Will cutting the area under the grill out let more fresh air in to the fan to circulate worth doing, my vs built car doesn't seem to have any holes cut in the "firewall" to let air in, would put a velcro or other way to secure a rain curtain in place for down pours. motor is a stock 1600, thanks.
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So cutting the engine lids rain shield is the plan? Why not cut the firewall like VS did in most models? It doesn't have to be round like they did. A square cut would work too. I like their idea of using course 1/4" hardware cloth to prevent junk from getting sucked into the fan. Suspect cutting with a 3" grinder or air powered file from under neath would be doable?
thats whats on tap for today, firewall relief thanks
The holes in the firewall did nothing (good) for me, but go ahead and try for yourself.
I cut two giant 8" holes and put fans in to supply air (on the recommendation of guys who've never done it, or don't have a completed car), and the car runs hotter with them on than with them off.
More air through the deck-lid works, more air from the firewall seems not to.
Your mileage may vary.
In my opinion, a stock 1600cc engine shouldn't be generating the same amount of heat as say, a 2,110. I don't know how much aircooled VW engine experience you have so bear with me if you already know this:
Does your engine have a stock VW fan shroud or is it aftermarket? In general, some of the aftermarket shrouds aren't as effective as an OEM VW version.
If it is OEM VW, does it have the air vanes and thermostat installed inside to manage cooling?
Either look or reach behind the fan shroud to see if the air vane actuator arms and linkage bar are in place. They should be down towards the bottom of the fan shroud and the linkage bar goes across the back of the engine. If there are no air vanes then in my experience the engine will run hotter.
Also, check under the engine on the passenger side and in between the middle pushrod tubes to see if the bellows thermostat is there. It sits on a metal bracket attached to the engine sump and has an actuator rod going straight up between the cylinders into the fan shroud. If you find it and wish to check it for correct operation, let us know and I'll get you the procedure from my Bentley manual for you.
I think that making sure your engine is cooling as best it can is the first step before modifying the car for more cooling.
I think the smaller firewall hole might create a desirable Venturi effect. I vaguely remember a lecture on the Bernoulli Principle back in physics class. I've even seen venturi rings for the back of the shroud air intake - on 356's and VW.
does this mean it SUCKS?:{}
Anyone try the $70 venturi ring?
Increase your cooling air by 10% with no other changes! The venturi shaped ring smooths air entry into the fan, and less turbulence means more airflow and better cooling! VW added these to the FI fan shrouds, since those engines had such a tough time keeping cool, and now these are available for you to add to your doghouse fan shroud! These operate on the same principle that a Velocity Stack does to increase airflow into a carburetor!
I have the venturi ring installed. Awesome Powdercoating installed it on the shroud I bought from them.
I also had one installed on the stock VW shroud before the far fell down on it.
Is this a vintage speedster issue?, I have no extra air inlet holes in my Beck engine compartment, just the grill lets in air, and I have no overheating issues. My engine compartment is completely sealed.
Maybe it's a VW pan-based issue so not applicable to Beck's custom frame. VW kept adding vents as the horsepower went up. First above a solid engine cover with vents. Then added to the engine lid too. Vents on either side of rear windows. And finally the venturi added to FI engines. ????
Airflow is a problem with any vehicle with a rear-mounted air-cooled engine (aside from maybe your zero-turn mower). Some shapes are worse than others, but aerodynamics are working against you in all of them. There is zero aerodynamic difference between a Beck or any other replica.
The climate the car is operating in makes a huge difference. It gets hot in the Midwest, but it doesn't get Barstow in August hot. What is 100% adequate in Boise probably doesn't work as well in Phoenix when it's 115. I get a kick out of guys telling people in west Texas that they don't need aux. oil coolers on their cars because a stock shroud with all the flaps works fine for them in Boston. Where you has a huge amount to do with what will work.
How you operate the car also has a lot to do with heat management. The faster the car is moving, the worse the aerodynamic problems are going to be. Also, if the engine is laboring to maintain a high speed, a manageable problem is going to slide into becoming unmanageable. If all you do is putt around town, you'll never have a problem no matter where you live. If you have a 1914 with stock heads and drive 90 mph on the interstate for hours at a time through 95 deg weather, things might not work as well.
Some engine combinations run hotter than others-- and higher compression and bigger displacements will always make more heat at full load. But a lot of times, a more powerful engine will be loafing along where a smaller engine is laboring greatly to maintain the same speed, and the smaller engine will run hotter. There is a sweet spot in combinations -- enough power that the engine is not laboring to maintain the preferred speed, but not so much that the combination gets out of control in mild operating environments. A 12:1 3L Type 4 is probably not a great idea no matter how many holes you cut in the body, but neither is an 1835 with thin-wall cylinders, stock heads, and a restrictive exhaust.
Finding the line where heat management goes from being an easily manageable problem to being a big and uncontrollable problem (and falling well under that line) is the secret sauce. I'll bet a donut that Carey knows what combinations work well in nearly every situation and builds accordingly.
I would suspect some combination of these things are how your car runs cool @LeadPedal.
I'm not very enthusiastic about that VS hole in the fire wall either. Fresh cooling air is supposed to come in thru the grill on the bonnet only. The engine compartment is supposed to be TOTALLY SEALED to insure this happens.
However, there IS a restriction in that rain guard under the grill. Not much but still, a restriction. It's where the air passes into the engine compartment on the right and left sides under the bonnet. Those areas restrict the area down to less than one fourth the area of the grill. Cutting that area back to make it larger and less restrictive will allow enough air flow. I have never measured the amount of airflow there but I have measured the amount of restriction using a Manometer. Opening up those two areas or drilling a 4" hole in the center of the rain guard will eliminate the restriction.
The 4" hole is not as good because it somewhat reduces the effectiveness of the rain guard.
If high temps still exist, I'd be looking elsewhere just as Stan and others have mentioned...............Bruce
I forgot to post the photos..........Bruce
just got a hand held temp gun, will take it out and try it. Not sure it runs hot, but the temp guage shows the needle 3/4 over after running the highway at 3500 rpms which is about 70mph after 25 minutes to get to beach house. It seemed my cmc never registered that high up the guage , even after putting a 3.88 transaxle in it that I assumed slowed fan speed down as rpms went down, will know something a little more definitive on the next nice day and let you know what I find out instead of guessing with the guage and maybe a over active sending unit.
I've not seen wind tunnel results of whether at speed, the rear grills sucks are in or blow it out. Seems it would be a low pressure area so it would suck air out?
pretty good article on application of aerodynamics by Porsche. That Porsche Type 64 looks about as air flow smooth as one could get.
@aircooled posted:I'm not very enthusiastic about that VS hole in the fire wall either. Fresh cooling air is supposed to come in thru the grill on the bonnet only. The engine compartment is supposed to be TOTALLY SEALED to insure this happens.
However, there IS a restriction in that rain guard under the grill. Not much but still, a restriction. It's where the air passes into the engine compartment on the right and left sides under the bonnet. Those areas restrict the area down to less than one fourth the area of the grill. Cutting that area back to make it larger and less restrictive will allow enough air flow. I have never measured the amount of airflow there but I have measured the amount of restriction using a Manometer. Opening up those two areas or drilling a 4" hole in the center of the rain guard will eliminate the restriction.
The 4" hole is not as good because it somewhat reduces the effectiveness of the rain guard.
If high temps still exist, I'd be looking elsewhere just as Stan and others have mentioned...............Bruce
Regardless, it won't stop multiple comments advocating for the amazing miracle firewall hole the next time this topic rolls around.
It's 2024 -- you posted your data in 2015 and I posted the results of my little science project even before then. I'll bet there have been at least one of these threads at least every 6 months since then, with the same advice and same pictures.
@widebody boy posted:just got a hand held temp gun, will take it out and try it. Not sure it runs hot, but the temp guage shows the needle 3/4 over after running the highway at 3500 rpms which is about 70mph after 25 minutes to get to beach house. It seemed my cmc never registered that high up the guage , even after putting a 3.88 transaxle in it that I assumed slowed fan speed down as rpms went down, will know something a little more definitive on the next nice day and let you know what I find out instead of guessing with the guage and maybe a over active sending unit.
Get a candy thermometer, and stick it down your dipstick tube when you're reading 3/4 of the way over. You'll know a lot more once you know what your actual temperatures are.
Anything less than 180 is too cool. 200 is fine. 220 is getting hot. 230 is approaching critical -- not because of the oil breaking down, but because the heads are considerably hotter than that and aluminum (what the heads are made out of) expands more rapidly than steel (what the valve seats are made out of). IF the head gets too hot, the valve-seats will loosen up and "drop".
That's bad and expensive.
Wolfgang......I don't have any idea on a coupe. Perhaps due to the airflow over the "wing shaped" roof profile, the air may create a negative pressure.
On a Speedster, I think I recall there was a negative pressure of 1.5"/H2O with my manometer. That was with the top down at 60-70 mph. I did these tests in 2015 but can't find them now.
Also in my last post about the rear deck lid rain guard. The approximate opening thru the rain guard was 39" to 40" of area. That works out to about the size of a 7" diameter hole. The grill is what ? 12" by 18 " or so. (I can't remember exactly) but if it is, that means the air going in the grill is then restricted by 80% in the rain guard ?
On my car, with a totally sealed engine compartment, I measured a vacuum (negative pressure) of 1.5"/H2O @ 60-70 mph. That's not disasterous but it certainly indicated where the restriction was and easily correctable.............Bruce
I am so happy that my oil temp and head temp are good on my CMC with an unmodified deck lid and the CMC hole in the firewall.
The area behind ANY vehicle is a negative pressure zone. That's why an air-cooled engine in the back is a challenge.
The entire idea of an air-cooled engine is to supply it with air that can be sucked into the fan, blown over the heads and cylinders, and out the bottom. Insufficient air to the fan is similar to closing off the inlet, or having a completely plugged filter in your home furnace -- because as a simple matter of fact, the air requirements of the engine and the fan are at least as much as a residential furnace. That fan moves a LOT of air to cool the engine. The engine itself sucks a lot of air down the intakes in the process of propelling the car down the road. More air is more of everything the car needs. That air comes from somewhere. Ideally, that air is clean and cool.
In 2015, we were having this same discussion and I said:
@Stan Galat posted:The cooling fan is not small- and contrary to how it looks, it's actually a pretty sophisticated design. It's a backward inclined fan, capable of overcoming huge static pressure differentials. Other types of fans move more air with less horsepower, but I think it's telling that Dr. Porsche used this kind for the VW Type 1 and 356. They self-stall, and they can overcome static pressure differentials of up to 20". A backward inclined fan can suck harder than the negative pressure zone behind the car, and still move air from the top side (what we see as the engine compartment) to the bottom side where it is expelled out the back. This is no small amount of air we are talking about- the fan takes up to 20 hp (by some dyno observations) to drive. It moves a lot of air across some pretty crazy static pressure differentials.
The carburetors also require a lot of air. I have a 2276, which means that over two and a quarter liters of air move through my carbs at half the engine RPMs. So as I'm driving down the road at 3500 RPM, my carbs are sucking 2276 ccs of air 1750 times a minute. That's almost 4 million ccs of air every minute, or 140 cubic ft of air. And that's for the engine at 3500 RPM. My engine is capable of turning 2x that much. That's as much volume as a good sized bathroom. Every minute the carbs suck all that air down and throw it out the exhaust. Perhaps a better picture is to think of the volume of your exhaust. That exhaust came from somewhere- the vast bulk of it was sucked down your carbs.
That's a freak-load of air being sucked down your carbs. The combination of that air, plus the air your cooling fan is moving, is a huge amount of air. All that air has to come from somewhere. The idea that holes in the topside of the car let air out just fly in the face of those air requirements. It really does have to come from somewhere.
In 2021, we were having this discussion again, and I tried again and said:
@Stan Galat posted:Al and I agree regarding the shape of a Speedster in profile (that it is essentially an airfoil), and everybody knows that because of the shape of the thing, it's super-hard to get enough air to the (air-cooled) engine.
We disagree, however, regarding how to get more air into the compartment. This isn't facebook and we're actual adults, so we know how to disagree and still remain friends.My way of looking at it is like this:
We go absolutely apoplectic when a guy leaves his tins off, because we all agree that there is a top and a bottom as it pertains to the cooling of the engines. Air comes into the fan on the top, blows through the cooler or over the heads and cylinders, and exits on the bottom. Between the two is a great wall of tin that keeps the hot side hot and the cold side cold.
I understand the arguments that air from the underside of the car up by the firewall is not the same thing as air that is discharged across the heads and cylinders, but no matter what you believe regarding airflow under the vehicle while in motion - it is the in the same cavity as the discharge of the stock doghouse air-cooler. At a minimum, pulling air from this cavity is pulling some of the reheated air from the oil cooler into the intake. Also, the argument presupposes that the vehicle has all of the sled tins (almost none of them do) and is always in motion and discharging air out the back of the car, which is not always the case. Several of the times I've come the closest to overheating have been in stop-and-go traffic.
I drank the Kool-Aid and put not one, but two giant holes in my firewall, and filled them with fans to force air into the engine compartment. The car actually runs hotter with them on than off, and hotter with the holes than before I had them.
Everybody talks about the infinite wisdom of the Sainted German Engineers (hats off, please), especially as it pertains to cooling - then advocates for the thing they most tried to avoid, which was pulling air from under the car into the engine. They pulled air from the top side. While the shape of the car is working against this effort, it's the only game in town. ANYTHING we can do to get more air into the engine compartment from the top is useful. The SGEs cut louvers in the Carrera decklid, and just added a second grill on later 356s.
Opening (or even removing) the rain tray is on my short list of useful projects. The IM/911 hole behind the plate is another method. I've seen one or two Speedster replicas with a second grill (like a 356C had). The Carrera louvers look cool, and can't hurt, but they provide very little by the way of open area.
Terry Nuckels reported that his car ran cooler with a luggage rack and a suitcase - which makes sense in that the airflow over the airfoil of the car is disrupted by the suitcase back there. Almost anybody who's driven where it's really hot will prop open the decklid by a couple of inches - I've had my oil temperatures drop 15* in the desert with this change.
It'd be nice to have some definitive, actual data, but the closest we've come it when Bruce did his manometer tests a few years ago, and they confirmed what I'm saying.
Regardless, guys (me included) are going to believe what they want to believe until there is conclusive data to prove otherwise. I'm going to continue to seal the top from the bottom..
The idea that there's a better place on the underside of the car to get air than through the intake grill on the deck-lid (in the low pressure zone), or that we're trying to get air out the grill rather than into it are misconceptions that just won't die.
Like a Zombie -- It. Will. Not. Die. It cannot be killed, it cannot be overcome with logic or time. It has moved into the realm of folklore and common knowledge. I'm giving up.
Carry on.
I recently dropped a valve seat and it wasn't pretty. These heads are mini wedgeports and had 12k miles on them. I had the heads welded to fix the damage around the seat area and of course I had a new seat installed. There was some damage to the top of the piston so I ended up getting a set of forged pistons. It took several months to get it all squared away but my car is running great now.
I monitor number 1 and 3 cylinders via head temp gauges and there was no indication of over heating. My oil temp runs from 190 to 220 depending on driving conditions. If I drove 80 mph for longer than 20 minutes the oil reaches 220 and I slow down. The temp comes down pretty quickly. This is a 2480 cc engine .... 90 mm crank and 94 mm pistons. nine to one compression. This is one of those cases with a slight cam drop to accommodate the longer stroke.
Used a 4" inch hole saw to put a hole under the rear grate, @ 70mph gauge stayed steady in the middle of its range, dipstick temp was 195 degrees, outside temp was 78 outside. car doesn't get driven anytime but summer and not if rain is forecast. Made a 4" rubber plug that will be behind the seat if I got caught in a downpour as it only takes seconds to pop in hole after opening engine cover.
That temp, at turnpike speed, is just about perfect, in my opinion.
Drive it, and don’t worry about it!
Wide body boy............I never heard that before ! A Rain Guard Plug.....RGP ? Why not !
Thanks for that !
Paul Ellis lives in Phoenix. I' surprised that more people over there don't suck a valve or seat more often. Summers there are hotter than a two peckered goat !.
Cyl. head temp. gauges. Stan has 4 gauges and monitors all the heads....very nice. You amaze me !
I was too cheap. I used 4 temp. sender rings connected to one gauge thru a rotary switch but mine was only temporary.............Bruce
