Pressure drop results *action packed story-interesting results too*

[Dave]

I was bored tonight and decided to perform a pressure drop test across the board. For those who might not know what I'm talking about, what a pressure drop test is, is where you messure the manifold pressure (end) versus the compressor pressure (beginning). Real easy algebra here, MAP - CAP = Pressure loss

So I teed into the compressor housing's boost controller line. First I set my manifold pressure to 18.5-19psi... depending on which gear I'm in, it usually increases a 1/3 of a pound throughout each gear.

I go out to Rt. 5, a nice long stretch of road and womp it... bam 18.5psi in 1st and 2nd gear, then a nice steady 19psi in 3rd. Nice having no traction when I pull back 3rd gear and spin the tires.

Cap off the line for the boost gauge that goes into the intake, and route it into the homemade tee. Take it back on Rt. 5 and, oh what's this? No vaccum is read at the compressor housing? INTERESTING! I nail it, again no traction in 1st gear and little in 2nd, and it reads boost a lot sooner than the manifold! It felt like 5psi but it was reading 10psi. Hmm... So the boost gauge is maxed out, 20+. I guesstimated in 3rd gear I was at 20.5psi.

I had anywhere from a 1.5 to a 2psi pressure drop. Kool! Not bad. My setup is like this, 3.5" cone filter, 3" intake, stock TII Garrett turbo, 2 1/2" intercooler piping, stock TII front mounted intercooler, Blitz BOV, and stock throttle body and intake. I was reading off an Autometer Phantom boost gauge (30/20). Need a bigger gauge, by the way... Mom? Dad?

Something else that was interesting was that once I let off the throttle the gauge's needle would flutter and then steadily and slowly drop back down to 0psi. It never went below 0psi. I'm assuming that since the wheel is always spinning it's always causing above-ambient air pressure? Any guesses??

So onto the action. While sitting at a light on the way back home, it turns green and I go to give it some gas and the throttle is stuck to the floor, yet the RPM's are at 800. Whaaaaaat thaaa faaaaak!? Luckily I was on a decent grade of a hill and could roll it down to the middle turn lane. Do that, pop the hood... the entire arm came off the throttlebody. Not the throttle bracket, just the arm. Push it down a hill and hop back in and get it on some side street. Poppa's got come down in the Acclaim so I got a reference to work with. Luckily again I was next to an AutoZone. Walk there and buy a 10mm nut (that's what came off, somehow!)... wrong size, shiat. Go back and get a 13mm, yay! Of course it's course-threaded and not fine. DAMN! Use it anyways!! Haha. Baby it home and found one.

So now I'm out to go cruising. Just thought I'd share some information with you guys. Everybody likes seeing results.

-Bryan

[iTurbo]

I need to try this myself on the Shelby Lancer. It's got 3" intake, with 2.25" charge pipes, all mandrel bent aluminum. I would guess the pressure drop would be much higher than that with the TII intercooler at that boost level. Unfortunately my compressor housing doesn't have any tapped outlets. I've run up to 20 psi in the manifold and always wondered how much psi is before the cooler.

[ShelGame]

The pressure in the turbo housing is before the throttle body. So, it will only ever be at just slightly below atmospheric, worst case.

[BadAssPerformance]

Cool idea.

To get all scientific, need to get a spare boost guage and do it side-by-side with the exact same length of hose going to each guage, take a couple (at least 3) readings, then swap guages and take more readings

[Dave]

Cool idea.

To get all scientific, need to get a spare boost guage and do it side-by-side with the exact same length of hose going to each guage, take a couple (at least 3) readings, then swap guages and take more readings

Bah, too much work! This was just a simple, rough test. The vaccum line going to the boost gauge isn't all that much and I used the same length.

It was a cool test, but I'm paying for it now with only a 1/4 of a tank when I started with over a 1/2. Ouch. Payday isn't 'til Wednesday.

[iTurbo]

How would I go about putting a nipple on thin-wall aluminum pipe? I'd prefer to tap it with a 1/8" NPT female thread but it looks too thin. I would try this test in the next few days if I could get a boost gauge plumbed in the lower pipe somehow. I have two new Autometer mechanical 30 in/hg-30 psi gauges.

[iTurbo]

Just remembered this:

http://www.atpturbo.com/Merchant2/me...egory_Code=FTG

I'd still rather install a permanent fitting into the thin-wall pipe though.

[Dave]

How would I go about putting a nipple on thin-wall aluminum pipe? I'd prefer to tap it with a 1/8" NPT female thread but it looks too thin. I would try this test in the next few days if I could get a boost gauge plumbed in the lower pipe somehow. I have two new Autometer mechanical 30 in/hg-30 psi gauges.

Just tap into the pipe. Get a hose barb that will match the threads and wrap the hose barb's threads in that white tape(crap, I forgot the name of it).

Personally I'd go with that hose barb that fits through the silicone pipe. Pretty kool! Only $10... c'mon.

[turbovanman²]

Cool idea.

To get all scientific, need to get a spare boost guage and do it side-by-side with the exact same length of hose going to each guage, take a couple (at least 3) readings, then swap guages and take more readings

Thats what I did with my van before I swapped out the old, small IC.

The results were very eye opening.

[Pat]

The faster air moves past the nipple on the compressor outlet, the lower the pressure of that outlet will be. Remember the Bernoulli Principle from science class? Because the velocity of air over the flat opening of the nipple through the small compressor outlet is so fast, the pressure differential measurement is not quite as accurate. High velocity of air over a surface actually creates a bit of vacuum, offsetting a bit of the actual pressure in the system from where you are measuring. You need to tap someplace where the velocity is not so high to get a more accurate reading, like in the IC end tank.

I guess I just let the cat out of the bag that I'm not that far removed from my science geek sibling....

[86Shelby]

I guess I just let the cat out of the bag that I'm not that far removed from my science geek sibling....

I thought both of you were rocket scientists???

[Pat]

I thought both of you were rocket scientists???

Ha. If that was the case, I'd hope my bank account would look better than it does and my nice car wouldn't be a Neon! LOL!

[bansheenut420]

Ha. If that was the case, I'd hope my bank account would look better than it does and my nice car wouldn't be a Neon! LOL!

Could be worse, your nice car could be a honda!

[Chris Faulk]

Cap off the line for the boost gauge that goes into the intake, and route it into the homemade tee. Take it back on Rt. 5 and, oh what's this? No vaccum is read at the compressor housing? INTERESTING!
-Bryan

There will be no vacuum measured from the compressor housing...this spot can physically only be pressure. The blades of the compressor are ALWAYS spinning causing flow of some kind. Did someone explain that and I missed it?

[WVRampage]

the little flutter you were geting on the guage was compressor surge,maby the bov is out of adjustment or you need one that flows beter.Also I would agree that in the compressor housing you shouldnt ever see vac.

[Dave]

That makes sense. I guess I'll have to tap the IC. I like tapping it.

[Phreakish]

the velocity effects would be next to nothing in most motors...

A 3" pipe has a x-sec of about 0.05 sq feet. A stock turbo flows at most, around 27 lb/min IIRC. Density of air at 300 degrees (uncooled boost) is about 0.052 lb/sq foot (I'm assuming these numbers are in lbm, not lbf, as thats what they SHOULD be, but this is quick 'n dirty, so I dont care enough to go look ).

That means that for mass flow = rho*V*A, then V (flow velocity) is equal to M(dot)/(Rho*A)

So a velocity of about 173 ft/second. Now, speed of sound at 300 degrees F, is sqrt (1.4*1716*(300+460)), or about 1300 ft/s, at 173 ft/s, that is a mach of about 0.13...

And if ya know much about aerodynamics, compressibility, or bernoullis, thats not enough to do much...

I could do more, but I dunno how many would understand

[Phreakish]

forgot to also add, that unless you put the tap in a stagnated flow area, you wont get rid of the velocity effects, and the fact that the boost is probably more turbulent than ground-effect is from a large plane with full high-lift devices hanging out... that the pressure reading is going to be pretty close to the same everywhere, except for before-and-after a restriction.