COLD AIR VS RAM AIR

[Torquemonster]

There has been a lot of discussion over this topic lately. I came acorss this study done by David Vizard in a paper he prsented while on tour here in NZ a few years ago - thought some might be interested....

He graphed the benefits of true ram air and also of cold air and then combined.

results:

At 30mph no benefit from ram air; cold air was worth 1%... summary - no gain would be picked up by a chassis dyno


In fact although the gains by 100mph are - 1% for ram air - still no measurable on a chassis dyno - but cold air is worth 5% by 100mph - so a 6% gain in total by combining both cold air and ram air at 100mph. However these conditions cannot be measured in a dyno - only in a wind tunnel or on the track.

By 150mph - the impact is: ram air is worth 2.5% (barely within accuracy zone of many dynos) and cold air is worth 8% - so combined is 10.5% power gain.

Conclusion: you will never see a gain on a chassis dyno, but you will see a benefit of cold air vs warm underhood air on a track or in a wind tunnel. Ram air is a waste of effort except for very high speed and very modest gain.

Above figures are based upon affect of underhood intake air being at 150 degrees and the impact of speed at cooling it. By 150mph the air is cooled to 75 degrees.

Vizard is one of the worlds guru's on engine mods - I would argue with him.

 

[ViperJoe]

Vizard is one of the worlds guru's on engine mods - I would argue with him.

So you just like to argue then??
Even though he's a guru??

 

[Mike Brunton]

Vizard is one of the worlds guru's on engine mods - I would argue with him.

So you just like to argue then??
Even though he's a guru??

***-stirrer!

 

[Cris]

Would not the amount of ram air pressure or temperature difference need to be known in order to create such a statement. The pressure side can be estimated as there is a maximum (i.e. infinitie collection changing the maximum air velocity totally into pressure. By definition that would mean no exit velocity, which is not possible as the engine better be consuming air. But the infinite collection minimizes that effect.

But temperature increases are vehicle specific. And I fail to follow the logic that the temperature difference increases with speed. I would think that at a constant power dissipation the delta T across the radiator would decrease with added air flow (same heat - more air). That would lower the underhood temperatures making the difference between ambient and underhood air smaller, thus reducing the cold air benefit.

 

[Torquemonster]

Vizard is one of the worlds guru's on engine mods - I would argue with him.

So you just like to argue then??
Even though he's a guru??

OOPS! Sorry - I mean I would NOT argue with him.... thanks for pointing that out - how embarassing.

I have the entire article - the key is that ram air is pretty useless for most cars but that cold air into the intake rather than hot underhood air does help as speed increases provided that it is actually not heating back up as it enters the intake - which it could! Air speed does cool as it increases - look at wind tunnels in the desert where water can turn to ice while it is 140 in the shade outside.

All in all the article confirms what many knowledgeable people on this forum have been saying all along....however a chassis dyno can't test these things - it has to be done in on the road in real world conditions or in a wind tunnel to simulate it - blowing a fan doesn't cut it.

As for aftermarket air intakes - it may be that the factory intake gets enough cold air to supply its needs and therefore there is little to gain - there will be a point beyond which extra cold air will benefit the engine at higher speeds and that point will be if a modification can get cooler air in than it was getting before the mod, or if the stock air flow is inadequate... common sense. If a mod doesn't fit either of those then the stock one is as good.

 

[joe117]

Saying that air get's cooler as it goes faster is just not true.
I agree that if you have air expanding it will get cooler. If you want air to go faster in a pipe, you put a restriction, venturi, in the pipe and the air will go faster and get cooler.

Air running through a radiator will be heated by the radiator. How hot it get's depends on how fast it goes throught the radiator. But it can never get cooler than it started out.

If you direct a 70deg stream of air on a thermometer and then double the speed of the air stream, you will see no temerature change.

I don't know what kind of wind tunnels you are talking about. If you blow air at water you get evaporation. The evaporation of 1cc of water will **** up 540 calories, just for the change of state from liquid to gas.

This, wind chill, has nothing to do with cars, radiators or air indcuction systems.

 

[Shelby3]

"Saying that AIR GET'S COOLER AS IT GOES FASTER IS JUST NOT TRUE.
I agree that if you have air expanding it will get cooler. If you want air to go faster in a pipe, you put a restriction, venturi, in the pipe and THE AIR WILL GO FASTER AND GET COOLER."


Huh?

 

[PhilC]

Aren't our cars (at least the ones with the stock air box) getting air right from the scoop through the box and into the throttle bodies as opposed to getting the heated air within the engine compartment. If so, I fail to see how any of this even applies.

 

[FE 065]

Your airbox is wider than the hole in the hood.
The parts (about 2" wide on each side) not behind the NACA duct could be getting air more from the heated radiator nearby, rather than from the relatively cooler outside air.
Though I wonder at speed, how much heated radiator air stays in the area, rather than being whoosed out the back somewhere-I'd bet incoming air through cracks, gaps etc do alot to moderate any hi temps trying to exist in front of the airbox.

 

[joe117]

"Huh?"

What is it that you don't understand this time?

This would be lots more fun if you told us what you think, yes, that would be a hoot.

 

[Shelby3]

"Huh?"

What is it that you don't understand this time?

This would be lots more fun if you told us what you think, yes, that would be a hoot.

"Saying that air get's cooler as it goes faster is just not true.
I agree that if you have air expanding it will get cooler. If you want air to go faster in a pipe, you put a restriction, venturi, in the pipe and the air will go faster and get cooler."

In your first sentence you state that "saying that air get's cooler as it gets faster in just not true." Two sentences later you say the "air will go faster and get cooler."

 

[Frank 03SRT]

From many years back, studying thermodynamics, I believe the reason it gets cooler is because of the venturi, which is nothing more than a restriction, where you go from high pressure to a lower pressure, slow speed to high speed, and in so doing, the air gives up some heat and gets cooler. Without the venturi, simply increasing speed doesn't do anything, other than possibly heating up the air due to friction in the pipe.

(Actually, just wanted to be part of the long threads and try to understand the questionable value of the Vipair device.)

 

[Vreracing]

I remember a thread similar to this.

I would imagine that ram air is very specific to the speed of the vehicle. The flow would have to be smooth to avoid turbulence. The same Ram air at 5000 rpm at 50 mph would not be the same Ram air at 120mph and also 5000rpm.

One reputable source made the description of the opening being smaller to get a better ram air effect. It may have had something to do with temperature.

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The impression I have is that if it makes a difference its pretty slight.

 

[Torquemonster]

If I knew how to scan the graph I would - maybe you guys would interpret it different to me - all I know is that it showed temps dropping as the speed rose - I didn't bother to find out why.

re ice in tunnels - maybe the tunnels are a venturi - but "wind chill factor" is pretty well known - also the faster a car goes the greater cooling on the radiator... it may not cool the air but it does take more heat out of the water.

Fast air from outside also has less time to heat up as it travels intake.

Just a few random thoughts.

to check the Vipair - I would run several 100mph to 150mph runs and take a best, worst and average times in stock form, then do same with Vipair installed - 2 way averages to isolate differences is wind etc. If there was no difference - the stock one is doing a great job and any change is simply cosmetic.

Results could change as more Hp is made from other sources and the stock system eventually becomes a restriction. So it would be interesting to do same test on a 700hp Viper.

No gain on a dyno does not surprise me at all - I don't think a dyno could measure any gain from such a system, but real world high speed performance might... and I say might - because it assumes the stock one can be improved on - and that assumtion may not be correct at near stock power levels.

 

[joe117]

Shelby3 you just don't seem to get it. Frank 03SRT has it right.
If you were to hold a dry thermometer outside your car window as you drove down the highway, you would not see any change in the temperature of the air as you changed speed.

If you had some air going through a pipe and you placed a restriction in the pipe at one point.
The air reaching the restriction would start to go faster in order to pass through the smaller opening.

Measuring the pressure in the restriction, you would find it lower. Measuring the temperature in the restriction, you would find it lower due to the air expanding when the pressure is lowered.

There is no such thing as wind chill when we are talking about mechanical parts.

 

[Shelby3]

Shelby3 you just don't seem to get it. Frank 03SRT has it right.
If you were to hold a dry thermometer outside your car window as you drove down the highway, you would not see any change in the temperature of the air as you changed speed.

If you had some air going through a pipe and you placed a restriction in the pipe at one point.
The air reaching the restriction would start to go faster in order to pass through the smaller opening.

Measuring the pressure in the restriction, you would find it lower. Measuring the temperature in the restriction, you would find it lower due to the air expanding when the pressure is lowered.

There is no such thing as wind chill when we are talking about mechanical parts.

Joe, Yup Frank got it right and so did you this time. I thought your first comment was incomplete because it didn't explain that the expansion of air was due to the LOWER PRESSURE in the restriction. I thought it was obvious to you (my mistake) when I quoted your statement the "air goes faster and gets cooler." That seemed to contradict your first statement and I was merely giving you an opportunity to expand the discussion.

 

[joe117]

Thank you, perhaps it was a little confusing the way I worded it.
We are all on the same page now.