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Aero question regarding front bumper / valence

Hi -

I have been thinking about replacing my impact bumpers with fiberglass units to save some weight. The front valence I have now (pictured below) mimics the IROC bumper but with a splitter molded in. The center oil cooler opening is not cut out as the car is a stock 3.0 that does just fine with the Carrera cooler in the fender.

From what I've been reading the lower the front bumper the better. I am pretty much as low as I'm willing to go with what I have now. Getting in and out of my driveway makes me cringe every time.

I am toying with 2 options:

1. Replace like for like. I've seen companies that make the IROC front bumper with the splitter built in. It'll basically be what I have now except lighter.
2. Install an IROC bumper without the splitter. I might be doing a 3.6 swap and the center opening might come in handy. I'd then add a custom splitter under it that way I can protect the bumper and be able to replace the splitter once it gets all scraped up.
3. Install a SC RS front bumper. No center cooling hole and it may not be low enough. I could always add a lip onto this as well but it'll take some development work (and time).

Would love to hear your input and experiences. Also open to other options if they exist.

-S

Untitled by sicklyscott, on Flickr

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Old 06-28-2016, 06:29 AM
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It looks like your car is still driven on there street and not a track only car.
From the "been there, done that" experience, I'd suggest you simply have the existing bumper cover repainted and be happy knowing that you saved a bunch of money. The weight difference will not make any real difference in your lap times (even for a pro driver). Wait until you know you are going to make a significant modification to the car where you need to change the front end before you spend the money.
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Old 06-28-2016, 08:47 AM
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How much does your car weigh now? Are you planning on doing a major stripping to reduce weight?

I agree with Tom. It's quite a bit of work to put on a FG bumper. For just weight savings, you could just change out the bumper shocks with the euro style.

Definitely stay with the option for a front cooler. Probably a good idea if you go with a 3,6.

That said, I really like the look of the IROCs. If I had a IB car that's the look I would go for.
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Old 06-28-2016, 10:05 AM
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The plan was to try and drop 200 lbs out of the car. I noticed a significant difference in how the car behaved with and without my instructor on the track. FG bumpers, rear deck lid, lightweight battery, AC removal, radio and speaker delete and backseat delete should get me around that 200# figure from what I've read. That should result in a sub 2500 lb car (corner balance scale said ~2800 with 150 lb driver).

I also had a guy tell me at the last track day that with the closed bumper opening it acts like a parachute. He was quite vocal about it too like I broke some rule.

Looks like the 3.6 is going to happen, I need to figure out what the center oil cooler ducting needs to be like behind the cooler.
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Old 06-29-2016, 04:47 AM
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What Tom says. Plus an all glass unit will be really fragile. One little bump while parking and it's broken.
Personally I'm more interested in losing weight from the rear of the car, not the front. If you do the 3.6 swap that little bit of weight won't amount to much anyway.
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Old 06-29-2016, 06:39 AM
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Quote:
Originally Posted by Sicklyscott View Post
I also had a guy tell me at the last track day that with the closed bumper opening it acts like a parachute. He was quite vocal about it too like I broke some rule.

.
Hahaha...not everyone can be a winner. Blocking off the center opening is actually better for aero. Look around the paddock; on cold days the sharp end will have them partially taped/blocked off.

As for front bumper, I'd go with the standard RS without splitter. If you're just running a tea tray that is the correct balance. The splitter is needed if you add 2"+ gurney to a tea tray or go with a leading edge wing. And as others have pointed out, it will be much easier to drive around town
Old 06-29-2016, 12:12 PM
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Regarding the parachute comment...

People have strongly held opinions, just not always based on facts. I've been told the rear bumper cover acts as a parachute too. And if I was to remove it, the car would be much faster due to improved aero. Well, I had the rear bumper removed at Road America a couple years ago due to an off in the rain. I can tell you that the car was no faster without it, in terms of acceleration or top speed. At RA, I hit terminal velocity in 3 different places on the track, so it's the perfect track for making the assessment.

I've also closed off the front of my car (which makes it end up like yours) at Fontana/Autoclub Speedway to try and reduce the air and increase top speed and it had zero effect. I've tried a lot to get my car to go faster than 142 mph and the only thing that might work is more horses.

Save the money and spend it on more events and instruction, it will have a bigger and better impact there.
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Old 06-30-2016, 04:21 PM
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The G model 911's - especially with turbo flares have the aerodynamic efficiency of a small refrigerator. Seriously. A standard IROC front has little downforce in the front - you are better with keeping the one you have.

The best aero you can do is install a smooth bottom panel - from there it's better to go with a 996 type body (see Pat William Racing)

I used to touch up my fiberglass valence on a quarterly basis - easier with black tough.
Old 07-01-2016, 06:10 AM
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Quote:
Originally Posted by JeremyD View Post
The G model 911's - especially with turbo flares have the aerodynamic efficiency of a small refrigerator. Seriously. A standard IROC front has little downforce in the front - you are better with keeping the one you have.

The best aero you can do is install a smooth bottom panel - from there it's better to go with a 996 type body (see Pat William Racing)

I used to touch up my fiberglass valence on a quarterly basis - easier with black tough.
+1 930 flare cars + huge drag

standard IROC front has little down force and the relieve notch out panel behind i would assume add lift since it exits at the wrong trajectory at the worse area. im keeping mine iroc bumper with out a splitter since i shooting for a period correct look and put up with the added lift.

i might seal it underneath so u cant see it visual and hope the exiting air will find its way out of the wheel wells. not a lot of room back there between the back of the cooler and the trunk panel unfortunately.

you can learn a lot from the 964 cars which are still essentially a G body panel wise. intake in front exit at front wheel well which are effective low pressure area. this is mimicked in most of the newer water cooled cars. the 964 have different front structure for more room to move the incoming air cross-car. i notice some of the very early G bodies seem to have more room in this front structure for airflow than my 84 TL?

small details differences,help guide or trip the airflow along with the under-panel makes the 964 the lowest drag air-cool

here is a interesting study .27 cd 911...thank god they didnt go all out producing this ungainly looking car!

Porsche's Aerodynamic Concept Foreshadowed The 964 and 993 Models - @FlatSixes - the blog about Porsche
Old 07-01-2016, 09:39 AM
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For the SC based 3.6 conversions, the 964 type noses allows a 72 row front mount oil cooler to have some decent space behind it for air flow exiting. I was able to get about 3 inches of space from the rear oil cooler surface to the tub front with the 964 nose. The IROC nose I had prior only allowed about 1.5 inches of space from oil cooler to tub. Form, fit and function is a balance in a conversion.
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Old 07-04-2016, 10:05 AM
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Part of me wants to do a second fender mount cooler on the drivers side so I can have fans on both. I'm more worried about getting caught in traffic than track temps at the moment.

If I had my way it'd have a long hood S front end. But that's money and time I don't have at the moment.

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Old 07-04-2016, 10:09 AM
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