cold air supply

[7783911]

has anyone investigated how to enhance the fresh air supply for an 83 sc engine so it is drawing colder air from outside the engine bay versus drawing in warm air which is less efficient?

[Iciclehead]

Not an issue, if you look at the location of the air inlet snout relative to the engine grille, it is pretty well a direct line.

Also the engine fan draws in a lot of air, some of which spills more broadly into the engine compartment including the intake.

My recollection is that a member tried to do this and found zero effect....but can't find the thread, but then again it may have been in Porschephiles in the late '90's

Dennis

[pampadori]

Since I have converted to EFI and use an air intake temp sensor to determine density of the air. i have the sensor mounted inside of my air filter on the left bank. i can tell you that the temps in the engine bay are not that hot at all. The fan constantly pushing air down thru the motor's fins and out under the bottom of the car keeps the temps much lower than what you see with other water cooled cars under the hood.

I actually installed my ECU in the engine bay. I was told by many folks that it wouldn't get anywhere near hot enough to worry about it there. They were right.

[IROC]

This subject came up at a PCA tech session back in the '90s and the gentleman giving the talk (Bruce Anderson, I think) said that they looked into this when they were racing 935s and even went to the trouble to design and install some fancy ducting and in the end it made zero difference.

The takeaway was "don't worry about it".

[7783911]

Good, thanks all, i am putting this idea to bed now

[tirwin]

It is interesting that the new Williams designed engine used in the Singers has ducts integrated into the rear quarter windows. I presume this is for better airflow and not for cooler air?

I took this pic at RRVI. The display didn’t have the window ducts attached. I overheard someone say that the stand broke or something like that so you’ll have to use your imagination.

[spuggy]

Originally Posted by pampadori

Since I have converted to EFI and use an air intake temp sensor to determine density of the air. i have the sensor mounted inside of my air filter on the left bank. i can tell you that the temps in the engine bay are not that hot at all. The fan constantly pushing air down thru the motor's fins and out under the bottom of the car keeps the temps much lower than what you see with other water cooled cars under the hood.

This. To quote Wil Ferch from post #18 in this thread Engine Fan Drive Ratio:

for fan sizes / blades / air flow:
1965-74/75....245 mm / 11 blade... 1.3:1 ratio..1390 liters air/sec
1975/76- 77.....245 / 5 blade.......1.8:1 ratio....1265 l/sec
1978-79...........226 / 11 blade ...1.8:1 ratio...1380 l /sec
1980-89.........245 mm / 11 blade...1.67:1 ratio...1500 l/ sec

Turbos used the 245/11/ 1500 set up.

1500 litres/sec is 3178 CFM. Consider how big the engine bay is; the air is constantly being changed at anything over idle. I find if I switch off hot for a few minutes, heat soak will spike my intercooler IATs 10-20C on re-start - only to read ambient again very quickly after driving off.

Originally Posted by pampadori

I actually installed my ECU in the engine bay. I was told by many folks that it wouldn't get anywhere near hot enough to worry about it there. They were right.

Snap.

[Fly911]

The issue on all air cooled Porsches is not engine compartment air temperature, but engine compartment air pressure.

The cooling fan is drawing a much larger amount of air than the motor "air pump", and creates an under pressure (below atmospheric). So the engine has to suck air from a compartment with a lower than atmospheric pressure. Not ideal, and you will lose power.

The way around it is to make a duct for the engine air intake directly to the deck lid grille, duck tail or spoiler. Doing this right, you can actually get a ram air effect, increasing HP with increasing speed. Porsche has done this on the GT3s since the 997, and claims around 10Hp gain at 200km/h.

You can do this scientifically, and measure the absolute air pressure in the engine compartment under full RPM and full engine load, for instance on a dyno. Each 1% drop in air pressure compared with atmospheric, would be basically be 1% drop in engine power. And then open the lid and do the same test under atmospheric pressure.

Unless you are counting 1/100s of a second on a race track, I believe that most drivers will not be able to feel the difference one way or the other.

[chrisbalich]

Sounds neat on a race car, but like a recipe for funneling rain water into your engine for a street car.
Certainly some interesting physics going on in that engine bay.

[ian c2]

Porsche raised the filter-box “trumpet” thing on 993 cars with fixed wings to move it closer to the wing vents compared to the stock 3.2 , 964 , 993 set-up low down at the filter box .
I presume this catered for the different vent angles between a stock angled rear lid and one with a horizontal wing .
I have talked to a few experts years ago about ram-air efforts and have been told lots have experimented and found it not worth while , but I believe as it’s taking its air from a true atmospheric and ambient area rather than down in the depths behind the fan shroud it should be better .
But because the 911 has a cool “top end” (if all tins and seals are in good shape) and runs close to ambient , the gains are so low that I believe the main benefit might be an oversized plenum supplying an instant supply of air rather like the stock airbox .
Considering only people like Alonso would even notice a difference in driving the car , it’s not really worth the effort for such gains considering the top of the engine lid has an opening for rain etc so the inlet is pretty well protected where it’s at right now .

Drain holes are normally drilled in some ram air setups to drain water , just like they are in some filter boxes ...
I’ve not looked on my 997 , but it takes its air straight from the vents in the decklid .

Btw , I’m far from being an expert on such matters but did look into it many years ago as I have a fancy 964 rear wing but no intercooler under it .
At the time 911 parts where relatively cheap , so I looked at getting an intercooler to modify into a ram-air system .

[7783911]

i ve put his idea to bed but to all, thanks for the feedback