I have noticed in some pic's a hole cut in the firewall at or near the fan intake. Is this a modification that has any merits? I have built many high HP and RPM VW
engines in a VW Type 1 that didn't require any additional air intake. ie raising the deck lid or hole in firewall.
Ted
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There is so little air intake in most speedster engine compartments that it's definitely needed.
Instead of holes, what about this? Same concept?
Are you going to put holes in the firewall behind it? Have you calculated how many square inches of air intake it provides?
Are you going to put holes in the firewall behind it? Have you calculated how many square inches of air intake it provides?
i put a 3" hole right behind my fan. that hole is ducted to a 12v bilge blower that is temp activated based on oil cooler input. the bilge blower draws air from under the passenger seat (over tranny and beside trailing arm.
i literally have NO room under my car for more stuff. 
i put a 3" hole right behind my fan. that hole is ducted to a 12v bilge blower that is temp activated based on oil cooler input. the bilge blower draws air from under the passenger seat (over tranny and beside trailing arm.
i literally have NO room under my car for more stuff.
Bill- Is that on the oil temp gauge?
The way my engine lid is cut for air intake (1 slit on each side of the grille in the inner skin of the engine lid- 8 or 10 square inches total?), if the rest of the engine was sealed properly from the surrounding area I don't think a stock 1200 would survive long term. I'm guessing a healthy 1776 or 2 liter (which will use several hundred- 1,000 cfm more air than the 1200 at highway speeds) wouldn't last more than 5 or 10,000 miles. Unrestricted air intake into the engine compartment is THAT IMPORTANT!!!
Gene Berg, in 1 of his technical articles, tells about looking at a kit car for an owner that couldn't seem to keep motors in the car. He said that upon inspection there was almost no air intake at all, and when he asked the guy how long the motors in the car were lasting, the longest was 4300 miles. IIrc, he also said that a 10' reduction in oil temps could mean as much as 10,000 more miles life to a motor.
I know some guys think I harp about this a lot (it sure seems to me that I repeat myself a lot), but making sure there is enough air intake for your motor should be the first thing you do if overheating or oil/head temps, or even just running warm seem to be an issue. I've mentioned the aquarium air tube pressure test several times over the time I've been active on this forum for a good reason; it's a cheap, easy and quick way (15 feet of tubing is less that $5 and you and a friend can have results in an hour) to get definitive results.
It doesn't matter how well tuned or conservative the motor is, if there isn't enough air getting to it, running hot will be an issue and you will be compromising it's life.
Bill's discovered what I've been talking about...Al
Bill- What does your car have for air intake into the engine compartment?
If I recall correctly Jack Crosby once stated that he noticed an alarming rise in (cyl.head?) temperature, and found that his firewall air intake 'hole' had allowed debris to be sucked in and obstructed the dog house cooling fan....Something to be aware of.
Yes, that was on the oil temp gauge. I also have a 4" aluminum duct attached to the cut out in the bulkhead in front of the fan inlet that goes down under the b-pillar on the passenger side to scoop air to the fan.
Sorry to resurrect a dead thread, but I wonder about the original Speedsters. Having a similar grille area, how did Porsche get sufficient air into the engine compartment for induction and cooling?
Not a Speedster owner at the present time, so please excuse my lack of knowledge, but I have a couple of other questions:
If one did cut an additional hole into the firewall at the cooling fan location, would said hole be visible from the cockpit? Is there space between the firewall and the rear cockpit bulkhead? Could one guard somehow the opening the "outside world" with, say, something like hardware cloth to prevent sucking up leaves, plastic WalMart bags, and various road kill?
How to get the correct amount of cooling air to the engine compartment is never a dead thread. It gets recycled all the time. Al is correct that cool engine air is a necessity to air cooled engines. However, there is very little agreement on how best to accomplish this. If you doubt that statement, check out the 356 registry some time on the subject.
Much of the engineering talk and science is over my head, as laminar flow and coefficients of expansion were not part of my course work at school. Some owners swear that additional louvers are the hot ticket, while others suggest a firewall opening to let in more air flow. Of course, there is always another scientist that says those suggestions are rubbish, due to the following incomprehensible equation: -------.
Here's my take on the subject: There were about 76,000 356's made in various models, with varying engines, but even the 356C in 1963 only had 95 HP. Most auto engineers agree that 1/3 of an engine's power goes for work, 1/3 goes out the exhaust, and 1/3 goes to removing heat. Yep, that much energy goes to cooling. Most of us have lots more power than Porsche designed in that engine compartment (actually, only the deck lid is Porsche, while the rest of the design, including engine tins, is pretty much '60's VW). More power means more waste heat, which means you need to improve the means to rid the engine of excess heat, as the stock cooling elements may be inadequate.
You see lots of diffferent scoops, raised lids, deflectors, bilge pumps, cooling shrouds, etc., all designed to pull in cool air to the engine compartment, or to place the available air in the most effective site on the engine (DTM, etc). Most owners bypass the problem by adding one or more oil coolers, and increasing oil capacity. There are lots of owners on this site and others who are way smarter than I am about methods of improving the heat dissipation of a/c engines, especially 2+ liter variety, and, even among them, there is little agreement.
Some would suggest that Porsche's entrance to the water-cooled world was prompted by going as far as they could with late 356 and early 911 air-cooling, and that water cooling frees up the additional design elements necessary to make more efficient, big power.
Part of the reason why big a/c power costs so much is that parts really need to be bullet-proof to withstand the less-than-optimal conditions they will be forced to run in, which mostly means high operating temps. There is no simple answer, or we would all know it by now.
There is a space between the fire wall and the back of the rear seat of about 4 or 5
inches . I think hardware cloth would strain out the big chunks and you should get fairly clean air, unless you go off road or something crazy. I've been wondering myself, if it's worth cutting a hole while my engine is out, or leaving the tin that's against the fire wall off when I reinstall the engine to get more air in there.
On all my past builds I leave a 1.5 in space between the rear firewall bottiom and the motor tin allowing for additional cool air.
On all my past builds I leave a 1.5 in space between the rear firewall bottiom and the motor tin allowing for additional cool air.
I'm wrestling with this decision right now. Presently, I'm leaning towards installing the rear plate and then doing some air intake testing.
How to get the correct amount of cooling air to the engine compartment is never a dead thread. It gets recycled all the time. Al is correct that cool engine air is a necessity to air cooled engines. However, there is very little agreement on how best to accomplish this. If you doubt that statement, check out the 356 registry some time on the subject.
Much of the engineering talk and science is over my head, as laminar flow and coefficients of expansion were not part of my course work at school. Some owners swear that additional louvers are the hot ticket, while others suggest a firewall opening to let in more air flow. Of course, there is always another scientist that says those suggestions are rubbish, due to the following incomprehensible equation: -------.
Here's my take on the subject: There were about 76,000 356's made in various models, with varying engines, but even the 356C in 1963 only had 95 HP. Most auto engineers agree that 1/3 of an engine's power goes for work, 1/3 goes out the exhaust, and 1/3 goes to removing heat. Yep, that much energy goes to cooling. Most of us have lots more power than Porsche designed in that engine compartment (actually, only the deck lid is Porsche, while the rest of the design, including engine tins, is pretty much '60's VW). More power means more waste heat, which means you need to improve the means to rid the engine of excess heat, as the stock cooling elements may be inadequate.
You see lots of diffferent scoops, raised lids, deflectors, bilge pumps, cooling shrouds, etc., all designed to pull in cool air to the engine compartment, or to place the available air in the most effective site on the engine (DTM, etc). Most owners bypass the problem by adding one or more oil coolers, and increasing oil capacity. There are lots of owners on this site and others who are way smarter than I am about methods of improving the heat dissipation of a/c engines, especially 2+ liter variety, and, even among them, there is little agreement.
Some would suggest that Porsche's entrance to the water-cooled world was prompted by going as far as they could with late 356 and early 911 air-cooling, and that water cooling frees up the additional design elements necessary to make more efficient, big power.
Part of the reason why big a/c power costs so much is that parts really need to be bullet-proof to withstand the less-than-optimal conditions they will be forced to run in, which mostly means high operating temps. There is no simple answer, or we would all know it by now.
Mr. Kelly, thanks for your detailed and considered reply. The idea that you espouse does, I think, fall in line with my thinking: That if one installs an engine of similar displacement and horsepower to what was originally installed, then the cooling capacity and air intake volume is sufficient. But go with an engine that makes "big" power, then cooling becomes problematical.
Remember that these engines are "hot air" engines which produce power by heating a volume of air (by mixing it with gasoline and igniting it) which expands inside the cylinder, and this expansion actually does the work. Also keep in mind that there is a given amount of heat energy that can be produced by burning a given volume of gasoline. So, if you want more power, you have to introduce more air, plus more gasoline to heat it, and this will produce more heat. You don't get something for nothing.
What is true, of course, is that a larger engine does not necessarily ALWAYS consume a proportionally higher volume of gasoline to heat that larger volume of air that it consumes. That's what a throttle does for us. But, considering that the fuel metering system of the engines under consideration here is less than precise - a carburetor is more of a plumbing device than anything else - a larger engine can be presumed to consume more fuel in a general sense in all operating modes than will a smaller one - and thus make more heat.
So where does that leave us? I am thinking along the lines of a 1600 "Normal" engine with regular "non freeway flyer" gearing. These cars are approximately the same weight of a "real" Speedster (merely about 120 to 150 pounds lighter), and should produce similar power. The cooling system, sans any extra air intake volume, should be sufficient. Use OEM Volkswagen cooling tin and fan shroud, working thermostat vanes, and "tower" oil cooler, and I would expect to be OK.
However, go with a bigger engine, and I think I would explore "Carrera" louvers on both sides of the stock grille (simply to get more air intake, not to isolate carb induction from cooling air). And if that didn't work, then opening up an additional vent in the firewall, and adding a road-kill screen, would probably be called for.
As I mentioned in a previous post, when I get my IM back I plan on doing some air intake measurements. For reference my IM has a 2276 engine, with dual throttle bodies, and should put out somewhere around 160 hp.
I have a standard 356 style single grill and no extra air intake vents/holes.
When I get the data I'll post it.
Tpelle- As Jim said, this issue is never done with. If every time we discuss it, one person gets something out of it (check out Wildbill's Oct 6th post above) then it's worthwhile. And with new Speedster owners entering the ranks every year, we'll never be done with it. But that's ok, because these motors are a little different than your typical waterpumper....
Someone once said on the Samba that the stock beetle's air intake openings below the rear window measured out to about 30 sq. inches (I don't know how accurate that is, but let's use it for now as it's a nice round number to work with). In 1971, when VW introduced the "doghouse" fan and shroud (the fan is 1/2" wider than the earlier unit), they added 2 sets of louvers (5? sq." each) to the engine lid and in 1972 added 2 more. Again, rough calculations, but for a stock 1600 (with the doghouse shroud) that's now approx. 50 sq inches of air intake. I would hazard a guess that for around town that's way overkill, but with the cooling air having to change direction and enter the engine compartment through these openings (through the turbulent air mass being dragged behind the car starting at the rear window) at highway speeds, this is what the engineers at VW felt was needed. Add more displacement, cam, heads, carbs and exhaust to turn higher rpm's and it's still not enough.
Guys (again, in Beetles) have gotten inventive in bringing more air into the engine compartment; engine lid standoff's at the top (not really useful for us), a slit tennis ball over the latch to space the bottom of the engine lid out (as Wildbill found out, it works, but in a Speedster the pool noodle is a little unsightly and in a beetle at lower speeds can let already hot, spent cooling air back into the mix), cutting holes in the sides of the engine compartment (best when close to air cleaners for best draw), leaving the front (flywheel end) breastplate off or putting holes in the lower parts of the firewall (a bigger hole right in front of the fan access doesn't work in a beetle, as the firewall is the rear wall of the passenger cabin), and even putting access holes in the engine lid under the licence plate. People have stamped raised louvers into engine lids for more air intake, but at higher speeds the raised edges act like airplane wings and create low pressure zones, pulling air out of the engine compartment instead of letting air in.
Now, I realize a Speedster body probably has somewhat smoother airflow over the engine lid (and grille), so less area may be needed to provide enough air for the carbs and cooling system. If there was no inner structure blocking air movement under the grille (14x8", 112 sq") it would be plenty. My older Intermeccanica engine lid has 2 side openings underneath the grille for air intake- about 10x1.5-2" each; 35 square inches or so. While that sounds like enough for a stock motor, from what I've read here, even a 1600 with dual carbs runs cooler when more air intake- usually a 6" round hole (28 1/4 sq in) in the firewall in front of the air intake of the shroud) is added. The object here is to keep overheating conditions from developing- I stated in my earlier (Oct 7) post Gene Berg's findings that engines operating within normal temperature perameters last longer and give the least trouble. And as Al Gallo mentioned, the firewall hole isn't seen from topside. Any type of screen to keep leaves, shopping bags and rags from entering the engine compartment will do. And I've never heard of hardware cloth? Going to have to ask next trip to the hardware store...
I would do the firewall hole before the Carrera louvers (if working on an already built car)- I think the louvers alone, because of their raised edge design, may pull air out, instead of let air in at speed, and without the airflow in from the front, may not be enough. With the firewall hole this may be a good thing, creating even more airflow through the engine compartment (and removing more heat). But I'm only guessing...Al
PS- Does anyone know what the underside of a real 356 engine lid looks like?
Something else worth mentioning- Simply adding an extra oil cooler to an overheating engine is only treating the symptom; yes, oil temps will drop (and everything will seem fine) but if the heads are still running too hot (this is where the extra cooling air volume comes in), only a cylinder head temp gauge will tell you and you'll toodle around merrily until the heads melt down and it dies at the most inopportune time. The heads will not hold guides or valve seats any more and will be scrap(and just think of how much all that nice port work cost!), the piston/cylinders will be junk and even the magnesium case may have been overheated too many times to keep it's shape and may need to be replaced. I've seen a guy ruin a nice 2 liter (150hp?) in less than 10,000 miles that just ran a little "too warm" occasionally and someone toast a just rebuilt motor in less than 100 miles (ok, that one was so his fault because he ran way too much compression, but still...).
It doesn't matter how well tuned or conservative the motor is, if there isn't enough air getting to it to cool it properly, running hot will be an issue and you will be compromising it's life.
I know I said this earlier, but it bears repeating. If you fail to realize how important that statement is, read it again. And again. And...
PPSS- Ron- We'll have to get together in the spring...Al
So it looks like there's not much of a downside to cutting a hole while I have the chance. Thanks
So it looks like there's not much of a downside to cutting a hole while I have the chance. Thanks
I don't see any Al; people's argument's for not leaving off the front breastplate or not putting holes in the firewall have always been the worry of hot air from the front exhaust pipes entering the cooling fan (and it's been proven that more warm air is better than No air, as it still carries heat away; just not quite as much) and a rag, bag, leaves or grass blocking the fan, and with a cht gauge you'll know right away from the sudden rise in temperature. In a Speedster, the hole in the firewall is higher and less subject to preheated air from the exhaust (which in reality you only would have to worry about at low speeds, when there's less worry about hot temps, so I don't think it's an issue). And any screen over the firewall hole will take care of anything potentially blocking the fan. Al
Ps- as I said earlier, a 6" hole provides 28 sq " of air access. A 7" hole is 38 sq " and an 8" hole gives 50sq".
Hardware cloth is a steel screen, usually half inch square holes.
I question that the purpose of the grille is to 'pull' cooling air into the engine compartment.
The curved shape of the entire speedster, especially the turtle deck, acts as a 'lifting' airfoil...creating negative pressure and 'pulling air out of the grilles, louvers, vents. Sucking air in through those apertures isn't going to happen.
Chuck Martin and I discussed this in some detail, and at his suggestion I taped strands of yarn to the grille...At 25mph the strands stand up and limply wavy...At 60mph they're stretched straight up! The engineering purpose of those apertures is evacuation not induction.
I cut two circular 4" holes into my VS's side walls just opposite #1&3 spark plugs for easy access, and fitted the holes with the neck and lid from a Milk Bone brand doggy treat container. An unintended benefit (if the lids are unscrewed and left off) is a noticeable cooling of the fan shroud and the surfaces of all the other things stuffed into the engine bay.
So this is telling me that if there's no negative air pressure (as there apparently isn't in the wheel wells) the high negative pressure above the engine lid is sucking air in through those 4" holes and expelling it out through the grille...resulting in a cooling effect in the engine bay.
If that's true that air only gets evacuated from the deck lid openings, where does incoming air come from? Why go to all the trouble of separating upper and lower engine parts with tin, foils, etc?
Good question Jim,... and I simply don't know!
All I can do is report the visually observation of how the 'airfoil' induced negative pressure effects the strands of yarn...and tactilely feel the lower engine bay temperature after a spirited run with the Milk Bone lids off.
A good test, Carl. It would be interesting to do a few other tests to identify high and low pressure areas. I know that my heater core that is placed fairly high up in front of the firewall and aft of the rear seat back seems to a high pressure area. With the heater turned on and the heater fan turned off, I still get plenty of heat coming into the cabin area.
I'm with you, Carl. I'm not breaking your juevos. I don't know the answers either.
I do know that if I was sitting next to Al during exams at school, I'd be sneaking a peek at his answers. Maybe we should just give the whole thing to Mythbusters. They could rig up some flares or smoke-producing appliance in a wind tunnel, place the smoke by the deck lid, change wind speed, go at different speeds with cameras, watch if smoke goes in or out, etc., etc. The Porsche engineers knew their stuff. They had some method of calibrating engine air availability, and the best way to achieve that needed volume. Granted, that was mostly for less than 100 HP.
Great info Carl! Data like that is invaluable. I think this shows how useful adding extra air intake is. For those worried about dirt in the engine compartment,here are flat K&N filters (round and rectangular) that one could use on the side panels so gunk doesn't end up inside; for that matter there are round filters that would fit the firewall hole as well.
If I get this right, Porsche designed the "cooling system" for the non Carrera Speedster to handle what, 75hp? The additional louvres on the Carrera deck then were not for looks but to provide more evacuation of hot air from the upper engine compartment and help to manage/ extend engine life.
That being said, is there a difference in Carreras in terms of what would be considered air intake, either through the shroud or "firewall", which would complete the picture assuming the goal was more air overall passing around the engine?
Since most of the heat is produced in the lower half of the engine, the tins make perfect sense as a heat shield.
Assuming more cc's/hp require more air circulation to maintain engine life, should those of us with 1915's, 2110's and up be looking at some alterations heretofore not considered standard to stretch life? Admittedly, I thought the air intake and circulation I have, combined with the benefits of a good external oil cooler was the ticket.
I have never pegged the temp gauge, but have had the needle in the upper third of the gauge for as much as an hour or so during "spirited" driving in the summer.
What am I missing here?
Al,
Pearl has a big hole in the firewall, as all CMC's had. She sits at 200°-205°F oil temp up to 95°F outside temp and a sustained 70-75+ mph.
The hole dimensions are as follows:
Hole diameter = 7-1/4" This could be opened up to 8" or so, no problem.
Hole Center: 5" left of the passenger hinge mount, 12-1/4" down from the inside of the cowl (measured straight down the firewall surface from the top). That should make it line right up with the fan opening.
Remember, though, that the CMC's not only have that firewall hole, but the hole is incorporated into a horse-shoe-shaped collar on the firewall to help direct the cooling air into the fan opening more directly. This could be as simple as grafting a piece of PVC pipe onto the firewall to act as an air conduit. THAT part would be simple if the engine is out of the car. The collar protrudes from the firewall about 1-1/4", which puts the "business end" about 1-3/4" away from the shroud's fan inlet.
I fab'd a piece of 1/2" square galvanized mesh screen over the horseshoe collar and screwed in on to keep anything big (leaves, rags, etc) out of the fan.
Here's a picture:
I, for one, am amazed that all VS bodies don't have this same firewall opening. In fact, I once thought it was standard on all Speedster bodies but that's not the case. Maybe it should be?
Bob- What does your car have for air intake? Even a pair of kadrons (with 28mm vents) will draw 250% more air (than a Solex 34-3) at full throttle; combine that with the increased air requirements of more displacement and a wider doghouse fan (200-400 more cfm at 3500rpm) and you can see why the need for more air intake is so important. What do you have for a motor? How high does it rev with power? Does it have an extra cooler plumbed in? A dipstick thermostat http://www.geneberg.com/cat.php?cPath=118_2734 will tell you exactly how hot your oil's getting. Berg no longer carries them but they're in the Samba classifieds.
Gordon- It sounds like you've got it pretty under control. 70 and 75 mph are what rpm's in your car? What happens to oil temps on those 95' days when you try to run faster? What size is your motor?
Wildbill- After the pool noodle experiment, any plans to add more air intake?
Gordon- It sounds like you've got it pretty under control. 70 and 75 mph are what rpm's in your car?
3,500 to about 4K around 78mph
What happens to oil temps on those 95' days when you try to run faster?
I've run in hotter outside temps - pushing 100°F or so - and at regular turnpike speeds for well over an hour and it just sits there at 200°-205°, depending on the height and length of big hills. I have never seen it over 210° since installing the full flow, fan-assisted oil cooler.
What size is your motor? It's a 2,110 with a '73 fan shroud, wider fan, later oil cooling tower, working air vanes and thermostat, including the fan intake modulator (big moving ring at the inlet).
Gn
BTW: a while back I toyed with the idea of a powered engine cover to operate from the cockpit, but never did one.....
A powered decklid is doable. Todd El Taher has exactly that, boys. I think he says it works just fine.
Yeah, I had a power door window actuator from a Toyota I was going to use. It was arm operated, rather than spiral cable and fit the space well, too.
Really easy installation and operation, but the red Speedster build got in the way, and then a lot of elder family issues and eventually the actuator found it's way to the scrap yard when we moved back North.
ALB:
2110cc
Dual Dell 40's
External oil cooler w/ fan.
The thermostat dipstick is a good idea. Merry Christmas to me, I'm getting a new dipstick (for the car).
Bob:
These folks have an excellent one, too. Scroll down to find it, and get the Type 1 version.
While it is neat (and probably very accurate as they say), you can't read it from the driver's seat...
Bob- Does your car have more than the engine grille for air intake?
PS- Here's an oil temp dipstick for $35 http://www.thesamba.com/vw/cla...etail.php?id=1428270
ALB:
No. It is a standard VS build.
Assuming more cc's/hp require more air circulation to maintain engine life, should those of us with 1915's, 2110's and up be looking at some alterations heretofore not considered standard to stretch life? Admittedly, I thought the air intake and circulation I have, combined with the benefits of a good external oil cooler was the ticket.
I have never pegged the temp gauge, but have had the needle in the upper third of the gauge for as much as an hour or so during "spirited" driving in the summer.
What am I missing here?
Although you've "never pegged the gauge, you need to know how hot your oil's getting. The oil temp dipstick you're buying the car for Christmas will tell you that. When the thing starts lighting up the dashlight, try Bill's pool noodle trick. If it helps, then it's time to carve a big hole in the firewall. Or you could do the firewall hole now (at your leisure over the winter and not lose any cruising time during the summer) and not have to worry about it. And if you really want to do as much as possible, follow Carl's lead-
I cut two circular 4" holes into my VS's side walls just opposite #1&3 spark plugs for easy access, and fitted the holes with the neck and lid from a Milk Bone brand doggy treat container. An unintended benefit (if the lids are unscrewed and left off) is a noticeable cooling of the fan shroud and the surfaces of all the other things stuffed into the engine bay.
So this is telling me that if there's no negative air pressure (as there apparently isn't in the wheel wells) the high negative pressure above the engine lid is sucking air in through those 4" holes and expelling it out through the grille...resulting in a cooling effect in the engine bay.
