All Things Chev

[PeeBee]

If the fan created a low pressure area at the inside face of the radiator resulting is a crap load of air coming into the engine bay, this flows directly over the inlet manifold and hence under the intercooler. Would there not then be a high pressure area under the intercooler as a result of the radiator fan and hence would this negate the pressure differential across the intercooler thus making the intercooler getting stuff all air flow through it???

Rainsey, this is a bit of a weird 'long bow' concept I think. The fan is pulling air in from the grill and radiator cowl, which is OK at low speed and then increases in efficiency as the inlet air from outside increases in velocity and is forced into the radiator and then the fan. The fan itself does not really have a duct to take advantage of the force feed - I think most of the air coming thru the radiator at high speed is probably bypassing the fan in shear, as the fan blades will only shift air up to a point - similar to a fan curve. Since the 'overflow of air' can't reverse, and its compressible, it gets forced around the blades by simple pressure. Does it pressurise the bonnet to the extent it negates the top mount - I think you have to remember that air will take the path of least resistance, and thats straight out onto the road below the vehicle. Batteries cook under bonnets due to high radiant heat loads, and if there was a high pressure you would think that would generate flow, BUT, the airflow is heading straight out under the vehicle and not swirling or scavenging air pockets from under the bonnet. I am throwing in some odd examples but they support the concept.
As the velocity of the vehicle increases, the pressure drop across the radiator increases to a point where the air flows over the bonnet and around the vehicle, like the bow wave. I have also read a number of articles on a couple of other forums and it seems the efficiency of front mount scoops disappears after about 40klm/hr. This makes sense when you look at wind tunnels and test patterns, as a negative pressure is probably generated directly near the scoop.

For me, the bonnet scoop gathers cooling air works up to a point, but as vehicle velocity increases, then the efficiency drops off. My supporting example of this is a mate who swapped his Air to air intercooler to a water to air intercooler on a Patrol 4.2 TD, and he says the performance is over a wider rev range than before, because he gets uniform cooling where the a/a drops off - thats my theory anyway.

I have purchased a pair of 'shark tooth style' bonnet vents that point to the rear. The vents sit flush with the bonnet. My theory is that I will supply an alternate path of air to that going under the truck, and hope to strip some heat out of the engine bay, which is cluttered. The negative pressure generated at speed over the bonnets will further increase the effect. At low speed I expect the hot air to simply vent out wherever it can, and since hot air rises, i have in effect added a couple of roof top doors to the bonnet.

Hope you are still awake by now, or not drowning in keyboard BS, just my thoughts on air flow. I have spent a lot of time in the ventilation, pressure flow and vacuum conveying arena, so am basing my thoughts around how I know air moves.

In summary, I don't think there is a net positive pressure under the body that would impact air to air intercoolers if top mounted, if anything they shoul impart better heat stripping flow from under the bonnet and. lower temps.

Interested to hear what you think!!!!