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Repeating a question posted late in the Engine Surround topic, where @aircooled and @Alan Merklin differ about the need for some air through the firewall. My current project is closing up the firewall of my 2017 VS build, blocking off the ugly screened air hole and the huge gap below it through which you could see the tops of the heater box flapper valves. My question is how do Vintage Motorcars builds address this issue. Do they rely 100% on air flow through the engine lid grill, or supplement it some way?

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Thanks, @Robert M . Mine has a remote oil cooler too and one reason I am sealing the firewall is to keep from drawing in heated air from the "between the bulkheads" space where the remote oil cooler lives. The photo galleries for VMC builds on BAT  don't tend to spy obliquely into the space behind the fan shroud and carbs where I can crib ideas. Hoping a VMC owner will respond as you suggest.


Remember, the 356 couldn't have had a vent on the forward panel because that would have opened directly into the passenger compartment.

And I'd think sealing along the top of the transaxle was more about keeping out slush, snow, and Schmutz than anything else (since once in, all that stuff would have collected there because the compartment was otherwise closed at the bottom).

If I recall, early Kirk era VS cars had no vent in that panel, but it was added later on cars with the 1915 engine, presumably for venting reasons. (Kirk usually didn't spend extra time or money on a build unless there was a good reason.)

While there's not much proof that the vent helps overall cooling, I haven't seen any evidence that it hurts anything, either.

When I moved the remote oil cooler from that forward space to the wheel well, I added a fan that forces air from there into the engine compartment. I eventually concluded the fan made no difference to oil temps if it was running or not. Didn't help, but didn't hurt any.

But I did discover one curious thing. I am cursed with the usual hard-to-start gremlin, if the car is run hot and then shut down for 10 minutes or so (say, at a gas stop). Restarting is much easier if I run that fan during the stop. It blows almost directly onto the carbs and I have convinced myself that reduces liquid gas percolating into vapor in them.

I don't know that I'd put any effort into adding the vent, but I also wouldn't bother covering one up that already existed.

One man's opinion.


“Someone” (@aircooled) went a lot further than that and did manometer readings.

We’ve talked a lot about this, and generally agree to disagree, but he (Bruce) is the guy advocating for sealing the entire engine compartment. His opinion isn’t based on feelings and supposition, but on data.

Based on “expert opinion” here, I cut two giant holes in my firewall and (like Mitch) installed two axial fans. They do nothing good, and I can prove that running the fans makes the situation worse (I monitor CHT on all 4 cylinders).

The engine sucks huge amounts of air down the carbs and into the fan. The idea that it should be pushing air out the grill rather than sucking it in is just silly. The aerodynamics are actively working against this, and a “tuft test” may show the yarn blowing up at speed, but that doesn’t mean that the engine’s requirement for air is any less.

It’s a problem, but (IMHO) pulling hot air from the bottom side is not the solution.

Last edited by Stan Galat


OK, I've already begun here, so why stop beating a dead horse, now?

Just to be clear, the fan I hooked up blows air from what I'll call the 'forward compartment' into the engine compartment. My thinking was raising the air pressure in the engine compartment should help both the engine fan and the carbs draw more (and cooler) air. Maybe it does, but that doesn't seem to lower oil temperature significantly.

There are a few complicating factors here that always liven up and confuse the discussion.

The first is that the most power Porsche ever put in the engine compartment that most of us have (i.e., with a single vent grille on top) was about 70 hp. When they got up to about 90 hp, they doubled up the vent area. When they got to 130 hp, they had double vents, plus two extra rows of louvered vents in the deck lid, plus a remote oil cooler at the front of the car. Who knows what they would have added if they'd ever gotten to 150 hp, as some of us have.

The second complication is where Kirk-era VS mounted their external oil cooler if you ordered one — in that 'forward compartment' I mentioned above. This has to be the worst place for an oil cooler, as it has little airflow through the compartment, trapping the heat the cooler is supposed to dissipate. What made the old VS installation even worse was that vent opening between the forward compartment and the engine compartment. Engine heat from the oil cooler would get drawn through the vent and back into the engine through the fan and the carb intakes.

Curiously, Greg now mounts his oil coolers in the same place. But I think the reason his cars no longer have a vent between the two compartments is to keep the oil cooler heat from reentering the engine. In my car, that forward compartment is open at the sides and bottom, so maybe heat buildup around the cooler isn't as bad as intuition would lead one to believe.

That forward compartment is just about the only convenient place to mount the cooler without having oil lines conflicting with headers and exhaust pipes, and it allows the oil lines to be tucked up out of the way. Putting the oil cooler in the wheel well does involve some fussy and, uh, artistic fabrication, which you probably don't want to entertain if you're trying to pump out cars on a production basis. The wheel well also subjects the cooler to potential damage from road debris. A good installation includes some shielding from rock damage, but that further complicates things. In seven years, I've had no issues, though. Good Karma, perhaps.

And how many have noticed that the Pat Downs 2332 no longer has an extended sump on the bottom? (Let's not always see the same hands.) Maybe Pat has been doing some secret research on temperature management in the oversized Type 1 motor? You just never know what he's up to.


Last edited by Sacto Mitch
@Sacto Mitch posted:


And how many have noticed that the Pat Downs 2332 no longer has an extended sump on the bottom (let's not always see the same hands). Maybe Pat has been doing some secret research on temperature management in the oversized Type 1 motor? You just never know what he's up to.


Deep sumps have little to do with cooling.  They are designed to provide more oil for more rpm.  Pat’s 2332 is not really designed to rev, it is built for low to mid range torque. Parts left off cost zero money and cause zero problems.

Heat is our enemy. Yes, you need it to get cars down the road and we've done a pretty good job of doing that over the last 100 years. But, we're still only getting around 35% efficiency. Most of the heat goes out the exhaust and the radiator (or cooling fins) and right back out on the street. Quite a waste of energy ! Too much heat kills the engine or transmission or brakes or even the whole car if it's on fire !

I have always thought VW/.Porsche did a simple thing by making engines air cooled. As someone above mentioned, " less parts is less cost and less problems" Hence, no water pump, radiator, hoses, etc. Their approach looks pretty simple but upon further review, it's not. They seem to be pretty direct in how they get rid of the heat. Suck it all in thru the grill and dump it out underneath thru the exhaust and the cooling fins. Extreme effort was taken to absolutely separate the intake air from the spent air by totally sealing off the engine compartment in any way for that not to happen. That is a simple and smart solution but not easily accomplished as we have found out on our little cars.

Yes, I am an advocate of totally sealing up the engine compartment in any way possible to insure air only comes in the grill/s and blows out underneath with the airflow down there. Even "down there" the Germans made sure the flow was directed to the rear by using more sheet metal !

Any of us can do this task and it should be considered in your sorting out your car from the very first. Once you are absolutely certain you have it sealed up properly, then, you can play with ideas that  (MAY) help to cool better.  Feel, seat of the pants feeling, assuming , guessing or other efforts don't count. Actual measurements do ! Stan has 4 cyl. head temp. senders and gauges. I had 4 senders but only one gauge and a rotary switch to monitor cyl. head temps. I also measured oil temps in 5 or 6 different locations. I used a Manometer to measure positive and negative pressure. (vacuum and pressure) all over my car including the engine compartment, that void in front of the firewall, the wheel wells, at the rear bumper, in front of the wind shield, along the body sides with stand-offs of differing distances from the body surface.  All of these results are in the archives on here. Posted in 2014 I think.

I tested air/fuel ratios with disastrous results when I realized that my pick-up bung I welded in my exhaust was too close to the collector.

Any of us can and will take short cuts (including me) to achieve our desired results. Sometimes we're successful and sometimes we're not. Sometimes we think we  were and come to find out we weren't !

Our engines are putting out a lot more power (read heat here) and do require a lot more attention to how the air is induced and discharged. Keeping it simple. Coolest air available in and hot air out. Never the twain should meet ?  Ha Ha

I'm in Mexico now and have more time to be on this site. If you'd like  to ask questions of me on this subject please feel free to PM me here.  I don't mind. There's a lot of others on here too, who are really experts (and you know who you are) on a lot more topics than me.

Just a final thought There applications where this engine compartment sealing is not applicable. Such as a Dune Buggy !  Or a full fledged drag car ! Heck ! Many of those don't even have a fan on them ( but watch how fast a fan gets put on them back at the pit!)................Bruce

Actually , cooling ducts and efficiency are very important for FV.

You need clean and sealed cooling ducts for the heads and cylinders, which usually dump the hot air under the heads which is mostly into the airstream.

You need the same sealed and clean ductwork to the oil cooler, and the exit for that goes over the trans, which is where the exhaust lives. My oil was running 215 to 225, I re-engineered my ducting and dropped it to 180-190F, at 80F ambient.

I also have a NACA duct on one side which pushes cool air through the intake manifold/carb area to keep it cool.

All this cooling is from ram air.

Last edited by DannyP

I run a 2.5 L Subie in my Coupe.  I have a radiator set up in the rear deck lid area as the Subie is mid engine on my car..  I found that I had to put closeouts around the whole radiator.

Then, I have two 10 inch fans under the radiator pushing air up through the radiator.  I have an additional 10 inch fan that is on top of the radiator and blows the air out the grill on the decklid.    The fans are set to come on at 190 degrees and do a good job on keeping things cool.  The most that I ever see the engine temp go up to is 205 degrees when I am running 70 mph in 5th gear over an extended period of time .

So far, So good......  I have considered an oil cooler and I may still do that but for the time being , I am running with the increased air flow solution via multiple fans.


Dr. Chris

That's actual pretty cool, Chris - using the natural high pressure zone under the car and low pressure zone above the deck-lid to your advantage, rather than fighting it as we do with rear-engine, air-cooled cars.*

Perhaps the solution for us is to mount the air-cooled engines upside down and draw from the bottom and exhaust the air out the top.**

... and back to eating my crayons I go...***

*Seriously, that's a great idea for a rear mounted radiator, and made possible by the setup. Well done.
** This is sarcasm, and an attempt at humor
*** This is because I'm not one of the smart guys in the room.

Last edited by Stan Galat

When I got my VS the optional chinesium cooler bungs were stripped and leaking, so I junked it.  I got a Setrab cool pak with a fan and made brackets which mounted it at a downward angle so it would pull air thru the cooler and blow it out below the car.  I then put a 190 degree thermostat on the cooler and a 200 degree switch on the cooler fan.

     After I did this, the cooler fan never ran even after a heat soak on a hot day so I know the oil temp was staying below 200.  The Setrab cooler is night and day better than the one that came with the car.  My car had a 150 hp 2110 in it.

Great info on the previous posts. I believe the air flow on the single decklid grille on a fiberglass replica is restricted as compared to a real steel Porsche. My approach is to try to keep the compartment as sealed as possible around the engine and rear of the car itself but the area behind the fan shroud is not that critical especially if you don't have a remote cooler expelling heat and mounted on top of the transaxle or in that general "between compartments" area. My thinking is that any air that gets in the compartment aft of the motor or from the decklid grille above is cool; air expelled from the engine to the back is hot so you don't want any of it entering the engine compartment through the back of the engine compartment or the taillight area which is open in many of these cars. Many years ago using old Gene Berg literature I did fashion a little aluminum 1" x 12" scoop that I installed on top of the right torsion bar and hooked it up to a regular VW heater box hose which I then attached to a hole I cut on the back engine tin on the right side. Still not sure if it's that effective but the car seems to work fine. The only time I seem to get higher oil temperatures (oil light flickering using the Gene Berg oil temperature dipstick) is under sustained highway speed driving for a fairly extended time; (meaning 3,000 rpm and over) which I suspect is  a lot of people with cars without external oil coolers (mine doesn't have one). My car doesn't have the hole on the firewall because I had ordered a 1776; at the time they didn't have any so in an executive decision Kirk installed a 1915 (I would've preferred 90.5's) on the car which was prepared for a 1776 (so obviously no hole in the firewall).

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