water run off channel

I heard that there is a major aerodynamic improvement if you remove (grind off) the water drain channels that run over the windows and down to the rearwindow post. Is this true and if so, how do I do it and what are the disadvantages?

Keep in mind that this is not a daily driver and probably won't be purposly driven in the rain.

Can't remember where I heard this....

Adam Roseneck

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1978 911SC 3.0
roseneck@cyberbeach.net

I saw this done on a late '70's to 993 conversion. I'm sure it would improve the drag coefficient of the car, but the real world improvement is primarily aesthetic in my opinion. It also seems to me that it might weaken the joints if not done properly.

The 959 came without those channels, I think that's where people got the idea.

On some of the 959 conversions that people used to do, they would grind the channels off, so it definately can be done. I've seen a couple. I think it actually looks kinda cool without the channels. The car looks different without them, but most people can't readily figure out why.

I'd imagine that there is some aerodynamic advantage, although its hard to imagine that it would be "major", esp. at US type speeds.

Disadvantages? Probably would cost quite a bit to do right. Probably would hurt the resale value of the car, too.

RUF also did it to some of their cars. I remember seeing one in ROAD and TRACK around the early 90's

As for resale value, It doesn't matter to me. With the modifications that I'm doing, I'll NEVER get my money out. I'm okay with that.

The car is going to be stripped and painted so at this point, I'm sure It can't cost that much to remove those suckers.

Still, I would like to hear some more opinions about this so that I don't go and do something drastic before having all the facts.

Adam Roseneck

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1978 911SC 3.0
roseneck@cyberbeach.net

That's from this web site. They might be able to give you some advice (do or not do).
http://www.wholesaler-usa.com/rennspeed/

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Clint
73T mfi coupe

[This message has been edited by Rustbucket (edited 03-28-2001).]

If I recall correctly, the channels are a folding and welding area for the body to meet. When you simply grind these off, you are essentially take out the framing of the body. I would anticipate this will possibly damage the body and remove the safety torsional stiffness of the car. If you have this done, make sure these areas will be re-welded by a competent body and frame shop who are familiar with the 911 design. I would also think you will need a roll-bar after such modifications.

You mentioned "Keep in mind that this is not a daily driver and probably won't be purposly driven in the rain."

Does this mean it will be a track car? If so, talk to the guys who race. Find out what they think. And find out what modifications they have done.

I don't think you will gain much on a street car. So unless you plan on being over 100 M.P.H. over 80% of your driving time, I don't think you will gain much by shaving the rain gutters.

Just my .01
Nick

Perhaps the rain channels act as a deflector if the car was to get sideways at high speeds. NASCAR mandates such deflection devices on their cars to prevent the car from acting as an airplane wing when the car gets sideways and becomeing airborne. The P-car channels are not that much, but they would cause some turbulance over the top of the car to prevent lifting.
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Paul
78SC Targa

RUF popularized this modification as somebody already said. I'm not sure if it was for aerodynamics, looks or both. Without a wind tunnel and real data it's hard to say. It does change the looks in a subtle way. By the way, 993's still have this rain gutter.

As far as strength you don't have to be a genious to realize that this joint is a major source of stiffness to the car. By breaking that joint you are going to have to do a full seam weld along there. Maybe you should send an email to Alois Ruf himself and ask him about his experiences with this sort of modification as far as chassis strength and longevity? Obviously you don't want cracks to form later. My guess is you'll be fine if you seam weld it.

Alright, here is the low down from Ruf (a dealer anyways).

Those rain gutters are nothing more that rain gutters. No structural significance whatsoever. He told me that you can just grind the suckers off and that it is quite a nice look (they have done several). I'm not going to take the grinder to the Porsche just yet, but will am definetly planing on doing this before I paint the car.

By the way, he also mentioned that the technical reason for doing this is infact aerodynamics.

Thanks for your advice guys, its good to hear opinions before making an irreversible decision like this.

If you have any other question pretaining to RUF I found a great source in Oscar at Weissach Automotive in Vancouver Canada. Phone (604)738-3911.

On an aside I also asked about the polyeurothane bumpers for the SCR, $2100 CAD each. I think I'll stick with aftermarket fiberglass.

Adam Roseneck


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1978 911SC 3.0
roseneck@cyberbeach.net

When you grind off your gutters, do a few inches at a time

Dean

There is a tar like sealant between the two pieces of sheet metal where they meet and fold to form the gutter. Don't try to weld the seam created from the removed drip rail. You will need to weld a thin flat strip about 2" wide along the now removed drip rail area to reinforce and cover the area to prevent this sealant from contaminating the weld and having the paint bubble up 3 years down the road (learn from my mistake). Also as someone said do a small section and let it cool so you don't have warping. And remember the sparks from grinding will pit any glass and burn pin holes in any upholstery in the area.

Hello

Cuting the rain rails will lower the chassisflexabiltys to convertible standards.
Still very streetusable and much better then 90% of all other cars driving around.

Porsche startet grinding them off on the 935 but the 935 also has a different cowl and more raked windshield and not to forget a full harness brace. The 959 has an composite roof.

Yes the reasons are highspeed aerodynamics. The lows are more dirt on the glas and wet seats if you open the door in the rain.

An old racer trick was to shave the A-pilars only.

Ruf did not just grind the rails away he removed the complete roofpanel including cowl and welded reinforcements under it.
It is a long tube going along where the rail was.
CTR cars get a invisible full harness this way.

Just mail him direct or search his HP about that subject.

Grüsse

I plan on installing a roll bar (not cage) would this help with torsional stiffness?

Adam Roseneck

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1978 911SC 3.0
roseneck@cyberbeach.net

In my opinion, this is one of the most ludicrous alteration I have heard of. WHY? Aerodynamics? Unless Craig Breedlove is driving our cars, how much of a difference can it make. An inch long piece of metal that runs length wise with the airflow can't be altering wind flow appreciable. So if that isn't much of a factor, you would be willing to take a die grinder to your car because it looks cool? Other suggested alteration while your at it. Loose the headlight and replace with 928 versions. Remove wiper blades and arms. Chop the top and install lower roof, car seat will have to be tilted back to allow headroom, (Laying back and driving is in style these days). Aerodynamics in a 30 year old car design....give me a break.

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8 9 9 1 1, The last of the line.

Actually, for the most part, I am interested in the look. I pursued the topic because many have mentioned that this modification adds a very nice, distinct look to the car. I am one who likes customization and I am also thinking of rebuilding my car as a RUF CTR replica (just until I buy a new one).

Some would say that anyone willing to put 5 or 6 thousand into a 23 year old cars engine would be ludacrous too.

So? Does a roll bar do the trick or would a roll cage be needed to offer the proper stiffness?

Adam Roseneck


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1978 911SC 3.0
roseneck@cyberbeach.net

Grinding off the water drain channels for aesthetic purposes is a purely personal decision, but I seriously doubt it will have any discernable effect on aerodynamics.

While the channels are long, you have to look at the car from the front, since that is the angle the wind comes from. The area of the frontal profile, as compared to the entire frontal area of the car, is negligible (the frontal area of the car is the emtpy space after driving through a piece of paper, as opposed to surface area). Thus, removing that small area won't reduce drag by any measureable amount.

Here's another way to look at it- the water channels could affect aerodynamics in a few ways: reduce drag coefficient, reduce frontal area of the car, or provide lift or downforce. Removing the water channels will have relatively no effect on any of these things, IMO.

Anyone have a wind tunnel we can use?

I'm sure I've spoken more than anyone in my own post, but I just wanted to reply to the last post.

When I talked to the guy at RUF, he said that it was for aerodynamics. But then again, he said that I could just grind it off and from what is mentioned here Ruf installed a bar in the roof to aid strength.

I'll email RUF tommmorow and ask.

Any more tips?

Adam Roseneck

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1978 911SC 3.0
roseneck@cyberbeach.net

ATR,

Keep us updated on what Ruf says. My car is in the paint shop at the moment so I am seriously considering this mod. Besides the fact that I think it looks ultra cool, I seriously do believe it can make a significant difference at very high speeds - according to Ruf, the difference between narrow and wide body is about 12-15mph on a CTR top end so who knows what the gutters are worth. And before anyone says it doesn't apply to road cars, lets just say it would make a difference to me I reckon it would certainly reduce wind noise around the A pillar anyway although I am concerned about the lost of rigidity. Personally, I think what makes the 993 targa look so good is the fact it doesn't have the water channels.

I would guess the effects of gutter removal are more aesthetic than aerodynamic. Probably not much of a fraction of the drag amount generated by the wide body flares.

As far as the wide bodied cars are concerned, those cars of course lose their speed because of the side bulges and tea tray spoiler. Adding the flares completely goes against the typical highly effective aerodynamic shape of say an airplane wing cross-section or the shape of a raindrop. Every little bit can help when you're pushing high triple digits but I don't think Adam is going to go that fast that often. Never know though. He did wreck the car 4 days after purchase. Sorry, had to poke fun there.

If you like the looks, that's pretty important. If I had the opportunity (and $$$) i'd like to lose the rain gutters. But not at the expense of body rigidity. They are a pain to polish around and the reduced wind noise would be nice, but i'll keep my coupe a coupe.

To gain a good amount of rigidity, the cage would be the more effective route. Some roll bar kits only reside mostly in the rear of the car. Whereas the cages run up to the front of the car to the pillars, providing additional bending resistance. Ingress/egress is becomes a pain in the rear with the cage. You make the call.


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Kevin
87 Carrera