Sun visor air dam drag

The old arm out the window one day alerted me to what I believed to be a much higher air flow at pressure flowing from the windscreen around the drivers side door area same on passenger side, you know,Idleing along at 75 klm slight uphill and gentle 10 knots breeze on the nose, pedal to the metal with the trusty old Perk puttin out it's usual honest best an giving the occupants plenty of stress free time to contemplate their navels or even ponder how To turn this snail into a rabbit without havin to get out the balaclava and the gun.
With regards to the latter you can't , however you can lessen the head pressure substantial by altering the design of the visor to allow free flow over the top, I used some blue tack and ribbons placed in the centre of the screen from the bottom to the top and the results were what I expected, yep they streamed out around the side of the screen and gently patted my face, none were streamed through the vents.we removed the visor and repeated the dose, all streams went over top, it's one big air dam.They certainly didn't use an air tunnel back then for efficiency.
It's worth taking the visor off and feel the difference on the road .
Safe happy kms to all
Doc and Lyn Davey

I had the visor off for about 30 seconds the other day - but it looked so awful without it, it went straight back on again. The OKA looks truly ugly without it, quite personable with it. I'll be keeping it on. Efficiency be damned.

Yep I hear ya, my point is that for owners without luxury power a good inexpensive mod is to re design the visor slats to allow free flow, the old Perks embrace any relief they can get as in downhill with the wind up ya clacka. 308 and 132 are wearing ally heat exchangers in stead of the slats with some spahls on top . I certainly didn't decide on Oka's for their looks but quite comfortable with the now that's a serious Poor wheel drive ambience.
Cheers Hal

Hal Harvey wrote: I had the visor off for about 30 seconds the other day - but it looked so awful without it, it went straight back on again. The OKA looks truly ugly without it, quite personable with it. I'll be keeping it on. Efficiency be damned.

Hahahaha!! Listen to the Duramax owner with plenty of power to spare! Gold, Hal! As Doc says: you wouldn't be saying that if it still had the Perkins.

Hey Doc,

Using the blue tac and ribbons is the technical way to go about it
and the result is obviously true scientifically; But in your test
without the sun visor, was there any noticeable difference with
power on tap. Not that an OKA with a Perkins has power on tap.

I am with you on the revamp of the sun visor, allowing are to
flow over top, as it not only should give you more power but it
also should assist fuel economy as these two go hand in hand.

Cheers Brian

DarrenWebster303 wrote: Hahahaha!! Listen to the Duramax owner with plenty of power to spare!

Hey, I was still running around with the tune dial on #1 poverty pack setting at the time! I've since been playing around with the 'burn more fuel' settings... in anticipation of a run at the Motorplex this Wednesday night... which is why I looked at taking the sun visor off in the first place, but it mustn't be done.

Never had a sun visor so I don't miss it.

Hal Harvey wrote: [.. in anticipation of a run at the Motorplex this Wednesday night....

Surely this needs to be shared on youtube......

No air goes through our sunvisor

Hello Doc,I did the same test with the ribbons in Newman
back in 2012 when I was planning the fitting of an Optiair 1100 air box to 96, with the same result.I was looking at any way of increasing the air flow into the air intake and was thinking the air flow off the windscreen might be increased by being forced through the sunvisor and that I could use the increase to advantage. Not so. As with you,the ribbons went around the door pillar just above the mirror bracket and stayed there.
Watching the ribbons and thinking about the results of the test,it was obvious that the air passing along close to the glass and therefore the air intake was very turbulent making it even harder for the engine to get enough air. I got around that problem by modifying a pvc plumbing fitting, to be exact, a 45 degree,100mm squashtop which gave a air intake throat of 240mm x 75mm and moved out 65mm from the body into clean air.
A bit at risk from branches etc.so I will just have remember it is out there. I am keeping the visor even though it is a big handbrake.
A bit of a wander off topic I know but something may be of interest to someone. Regards Chris.

i like that the sunvisor keeps A LOT of sun off the dash, but yes, maybe a mod could be done... I've always liked the idea of making an ally sunvisor and replace that flappy heavy current design so i might include your suggestions then doc.

On another note, what you're observing actually may help aero as the roof flow may be closer to laminar without being affected by vertical windscreen flows. Any chance you could pay for some wind tunnel time doc, only take a day or so, i'm keen to quantify exactly how many kW's are lost either way???!!!

Cheers, Alister

I think for that I would have left it off Hal, I'd hate to think of an Oka doing a Malcolm Campbell Bluebird backflip around the sun-visor!!! By the way, setting 5 is the wrap the springs up & put the uni's in bind/ Eat HSV/FPV setting (after scientific tests & 2 beers) if you ask me. You must post the video of it mate.

I was contemplating putting a pair of 24" lightbars on top of the rear fin of the visor so they shone over the top of the first fin but I think they may be too heavy. I'll drop one on the scales tomorrow but pretty sure they are at least 5-6kg each. I can fit them to the ally frame on the roof if I have too.

Either way, visor is staying

DarrenWebster303 wrote: I think for that I would have left it off Hal, I'd hate to think of an Oka doing a Malcolm Campbell Bluebird backflip around the sun-visor!!! By the way, setting 5 is the wrap the springs up & put the uni's in bind/ Eat HSV/FPV setting (after scientific tests & 2 beers) if you ask me. You must post the video of it mate.

I'm pretty sure the front wheels came off the ground when Hal tried #5 with me.

Walked away with serious OKA envy.

TH wrote: I was contemplating putting a pair of 24" lightbars on top

If the driving lights are above the driver's line of sight, they can be shining into an oncoming driver's eyes over a hill long before the offender even knows there's oncoming traffic. So the top of the bulbar is no problem, but driving lights on the sun visor would be against the DoT recommendations, and rightly so.

And I personally reckon the LED light bars are too heavy; and any light is too susceptible to damage up there anyway.

Good point..... back to the drawing board I suppose.

DoT VSB IB 123A wrote: There are no height restrictions with regard to mounting position.
Note: A driver must not use, or allow to be used, any light fitted to or in the driver's vehicle to dazzle, or in a way that is likely to dazzle, another road user.
Therefore the fitment of driving lamps higher than the driver’s eye level is not recommended.

Grey area. They'll likely be reflecting into my eyes if I have to mount them further back anyway.

Yep, we we pumped her down the road and the difference was notable after 65klm an hr quite so in fact, probably better than an intercooler. Aerodynamics is basically what it's all about when all said and done I reckon it went from a brick to 3/4 of a brick in technical jargon.The three downsides to the Oka designs were Weight, aerodynamics and power, I'm working on all three gradually simply because our monthly trips outback cover approx 3000 ks and economy is less fuel more distance.Going ally visor, roo bar tray,tanks , doors , really got em on a diet.The P 400 s not bad on fuel but the 6.2 chevs NA are brilliant and am custom building one around 190 HP for the third Oka.I believe that will be plenty. They are a tried and proven donk.
Happy travels all
Doc

Doc we found that the 6.2 was very economical in our Humvee as long as the revs were kept under 2300rpm. Was amazing really that with all the drivetrain losses(portal hubs etc) that we could get it down to 13-14l/100k at cruising speed around 95kph on the highway.
While it was wide and had the aerodynamics of a brick with vertical windscreens etc the frontal area was pretty small and there was no drivetrain hanging underneath so the sir could flow under there pretty freely.
With the original TH400 tranny and no overdrive it was revving at 2850 at 95kph and drank like a fish never mind the noise, fitting a 4L80E and Compushift brought the revs back to 2100-2200 at the same speed and it stopped drinking and only sipped.
Fitting the 4L80E and Compushift behind the Perky has had a similar effect, revs rarely go over 2500 and then only on long steep hills, it cruises at 2200 at 100kph and can get down to 14l/100k despite weighing in at 5650 loaded complete with visor and four solar panels, two over the cab.

Alister McBride wrote: I've always liked the idea of making an ally sunvisor and replace that flappy heavy current design

Alister if you fabricated a visor using Kavs AutoCad version (which is similar dimensions to the one I made ), you could play with the angles and positions of the blades and see if there is a better setting.

But it's a balancing act between smooth airflow, sun deflection and aesthetics. These would be effective in 2 of the 3 criteria:





If I keep the speed down to 85kph max, fuel consumption is much better, which reflects the lower air resistance which, for a bevelled brick, rises exponentially with speed.

The flat rear end suction effect contributes 25% of the drag as well.

Reckon you need these on each side, Doc.