rrounds

On my truck I used a gauge almost like the one I put on my "S", I used that gauge to show me when I needed to change my filter(I would get 400k miles on my truck filter) and that is why I put it on my car. I figured if it was good enough for my $130k truck it was good enough for my $20k "S". I would like 0 vacuum or even a little pos. pressure at speed, but to just have 8" of vacuum on the intake after the filter just by putting the top on is not right. Any way you want to call it a vacuum on the intake is not good.
Not to argue but it's like taking a drink with a small straw, you have to work to get the drink out of the glass. Anyway, I put this on my car to tell me when its time to replace my air filter(not to go by the miles driven), I was just surprised to see a vacuum on the intake and I will modify the box to get rid of it.

ROD

mattstryfe

I am not an engineer but I have fiddled around with this for a while now myself. Everything has rules. For exhaust it's about achieving the lowest back-pressure without sacrificing velocity. Which is why sometimes larger exhaust pipes see performance loses. However, with intake I tend to agree with your sipping air threw a straw analogy. In fact, a friend of mine said that exact same thing.

Rules for intake are fairly straightforward also. Increase air volume to the manifold + decrease air temp as much as possible.

Take for example an AEM CAI. Long tubing that's relatively the same size as the actual inlet on the manifold. The goal of the AEM intake is not to improve air volume, it's to improve air temperature. It accomplishes this buy pulling air from a different location. I believe it runs down around the radiator. The filters resting place is in front of it. Thus, getting cooler air into the piping and ultimately into your manifold. However, one thing the AEM also does that may or may not effect it's effectiveness is run piping away from the hot side of our engine. THIS, is why I believe the AEM is effective.

My main issues stem from the location of the stock air box not really where it gets its air from. In reality it does pull air from "in front" of the radiator via the small vents underneath the hood latch. Again, it's not the air temp that I am concerned with when talking about the stock box. It's the fact that the d@mn box gets nearly as hot as my header due to the location of it.

I think we could all agree that the best case scenario, though impossible, would be to have the filter hanging right off the intake manifold. So long is it would be in a cool area this would be optimal.

Billman250

Dont underestimate the stock air box, or over estimate any type of snorkels. Trust me on this one.

Do a roll on test with another s2k. take the lid off one car. Equal speeds in say third gear, and just take off at the same time. The car with the lid ON will pull away, signifigantly, every time.

Saki GT

Fwiw I have never seen any temp measurement at the throttle body/intake manifold that shows how different intakes effect temps, good or bad.

Saki GT

Help me understand this - there is a vacuum but there is still air - does a vacuum indicate thinner air than normal or normal atmosphere just that its being drawn in? It doesn't inhibit the volume of air or its velocity through the space.

Sucking through a small straw (versus normal) would indicate lack of volume through the tube, not vacuum. That you are sucking on the straw versus the juice just coming through the straw is the real point here. In most cases with a straw, you can easily apply a slight vacuum and get all the juice you need. I'm not discounting what you've done, just trying to figure out what it really means. How does a vacuum at the intake effect air density? Is the vacuum big enough that it causes the engine to starve for air? Intake manifolds operate at a vacuum last time I checked. Actually, rather than an instrument that shows you the peak vacuum that can really happen at any time during the test, an actual manifold gauge that allowed you to see how vacuum changes as you drive would be a lot more useful, wouldn't it?

SgtB

If you can make a vacuum at all it's a restriction. If the intake had no restriction it would indicate 0 vac. It's all in the frame of reference. Yes the engine pulls vacuum to gulp air, but the intake itself shouldn't be under vacuum if it is large enough.

The engine creates a vac and atmospheric pressure forces itself in. Vacuum is an indicator of lag.

SgtB

The length of the AEM is really the only thing that helps. People really worry about IAT too much. There are standing boundary layers that form in side of the box. Graph IAT at launch and you'll see how fast it drops.

rob-2

While I find this measurement interesting I'm not sure how to use the found data.

Since we know the air box works very well, and there are almost no gains with different intakes... what should we draw from this?

rrounds

I call it vacuum but the gauge really measures the restriction in my intake up to my intake manifold.
http://www.filterminder.com/hfmw_air.asp
If I was racing then starting with 8" of vacuum would hurt performance but on the street I will change the air filter at around 15" of vacuum. If you have a vacuum at anything other than WOT then you have problems. The LED gauge I had in my truck was in the cab and I could see if I had any vacuum at any speed or rpm, also had a fuel filter restriction gauge that told me when my fuel filter was getting dirty.
I had a round gauge like this one
http://www.filterminder.com/leddisplay.asp
Since I knew my car would not have any vacuum at part throttle and I didn't want a gauge on my dash, the locking vacuum gauge was what I went with and I put it on to tell me when to change the air filter-nothing else.
If I blocked the opening to the air box a little won't the vacuum go up? Is that good or bad for performance? Or if I cut a 3.5" hole and run some tubing down to the wheel well to help draw some more air up to the stock box would that make the vacuum increase or decrease? The harder the engine has to work to suck air in the less power it will make. Like I said 8" even 12" won't mean a thing on the street but on a race track when you want to be faster than the guy next to you yes it will, don't forget its not the "one" thing that makes the difference its all the little things you do that add up to make your car better.

One more thing, think of vacuum as the opposite of boost. Boost makes power and vacuum takes it away.

ROD

Saki GT

Thanks for the posts. Interesting stuff.