Bill Ball

Did you guys figure this out yet? I'm getting worried mine might be going the wrong way.

dr bob

If it's a serious concern, one that might cause you to lose sleep or miss lunch, remember that you can always move the venturi in the intake duct forward, so that the huge pressure drop acroos it will draw a little extra air in from the belt covers. If it's a real serious concern, one that has a negative effect on your ability to drink beer or something equally risky, you can always add a couple e-ram fans downstream so that there is more suction from the covers. If you decide not to move the venturi nozzles but still want the same effect, you can always put a couple of those Air Tornado devices in the air duct just after the radiator. The swirling air in the duct will work with the smooth airflow in the belt cover to cause even better total mass extracted. With the additional airflow and cooling in the covers, you could easily add 20-30 miles to the projected t-belt life. Think how valuable that would be! You could drive just to the point the belt would have broken before, and still have enough miles to get home or to a repair shop! No bent valves this way! Plus better gas mileage and tire life!


Merry Christmas to all!

danglerb

Something maybe easy to try, pull off the intake tube on a newer 928 with electric fans when its still cold enough not to have them running, and hold a bit of paper over the vent and rev the engine and see if the spinning of the cams and movement of the TB sucks it down, or blows it up.

PorKen

You could box in the area under the damper, over the oil level sensor, and connect the alternator hose to it. This would ensure a constant flow of air at all speeds.

dr bob

You should probably add a K&N filter to the front of that hose so the junk vacuumed through there would not end up in the alternator. The cathode end of each of the alternator diodes is a dust magnet. That would precipitate other problems no doubt. Get the dust ***** spinning around in there and your lights will dim as centrifugal force draws the charged particles out of the flux field. Certainly don't want that to happen!

Bill Ball

Ken - None of this applies to you! Your belt is rather fully ventilated.

mark kibort

the pressure checks are all done with the vent open, except for the last runs.
now, with the vent closed, it will only raise the back side of the radiator test. all other tests will not be effected. (intake tube pressure, etc) I suppose the .1psi vs the .12psi difference of the intake tube and front of the radiator, could be equaled out with the sealed hood vent .( ie, both would be .12psi) ill double check this tomorrow for ya.

Mk

mark kibort

your vents are going the wrong way thats just the point where the pressure starts to rise, so you would have flow going down the vents to the underneath side of the car!

MK

mark kibort

put it this way, i dump out a handfull of sand out of the air filter, and none in the timing belt area. the air is not going down the vent, even though at high speed, the pressure differential is going to point to flow going down the vent hole. in most cases, the pressure is not really happening, nor is any real intake flow. (ie, part throttle or cruise). i would suspect its a convection cooling . moving the venturin to right over the vent in theory could work, but its just the flow is not that great to make any type of measureable pressure drop. Ill do some WOT runs on mine and see a pressure before, at and after the neck down. there is no "venturi" effect over the opening, as the real way there would be a drop in pressure in the air stream , if you were WOT and there was substantial air flow moving through the tube, but thats only if the vent tube was out of the boundary layer. looks pretty flush, so there is literally no air moving over the vent for it to source the lower presssure moving air.
the air moving through the tubes when i measured the pressure in the tubes, in the center of the tubes, could be the reason for the lower pressures at WOT. remember they went from .10psi down to near .7psi at 100mph.

mk

mark kibort

great point. think about it, with the fans running in slow traffic, you get some pressure through the radiator alll the way to the base of the engine where that inlet vent is, so when the fans are on, and you are not going real fast, that air is blowing into the covers and venting out the cam cover vents.

mk

danglerb

To make a grain of sand change direction mid intake hose and go down the vent would take a LOT of flow down the vent, which is good since you don't want sand down there.

I'm still confused by this
"they went from .10psi down to near .7psi at 100mph"
.10 psi is less than .7 psi, so is that up to or .07?

mark kibort

there is a pressure statically when going 100mph. when you open the throttle, the air requirements of the engine can even take the intake pressure tubes to vacuum! however, i have a heavily vented air box, so the reduction of pressure only went down from .1psi to .07psi WHILE at WOT.

getting back to your point about a grain of sand, trust me, dirt and even sand can fly pretty easily. think aobut what the sand has to do to get in the air box! and i have a pretty open vented air box in the rear. yet, i still end up with a pile of sand! sure, large particles wouldnt get pulled down the vent, if there was a differential pressure, however, even a little pressure differential could cause a flow of dirty air with substantial particles , to go down it. however, i think as we can test, the flow is up. whether by convection or the electric fans, is upwards.

mkm

danglerb

I was surprised how much stuff must be on the tracks listening to those videos. Places like Willow Springs the air is just filled with dust. Last time I think I got a cup of sand out of my nose.

SharkSkin

The differences may be small, but they may also cancel out at cruise. For example, if the pressure on the backside of the radiator went up, you might very well find that the pressure on the front side of the radiator increased by some amount; this would then logically have the potential to increase the pressure inside the intake tubes.

I did notice something interesting about the measurements you posted. You show equal pressure at the balancer and in the tube at 100mph, less pressure at the balancer at lower speed. Yet WOT at 100mph would yield .1 psi at the balancer and .06 psi in the tube -- resulting in significant flow right at the time when the belt is under additional stress. If this holds true for a more stock setup, and for a wider range of speeds, we might conclude that the system was designed to move more air while under a greater load(which is when the belt system would generate the most heat).

I think it's a foregone conclusion that air moves upward out of the TB cover at least some of the time, or folks wouldn't find bits of shredded belt in the air cleaner. I'm guessing it moves the most air at WOT and higher speeds.

If you are interested in doing more tests, closing off your airbox(you have vents in the top shell of the airbox, right?) may also result in different readings.

mark kibort

you got it!

I dont think the belt knows if you are at full throttle or not, there is slight acceleration, most of the forces would be on throttle blips, out of gear. I think the forces are greatest at higher RPMs . However, at WOT, you did notice that the pressure drops considerably in the intake tube, giving the greatest differentital pressure of the front of the engine to the intake tubes, certainly causing flow into the tubes. an other interesting test would be to just do the reving of the engine and see if the belt and pullies creat some type of flow out of the vents. i think the key thing at cruise, is that you will have near the same pressure at the harmonic balancer area as the intake tubes, so there will probably be very little flow. I bet'cha most of the flow upwards is just the hot air rising. But, certainly during high load there will be flow out of the timing belt covers.

mk