Ram Air Worth 15 HP

[jyl]

Finally, some data on the effect of "ram air" intakes. This month's Excellence article on the latest 996-based RS mentions it has ram air intakes under the rear fenders, which Porsche determined increase intake pressure by a bit over 1 PSI and to boost power by 15 HP. However, that's at over 180 mph . . . Does that mean that at 90 mph those ducts would add 7 HP? Is it linear?

Come to think of it, I recall that current F1 cars are required to have vents in their raised air intakes (the ones above the driver's helmet) precisely so that they don't act as rams and create boost. They hit about 190 mph too.

Who'll volunteer to snake a big snorkel up and over his decklid, and go get the mother of all speeding tickets?

[sammyg2]

No, it is not linear, more like exponetial.
At freeway speeds there would be no real increase in power EXCEPT for the increased density of the air because it is cooler.
That is where the real advantage is, the increased density of the cooler air, not the compression of the air.
Even that increase would be negligeable. The ratio of results compared to the effort (for a street car that isn't taken to 180 mph) puts this one very close to the "ricer" category.

[bell]

Originally posted by sammyg2
The ratio of results compared to the effort (for a street car that isn't taken to 180 mph) puts this one very close to the "ricer" category.

i wouldn't go as far as calling it a ricer mod......
clean cold air is always ideal for performance, it's how it's executed that determines if it's rice or not.

[bigrubberjeep]

I doubt the last model of the "Ram Air" Trans Am is concidered "Ricer" by anyone.

[Bill Verburg]

The 996 GT3 and Cup cars use a cold air intake that is nicely integrated into the spoiler and sealed, the intake is placed in an aero induced high pressure area and sealed in the engine compartment so that only external air is inhaled. These types of cold air packages have been used w/ usually mediocre results for years, the 993RSCS and '98 GT1 were two of the more successfull early versions

[sammyg2]

On the contrary, I consider ram air on the trans am to be consistant with what most people refer to as rice or more PC, "import tuning".
Something that is designed to look like it performs more that it actually does.
No I don't want to argue the effectiveness of ram air on a trans am. If you believe it makes a big difference, great. I (and the man who designed and tested it) both think otherwise.
Cold air makes a little difference. Prolly not enough to notice, but it might.
My point was that the effort and cost can dramatically outweigh any benefit.
It looks cooler than it works. That is the definition rice IMO.

[bigrubberjeep]

Originally posted by sammyg2
If you believe it makes a big difference, great. I (and the man who designed and tested it) both think otherwise.
Cold air makes a little difference. Prolly not enough to notice, but it might.

Interesting point of view, concidering GM has posted on many aticle that the difference in performance form the camaro to the trans-am with ram air was due to the ram air. Both cars are equally heavy and have the same drive train, yet the trans am is quicker.

How big of a difference? well that's subjective, big enough to write about it in many magazines.

[john70t]

I've heard of an effect in which ram air actually hurts performance because there's so much airflow going past a very small scoup that it makes a backpressure "shield" over the opening which acts as a reverse venturi sucking air out of the intake.
Alternatively, having a big scoup probably doesn't do anything if the intake is not the worst restriction in the intake/engine/exhaust flow. That's like saying an air cleaner twice as big will make the car go twice as fast.

Ram air probably works best by passively providing slightly higher intake pressures over stock through all(!) rpm/mph ranges.

[strokher racing]

I have tested several different air intake systems over the years. From 14 inch K&N cone filters to under the bumper ram air setups. On the track I have found there is no difference in ET or mph with a ram air over a properly routed cold air kit. The ram air kits are usually routed under the bumper so they pick up everything as well as hot air off the road. Rear engined cars are a bit different, and require a bit more work to make a good ram air kit. I am trying to come up with a design on my 91 c2 turbo which has a gt1 wing for an air cleaner assembly. I will post my final design once it is done.

Eric Hood

[Craig 930 RS]

A guy here in the Kirkland Redmond area is trying an external scoop for his 930 intercooler - it will be a big monstrous affair

[Wil Ferch]

look here for some interesting tests and experimentation...interesting, as it runs counter to my oft-cited thoughts that the amount of cooling air brought in to the engine compartment is so large....that ram air would have little effect....

Experimental data for Cold air intake

Wil

[sammyg2]

I am basing my information on an interview with the designer of the ram air hood I saw on one of those muscle car shows. Might have been car crazy, can't remember. He stated that while it did allow cooler air to get to the engine, his original design (apparently a huge piece) was modified to the point where it had little ram air effect although marketing played it up big time. Right from the horse's mouth.

One of my buddies in High school had a 440 GTX with that little scoop that opened up when the secondaries did. It was inoperable for a while and when he got it functioning again I asked him if it made any difference. His response was, "well, it looks cool, that's about it".
I spent alot of time in the driver's seat of that car and can verify it was more marketing hype that engineered performance.

[Wil Ferch]

Sam:
Perhaps true enough...but we have a different set of operating conditions when an air-cooled 911 brings in a hellacious amountof cooling air into a sealed 911 engine compartment.....

That's why I posted the interesting study done by TBitz in the thread before....

--Wil

[Todd Simpson]

...and just because it wasn't effective on an old muscle car doesn't mean 30 years later Porsche can't use the same idea to create a (small) improvement.

[Craig 930 RS]

A ram air system that I believe would post a real & objective gain would believe would meet these parameters:

A modern system, design by a professional & credible car company - Porsche

[Wil Ferch]

Craig:

Although true...this is somewhat of a surprise answer coming from you...after all,...ther factory didn't build a 3.6 SC...yet *some* people have done these hot-rods as home-brews with good effect.

I think Tbitz' pioneering work in this area is something that should be looked at more closely.......

- -Wil

[Craig 930 RS]

If Porsche claims a 15 hp gain, I truly believe it is factual.
It almost goes without saying that they have the resources to develop & prove these gains - and are unsually conservative with claims.

I do like the TBitz thread above. Facts & data!
BTW, I am happy with the temps @ intake on the 3.6 conversion in my 911 - they are ambient (air) temps with the completely cut air box lid (only frame remaining). As long as the speed is above 20 mph - air temp = intake temp!

We are speaking of Ram Air here tho - cramming in air for a mild supercharging effect. Was TBitz not dealing with TEMPS?
(As opposed to ram air)

[gerry100]

Wouldn't any scoop that would create a significant "ram" effect create addtitional drag?

The increase in drag would be exponential w / speed, possibly more than offsetting the "ram" effect.

[Craig 930 RS]

Data point -

F1 ram air scoop. Whatcha'll think of that?
Tossing this out to chew on -

[masraum]

Cold air makes a little difference. Prolly not enough to notice, but it might.

I can't say about any "ram air", but depending upon the temperature differential cool/cold air can make a big difference that's very evident.

Wouldn't any scoop that would create a significant "ram" effect create addtitional drag?

The increase in drag would be exponential w / speed, possibly more than offsetting the "ram" effect.

There are a couple of things to remember for this, yes, you may have some drag, but depending upon where you get the high pressure air may make all of the difference in the world for how much extra drag is made. Also, chances are you aren't creating any more frontal area which is also important. Remember, adding a tail (I think duck or early Carrera, can't remember) actually reduces the overall Cd of the car. I know, it's hard to believe, but there are hard numbers in Paul Frere's book showing that the factory found that adding a front and rear spoiler actually made a 911 more slippery, apparently more because of superior air management.