Hood splitter for my vw

[euromodder]

Originally Posted by Varn

The more I consider what has been said The more I believe that a full width hood bulge is not what is needed.

Going by your drawing of the raindrops, it's reduced on roughly half the windshield - the center part - which happens to roughly compare to the width of the hood fairing.

Consider what the windshield of almost any streamliner looks like.

The hood - canopy angle is far more gentle; the canopy bulge is about as wide as the top of the fuselage, with gentle curves to the sides and aft, giving the air every chance to move aside or over it.

If anything, your Varna is pointing to a full width, gently curved fairing

[aerohead]

If viewed from above,the Template produces a semi-hemispheric full compound curvature windscreen as on Varna,or as Paul Jaray called the curved glass panoramic windshield ( with radiused header ).
On my T-100 I have tin-canning of the hood occurring at the cowl area do to the high stagnation pressure there along with thin sheetmetal.
I would like the $3,000 GTP,laminated safety glass windshield which is very much like Varna,or visa-versa,and my hood blister is an attempt to soften the pressure spike in this area,fill in any areas of circulation,and alter the angle of attack of the airstream as it moves towards the glass,A-pillars,and windshield header.
Since 2005 I have added Plexiglass side wings which actually contact the leading edges of the A-pillars and an aluminum spoiler along the trailing edge of the blister with just enough clearance as not to interfere with the wipers.
I cannot offer any scientific attributes to the blister.Rainwater is driven up it all the way rather than stall a foot in front of the glass.
Paul Jaray claimed a 10-15% drag penalty for the Tatra-77 because of its lack of 'panoramic' windscreen of which he had no control over Ledwinka's decisions.
The Cd 0.137 Ford Probe-V has an almost amorphous front end,hard to distinguish between bonnet/hood-cowl-windscreen.
Might be some 'high-hanging' fruit.

[Varn]

Since I made my hood splitter I have been rewarded by getting 50 mpg over 500 miles. My previous best was the last tank was 47 mpg. Now my last two tanks, 900 miles have been at 49 mpg average, the average since I bought the car has been 42. My max speed is usually about 65 with usual cruising speed of 61 mph. The has weather been getting warmer above the 50's by mid day. I always use the same pump for fill ups.

I am confident that the mileage is accurate. I have a GPS to measure the miles and I use a good technique to try and get the same fill each time. I'm generally fully loaded on the highway, 5 cats and 3 medium dogs. The trunk is packed to the top with clothes, food, guns and ammo and bible. Pretty much what the average doctor and nurse carry when fleeing from Illinois. The Jetta has a lot of space for what it is. We had to drive into town today to pick up some drainage tile. We got a 100' roll into an otherwise empty car today. It doesn't weigh anything but imagine 100' of 5”o.d. tubing snaked all over the trunk and back seat. I had the rear seat back out.

From what I have heard the newer diesels are more efficient than my 1986 engine is. I can't do much about it. I don't have any special instrumentation to help drive efficiently. There isn't a computer on this vehicle that I can tap into. I don't find out what makes it run more efficiently except in 4-500 mile increments.

I am thinking about aerodynamics and don't believe the scenario of that the front is good enough and the name of the game is entirely at the back. I do understand the importance of closing the rear but am working on better equalization of the pressure at the front. Reducing the high pressure spikes there of importance as well. .

My car is rated at 34 mpg as corrected by the EPA. Except for 3 small pieces of coroplast it is stock although the car has narrow winter snow tires on it. Getting 40 mpg in this car is easy, just drive it at 70 mph. Getting 50mpg was not that difficult. Guess I have to try for 55.... probably it is going to be exponentially harder. I am really getting grumpy with paying 3.74 a gallon for diesel.

[winkosmosis]

Originally Posted by Frank Lee

I was about to say forget it but upon further reflection I think everyone ought to concentrate all their efforts on this area, and let us know how it goes.

There's a reason some cars (90s Camaro) have deflectors in front of the wipers.

[winkosmosis]

Why don't you do a full width deflector instead of the D shape?

[euromodder]

Originally Posted by Varn

Since I made my hood splitter I have been rewarded by getting 50 mpg over 500 miles. My previous best was the last tank was 47 mpg.

From what I have heard the newer diesels are more efficient than my 1986 engine is.

It's as good as my 20 years younger car - as far as fuel consumption goes anyway.

The best TDi's from a FE point are the mid to late 1990's 1.9L engines with 90 hp - at best mated to a light car.

I am thinking about aerodynamics and don't believe the scenario of that the front is good enough and the name of the game is entirely at the back.

Have you seen the diagram with the streamlined brick ?
You gain by far the most by streamlining the rear end, even if the front is still brick-shaped.
You can gain a little bit by streamlining the front.
Streamlining both ends gives the highest gains - but it's not that much better than with only the rear.

So, modding the front is going to be less time/energy/cost effective than modding the rear.
But obviously, it'll still help.

Guess I have to try for 55....

Why not

[Frank Lee]

Originally Posted by winkosmosis

There's a reason some cars (90s Camaro) have deflectors in front of the wipers.

Let's see one and tell us what the reason is.

[winkosmosis]

Originally Posted by Frank Lee

Let's see one and tell us what the reason is.

Transitioning from hood to windshield with an angled deflector is better than transitioning from hood to wipers.

The 4th gen Camaro had a 0.32 coefficient of drag!

[Christ]

That's not really a deflector... The hood just happens to cover up the wipers in the parked position.

[brucepick]

In theory, I'll buy that there's more gain to be had by putting a kamm back or boattail on the rear, vs. cleaning up the front.

BUT the front is a lot easier to work on, assuming you don't have a full shop lift at your disposal. And IMHO, the underside is also easier to work on than the rear - though much more challenging physically than the front or hood. In general of course. YMMV as usual.