Lifting rear of roof, what are the benefits Options

[brant]

So technically we didn't "Raise" our roof.
what we did do was cut out all of the structure in order to open up the same gap that would be there if you raised one.

I used a hand grinder with 35grit poly-sanding paper on the inside of the roof.
cut through it like butter.

I cut out all of the inner structure on the back of the roof panel that normally attatches/anchors the latches. By cutting this out and attaching the roof into its normal position there is over a 1 inch gap between the targa bar and roof panel:

[brant]

We didn't end up buying the glass top, because we thinned our own.
I can't remember how much Sheridan's top was, but I think it was outside of our $50 per pound rule.

plus I like that the stock top has the stock texture, and stock color and appearance.

We used the same 35 grit grinding/sanding wheel to thin the stock top.

After grinding away all of the structure, nuts, reinforcement, and anything that weighed anything... it was really very light.

I sanded the inside of the whole top.
In fact right in the middle I went through a tiny bit and had to put a tiny patch on it to seal it back up.

you can take off a couple of layers and take off about 10+ lbs.

have to use different attachements obviously.

and its thin enough that I can take my pinky finger and easily "flex" the top now from the outside with very little pressure

here is that rear area sanded away... that creates the gap for air:

[john rogers]

Jeeez Brant has put in a tad more work in the rear roof gap than I did......As he noted, any increase in stability would only be noticable at a track like the CA Speedway which is so smooth and fast that small changes are very apparent. We found that by putting in 1/8 inch of toe in instead of straight ahead like I usually run made the car feel much more stable on the front straight and when riding the yellow line in turns 1 and 2 flat out.

[kdfoust]

Hey Brant that's pretty cool. With the conversion I've been considering what I need to do to deal with the aerodynamics of running 120 with the windows down.

When you made the change to the top did you notice any difference in your speeds at the end of straights or the wind inside the cockpit? OR did this go in in concert with the rear window holes?

Regards,
Kevin

[brant]

sorry Kevin,

when I made the change there were just too many changes at once to notice the difference. My before car was a PCA club racing production class car with differnent top, driveline, weight, etc.

[race914]

What a great thread! (IMG:http://www.914world.com/bbs2/html/emoticons/clap.gif)

I'm going to mod my lid for rear venting, to copy what Brant did, and also just ordered a set of vortex generators from the site recommended by TimT (www.airtab.com) so I can copy the Wayne Baker setup!

Thanks guys!

(IMG:http://www.914world.com/bbs2/html/emoticons/beerchug.gif)

[Dead Air]

QUOTE (race914 @ Jan 2 2006, 03:27 PM)

What a great thread!  :clap: I'm going to mod my lid for rear venting, to copy what Brant did, and also just ordered a set of vortex generators from the site recommended by TimT (www.airtab.com)  so I can copy the Wayne Baker setup! Thanks guys!   (IMG:http://www.914world.com/bbs2/html/emoticons/beerchug.gif)

[QUOTE]
(IMG:http://www.914world.com/bbs2/html/emoticons/chowtime.gif)

What about putting those window louvers over the engine cover. Does the car have to have origonal profile? This pic isn't quite right...
You remember... the ones they used on the 240Z's, etc!

[alpha434]

I like the rear louvers for the engine bay...

Al Lager, my guy in the know, says that the vortex can actually push the car forward, by creating a greater suction behind it than the wind resistance in front.

He says that the same effect made VW busses more aerodynamic than damn near anything out there at the time. Including ferraris.

But putting holes in the windows ruins the "catching" part of the effect.

On the other hand- he also says that putting the holes in is the best way to reduce drag on these cars.

SOOOOO.... I guess it depends on what effect you're going for. And it would be nice to know wich offers the most performance.

Al says that they always let him race with a passenger window in place and he used a small tab on the body work in front of the driver window in combination with a "safety net"- but not there for safety.

Then you could reduce the drag on the rear window by reducing the amount of air driven hard into the cockpit and maintain the unique area behind the window for the vortex.

I spent all afternoon pumping him and another guy for info- and trying to fit 7" wide phone dials under stock fenders..... (IMG:http://www.914world.com/bbs2/html/emoticons/sawzall-smiley.gif)

[bd1308]

what was mentioned, the air pocket...was mentioned oddly enough on MythBusters....apparently the micro air-pocket will correct the air flow over a truck-bed, reducing the drag effects caused by the tailgate being up. It's actually more fuel efficient to leave the tailgate up.

b

[alpha434]

Al knows. He was a national level crew chief. Won Sebring and some other stuff. He offered to have his rocket scientist give me all the data he'd already collected on it....

[john rogers]

If you leave the tailgate up on a pickup, the air in the bed will reach some equilibrium, but with a 914 we have a huge air pump sucking the air down into the engine bay and then out the bottom, in effect trying to lift the rear of the car off the ground. Leaving the windows up would probably be best for less drag, but we can't race that way, so we need a good way to get the air out. On the Wayne Baker #22 car, they had air inlet openings in the bottom of the side longitudenals and the engine cooling fans sucked air out the top rear sections of them. Acted sort of like a "sucker car", which we know how that one work so well.

[porsha916]

I wish you 914 racers luck with these aerodynamic changes, these generators use energy(drag) to create the vortex's, the question is do they direct air flow enough to reduce drag in other places, or reduce lift (perhaps increasing drag). The problems you need to overcome or use to your advantage: 1. The 914 does not have a very aerodynamic shape. 2. the engine cooling uses air from behind the passenger compartment and exhausts that air under the car. The key is to direct the airflow to minimize lift and or drag. Most likely it will be a compromise between the two. There is alot of things you can do to a 914 racer to decrease drag, but many of would seem to be quite odd, look at the history of aircraft design.
Take Care
Bill

[Eric_Shea]

QUOTE

On the Wayne Baker #22 car, they had air inlet openings in the bottom of the side longitudenals

So that's what those are. I've had quite a few 914's with that proble... errrrrrrr... feature.

[alpha434]

bump...

the fan isn't that big a deal. It's soft air- i.e. controlled. and its going to be really hard to do anything VTOL because of the fan. Take off your rear bumper, and its all good- nothing more you can do.

Some 356 guys use air passages down the body through the headlight holes.

+HP
-Drag

Back to the aero-
Air in low pressure is "soft". Soft air bends more easily when faced with high pressure air and solid objects.
here's a picture...

[john rogers]

If you ever get a chance to take a close look at it you'll find that the floor has been cut out and is a large aluminum sheet with a passle of small chrome molly tubes here and there that take the place of all the heavy duty sheetmetal that Porsche has installed. Same with the front and rear trunk areas and many cars now duplicate this sort of "original metal removal" and replace with tubes. Here's a couple of picts that illustrate some of the mods.

[alpha434]

whoops. try this

[john rogers]

Another, notice the extra sheetmetal beside the original side sections.

[alpha434]

Nice dash... The yellow doesn't distract you from the task at hand? (IMG:http://www.914world.com/bbs2/html/emoticons/lol2.gif)

[maf914]

QUOTE (john rogers @ Jan 2 2006, 08:16 PM)

If you leave the tailgate up on a pickup, the air in the bed will reach some equilibrium

Last year in Road & Track magazine there was a brief article in which the writer indicated that Ford had done wind tunnel testing with pickups to determine if drag increased and fuel mileage decreased with the tailgate in the up position. Ford claimed the tests indicated that drag was less and fuel mileage increased with the tailgate up, as opposed to with it down. But I don't think Ford would recommend that people drive with the tailgate down in any case. In the past I've tried driving my old Nissan pickup with the gate down, but could tell no difference. (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif)

[brant]

John,

got any more pictures.
I don't think it would pass for our local "vintage" club...
but it sure is interesting.

brant