Cold Air and 911 intake?

[sdether]

One thing i've been wondering about is the huge selection of modifications for "cold air intakes" in most non-porsche aftermarket scenes. I know when I had my MR2 turbo, keeping the air cold was a significant concern, both in shielding the actual intake, insulating the air pipes to and from the turbo and adding an intercooler, although i can't tell if the danger of heat was mostly due to the heat produced in compressing the air and not so much engine radiation.

For NA cars, I've never seen any dyno proof that cold air intakes really produce that claimed HP increase. Especially since most conversions are both a cold air conversion and a high flow filter conversion, so how would you properly attribute the gain.

On the 911, i've haven't seen cold air intake modifications. Most vents in fenders are for brake cooling. The whaletale is usually downforce and on turbo's provides air cooling to the intercooler.

But NA 911s have their intake sitting on top of the engine, using air from the engine compartment. So, is cold air just not as important as many people try to make it seem, or is the flow into the engine compartment under speed better than I assume?

[RickM]

While many NA cars have a tail air is brought in through the decklid grill on tail-less 911's. You also have the fan pulling quite a bit of air.

[randywebb]

search button will find a lot of thoughts if not much data

this is easy to measure and at least one person did so.

[sdether]

Originally posted by randywebb
search button will find a lot of thoughts if not much data

this is easy to measure and at least one person did so.

Ah yes.. I only scanned the first page of search results and decided to post not seeing anything there that fit the question. Second page of search results, different story.

Thanks

[Jack Olsen]

You won't see a lot of guys adding an accusump to their 911 either.

The blower keeps the air in the engine compartment very cool.

[Wil Ferch]

Therein lies the problem..

On the one hand...Jack Olsen's view mimics my own...the very large quantity of air brought in by the fan makes a cold air induction superfluous....

however.....

Tbitz ( ?) actual field testing with instrumentation seems to say otherwise...see archives..

So for me..the jury is still out.....


Wil

[Craig 930 RS]

If you have OBD/OBD2 one can monitor the intake temps.
They are nice & low - on mine - even with the stock 993 box which is cut open.

IMO one of those over-hyped things on a 911.
BUT there was a different case where high temps were shown -

[Wil Ferch]

I'm not sure if it's over-hyped... IF ..as Tbitz tests indicate....we're talking about 10+ degreesF ( maybe 20?) difference in intake air temp.....


Wil

[coolbeverage]

so how would you properly attribute the gain.

with the seat-of-the-pants-dyno that is the only one that really matters anyway isnt it?

[JBO]

Though not exactly on point, I have a question on airflow. It appears on my 911SC with a tail that the lower one half or so of the decklid has 2 layers of metal with a gap between (it may extend into a portion of the grill opening but I can't remember), and it would seem to help if the inside layer was cut out. If nothing else it would save some weight. Is that layer to help with water flow? It may not be at all clear what I'm talking about, but if anyone has a clue I'd like your thoughts!

[Craig 930 RS]

I'm not sure if it's over-hyped... IF ..as Tbitz tests indicate....we're talking about 10+ degreesF ( maybe 20?) difference in intake air temp.....

Correct, but YMMV depending on the year/setup ie CIS, 3.2, carbs, etc.

On my 993 engine, the intake temps were also the same as ambient temps so no mods or worries here!

[kach22i]

I saved this link a while ago, lots of good information on the topic.

http://www.bankspower.com/tech_coolair.cfm

[Wil Ferch]

I think if we "refresh" ourselves with this post...it might be a bit eye-opening.

Experimental data for Cold air intake

Craig....fold-in your last response with the general theme of this post. a lot depends *where* and *how* your temp sensor is located. Maybe I didn't fully understand your response...

Wil

[Craig 930 RS]

Sorry, it was a quickie response when I didn't have much time to elaborate. My sensor is the air temp sensor built into the factory 993 system; OBD2 monitors this temp and reports it via the OBD port. My temps via this sensor were the same as ambient air temps outside, so *in my situtation* the air intake temp was a-ok and no changes were needed to make the intake air cooler.

Now on other systems, as shown by another thread and another engine that was not a 993, there was a difference when mods were made to use cooler air - and these mods should be performed.

Depends upon the engine and the air intake location/engine lid etc as to what temps an engine is actually sucking in. As in many other things engineering, everything is on a case by case basis, and until objective tests are made..........until then, "it is only guesses"

All this said, cooler air is better of course. But abstract theory ain't so hot until these cold air dealie inventions are actually tested for each application. Some of the Japanese cars have HUGELY long air tubes...I've seen a loss of 4-5 hp from these "Cold Air Intakes" - !

[Bill Verburg]

Craig is correct the 993 measures intake air temp in the intake tube, the engine fan keeps the ambients in there very near to that outside while the car is moving, at idle air temps will go up some.

[Wil Ferch]

Bill and Craig:

This is interesting...consider:
- the 964/993 uses the curved fan that flows less air than the previous fans.
- the 3.6 engines produce more power ( hence more waste heat) than the previous versions.
- yet this configuration doesn't show temp increases
- yet Tbitz experiment with the older 3.0 engines, etc...do indeed show inlet air temp drop if the air "horn" is brought closer to the grill..otherwise there's a temp increase....

.....Why ?.....

Wil

[Craig 930 RS]

"- the 3.6 engines produce more power ( hence more waste heat) than the previous versions.
- yet this configuration doesn't show temp increases"

You mean intake temps? This is just a function of intake placement and compartment config/cooling. The inlet layout of a 3.0 vs. 3.6 is really different - it couldn't be more, different in fact.
I think real-life practice seems to show that the 3.0 location is hotter than the 3.6 - but I would have thought the opposite.

Testing is the ultimate 'definer' - !

I think you do mean overall engine temps aka oil (?) Oh yes -- the 3.6 certainly does! I have both a Carrera radiator with *2* fans and a front cooler - and the *oil* temps get pretty high at times. These babies put out the engine heat in an unbelievable fashion - and the engine drops the hp output tremendously when hot!

[Wil Ferch]

Craig:

Although this doesn't serve my case at all...yes...I meant intake air temps.

I meant to point out that a higher HP engine operating at roughly the same thermodynamic efficiency...with a less efficient fan ( less air flow sucked into the engine compartment) to boot....why wouldn't we see increased inlet air temps??

I think you hit it when you said the incoming air architecture is totally different. That may be "it" because I have no direct experience with the changes. Just how different is this, Craig, is there a simple way to describe the major differences? Does a 3.6 pick up air from below or something ????? I thought it was about the same. As I recall, the air filter for a 3.2 and 3.6 were the same and it picked up air in the passenger side of the engine compartment.....

Wil

[Bill Verburg]

All 911s from 3 liter up have their astock intake located near the decklid opening. This is where mine is w/o the spoiler obstructing the view.


Even at the 3.6 reduced flow rate of ~1000 l/s at speed that's still ~35ft³/sec. flowing into the engine compartment.

That's a heck of a lot.

[Craig 930 RS]

Mine is similar to Bill's - but the snorkle cover is cut down to a frame - so the air is sucked in along the entire circumference of the filter edge etc area.

So based on what Bill said above - he is correct - the intake temps all should be similar

?