Engine Compartment Temperatures Measured

Good Work Michael !  Once again....Seal up that engine compartment to the Max !!

Some of my testing a few years ago indicated that the engine comp. grill is adequate and didn't create a negative pressure (vacuum) in the engine compartment at any load.  BUT...That "rain guard" under it does ! There are about 4 common remedies that are brought up on this site occasionally.   To raise the hood a little.   To cut holes in the rain guard but this deletes the purpose of the rain guard. To drill holes behind the license plate.  To enlarge the inlet opening between the rain guard and the hood on the final inside opening into the engine compartment.  I like this last one because it really doesn't show any noticeable change or modifications.  Maybe a little more work to remove the hood but at least your project will be on your work bench with a cold one sitting next to it.

Again Michael Thanks......this kind of data is always good to know.  Posting it on here will perhaps help someone in the future........Bruce

Well done Michael!  Did you notice any difference in how the engine felt at the lower temps?  The reason I ask is that whenever I was able to lower intake temps when it was warmer out in my Cal Look Beetle, the engine performed better, being closer to optimum tune more of the time.  Engine lid stand-offs were great, letting a lot of latent heat radiating from the engine itself rise, and removing the engine lid altogether was even better- the engine just felt happier.  Unfortunately I didn't like the look of either and had thought of experimenting with ducting cooler air from under the car into the engine compartment, but sold the car before getting to it.

I suspect that intake temps may not be quite the issue with fuel injection to the extent it is with carbs...  Al

I agree Al. Excellent work, Mike!

The intake temps are true temps because there is no fuel there to cool the sensors.

There might be in a carbureted car, which would possibly lower the carb temperature itself and in turn the intake air.

The throttle bodies spray from the below  the throttle plate down the manifold. The carburetor's accelerator pump and main jet do have a cooling effect, hence the term "carb icing".

Cool air is better air. It's more dense, which allows better cylinder filling for combustion. It does a better job of cooling (and not just because it's cooler to start with - the density thing helps here as well). It's just better.

It's why racers will throw a bag of ice on the intake between rounds. It's why the first thing tuners do to their 1994 Honda Civic is put a cold air intake to go with the coffee can exhaust. It's why turbos use innercoolers. It's why your car runs better first thing in the morning, or on a cool night.

The holy grail is when the air is cool and misty. The latent heat of evaporation works miracles here. Water/ethanol injection is a real thing, used on WW2 piston aircraft (the high-water mark of piston-engine awesomeness).

I've always wanted to try an EFI 12:1 street T1 with alcohol injection.

Well done, Mike.

Nice scientific investigation with concise summary! 

The engine has an external oil cooler (no internal cooler). Just to clarify - no OEM internal shroud air cleaner/dog house shroud oil cooler? Is you external cooler piped off where OEM cooler was or the usual add-on off the oil pump?

Early IMs don't have the later CMC cut 1/2 moon cut out in fire wall behind fan shroud (or the VS circle air intake)?  Is the area above flywheel open to allow fresh air into engine (per CMC build manual - it isn't tightly sealed there).  Wonder if this would make difference? 

I'm in Hot NW FL so curious.

@WOLFGANG posted:

The engine has an external oil cooler (no internal cooler). Just to clarify - no OEM internal shroud air cleaner/dog house shroud oil cooler? Is you external cooler piped off where OEM cooler was or the usual add-on off the oil pump?

Early IMs don't have the later CMC cut 1/2 moon cut out in fire wall behind fan shroud (or the VS circle air intake)?  Is the area above flywheel open to allow fresh air into engine (per CMC build manual - it isn't tightly sealed there).  Wonder if this would make difference?

I'm in Hot NW FL so curious.

Good questions, Greg. I'm running a 36hp doghouse fan shroud with a block-off plate where the OEM cooler was. The external cooler is piped from the oil pump area. I think you are correct about early IM not having the CMC firewall cutouts - mine doesn't have one. The area above the flywheel and along the front of the engine isn't tightly sealed. It's still pulling air from the open space between the package tray and the firewall.

I haven't measured the temps behind the firewall (yet). For me, it wasn't a priority because I located the big AC condenser and fan there and didn't want a lot of air mixing.

Stay cool!

Some of the questions made me think to add some details about the setup. The engine is controlled by a Speeduino ECU. It has a pair of 45mm throttle bodies and the fuel injectors spray into the intake manifold ports. The Speeduino unit is setup to add or subtract fuel depending on the temperature of the intake air, so theoretically it can always hit the desired air:fuel ratios regardless of engine temp or ambient temps.

The rain tray on the engine lid was cutout by the previous owner. I've never replaced it or seen any problems, but, we live on the dry side of the island. As Greg notes above, early IMs didn't have the license plate cutout. I added one during the rebuild.

There is no cutout in the firewall. I located the AC condenser behind the firewall and didn't want to mix the air, so I didn't add one. The front of the engine isn't tightly sealed, so some air does come in.

The previous owner put rectangular cutouts into the wheel wells on the outside of the carbs (throttle bodies). Temperature measurements at the open cutouts showed that they provided no cooling so I blocked them off.

The engine lid has the Carrera louvers on either side of the grill. It has rubber standoffs that leave around a 1/8" gap when the lid is closed. Here are some pics:

Carrera lid and license plate cutout

Measuring air temp coming into grill area - no rain tray

Measuring temps outside the air cleaner to verify that heat soak wasn't raising the intake temps inside, where the intake air sensor is permanently mounted (temps were the same)

Firewall with NO cutout (at top of pic). At bottom of pic, package tray area behind firewall where I located the big AC condenser (small one up front behind headlight). You can see the Speeduino ECU and Bosch coil pack temporarily located on the firewall. They are now relocated.

Thanks for taking the time to do the testing,

Is there a way to check airflow and dead spots by using yarn tuffs  and GoPro type camera around the engine?

Or maybe a smoke bomb stick ,  just to see how the cool air enters from the grill etc and is sucked into the fan.

Any ideas if Porsche ever did tests in the engine compartment  to measure airflow ?

Great testing and reporting on this Michael.  Air Cooled engines do so well in fall weather IMO the car just seems to be so responsive with all that cold dense air.  Must be why a friend loves to fly in that time of year as well.

@ALB, I didn't really get on the throttle too much during the testing and didn't notice a difference. However, as @Stan Galat and @IaM-Ray note above, cool, dense, air always makes the engine perform better. On cool mornings, I can definitely feel the improvement.

Regarding air/alcohol injection, I autocrossed a supercharger equipped Miata a while back. I played around with air-water and air-air intercoolers on the Miata. Cooler air lets you add more timing advance without the knock.

On top of that, I added a water-methanol injection system that really kept hot engine knocking away and kicked up the performance. My 60% water - 40% methanol solution was just some windshield wiper fluid that is currently banned in a lot of places (right @Sacto Mitch?).

Ah, but tweaking supercharged and turbocharged beasts is far behind me. I'm just going for perky and reliable these days.

.

There's a lot to be said for perky and reliable.

Maybe it should say 'Perky' on the side instead of 'Speedster'.

Sometimes I think most folks who stop to chat just want to pat it on the head and scratch it behind the ear.

.

"Perky?"

More is more.

@Stan Galat posted:

"Perky?"

Get your mind out of the oil sump, Stan 🙂

@Michael Pickett posted:

@ALB, I didn't really get on the throttle too much during the testing and didn't notice a difference. However, as @Stan Galat and @IaM-Ray note above, cool, dense, air always makes the engine perform better. On cool mornings, I can definitely feel the improvement.

What I noticed, Mike- as well as the engine running and performing better when the engine intake temps were closer to ambient (outside the engine compartment), when you got on it and used the power on tap it performed better for longer and you didn't have to worry as much about the tune (and power) going away as it took way longer for engine temps to get outside normal operating parameters.