All Things Chev

[rainsey]

I have been reading with interest some old posts on an alternate forum re bonnet scoops and areas of high and low pressure on the patrol bonnet.

I'm toying with the idea of putting a bigger intercooler on an hence if I do this obviously a bigger scoop.

Which got me thinking, would a bigger scoop offer and advantage even before I enlarge the intercooler, that was until I read these posts.

The general gist was that the high pressure areas are at the immediate front and at the base of the windscreen and hence the scoop itself is not actually in the optimum place.

In reading one of the posts someone mentioned that the radiator fan does not actual work by sucking in air but rather creating a low pressure area that the incoming are follow in. Which got me thinking again ......

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???

Also, has anyone actually put a fan on the BD supplied intercooler, and if so, how the photon have you mounted it?

Kindest regards
Rainsey

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[MB]

G'day Rainsey, sorry no ones got back to you yet mate. Seems the only 6.5ers posting at the moment are Turbo&Intercooless NA's :-) Engine bay air pressures of big donks squeezed into smallish trucks has been one of my concerns for a while now. Finally about to install my NA reverse scoops wacky concept to increase theoretical flow through. I must admit the physics of top Chev/Trol mounted intercoolers with forward facing scoops has always confused me for fighting air pressure performance. Front mount IC is probably the go but again more hinderence to your already stressed radiator system. @Kimbo mate, how does your beast run so perfectly as driven :-)


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[rainsey]

Hey, no probs mate. I'm not one to poke if there are no responses as I assume that no one has an answer. Would rather silence than smoke up my butt




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[MB]

Fair call mate :-) From my experience, theses donks are great, we just need to get that friggin hot air out somehow! Oh, and cool the oil too :-) !

[rainsey]

Fair call mate :-) From my experience, theses donks are great, we just need to get that friggin hot air out somehow! Oh, and cool the oil too :-) !

Spoke to Greg @ BD yesterday. He is shipping me over a couple of lower temp thermostats.

Also a bit of a weird statement from him yesterday also that I have not heard before was that he thinks I might be running a bit lean. He told me that when my engine was installed he thought it was a bit under powered but opted to not do anything. He has suggested that I ramp up the injector pump by an 1/8th of a turn.

Re the whole under bonnet heat thing, I think it has now become a personal challenge to understand the problem properly. I was reading a article yesterday where a guy with a turbo intercooler Peugeot put a manometer either side of the intercooler and the pressure differential was 0. Pressure at the top was the same as the bottom.

I'm tempted to buy a cheaply off flea bay and do the test myself with the existing set up.

The more I read the more I think that haphazard changes may not be conducive to positive results.

Cheers
Rainsey



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[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!!!!

[rainsey]

Hey thanks for the input.... not drowning yet, but my thoughts..

Re the air taking the path of least resistance, I hear you and agree. My only concern is if the underside of the vehicle is a high pressure or low pressure area.

In my naive understanding I would have thought that it would be a high pressure hence causing air to be pushed up into the engine area. If this was the case it would exacerbate the pressure under the intercooler and hence make the efficiency less.

Again, without any quantitative measurements I am probably speaking out of my rear end.

I do not know what your vehicle is like but the under bonnet temps are bloody rediculous. I have also toyed with the idea of putting vents in to extract the heat but I'm now reluctant until I can get my head around the whole pressure thing.

I have been looking at Magnahelics on eBay and you can get some for the couple of hundred dollar mark. I am seriously thinking of getting one and just playing with it to see if I can map out the pressure areas around the bonnet.

Kindest regards
Graham


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[rainsey]

Oh. My other thought was in regards to the excessive heat in that hot air does rise. If this was the case it would exacerbate the whole under bonnet pressure issue .... i think..


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[nissannewby]

By some wool and sticky tape. Stick short lengths all over the bonnet and you will see what the air does.

AB did some testing like this a while back as he wanted to space the rear of his bonnet up to add flow. He used the wool idea and found after about 40km/h the wool was drawn in to the bonnet engine bay area.

[nissannewby]

Spoke to Greg @ BD yesterday. He is shipping me over a couple of lower temp thermostats.

Also a bit of a weird statement from him yesterday also that I have not heard before was that he thinks I might be running a bit lean. He told me that when my engine was installed he thought it was a bit under powered but opted to not do anything. He has suggested that I ramp up the injector pump by an 1/8th of a turn.

Re the whole under bonnet heat thing, I think it has now become a personal challenge to understand the problem properly. I was reading a article yesterday where a guy with a turbo intercooler Peugeot put a manometer either side of the intercooler and the pressure differential was 0. Pressure at the top was the same as the bottom.

I'm tempted to buy a cheaply off flea bay and do the test myself with the existing set up.

The more I read the more I think that haphazard changes may not be conducive to positive results.

Cheers
Rainsey



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Running lean will make things cooler in a diesel.

Lower twmp thermostats wont reduce your under bonnet temps. 2 extra cylinders pumping out heat will bring them up. I would be more inclined to be looking at reducing the radiant heat from the exhaust manifolds. This can be done in the form of coatings, wraps or heat shields.