which wud b better to put on my stock 87 rx7 NA......short ram or cold air??

 

cold air.

search man. there are plenty of threads covering this.

 

what would be better is if you wrote in english,

replacing the intake will result in greater heatsoak, so just stick with the stock one put a k&n filter in and your good

 

So you're saying that a K&N replacement drop-in, will give just as much performance as a full cold air setup?? (NOTE: not flaming, just asking)

 

Definitely not. It will probably, however, be more effective than a cone filter withOUT a cold air box.

 

I'm not sure what you guys are saying here, I see different ways of reading some of the statements made so far.

Isn't ram air essentially cold air plus extra intake pressure?

 

"Short ram" is a completely bogus marketing term used to sell over-priced pipes to kids who don't know any better. Unless you plan on having something stick up through a hole in your hood, your intake will be neither "short" nor "ram".

Complete waste of money. You will see ZERO power improvement from upgrading just the filter. The filter's restriction is a tiny fraction of the restriction from the rest of the intake and exhaust systems.

A true ram air intake is a forward-facing intake located a point of high-pressure, undisturbed air. By definition then this is also a "cold air" intake, since it's taken from outside the engine bay.

 

That's why I asked, because yes it's taking air straight from outside. Now when you say undisturbed air, I suppose laminar airflow creating intake pressure will flow a little better than turbulent airflow will, but sometimes you take what you can get. Since the FC engine bay is as packed as it is, I would think that to make a ram air without shifting a bunch of things around and without making unsightly modifications you'd have to go with a hood hole or reroute the intake, the first still unsightly and the second might not deliver magnificent results.

 

The "short ram" is actually very short, and is usually just a fancy name for a cone filter with an AFM adapter. Yes, it is completely bogus, but it is short, lol.

That is usually true for a TII or ported NA engine, but a mostly stock NA can usually see a very slight power increase from the drop-in K&N filter. Also, the K&N drop-in is not a complete waste of money, and will actually save money if the car is retained for the entire 10 year or million mile life of the filter.

$55 K&N Drop-In Filter (10 years)
$10 K&N Recharge Kit (10 years)
$65 Total for 10 years

$27 Stock Air Filter (30 months)
x4
$108 Total for 10 years

$108
-$65
= $43 savings of K&N vs. stock filter over 10 years

A true cold air intake would chill the air below ambient temperature. Therefore, "Cold Air Intake" is yet another bogus term.

Also, "undisturbed" is not such a great term to use in this definition as per aerodynamics, but I suppose the regular forum members will take that meaning the way you intended.

A ram air intake directly ingests the "relative wind", which is the ambient air that is put into relative motion due to the path of the vehicle traveling through the air mass. The ram air contains both static pressure (the ambient air pressure) and dynamic pressure (air pressure created by the movement of the vehicle). An intake that does not directly access the oncoming air will have less, and sometimes zero, dynamic air pressure.

Also, "ram air" often describes an intake that generates a ram air pressure rise. The commercial "ram air intakes", including those on most of the American muscle cars, do NOT do this. An actual ram air rise intake requires a closed system with a divergent duct, and there is a ram air temperature RISE associated with any boost pressure that is produced.

Warning - The Wikipedia article on ram-air intake is WRONG! Hopefully I will have some time to edit it soon. Dang open-source dillweeds....

 

I haven't been going off commercial products. It should be obvious that a ram air system won't work right if it doesn't have a sealed system with positive pressure at the entry point.

 

What isn't so obvious is that a ram air supercharger requires a divergent duct to convert the air velocity into pressure.

 

Like so on the right side of this illustration:
http://www.globalsecurity.org/milita...06/Fig2-10.gif
That's interesting and good to know.

 

You'll have a really hard time convincing me of this. I've seen numerous intake system pressure-drop tests, and the pressure drop across the filter element was always around 1inH2O (0.036psi) or less. That's less than 0.3% of atmospheric pressure. Since removing intake system pressure drops effectively increases the pressure seen at the intake ports, I can't see how such a minute increase could make a noticeable change. In those tests the airbox itself always caused far more restriction than the filter, and some of those airboxes flowed a lot better than the FC's.

Have a read of this and see what you think.

http://autospeed.drive.com.au/cms/A_2232/article.html

This is true, but how many people manage to get 10 years use out of one filter and cleaning kit? I bet it's very few. Cars get sold or modified, cleaning kits get lost, etc...

And if you did make it last 10 years, I doubt you'd look back and notice that extra 1.2c/day in your pocket.

Yeah but Not-As-Hot-As-The-Engine-Bay Air Intake doesn't have quite the same ring to it. Besides, when I got into my car this morning, the air was cold!

 

yeah erm i had a K&N open cone and i switched back to the stock intake system with a K&N element, the car seems happier, the factory intake IS a cold air intake, it pulls ambient air from in front of the radiator . . .