hood vents: ideas...

[Xnke]

That's pretty much in the ideal location as far as pressure differential goes, too. I bet there is a LOAD of air moving through those vents at speed; have you done a yarn test?

[rsicard]

I purchased a Dwyer Magnahelic gauge to measure differential pressure over the hood, and found that the highest difference was right about the middle of the S30 hood. This is measuring both top and bottom of the hood at the same time, on a differential measuring tool.

 

About a 10" long section, from the side of the hood bulge out toward the outer frame of the hood, starting at the front corners of the bulge and coming back. This is where I measured the highest differential pressure, of 4.8 inches WC at 80MPH...too chicken to go faster on a public road.

 

Fun part...the gauge showed low pressure on this spot of the hood from about 15MPH up!

The way to test is have the ambient port of the gauge inside the cabin and the higher pressure port on top or bottom of hood at the same point for the conclusions to make ANY sense.  Have 38+ years in Aviation testing pitot/static systems.  Am VERY familiar with Water and Mercury Manometers and aircraft instruments and Digital Air Data Systems.  Should rerun the tests with precision to get good results.

 

I would like to have a data acquisition system with 16 Analog to Digital ports and map 16 airspeed sensors in several different spots on the car.  This is what should be done in the Wind Tunnel.  The results could then be recorded and graphed appropriately.  This would lead to a lot of knowledge about the aerodynamics of the 240/260/280Z cars.  Do it both for laminar flow and non-laminar flow.

[JMortensen]

Someone say hood vents?  These are working well for me.

 

 

 

Also on the topic of fender vents.  Just did this but haven't had a good test to understand effectiveness.

Very nice Cameron. I poked around through some of your other pictures, wasn't really getting what is going on with the vent on the LH side of the grill area. Also didn't see how you have the rad ducted. Do you have more pics of those things?

[Xnke]

Risicard, The gauge I have is designed for measuring differential pressure or absolute vs. a fixed reference, and I wanted to know the DIFFERENTIAL pressure, not the absolute. It also only swings positive, it's not a center-zero gauge.

 

I have made myself an absolute map over the hood on 4" grid squares, but for hood vents that's not the data I want...I want to know at what point on the hood is the DIFFERENCE between the top side and bottom side of the hood the greatest.

 

When I was measuring in the open area at the front of the car, I was graphing absolute pressures, measuring in the wheel wells, measuring over the hatch area, I wanted to know the pressure relative to the cabin.

 

For vents or for enhancing airflow through the coolers, I want differential pressure, so I can work out what produces the greatest flow potential.

Edited July 24, 2013 by Xnke

[heavy85]

Very nice Cameron. I poked around through some of your other pictures, wasn't really getting what is going on with the vent on the LH side of the grill area. Also didn't see how you have the rad ducted. Do you have more pics of those things?

I'll take some more pics. The upper left grill area is the air filter inlet. The rad is boxed in with the inlet just above the aid dam.

 

Edit here they are

 

 

 

The taped off area above the bumper was a test opening to see if it helped cooling.

Edited July 25, 2013 by heavy85

[rsicard]

Risicard, The gauge I have is designed for measuring differential pressure or absolute vs. a fixed reference, and I wanted to know the DIFFERENTIAL pressure, not the absolute. It also only swings positive, it's not a center-zero gauge.

 

I have made myself an absolute map over the hood on 4" grid squares, but for hood vents that's not the data I want...I want to know at what point on the hood is the DIFFERENCE between the top side and bottom side of the hood the greatest.

 

When I was measuring in the open area at the front of the car, I was graphing absolute pressures, measuring in the wheel wells, measuring over the hatch area, I wanted to know the pressure relative to the cabin.

 

For vents or for enhancing airflow through the coolers, I want differential pressure, so I can work out what produces the greatest flow potential.

One port of the manometer, be it electrical or mechanical, MUST be a (static) absolute pressure REFERENCE!!!  The other port should measure a positive differential from the reference.  This is the ONLY meaningful way to measure relative wind over the car or sources of differential pressures.  With the curvature over the hood, it should provide a negative or lesser pressure than the reference as in an airplane wing effect wherein the top of the wing generates LOWER pressure with respect to ambient (static) absolute pressure.  I have been doing this part of science for 38+ years.  In other words, I know what the HELL I am talking about!

[Sideways]

 It (magnehelic gauge) also only swings positive, it's not a center-zero gauge.

But they can measure negative pressures

[JMortensen]

When I was measuring in the open area at the front of the car, I was graphing absolute pressures, measuring in the wheel wells, measuring over the hatch area, I wanted to know the pressure relative to the cabin.

 

What did you find on the wheel wells?

 

EDIT-- Clarification, you measured the pressure in the wheel wells compared to the cabin? I think what makes more sense is to measure the engine compartment side of the wheel well to the fender side of the wheel well.

 

Thanks Cameron for the pics, nice work. Did you see that circle track mag article? Looks like you might be able to improve your rad duct design.

Edited July 25, 2013 by JMortensen

[heavy85]

I may try that Jon - thanks for the idea. More I play with this, the Z is front aero limited and I think the big bottleneck is the blunt radiator opening. One related issue Im trying to wrestle with is the front edge of the hood dips down as the hood opens. This means you need either a lift off hood which is a PITA as big as it is or are forced to recess the block off plate back into the grill as I did which has to hurt both downforce and drag.

 

Anyone tested dive planes on the front of a Z to see what they do?

[Sideways]

EDIT-- Clarification, you measured the pressure in the wheel wells compared to the cabin? I think what makes more sense is to measure the engine compartment side of the wheel well to the fender side of the wheel well.

If I'm not mistaken (And I may very well be!), I think as long as he uses the cabin as the low-pressure side again while testing the engine bay side of the fenderwell and drives at the same speed that he measured the tire side at, hell get a useable set of numbers to compare

 

[Xnke]

I found that the wheel wells were a slight negative pressure area in front of the wheels, and basically ambient pressure behind the wheels, relative to the cabin. The base of the windshield, down to about 12" in front of the windshield, showed a high pressure area relative to the cabin, at all speeds. This effect got washy for about 8" from each A-pillar, but was pretty steady in the middle. Once the car is running again and I have a few good calm days I'll finish the grid across the whole car.

 

I figure Dwyer knows what their gauges are made to do, and since the instructions for use clearly show how to use both ports to measure difference in pressure, I figure it's meant to be used that way. If my numbers don't mean anything to you, Rsicard, that's fine...but they work fine for me and thousands of other people who install them this way every day in HVAC ductwork. (where they're used to measure pressure drop across a filter element, to know when to change the filter.) The magnehelic gauge is really nice for indirectly measuring flow through a heat exchanger, too...provided that all the air must go through it, and cannot go around it. Simply measure pressure before on the high port, and pressure after on the low...you get the pressure drop through the core and can work out the flow rate based on the pressure drop and the area of the exchanger. I just use it to measure if the difference in pressures increases or decreases based on what I did.

[JMortensen]

I figure Dwyer knows what their gauges are made to do, and since the instructions for use clearly show how to use both ports to measure difference in pressure, I figure it's meant to be used that way. If my numbers don't mean anything to you, Rsicard, that's fine...but they work fine for me and thousands of other people who install them this way every day in HVAC ductwork. (where they're used to measure pressure drop across a filter element, to know when to change the filter.) The magnehelic gauge is really nice for indirectly measuring flow through a heat exchanger, too...provided that all the air must go through it, and cannot go around it. Simply measure pressure before on the high port, and pressure after on the low...you get the pressure drop through the core and can work out the flow rate based on the pressure drop and the area of the exchanger. I just use it to measure if the difference in pressures increases or decreases based on what I did.

Seems to be some backbiting going on in this thread between a few people. Please don't involve me. I'm just trying to get info. FWIW, we know there is low pressure on the fender behind the tire because of the turbulence shown by the yarn tufts in the tunnel, so if there isn't a lot of low pressure in the wheelwell, that indicates to me that we need a better path for the air to get out.

 

 

If I'm not mistaken (And I may very well be!), I think as long as he uses the cabin as the low-pressure side again while testing the engine bay side of the fenderwell and drives at the same speed that he measured the tire side at, hell get a useable set of numbers to compare.

That makes sense, just makes for twice as many tests. If you want to see if air will exit out the fenderwells from the engine compartment, testing the pressure of the outside of the wheel well vs cabin pressure doesn't tell you anything useful in and of itself. If you test the inside and the outside vs the cabin, then you can compare the inside and outside wheelwells against each other after running 2 tests, but you could have just tested the inside and the outside against each other directly and gotten the result with one. Maybe I'm somehow making it easier than it actually is.

 

 

[rsicard]

If I'm not mistaken (And I may very well be!), I think as long as he uses the cabin as the low-pressure side again while testing the engine bay side of the fenderwell and drives at the same speed that he measured the tire side at, hell get a useable set of numbers to compare

 

The cabin, with closed windows, would be the least influenced by ram air pressure at speed.  Therefore, it can be used as a REFERENCE.  One side of the manometer should be vented to the REFERENCE and the other side to the point to be measured whether is be negative or positive pressure with respect to the REFERENCE.  That way you can tell which are higher and lower pressure areas.

[peej410]

Its like measuring chevy water pumps. Instead of measuring the height of both and calculating the difference you put both on a flat surface and using a straight edge on one mounting flange you measure the distance to the second. By using a reference you eliminate potential variables.

[Sideways]

That makes sense, just makes for twice as many tests. If you want to see if air will exit out the fenderwells from the engine compartment, testing the pressure of the outside of the wheel well vs cabin pressure doesn't tell you anything useful in and of itself. If you test the inside and the outside vs the cabin, then you can compare the inside and outside wheelwells against each other after running 2 tests, but you could have just tested the inside and the outside against each other directly and gotten the result with one. Maybe I'm somehow making it easier than it actually is.

I can think of some pros and cons to doing it both ways.

 

Say for example youre comparing the pressure difference between location A and location B.  Location B has a higher pressure than location A, and when you measure the difference you see this (dur, i know).  But what if location A has a pressure higher than the ambient air youre moving through- and youre after not just a good pressure differential between A and B, but also after lowering the pressure in location A as best you can at the same time?  Because the pressure in B is higher than A, youll see location A as being a negative zone compared to B, even though A is still higher than ambient. 

 

On the other hand you could measure just location A first vs a reference pressure, then location B against the same reference pressure.  Doing this you might see that location A is at +.1, and location B is at +.2-  So now youll know not just the difference from A to B, but how far above that ambient reference pressure both of them are as well. 

 

Hopefully this makes sense?  And again its assuming im under the correct impression (Pretty sure I am though, hah)

Edited July 27, 2013 by Sideways

[rsicard]

If measuring a lower pressure area against a higher pressure area or vice versa, this type of measurement is MEANINGLESS.  The meaningful way is to measure the two different pressure areas is each with respect to a reference/ambient/static area.

[Sideways]

If measuring a lower pressure area against a higher pressure area or vice versa, this type of measurement is MEANINGLESS...

Apologies- But why would it be meaningless?

[heavy85]

Hey Jon - this look any better

 

 

Now I'm not sure how to get low pressure into that cavity.  It's sort of sealed off so not sure any downforce can be made without connecting it to a low pressure area?

Edited July 28, 2013 by heavy85

[JMortensen]

I think you would need to cut into those side panels quite a bit. Maybe do like I did for my dash. Take a piece of AL fuel line, crimp the ends and bolt it in like a strut at the top and then cut the sides out mostly or entirely.

 

The duct looks just like the one in the magazine though. I hope its worth as much downforce as they said it was for the NASCAR...

Edited July 28, 2013 by JMortensen

[heavy85]

The near side in the pic seals off the (hopefully) high pressure area for the airbox.  The far side could be cut out to make a single bigger area but then it's still basically just one bigger sealed off areas instead of two.  That area is connected to the interior through the fresh air vents that run through the front frame horns.  Should I open that vent to the interior?   Should I take out the duct so this area is open to the engine bay?  Cut the floor out so it's connected above the splitter?  What's the nearest low pressure area to feed it?