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Originally Posted by ERA2076
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Thanks - now I see. The down side is lift i.e. low pressure on top of the hood with the high pressure at the intersect of the rad to the roof wall, but a much reduced surface area compared to a stock cobra and your nozzle is really cool. If you could tip it forward you could put a floor in and the roof area is minimized. The air pressure will sit on the intake tract floor (possible down force) with pressure escape thru the roof i.e. rad . This greatly reduces the static pressure area on the intake tract roof.
In theory a shorter rad with thicker core could provide needed cooling surface area while allowing for more flexible packaging, but its a lot of work to find out it won't cool .
Will you will block off the rest of the front of the nose?
Is the air box, tract, and radiator sized to the volume needed to charge the engine?
Love your nozzle - wish there was away to package them not so steep. I have considered a shorter rad with thicker core that would provide needed cooling surface area while allowing for more flexible packaging, but its a lot of work to find out it won't cool . 
I agree with you - it is not a straight forward endeavor. It seems all one can do is build,test, and then rebuild - 
Appreciate your work and sharing your thoughts.
x-chr |
Thanks for the kind words, however,I don't really know how to put it gently and also don't want to start an internet pissing match, so I just be blunt. Your assumptions are incorrect in regards to the potential for lift and heat exchanger flow characteristics.
Lift or down force with a heat exchanger within a sealed duct are essentially a non factor. Pressures will average out over the assembly with a net of zero. Obvious exception being the mass of air entering at one elevation and exiting at a different elevation and direction, and the effect of that air on surrounding aerodynamics. The only gain I would get from tilting the radiator in the opposite direction is the air flowing through the core currently moves downward 1" before moving back upwards and out the duct. No doubt there is some energy consumed with this movement, but not much. It's a bit more complicated, but think Newton's third law. Another way to think about it is an inflated balloon. Internal pressure is irrelevant with the exception of the area opposite the open nozzle.
While small thick cores are still the topic of internet debate, thin heat exchangers at an acute angle are superior in terms of flow, cooling, and drag. This is why top F1 cars use the method. See pic below for an example
While the forward area of the hood is relatively low pressure, with a boundary separation device this will assist with duct evacuation. This eliminates an area of significant pressure differential on a stock cobra. Remember, the more lift you eliminate, the less downforce you need.
The premise of the build is to keep a relatively period correct look as compared to what was being raced in the late 60s so the front will not be blocked. Rather than harm the car's looks while attempting to redirect very high pressure air, the air is being allowed to flow through the car while being productive for cooling and a little downforce. On the other hand, the underside is getting the full treatment.
I'm not sure what you mean by nozzle, but thanks for the kind words. If you are talking about the ram air ducts, the angle isn't as acute as the photos make it look. If I don't get at least 50 hp from the system it will be a failure. While it may appear oversized, it is correct for the motor. The motor is an all aluminum 8,000rpm 432 Windsor with a 4" stroke, 235cc TEA ported twisted wedge R heads, Jesel shaft rockers, .700 solid roller, full custom equal length headers, and one massively ported Super Vic intake.
Here are some examples of proper heat exchanger plenum design. While designers tend to favor tilting forward, it isn't necessarily better and isn't always the case.
