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Discussion Starter · #1 · (Edited)
I am working on reducing drag on my mid engine s10 pile by curving the backside in a effort to pull air around the cab.

There are also areas that will have air flowing under the lower front of the cab between the frame and rear tire (around the exhaust acting as a heatshield/aero tube) and straight out the back.
Now this thing is not at all designed to be stream lined. It is designed for easy maintance, cheap replacement cost, 55% rear weight ratio, and a respectable power to weight ratio.

That being said I have built in a good amount of drag in this back end.
Vehicle Car Automotive lighting Automotive tire Hood

One of my napkin drawings from years ago had a tunnel going right through the cab between the seats and out the back.

Looking at this I can make that happen fairly easily. I could have the hood taper and feed into a opening here(cardboard)
Tire Wheel Hood Vehicle Automotive tire

Motor vehicle Hood Bumper Vehicle Automotive exterior

That would feed into a (removable 2 piece) duct that would end where the angle is touching under the bracing spot welds)
Wood Floor Gas Metal Composite material

Then feed right out the back(center panel below tack weld line) punching a hole in the rear wake
Vehicle Car Automotive lighting Automotive tire Hood


Because we are talking feeding into open air in a area that will have a low pressure area. If I just make a venturi tunnel where a section directly tapers down lets say 30% in the exact center of the tunnel then at the rear of that venturi I could actually create a suction and increase drag.

So I "think" I need to move the part of the tunnel that is 30% smaller to the rear(or maybe have it 30% larger at the rear) and possibly have a extension out the rear (of around 2") to pull air off the back of the cab.

But I really don't know here. I know basic hydraulics. But fluid dynamics especially in relation to air is proving to be difficult to grasp.

I can't find any kind of reference of someone doing similar although it seems like it would be beneficial if properly done.

I am going to do it and then refine the heck out of it with real world testing. But I would at least like some idea where to start before I cut holes that turn out to be to big.
 

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Discussion Starter · #5 ·
there is a reason we seal off the engine compartment from the passenger compartment
carbon monoxide, even at low doses can be fatal
just cut out the cowl vent area
Im not running it through the engine compartment.
My hood is just over the top of the intake(in an arch) in the middle then would drop down feeding into this duct. The engine is covered and my exhaust runs outside the frame.
 

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Discussion Starter · #6 ·
What about a hatch spoiler like the 1st gen S10 Blazer has/had? I think those send downward air flow to reduce the wake. I mentioned the 1st gen because it might cut down on fabricating one.
Yes a 12 degree (down) spoiler above the back glass will be used to lessen wake.

It is just not enough.
 

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Discussion Starter · #7 ·
Interesting idea. My only reservation: with all the work done by automotive engineers in wind tunnels, etc. I don't see this concept being used. I see lots of air ducted to brakes and around spoilers, but no one is ducting it through the middle of the structure. Are you "overthinking" this?
Of course im overthinking this. The whole build is napkin sketches and saying "why not"

I need to reduce weight. Ok what do I absoultly need? Well I need the cab of course what if I moved that over the rear wheels.

Humm well thats going to let me set the engine really far back which is good. But then I have a stupid long hood. What if I shortened the wheelbase?

And so on.

So when I got to the rear and was like. I really cant just use round flat lights they need to be seen from the side. What if I used rounded lights that could be seen and would lessen the seperation angle reducing wake on the sides.
Then I look at that flat back and think. What can I do with this?

I was hoping to find something from a racing series when they still had mechanics or a spotter(2 seats) but a majority of those were all front engine streamlined.




With a mid engine 2 seater with the engine behind the driver it would seem a duct allowing air at the center of the hood to run through the cabin and out over the engine(my idea backwards) would have been used. You still pull air around the car of course. But that middle under the windshield where drag is known to accumulate could be reduced.


I am going to do some kind of duct. I just don't know about the shape of that duct at this point.
 

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Discussion Starter · #8 ·
I am leaning towards starting with this geometry (it is called an ASTAR nozzle).
Water Azure Slope Rectangle Mode of transport


Now I am looking at a rectangle at the front and rectangle at the rear(much easier construction). But the friction should be similar. I will need to play with the convergence point with real world testing. But I think this geometry will work as a starting point.
 

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Discussion Starter · #9 ·
After checking the truck over taking measurements I came up with this. Just the top to figure out where my shifter needs to go at this point.
Road surface Wood Flooring Floor Rectangle


12.5opening tapering 18.75" back to a 3.75" opening that is 3.75" long then tapering 36.25 back to a 5" opening.

Now thats the top.

The side goes from a 5" tall opening 18.75 back to the 3.75 opening thats 3.75" long then that tapering back the 36.25 back to a 11.5" opening.

Rough 3d sketch.
Triangle Gesture Handwriting Font Slope

I expect a slight increase in velocity while having minimal friction against the duct walls.
Lots of real world testing. But I am making the thing easy to construct and leaving a good amount of room for modification.
 
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