Question: Cooling Effects Of Louvers

while I don't have any speedster-louvre experience I do have some 2nd hand beetle experience. A friend of mine purchased a beetle from an individual who claimed to have significant temperature problems that he couldn't figure out -tended to overheat on the highway. The PO had customized the rear deck lid with louvres, reverse ones that evidently sucked out air at highway speeds. After checking out everything else and finding nothing wrong my friend taped over the louvres= no more problems. Last I knew he was still running that way.
I think that the louvres also provide an escape for engine heat that can build up when the engine has been shut down. My 2 pfennigs.

Fred, thanks for that info. I wonder if the opposite would pull in air? Some members are using the engine lid rubber 'buttons' rather than the weather stripping to achieve additional cooling. I suppose that allows for fresh air to circulate in AND out, from front top to bottom or bottom to top... ?

This subject has been discussed before and I took time to research the threads on it but did not gain any "real use" knowledge on the practicality and effects of louvers other than reverse ones certainly bring in more cool air.

Those discussions took place about the time the current wave of Speedster Rs being built or retro-fitted with louvered rear lids was beginning.

Now that some of you have had louvers for some time I wonder if you notice any change in the oil temps on a daily basis? I am especially interested in hearing from those who have either had their decks modified or have driven cars with and without louvers.

They look cool and I like them... I just wonder if anyone has info on any enhancement to engine cooling.

Jim

IM uses "buttons" on the rear deck lid (so did Porsche). Anything that allows easier ingress of cool outside air into the engine compartment is a good idea.

Thanks George. I have sorted through some of your build pictures this afternoon and am amazed at some of the stuff you had done. That is absolutely a dream Tub. Regarding the "buttons", I either learn something new each day or have my memory refreshed. I'm enjoying the experience.

Jim,
My 1776 ran stock with no vents, no prob. Then when Ted rebuilt the bee-jeezus out of it, it ran warmer. I bought the louvred decklid and when it went in place, it was fit riding high like the old VWs becuase it didn't fit well...lots of air and lots cooler. On two occasions I bolted the lid down snug and ran with just the louvres providing the breeze and all went well, no noted heat difference, but it felt as if the carbs weren't as effective.

I am currently running the decklid snug with the stock weather stripping and the Big-boy engine temps are 220-ish. I've got the buttons riding around in the car, I just haven't gotten around to scratching and scaping the weather stripping off yet.

If you are jumping on the period correct bandwagon the louvres like mine or GBs are fine. As GB has stated elsewhere, if your engine is machined and matched accordingly, there shouldn't be any oil temp issues.

If you want to walk on the wild side, get some of them reversed louvres like that black speedster(?) #19 shown on the Emory site once upon a race car time...

Paul,

Thanks... I was thinking of you when I posted this... nasal hair in the paint job and all!

Yeah, I've done my homework and can see that a 56 GS (or T-1 57 GS)did not have factory louvers. However, in my massive collection of pictures ripped off the web for inspiration I see that nearly every T-1 GS I can find (other than the rare early ones) had louvers cut somewhere in their Speedster life. I have thought about asking on the Registry about the whys and whens, but would have to tell them I am applying them to a 56 Skylark with Trip Deuces rather than to a Replica 56 GS... ;-) From some of the stuff I read in hard copy or on the web, there seems to be some hybrid stuff going on with Porsche's American imports at that time, and there was all kinds of stuff coming out that did not fit our 2004 reference books. An excellent example is the 4 Cams turning up in 1600 Supers. So, I think a minor wink at the books is ok on the Louvers. Hey! They didn't have Biven's then either!!!!!!!!!!!!!!

Jim,

I have several Porsche Refence Books and some Carerra Cars have Deck Lid Louvers but under the Deck lid are Cone Shaped Air Boxes that fit over the Carburator Air Cleaners. The Louvers direct air to the Air Cleaners and are separate form the air enterning the Engine Bay.

Jack Blake

I'm not real sure about louvers drawing air away from the engine, but it wouldn't be the first time I've had screwed up logic.

Seems to me the surface area over the engine lid would be a low pressure area from the air moving over it. This would allow air to be drawn out from the engine compartment if it were open to air from below. If the engine compartment is "sealed" from air from below to prevent hot air infiltration, with the exception of CMC's that have a 'mouse hole' in the fire wall for air supply to the fan, I don't where air supply would come from to exhaust from the louvers. There is the additional factor of the cooling fan sucking biggie bunches of air for the engine. For air to be drawn out the vacuum over the louvers would have to be greater than the suction of the fan...I think.

Just an opinion from a marginally informed sort of newbie.
Bill

Here's one thought... if Porsche designed them that way, and used the 4 small lid pads, then there must have been a little R&D work that said this helps cooling... eh?

I've seen the boxes and some very cool other methods of forced induction on Speedsters. There was a Slate Gray GS at the 50th (look at the 356 Club pics) that has a very cool set up with filter tops styled in an art deco way with a forced air set up in between them... I'll try and find the pic.

I am going with the Louvres, I am just curious as to their real ability... keep the info coming. This is interesting.

Jim:

I went back and forth on the louvers too. Finally decided they looked nice and if they cooled the engine, all the better. If not, at least it looked like they would. I guess it is the old "Its better to look good then to feel good" thing. Anyway, good luck with it either way you go.

Take care,

Oz

Hey Jack,

I'm glad you brought up those air boxes... One of our builders told me that the louvres actually draw air away from the engine compartment. If this were the case, you 'spose those air boxes actually robbed fresh air from the carbs?

Jim, just don't go all Abarth on us. Some of those old cars looked as if the builder/owner/designer had an out-of-work brother-in-law that had a punch and press in his geerage!

New model 911 (or whatever they are) has sweet new rear deck louvres along with non-Boxster headlamps and hips! Yes, no more styling tips stolen from Volvo...the 2005 911 looks like it got its atttitude back!

Yep, gotta say I like the gnarly look of the louvres but they have to be part of a theme, IMO, like nerf bars, no hub caps etc. As to cooling, let me give you the benefit of some very expensive lessons. FIrst off. The Germans spent a lot of time and money figuring out the doghouse cooler configuration and the only time I have seen it fail is what happened to me when a piece of the fan shroud broke off and would intermittantly block the air exit. After I pulled the motor and removed the shroud, I saw the culprit. ITM, the previous owner had installed a large fan colled oil cooler, which of course did little to solve the problem. I installed a new shroud and dog house, sold the oil cooler on Ebay and cut two holes in the interior side of the wheel wells, which I covered with a fine mesh screen.
Now the car seems to run almost too cold AND no matter how fine the mesh some dirt does get directed into the engine compartment, but hey is'nt that what air filters are for?
Also, I may have done an overkill when I fabricated some small vents to direct the air from the inside of teh wheel wells into the engine compartment.
This summer I plan to block off the vents and see if it makes an appreciable difference.

Here is something to think of . Boats !!! They have enclosed motors. They have side louvers. Though they are water cooled they still draw in air.
I would think that adding the louvers would allow the engine compartment heat to escape faster. Think of engine compartment like a closed room with a space heat and you open a window to let the heat out. Now if you open another window opposite ,you will create a inlet and outlet. The room will start to cool down. If you can duct air into the fan inlet you will reduce the temperature. If you also can port air into the engine compartment heat will be pushed out of the center vent and or the louvers. I'll post some pictures of a neat little intake system I came up with . It may help you out.
Jim , go with the louvers you won't regret it.

Paul,

I believe the reason for the "Air Boxes" is to separate "Heated Mixed Air" from the Engine Compartment and the Carburators. The Carrera I've made mention has the area under the Engine Deck Lid totally "Open". The External Deck Lid Grille is all that separates the engine from the "Environmant."

As for the "Abarth Porsche" vehicles, the rear portion of the Body Work/Deck Lid are "Littered" with louvers.

I kind of side with the group that "Follows" the original VW/Porsche design and feel the engineers that did the R/D proved the cars bodywork functioned the best with the designed for actual operation/use.

I do feel the current engineering pieces offered in suspension, cam shaft profile, oiling/lugrication, Nickasle Cylinder Design and other
areas allowing added performance by current technology are worth a second look.

The 59' Porsche Speedster E-Production Southern Pacific & Northern Pacific SCCA Champion car had no louvers. This was a factory race prepared speedster and basically had a "Good Race Proven Suspension, Killer Engine and Really Good Driver - Dick Smith". I drove it a couple of times and the difference between my car and that car was the chassis was stiffer and the engine had a longer power band & more torque.

Those cars had to run single barrel carbuartors and a miximum displacement of 1800 cc. The primary car the speedster competed against back in those days was the MGB. Group 44's MGB was the heavy hitter on the Mid-West & East Coast National SCCA Level.

Anyway, Body Mod's, Wheels, Cute Interiors and Du-Da's are each and eveyone's option and choice.

I just try not to loose site of the feeling I had befor I had my current speedster and look forward each time the opportunity comes to driving the car.

I routinely "Chat" with a couple fo "Speedster Owners" and enjoyed this one.

Jack

Louvers can draw air away when located over a surface that has alot of streamlined air passing over it. This is the case with Beetles especially and I have seen its negative effects first hand.

I was able to score my old 66 Beetle because of this and the fact that no matter what the previous owner did he could not keep it from running hot.

I taped over the vents after I traded for the car and the heat issues went away immediately. In a speedster the air is not as streamlined over the rear deck as a beetle so maybe it doesn't matter as much- I never tested it.

The Carrera GT that I keep up for one of my customers has the louvered decklid and the bottom of the lid is carefully crafted to only be directly over the carburetors. I was told by a factory Porsche 4 cam technician that this was to help scavenge some of the fuel saturated air from the carbs out of the engine bay at higher revs on the race cars. The 4 cam has alot of overlap and that equates to alot of standoff from the carbs at midrange as power climbs into the top end. Filling the engine bay with this mixture could make for a very toasty condition.

Who knows, maybe someone with a louvered lid and some gauges could do some testing to see. All you would need is some tape and some time to go the same sped up and down the same road.

This thread keeps popping up and it is interesting. What I don't understand is how completly enclosing the engine compartment (i.e, taping the vents) would help cooling or running unless the engine is somehow running too cool - like I believe bigrigs do in the wintertime (Alan can probably expand on this technique). It seems no matter how you provide circulation into and out of the engine compartment, the better. I'm not sure why but CMC seems to have been the only manufacturer that recommended putting a hole in the firewall ahead of the fan inlet which would let cooler air into the fan housing and the engine compartment plus let the carbs breathe better. Similarly, if you then put more vents/louvers in the engine lid that would allow venting of any heated air from that area.

I vaguely recall vents/louvers in the area below teh rear window and above the engine lid on Beetles, where did that air go?

Bruce:

On later Beetle sedans, there was a louvered "grill" above the engine lid that, if you were to look through it, opened just above and slightly forward (car-wise) toward the engine fan shroud.

On convertibles, this area was shortened to allow stowage of the convertible top, so the louvers were put into the engine cover instead. There were also some other changes inside that engine cover, but I can't quite remember what they were (baffles, or something).

A common "California" trick to gain extra cooling (although I have no idea how effective it ever was) was to get one of those convertible engine lids and put it onto a regular sedan to double the cool air opening to the engine bay.

Personally, I believe the CMC trick of opening up the firewall is about the best you're gonna get, short of an external oil cooler, but having the CMC-style opening feeding the fan, PLUS ducting the engine cover air directly into a pair of isolated carburator boxes feeding the carb inlets is about what the upper-East-Coast 356 racer types did many years ago

gn
One of the "Speedstah Guys" from Beaufort, SC

This is a good thread for information and I thank all of you.

The cooling of my engine is really a non-factor here.. at least that is why I have Pat and Henry doing the pro work for me. I am confident in their expertise and am sure Henry will have this baby running smooth and cool for me. It is not a radical build... just a good strong runner set up for cruising.

With the CB Alumunim case there is a small heat disapation factor from what I understand. The trade off is in longevity on a stroker, even a 2110. We are going with a bigger cooler now just for a little comfort edge there. It is a 95 Plate, so that is a jump up. The rest of the build is by the checklist of quaility parts in a Pat Down's 2110. I also opted for H-Rods for the bottom end strength. When I get time I will post the crank, cam, valves, rockers, heads, extras, etc. on this forum. It is just a good solid build and I am leaving all that to Pat and Henry. I like engines, understand them from a users' perspective, and can do your basic Type-1 troubleshooting, and adjustments/tuning. But I do not pretend to be an expert... certainly not enough to suggest changes to Pat. I just sat down with both Henry and Pat and listed what I was seeking... and the 2110 fits. When I look at the engine build list I feel like Pat is giving me all that and more.

The Louvers are for style points and fit in the overall look I am striving for through Henry and a custom Intermeccanica, but I also hope to learn that they enhance cooling. I may do the Jake tape test one afternoon. I think that would be an interesting test. The third factor? What is the flow over the lid with the top up vs top down?

I hope we continue this discussion.. I am printing out this thread for another read tonight. This site is the best.

I'd like to see the results of the tape test on a Speedster with top up and down. Alot can be learned there!

A beetle with its high pressure zone positioned right over the decklid is no doubbt gonna have more of an effect than most any other car.

If those louvers were just turned the opposite direction imagine what could happen!

A cooling system does no good if air cannot be driven into the cooling fan, be it scavenged from the high demand of big carbs or the vacuum of reversed louvers. Without air charge its impossible to get any air pressure.

I don't have a speedster here to do the testing with, or I'd try it myself. I just got a new 8 channel datalogger and I'm itching to see what I can do with this puppy with in car tests!

Note that VW beetle convertibles had a cooling problem and the fatory solution was to modify the rear deck lid with additional slotted holes. Many high performance VW guys with sedans change their rear deck lids out for one of these convertible derck lids to improve cooling.

One more time: anything that allows more cool air into the engine compartment is a GOOD thing.

George is correct, AND note that these were slotted non directional vents, not louvers. The slots in early VW convertible decklids were verticallly positioned on the decklid and the later years were horizontally positioned.....

Here is a couple of photos of what the louvers were ment to do. Id post the pictures but they are not mine, so here is the links:

www.elevenparts.com/pictures/243-7.jpg

www.elevenparts.com/pictures/243-8.jpg

Those pictures clearly illustrate what I posted above in a previous post regarding what I observed from working with a 4 cammer Carrera..Those louvers were placed on the lid to separate the carb inlet air from the fan inlet air. The amount of standoff created by a 4 cam at mid and high revs is phenomenol, hence the need for those aggressive velocity stacks that are used to combat the condition.

They wanted those fuel soaked gasses out of the engine bay, hence the louvers.

Note that the cooling vent just above the fan is not louvered, it is a plain vent and positioned to benefit the air inlet on both sides of the fan shroud. This is just like ALL VW and Porsche aircooled vehicles from the Type I clear to the 550 all the way up to the 993! Not one used a louver from the factory.

And the louvers look good too! Good info Jim.

I've been following this discussion while reading from another source and find that very few, even amongst 356 owners, agree on the subject. There are two or three camps on cooling/vents/louvers/etc.

Here are the few points that I think most all parties are in agreement on: (Survey error factor 50%)

1. The first key to cool running is a properly built engine (Balanced).
2. External Oil Coolers are an enhancement, and a must on some modified builds. (especially in our big CC T-1s, T-4s)
3. Porsche saw the need for cool air on all type 356, Pre-A's, and 356A's by using the engine vent grill and also the 4 tabs on the engine lid instead of weather sealing.
4. GT Carreras were the FIRST Porsche built cars with Louvers. This was due to the cooling fan using up fresh air before it reached the carbs. So it wasn't a cooling issue, but a matter of fresh air distribution to the carbs.
5. Early GT Carreras did not have the sheet metal to separate air to the Carrera Fan and Carbs. This came as the car evolved in the mid 50s.
6. Four Cam Cars came from Posrche in all configurations of cars, including 1500S, 1600S and GS models.
7. The factory used twin grills in 59(?) to increase air distribution. Even some Speedsters returning to the shop were retrofitted with twin grills.
8. Louvered lids came from the factory in some cases as a retrofit to GS models that were 2-4 years old. So the factory DID recognize the benefit of Louvers WITHOUT boxes for the carbs. Most of these cars had the conventional dog house.
9. The remainder of venting mods came from Porsche repair shops, racing outlets, and home mods.
10. Many parties believe that on 356 Coupes (like on VWs)the air enters from the bottom of the lid and exits on the top. If a VW has factory weatherstripping then Louvers (as cited in the tape over studies) would not work as there would be no place for the air to vent....... they probably just create a void of air movement... so you need a place for air to exit too (this is my barnyard guess). Some will go through the engine via the carbs..., but the rest? There is the reason Porsche used the small rubber tabs.... and the use of Louvers only enhanced the entrance of air.

Now this is probably half wrong, but it is what I gather from several sources. I am sure there are other opinions. Let's talk about what I THINK I understand. Like I said, it's just my rookie, no background, thoughts..... OK?

What I take from it is this>>> Louvers on lid with a doghouse engine do serve a purpose in fresh air flow, as does the grill, and the tabs instead of weather stripping.

Great info Jim. Where did you find it?
Hey Jake.... Nice to see you are visiting again. Started assembling the oil and fuel lines. That Loctite 518 isn't the easiest stuff to find. Found it at McMaster Carr. Should have the 2270 cc T4 fire up end of Feb. I am going to play aroung with the louvers and the forced air issues in the spring. My Car will be equiped with two head cylinder temps gauges, air fuel ratio gauge and exhaust gas temp.
Joe

Joe,

I lurk the registry forum a little and learn some things. There is a lot of discussion on cooling in the archives. Now & then I see a name that I recognize as a supplier, a shop owner, restorer, or maybe the owners of a few cars I have admired via the web. I try to watch for their posts.

I've also started actually reading this pile of books on 356s, aircooled engines, and stuff. It's winter, I sold my VS Speedster, and so...

I now know just enough to be dangerous. And that's a fact. Probably 90% of this forum knows more than I do on this stuff. I am just repeating what I read. Some day I may actually understand 10% of it.

Jim

These sort of discussions are just one of the things that makes this site great! You gotta love it.

Whatever they do, cooling louvers are just way kewl, Daddy-O!

BD

Hey Bill, That's what I started with, and after a few days of studying the aerodynamics. cooling properties, flow in a north wind of 20kts going southbound with tape over the speedometer? Well I came back to my original thought. They look cool!

Jim

We had a similar discussion in college some 40 years ago. In a class on "Vehicle Dynamics" we had a heated discussion on the aerodynamics of air over a car body. Back then aero was largely eyeballed, and not yet measured (tail fins were considered aero, etc). A few of us carefully "instrumented" the rear of an early model red Corvair with about 50 pieces of black yarn and duct tape. We made a few passes up the local freeway with a chase car and a camera. Pictures definitely showed air went from the outside INTO the decklid louvers.

This was NOT all positive. We also had the subject car instrumented with some "manometers" to detect differences in AIR PRESSURE between outside the rear decklid and inside the rear decklid. We did detect a slight pressure DROP between outside and inside. In other words, the air WAS flowing into the car, but it was most likely responding to a partial vacuum created by the shape of the body above the rear deck, and NOT from the more beneficial effects of high pressure "ram" air. Of course we naively figured we

I remember reading that the Ram Air concept doesn't work. If you consider that a VW engine draws about 300cfm at WOT, you need to be going very fast to actually force air into the engine faster than the carbs are sucking it in. I havent' done the math to prove it however. Has anyone confirmed this?
Ron

The mechanic I rely on had made mention that I'd need to be goin' about 600 MPH to equal the air movement output of a stock doghouse fan... so I'm guessin' that scoops and placement, while meeting some needs, don't really rival some other engineering accomplishments...but 600 MPH does sound interesting!

I did a little math in my head while waking up this morning. Assuming 300cfm at WOT, you need to be going 90mph just to equal the intake of the carbs. However Paul, at 600mph, you would have a tremendous ram effect...

I think Mr. Mechanical was trying to deter me from cuttin' and choppin' any additional holes under the guise of...well, you know!

The Chevy CORSA guys have an interesting website also. Obviously they also are very interseted in air cooling. One of their sites is a very well documented restoration (body off) of a "Corv 8". That is a Corvair with a 350 Chevy V-8 in the back seat driving a modified Corvair 4-speed via a Crown adapter. The conversion included a well built engine cover to separate the driver's seat from the engine, which sat about 3 inches behind the seat. Overheating was a known problem in most conversions, despite a large front mounted radiator. The secret to good cooling was to NOT seal the engine cover. In other words, let the ambient engine heat escape by itself.

It seems we speedster folks are doing that, by using buttons and adding extra louvers and/or grilles. Perhaps additional air flow directed in and around the upper engine compartment might not hurt? I've ofter wondered about some 911 Turbo type of intakes just forward of the rear wheel openings? Directed to some sealed carbs, or just the general engine compatment? Sorry, I'm an outlaw type.