a CHT and oil temp gauge(I have both). As long as I'm underway, plenty of fresh air gets to the fan. The underside of the Spyder is wide open, no easy way to separate or isolate the fan intake. I will figure something out, probably involving some ductwork, but isolating top and bottom of the engine isn't real practical in a Spyder.

I added louvers:

And a hood prop. And 3" ducting from the front of the car to the firewall with a bilge blower. I have my fan-cooled external oil cooler. I have a CHT gauge as well as a calibrated oil temp gauge. My 2110 w/40 IDFs (34 chokes, 57 idles, 157 mains, 200 airs), 40 X 35 valves, 1-5/8" sidewinder, 6AL MSD box...

Although my head temps rarely exceed 300, my oil temps will find their way up to 230 in hot weather under load. In mild climates, around 200-210. My problem with funneling additional air is where I live: gravel/dirt roads in the rural foothills. I'm debating on adding the wheel well portholes like Carl has (with air filters, of course), or running air induction, like Danny's setup except I'd duct it to the front of the car. I know I need more air but it might be at the expense of a very untidy engine bay.

It looks to me like the inner lining on the engine compartment lid is to catch rain water and drain it off away from, mainly, the carbs.  The louvers shown in the post above might be ok in an area where it seldom rains, but elsewhere in the country, not so much.

I wonder if just simply lowering the liner to increase the gap would help?

You might run into engine clearance issues.

Terry- have a look at something like this- http://www.knfilters.com/search/product.aspx?prod=33-2238&pkid=867177&rw=1

After reading these posts, one question that comes to my feeble mind is how many square inches of intake opening is required to feed the cubic feet of air into the engine to let the carbs breathe and the cooling fan do it's job. Notes that I have saved from various sources are. Webber 44's 292.3 cfm Webber 40's 212.8 cmf per venturi. The cooling fan draws 1260cfm (not sure if small fan or doghouse larger fan). So total cfm needed would be some where around 2111 to 2429 cfm.

Al or others correct my numbers if you have better data than what I have.

Bill

It rains where I live. No water gets in through the louvers or anywhere else in the engine bay.

The cockpit is a different story...

Al, I'll take a look.

Reliable sources, such as aircooled.net, Gene Berg, etc. state that the doghouse wider fan will produce 1500 cfm.  It's interesting to note that the later bugs increased air inlets to the engine.  69 had a solid engine lid, 70-71 had 2 slots under the rear window, while 72 on had 4 sets of slots, and later vert deck lids had louvers.  Berg even suggested propping open the deck lid if you couldn't find a vert lid.  In every instance I have seen, air comes in above and exits below.  The VW guys who use stand off hinge plates swear by the decrease in engine temp.  Of course, you create a funnel for rain to enter the engine bay.  It shouldn't be hard to do a thorough test.  On a warm day, run the car until heat sink occurs, measuring oil temp and CHT's.  Let the engine cool down, run the same course at the same rpm, measure oil temp and CHT's again.   VW deck lid evolution may be more relevant than 356 deck lids, since hardly anyone is using a 356 engine.

I wonder if the air flow dynamics on a VW stand-off deck lid, at speed, is air entering the bottom (high pressure) and exiting the top (low pressure)?

I've wondered about that, too, since the car is basically wing-shaped (although the bottom of the car is pretty irregular, not smooth like the bottom of a wing). 

Given this, I'd think air flowing over the top of the car would be at a lower pressure than the air underneath it and that would make it harder for the carburetors + fan to draw air through the grill on the decklid than from the bottom of the car.      

BillM- The exact #'s aren't that important; you've got the right idea. These engines need copious amounts of air to survive, and adding more displacement and making them rev higher in the quest for power means they need even more air. I believe your carb flow figures are per carburetor (not each venturi, as a throttle plate would have to be removed), and even that can change as much as 50 or 100 cfm depending on the size of the venturis installed, but again, you've got the right idea; these things need a shitload of air to function properly. Depending on just the air entering the engine compartment through the grille is not enough, and the engine's life will be cut short if the air supply is not adequate.

Jim- I've used engine lid stand-offs on a bug, and they work! The thought (and advertising) at the time was that they let the heat rise and escape, and didn't actually scoop air into the engine, as some people believed. I think they let the intake and cooling systems access the air they needed to do their thing as well. And yes, your air filters better be impervious to water; in California it's not much of a problem, but in Vancouver,well, let's just say they didn't last long on my car...

Carl & Ted- Although there is relatively clean airflow under a Beetle (and a Speedster with a floorpan) at speed, below the top of the back window and down the airflow is a mess, all swirls and vortexes. The Beetle drags a lot of "dirty air" behind it at highway speeds, but there is enough air intake to satisfy a stock motor in all the conditions (and speeds) the car was designed to operate under. Add a bigger, higher revving powerplant (and higher speeds) and now it outstrips the car's air intake capacity and runs hotter at highway speeds. With decklid standoffs, I don't think air moves through the engine compartment as much as it allows air to enter and be consumed by the carbs and fan. 

Some numbers for people to wrap their heads around; the stock Solex 34-3 will use approx. 100cfm at full throttle. A pair of kadrons will draw 250-350cfm (depending on venturis), 40IDF's or DLRA's 500-over600cfm, 44IDF's or 45Del's 600-800, and 48's can consume up to 1100cfm. When you're at full throttle and there's not enough air intake, the carbs are stealing air from the fan (just when the engine needs it most).

Jim- Wildbill did an engine lid open and closed test on the first page. Not exactly super scientific, but the difference was certainly measurable.

After a drive with the lid closed (summer weather) I can't rest my hand on anything in the engine compartment.

After a drive with the lid open 3 inches (summer weather) I can rest my hand on anything in the engine compartment.

Is the extra incoming air cooling the engine parts, or is the 3 inch opening allowing hot air coming off the engine to escape?

Or is it both?

I would imagine with the lid popped open the fan and carbs are receiving cooler air, which is a good thing.

I dug through my library of Porsche 356 books today studying pictures related to the engine air intake grille, and what I will call a baffle beneath it.  What I determined was that, up until the C model, Porsche installed a single grille in the decklid of what appeared to be a similar size.  What DID change, though, was the baffle.  

On the earlier cars,the baffle looked to be not much more than a tray, and it appeared to be only about an inch from the outer surface.  I was unable to determine what sort of openings existed to permit air to flow from the inside of the baffle into the engine compartment proper.

However as time went on and engines increased in size, the baffle changed in shape and in the distance it was spaced beneath the grille.  I presume the openings into the engine compartment increased in size as well.  There is one photo of Prince Bertil of Sweden looking into the engine compartment of an early Carrera coupe (it had beehive tail lights), and the side of the baffle was entirely open - you could see the entire underside of the grille.  Also the bottom of the baffle was formed into a compound curve, where it was higher in the center and curved downwards to each side, and it also curved longitudinally so that it must have been three inches away from the engine lid surface.

There is also a cutaway (literally, as they took a 356 coupe and sawed it right down the center) that also shows the baffle as being curved downwards.

Some photos of cars that were "performance" versions intended for competition had no baffle at all, as the doghouse fan, etc, was visible through the grille.

In all cases, the outer edge of the baffle, where it existed, had a rolled edge so that it formed a "rain gutter" that looked like it would serve to drain incoming water towards the rear of the engine compartment.

Here's a pic that I found with a google search showing the baffle on a Carrera, it's shape, and the size of the opening to the engine compartment.  Perhaps this is what we should strive for?

Considering the "look down" license plate light, I think it's safe to assume that this is an early '57 or earlier speedster.

I think that what goes on here is that, with the engine running and the carbs and the cooling fan drawing air from the sealed-from-below engine compartment, the only place that the air can possibly be coming from is through the grille in the lid.  By consuming and expelling the air inside the compartment, cooler air is necessarily drawn in through the grille and past the baffle.  Essentially the air in the engine compartment gets replaced.  Running with the lid propped open just makes the engine work less to pump the air. 

my head hurts, and my eyelashes itch and I'm sorry I brought this up

^ 

I have to admit that I've never really given much thought to exactly what the air currents across the engine compartment were doing; all I've ever cared about was getting enough air into the engine compartment during fastest highway speeds on the hottest days anticipated. At a constant 3500 or 4,000rpm (if you're that brave) the fan is pretty well maxxed out (I believe that at somewhere between 4,000 and 4500rpm the fan starts to slip and just can't go any faster- this is why a smaller diameter "power pulley is used for situations where significant time will be spent at higher rpm's) and it's the most difficult for the air travelling over the engine lid at said highway speeds to make the turn into the grille and engine compartment through the turbulence above the back of the car.

Tpelle's observation that competition cars had the structural or rain baffle cut out is significant here; the engineers at Porsche realized that at higher rpm's and speeds there simply wasn't enough air coming in through the stock lid, and this is how they dealt with it. 

The object here is to feed enough air into the engine compartment to maintain positive pressure around the engine even under the most trying conditions (I know I'm repeating myself here, but think highway driving on hot days), and I don't think the grille (without cutting up the rain shield or "baffle") can do that. You have to add more air intake for these things to achieve a decently long life. Al

Al, MORE AIR INTAKE is the battle cry?...Then so it shall be!

I'm going to cut the centers out of my access lids to I&3 spark plugs and epoxy in a fine wire mesh to keep kicked up debris out.  

Carl- Look at the K&N filter link I put up for Terry (it's above).It would involve reshaping the holes a little bit. There are all sorts of flat panel filters. Merry Christmas everybody!

I'm thinking that the best thing to do is to take the cooling air supply from the top of the car, not from the bottom where the cooling tin dumps the air after it has absorbed the heat from the hot engine. With all due respect to ALB, I don't think you'd ever see positive pressure inside the engine compartment.  Between the fan and the carbs sucking air out of that space, I bet the engine compartment is always running at a negative pressure.  But the key thing, it seems to me, is not to ask the system to work against too much of a vacuum.

The fish tank hose vacuum test would tell one a lot.

Al, those K&N flat filters would certainly work but the original purpose of my 4"dia. ports was to easily get at 1&3 spark plugs. By unscrewing the lid the plugs are a mere, unobstructed, 3"away and starring me in the face!...But now those ports can also serve as incoming air vents if I cut a 3" hole in the lids and cover with a fine mesh or filtering cloth.

If my memory serves me, Paul Cormie (Mango) rigged a thermostat switch and small diameter bilge pump to push hot air into the cockpit...Why couldn't that be rigged to pump cool outside air through the firewall directly at the fan? 

The object of the exercise it to get enough air to the motor so it lasts; if you can do it through the engine lid grille, great. I don't think you can leave enough of the rain tray intact (so it's still functional)and get the airflow you're looking for. Remember, the bottom engine tin sends the spent cooling air out behind the engine, and we're talking about getting air from in front of it. And you're right; getting enough airflow so the engine compartment has positive pressure may be a bit of a dream, but with enough air intake area the carbs won't be robbing cooling air from the fan, and when you have that you're successful. Yes,the   aquarm hose will tell you a lot..

Carl- Whatever works for you; it was merely a suggestion. And yes, you could rig a pump to send outide air to the fan, but I don't know if you could find one with enough cfm to depend on it alone. Let us know what you find.

Again; Merry Christmas guys! Al

Carl, the max those bilge blowers blow is around 375 cfm, not nearly enough.

I have one on Penny and it offers little help.

Now if you made a larger opening and attached a fan like the one on your remote oil cooler - that would make a difference.

But, I think the holes next to the air filters will be enough. The carbs will suck air from the openings. Perhaps you could use turbo hats and plumb them directly to the side openings? I might try that.

Like BobG,  not only do my eyes itch but brain overload is causing some 'leakage'!

A sincere and warm Merry Christmas to everyone....Cheers, Carl