14.7:1 air/fuel ratio is called "stochiometric" ratio beacuse it's perfect ratio where all oxygen get's used in combustion process and where catalyst performs at it's best.

It's not optimal for max power tough...

tbitz,

looks like it's time for a trip to the dyno. Interesting results. Hopefully others, including myself will check this out too so more data can be collected.

cheers
-Brad
80SC

Fascinating. Is this similar to the RAM AIR design we see on most modern cars these days?

tbitz,
Thanks for exploring and sharing this with us. I would have guessed that the air temperature would increase no matter how much air is pulled into the grill opening. The engine is hot (lots of heat energy being released inside of it), and this heat radiates outward, warming the air around it.

Now if we could only find a suitable/convenient location or device to draw in just air (not water) from the grill. Under the car contains too much dirt, grit, dust and potential water splash.

Bill's race car pic shows an ideal location to draw in relatively clean, dry ambient air (through the engine bulkhead). If one had the A/C switched ON ..... :)

I don't want to wander too far from Tbitz's original thread but there's a device that lowers air temperature about 18-20ºF. It uses water and may only be justified on a race car or some other cooling application (intercooler, oil/water cooler, brakes, etc.); perhaps too radical for "normal" cooling. A racing customer reported using it directly under his turbo engine air shroud to lower cylinder head temps. approx. 45ºF.

Sherwood Lee
http://members.rennlist.org/911pcars
MPC

How about the location Porsche chose for the GT1? I'm assuming that the scoop on the roof provides ram air induction - is this correct?

I think "Ram Air Induction" is useless for a street car. At 100Kph the boost you get is nil.

The idea here is for a "cold air intake". A more appropriate name would be "ambient air temperature intake", because "cold air intake" implies the air is chilled somehow which it is not with a "cold air intake".

Peter Kelly's response to my posting:

"This is completely false information. Most race engines are tuned to run an air fuel ratio in the high 12's (12.7 to 12.9 to 1 air fuel ratio) The literature is full of proof that max power is achieved at around a lambda of .87... .87 x 14.7 = 12.789

The only thing 14.7 air fuel ratio is optimum for is emissions."

The info I posted was for a street engine which has to respect emissions regulations and be driveable. What's false about my posting? I never said race engines are not running rich (lambda less than 1) to make horsepower. Porsche likes to run as lean as possible so as to maintain the fuel consumption advantage (less fuel means lighter weight and less pit stops) and higher technology proves my point that lean burning does not mean less power or early destruction of the engine by running at the edge of efficiency.

tshih

I'm not sure its really a flaw, as opposed to a decision to not overly complicate things for 5 hp.

Car intakes have been designed to pull in outside air for decades now. But, on most cars, that is pretty simple, just run a short tube up to the grille/headlight area.

Not so simple on a 911, given the layout of the engine compartment and its design. It could, of course, have been done, but for 5 hp probably was not worth it.

The problem seems to be that the proposed position is not rain friendly - hence for all we know, Porsche tried and discarded it.

Just thinking, Chuck posted:

"I do recall reading someplace about a guy who carefully fabricated a cool air / ram air scoop. The author was dissapointed when after all his hard work the car showed no increase on the dyno. I just can't remember the source."

Was he feeding it cold air? I see ram air as being advantageous at providing a ready source of cold air flow - this might not happen on a dyno.

Perhaps if anyone goes to a dyno, they could also take 5 mins to try what Sherwood suggests (water misting, I assume).

Here is the final chapter on this topic.

On my way back from work today I hooked up my ECU to the porsche oil temperature sender. I could now monitor oil temperatures, intake air temperature, and ambient air temperature. All this data is captured while the car is moving.

I drove on the H/W at 100kph long enough that the oil temperature did not change anymore.

With the home made cold air intake installed I got the following data:

ambient air temp: 77F
intake air temp: 79F
oil temp: 184F

Then I removed the cold air intake and drove at the same speed until the oil temperature did not change. The following is the data:

ambient air temp: 77F
intake air temp: 103F
oil temp: 191F

The data shows that without the cold air intake the oil temperature increased by 7F. Also the intake air temperature also had risen by 24F.

With all the data I've gathered people can make there own conclusions if it is worth having. For those that only drive in dry weather, it is easy to hook up.

I will be looking into a better solution to the cold air intake once my CIS-to-EFI project is complete.

Cheers,

has anyone confirmed what these ducts on the fenders are for? They are factory.

http://forums.pelicanparts.com/uploa...1090014907.jpg

The rear fender ducts are for the intercooler (turbo S body and aerodynamics pictured), the small ones in the front bumper next to the turn signals are to duct cooling air to the front brake rotors, and the ones below them on the ends of the front air dam are for the air con ditioning radiator condenser and oil cooler. That's my best guess.

I just found this picture? Anyone have details?

http://forums.pelicanparts.com/uploa...1091562565.jpg

hallo
The rear ducts on a turbo S are for Brake cooling only ,as you see in the picture there are small ducts in the Tail ,these are for the Intercooler as well as the bigger Grill in the TT tails . The front ducts are for the front brakes .On the 996 TT the rear ducts are for the Intercoolers ( they are in the Quarterpanels on eaxch side one )
harald

Tony, did you ever come up with a more permanent solution for this? If there is a thread, please point me to it and I will read it.

Thanks,

on a kinda related issue- I seem to remember my old jag XJS had the gas cooled by the A/C for more power!.
Maybe the A/c should be redirected into the intake :rolleyes:


Also with high power marine deisels often the fuel will go through a sea water heat exchanger to reduce temps which have risen due to re circulation of unused diesel back into the tank.

Wow. Started this thread 3.5 years ago.

I haven't done anything more on the cold air intake, but now that I run EFI I have logs of intake air temperature and I can clearly see how the intake temperature is rising with the engine running.

Ben, who is on this board, is installing the EFI kit and is making a custom air box that will take cold air directly from grill. Check out this link:

AIR BOX

Tony

I local machinist and friend fabricated a plexiglass cold air intake for his SC. He claims a higher top speed on the front straight of Road America...

Cold air..hot air...we all know that cooler denser air is better than hot thin air...

I am very close I will post pictures later this week maybeeven tonight. As with all my projects there will probably be revisions but check it out

Pretty sure he's sponsored by Home Depot's Plumbing Dept.