JDS968

Is there something there on the Turbo RS that's not there on the Turbo S?

Or did Porsche SERIOUSLY install pointless vents on hand-built limited-production racing cars just to make them look symmetrical?

Not saying they couldn't do it...I just wouldn't expect that.

I now hate you, and want to steal your car.

LTCMontana

I believe you want to 'pull ' air from under the hood. There are many benifits from that versus trying to force more air under there.

Many rodders either remove the seal by the windsheild or raise the hood a little to get more air out of the engine bay.

Here is a more sophisticated way the Subaru guys are doing it...
http://www.octanemotorsports.com/Acc...tml#googlebase

odurandina

what about routing air to a big Crown Vic oil cooler, using a scoop and route the hot air,

\then exit back under the car.

ptuomov

Thanks! ;-)

I agree, but I don't understand how to route a lot of air first above the exhaust manifolds and then out above the hood. Can't think of a practical setup.

One possibility would be to do a full 968 turbo RS and add a hood vent to route out some of the radiator air thru the hood, reducing the amount of air going under the car. Then add the Naca ducts and route that air past the exhaust manifolds and under the car. The net amount of air going under the car might be about same, and the exhaust manifolds would be cooled possibly better.

There's a high pressure zone at the end of the hood / base fo the widnshield. If I unseal that, air is likely going to flow in, not out.

Too high up in my opinion to get the lowest pressure, but might work in getting more flow thru the exhaust manifolds with some additiona ducting. The problem is that there's not a hole helluva lot of room left under the hood for ducts and such.

I don't understand.

LTCMontana

Actually, there is a low pressure area at the base of the windshield because the air is being 'pushed' by the front of the car higher than the hood. If you ever look at wind tunnel tests on passenger cars, the air does not stay close to the area where the windshield wipers are. Case in point: When I replaced the wipers on my 968, I did not get the ones with the small spoilers on them. When I try to use the wipers above about 80 mph, they are worthless because they are being 'sucked' away from the windshield because there is such a low pressure.

Back in the early 70s, Chevy built 'Cowl Induction' cars. The idea was that the air at the base of the windshield was lower pressure, therefore cooler and would then be more compressed when it entered the intake. The cowl induction cars claimed 15-20 hp increase with the option.

Also, the center large duct on the 968 TS was to flow more air through the intercooler; not to cool the engine bay. The IC was situated so that the air would come in the front, over the IC and out the top of the hood intersecting with the air already coming over the hood. This 'heated' the air over the hood thus bringing it closer to the hood and windshield which, theoretically, produced a slight amount of downforce. So, they got kind of a 2 for 1 deal; cooler IC (which made more power) and a little more down force.

Another example is to look at NASCAR induction systems. Air to the carborator is channeled from the base of the windshield.

The GT2 uses the same concept but on a smaller scale.

ptuomov

Newtonian fluids are flowing in their graves! ;-)

Below atmospheric pressure marked with arrows pointing out, above atmospheric pressure arrows pointing in:



That's a Mazda, so does it apply to Porsches? Yes it does. Numbers on the scale are gauge pressures:



If this is true, why does the NACA duct on the 968 T RS pull in air from a low pressure zone? That's a trick accomplished by the NACA duct shape, it uses the air flow speed and converts it to pressure at some cost of drag.

Just one more thing. When you compress air, it does heat up. However, the density still goes up!

FRporscheman

Here's a turbo rs engine bay, I don't see anything under that passenger side duct but a distributor cap.

Lemming

I thought that cowl induction induction worked because of the high pressure at base of the windshield allowed for air to flow into the cowl. For the same reason, this is where the air intake for the heat/ac units are cars are also located.

As for hot rodders, I've never understood the lifting of the rear of the hood and removal or the rubber shield. At speed air would actually be pushed into the engine bay from the base do the windshield. Now, while slowly cruising around town the pressure at the base of the windshield would be low and allow head to escape.

LTCMontana

This guys seems to know what he is talking about....

http://www.datsuns.com/Tech/aerodyna...nd_cooling.htm

A quote from the article:
think the question was, "how do we use the aerodynamics of the car to increase engine cooling" or something like that. Nissan already attempted this in the 280 with hood louvers. Notice that the location of these louvers are as aft as possible on the hood but prior to the high pressure area near the wipers.This places them in a low pressure area, allowing the hot air in the engine compartment to vacate.This also allows the air stagnating on the nose to more easily pass through the radiator.


I am certainly not an engineer, this guy obviously is. While I wasn't exactly right on where the low pressure was on the hood, this guy seems to get very specific.

LTCMontana

By the way... Good discussion wtihout throwing stones. I need to get out of OT more often!

Lemming

On the 928, the low pressure area seems to be further forward than on a 280Z based on the Porsche figure (above and copied below).



And the 944 as well.

LTCMontana

Good on ya Tim. I tried to find the diagram for the 928 but was unsuccessful.

The article does make good sense.

ptuomov

Installed the belly pans and it helped noticeably with underhood temps. The bellypans must be directing the radiator air past the exhaust manifolds.

https://rennlist.com/forums/928-foru...treets-28.html

FRporscheman

That's good to know!

Lemming

Yes, belly pans are critical on these cars, the louvers help to draw air out and keep air from getting pushed up into the engine and creating a high pressure zone. There have been a number of posts to this regard over the years.