[johnbran]

I was wondering if anyone out there had any ideas on what types of OEM wings/spoilers from other cars were out there that could be adapted to fit the rear of the GT? Has anyone tried anything that worked particularly well? Most of the ones I've found are either too narrow or too wide and most would take major reworking to allow access to the gas cap. I'm well aware of what sources such as Opel GT source has to offer, but they're a little out of my budget right now. I've seen several different styles used on the GT, but most of them do not have any information listed as to what the spoilers came from. I would be interested in any info out there pertaining to front air dams as well, but I will probably fabricate my own air dam and spoiler for the front. If the budget would allow, I'd have a complete Steinmetz kit on it's way, but with the limited funds I have to work with, I decided the money was better spent on important stuff like brakes and driveline. So, if anyone out there has any suggestions on possible wings/spoilers, I'd really appreciate the info.

Thanks,
John

 

[chuckspeed]

John -

Betcha a Neon Expresso spoiler will fit with minimal difficulty. They're narrow; they use inboard mounts, and the oval design is in keeping with the lines of the car.

 

[johnbran]

I never thought about one of those. I'll check around and see if there's any in the parts yards around here. Thanks for the tip!

John

 

[johnbran]

Well, don't say it never pays to be a "pack rat". I was searching through my stash of old parts and came across a decent rear spoiler that I had completely forgotten about even having. It's a flat, stand up type spoiler with 5 mounting posts and doesn't look or fit too bad on the GT. I had to cut out a notch in the front of it for gas cap clearance, but this didn't affect the looks too much. The really cool part of it is that the spoiler ends curve downward and the width is almost perfect so that these seem to flow right into the curves of the GT's rear end. I have no idea what the spoiler origionally came off of, but it seems to fit the GT like it grew there, and that's the important thing.

Now, for the next body problem. I am working on a plan for redesigning a new air dam for the front when I repair the belly pan under the nose, but I have heard that this pan is critical to cooling and air flow to the radiator. Does anyone have any tips or things to avoid when designing a spoiler for the front? I am trying to decide whether to come directly off the front of the nose below the grill and flare it out slightly to "scoop" more air into the opening, or to design a small air dam below the nose similar to newer cars that would direct air up into holes cut into the bottom of the pan. I've seen the spoilers/air dams that OpelGTSource has, but I'm really wanting something different from the rest. I'm also more conscerned about the looks of the spoiler than I am about the function, just as long as it doesn't produce any negative effects in cooling or handling. Anyone out there have any suggestions on this? I'd appreciate any thoughts or ideas from the group.

Thanks,
John

 

[chuckspeed]

Most all new cars are 'bottom breathers' - they pull air from the high-pressure region behind the front fascia and ahead of the front wheels. GT's are kinda funny - while they look like bottom breathers, they are 'front' breathers - they pull air from the front of the car, under the front bumper.

While this may look like a good design at first glance, it's not as efficient as a bottom breather design. A fair amount of air 'spills' off the front end as it cuts thru the air and literally 'misses' the cooling opening. An air dam does exactly that - 'dams' the air from spilling off the front of the car and piling up under the front of the vehicle, causing lift.

Cars are funny when it comes to this. Low velocity air has a higher pressure than high velocity air - it's this function that provides aerodynamic lift to a wing. Unfortunately, the underside of a vehicle is a great place to 'catch' air, thus slowing down airflow. Meanwhile, the air is flyin' over the top surfaces at great speed - the result?

lift.

The effect can be significant - several hundred pounds of lift at 100 MPH on a poor aerodynamic design. An air dam prevents air from piling up under the car, thus reducing downforce. I did some experiments with an Escort on stock rim protector tires back in the 80's, and it was possible to make the car 'stick' like it had 50 series tires with 80 series rubber - at speed.

The car looked funny, tho. To get an air dam to work well, it has to be 'in the weeds' - no more than 2" off the pavement. At curb height (over 6") they are largely ineffective. In addition to the dam, side skirts are necessary to prevent air from spilling into the low pressure area under the car - the effect is tail lift. Racers get around this by putting the entire car 'in the weeds' - not much air can get caught when the belly's scrapin' asphalt. Rules cops spend a good part of their time checkin' vehicle height restrictions - they have a big impact on how the car performs, often much more than the engine mechanical restrictions in SCCA class racin'.

So - back to your question. Depending on how you config your airdam, you'll actually increase the amount of available air for cooling at the FRONT of the car. If you restrict the opening, you'll decrease it. Distance to the pavement will have a big effect on this. GT's are limited as to how far down to the dirt you can go with a dam - there's a LOT of front end overhang to contend with. Chances are you won't be able to go down much more than the stock chin - an inch or two, tops.

If you wanted to build a bottom breather, the hot ticket would be to build a deep airdam about 12" ahead of the front axle centerline. This will keep air out of the chassis and won't get bunged up in daily driving. From there, I'd cut a 12" x 30" opening ahead of the airdam to get air to the radiator. Rule of thumb on the opening is roughly 1.5 - 2X the surface dimension of the radiator to minimize pressure drop.

Just keep in mind that you can't get much more radical in your envelope dimensions than the stuff you've seen on the OGTS website. The front overhang and cooling requirements won't let you.

 

[johnbran]

Thanks for the incredible detail in your reply Chuck. That's what I love about this site. You guys really go to the extra effort to explain these things. As for the air dam, I'm still debating which way I want to go with it, but with your info in hand, it will make either way a lot easier. So, which design would you go with if it were yours? A nicely molded in full front air dam scooping air up into a mesh covered, origional size grill opening could provide a much more aggressive appearance, especially when combined with the hood scoop and rear spoiler. But on the other hand, a well designed bottom breather air dam might not change the looks too drastically, but could probably improve the cooling quite a bit. In reality though, for a street car that will rarely, if ever, see speeds above 65 mph and that will spend most of it's life on city streets rather than open road, is the function of the air dam that major of a concern? Or am I wrong to be more focused on the looks of the air dam than the function of it?

Thanks again,
John

 

[chuckspeed]

In a street application, the airdam is primarily a looker. The need to clear speedbumps and parking curbs prevents it from being truly functional.

When I did my first GT, I pulled the coffee-can turnsigs and bumperettes off the car, put in little recessed bullet turnsigs and covered the whole schmeer with expanded metal (mesh) not unlike the stuff used on a BMW M3.

Now the problem with expanded metal is it really restricts airflow - up to 50% reduction in effective area. So if you're going to use a mesh cover - make sure you add area to compensate for this.

Airflow management is tricky business - even the pros goober it up now and then. The New T-bird's intro was delayed several months due to an engine cooling problem connected to airflow managment. It was kinda spooky seeing hundreds of new 'Birds stacked up in an non-descript warehouse while the issue was being sorted out.

If it were me and I wanted an airdam on the car, I'd go with a design not unlike what gets installed on hottie 1st generation Mazda RX-7's. These feature a 'square' design - the front section is perpendicular to the pavement in side view. This design will do a better job of 'catching' air that spills off the front of the car than stock. Just keep that front opening BIIG...There's a reason why OGTS offers the Cali special airdam!

 

[johnbran]

Thanks for the info Chuck. Sounds like I'm kind of starting out the same way you did on your first GT. I've already pulled the coffee can signals and bumperettes and have been searching for a good breathable mesh with large holes to cover the entire grill opening without restricting too much flow. I'm not going to reduce the size of the origional opening at all, but will just add on below the opening. I'll probably try to come up with a design like you mentioned about the RX-7, with a squared off leading edge that is perpendicular with the ground. If for no other reason, this would be much simpler to construct than one with a lot of odd angles and such. So, thanks for all the helpful tips and information once again. You guys here have saved me from making several critical mistakes on this project and it has been greatly appreciated.

Thanks again,
John

 

[oldopelguy]

How cheap are you?

Take a look at the local hardware store's gutter coverings. (The material used to keep leaves out of your gutters.) They are @ 6" wide and have lots of large holes in them, come in several colors, are easy to use plastic or aluminum, and cost @ $6. I used some plastic ones to replace the fins between the main bars om my old truck and it looked 20 years newer.

 

[johnbran]

Cheap?? I'm not cheap.......I'm broke!!
Seriously though, I've not really got very far on my search for the grill opening mesh yet, but I'll check the gutter coverings out. I am actually debating whether to use the mesh, or make a new grill out of flat steel or aluminum strap material. I could fill the grill opening with about 4 or 5 strips, somewhat like a tube grill, but with flat stock instead of tubes. This might be less restrictive than the mesh covering and may, in fact direct the air better into the radiator. But, what do you guys think?

Thanks,
John