lightest SC weight WHILE preserving front weight?

[70SWT]

There are a lot of threads on attaining the absolute lightest weight in 911s. However, it has always occurred to me that to potentially improve the F/R weight distribution while lightening, and I often try to lighten my cars, I usually focus that effort on items located in the rear and high up.

So I wonder whether selectively keeping some relatively "heavy" items in the front seriously impedes total weight loss. I think the answer is no, but would love to hear the experiences of others.

In my current SC targa project (in which I am mainly grappling with EFI issues per another thread - but I'm taking parts off as I ponder that), I am also working towards this front weight-preserving weight loss strategy. My approach includes:

Removing the whale tail decklid - will replace with either a ducktail or a simple FG/CF lid
Removing the entire A/C system
Converting to a soft window targa kit
Removing rear seats
Using TRE 911R taillights
Using a FG rear bumper
Perhaps using a FG or CF targa top skin with a fabricated aluminum frame - doubtful ROI there, though...
Lighter exhaust

I speculate that all of that should result in >150 lb. weight loss that is substantially focused on the rear of the car. Will weigh items as they come off.

[stownsen914]

Removing weight from the rear of a 911 does make sense as you say. I’m not sure if you’ll get as much value as you might think by expressly avoiding removal of weight from the front. While I get the theory, I’ve never heard of someone removing too much weight from the front and ending up with a poor handling 911.

[Carbster09]

How much weight does the R type rear lights really save? It would be interesting to see a list of parts and weight saved. What about aluminium trailing arms versus stock on my '71? Too much effort for too little gain?

I would think, a lighter front windshield, and Lexan side and rear windows would offer a good level of weight for cost!

[RWebb]

there are several lists of parts and weight saved... you'll have to search for them

the tail lights are quite heavy, moreover you'd be saving wt. at the extreme end of the car which is important as you need to consider momentum for handling

Al trailing arms are lighter and also stiffer - well worth it

[IROC]

I think you're on the right track and make a good observation. I got my car down to about 2300 lbs ("street" car with a roll bar and I wasn't doing anything drastic) but in order to do this I had to remove the spare tire. That resulted in a little bit more rear-bias to the CG than I thought was necessary, though, so I usually ran it with the spare tire in.

Tail and rear bumper weigh a lot compared to fiberglass and obviously they are pretty far from the CG, so they are low-hanging fruit. My rear bumper weighs 7 lbs and I think my whole factory setup was close to 30.

[70SWT]

Originally Posted by stownsen914

...I’ve never heard of someone removing too much weight from the front and ending up with a poor handling 911.

I wonder about this - I think it depends on how fast the car will be driven. For a purely leisure-driven street car, it probably doesn't matter.

But, front end lift has historically been an issue in early 911s at speed. Removing substantial mass in the front is probably not the best approach if you are going to ever track the car or see serious speed on the road. The weight distribution will surely remain heavily rear-biased despite all of these efforts.

[Bill Verburg]

To improve the dynamic behavior of a 911 all weight loss is good, removing it from the front is as important and effective as at the back because the polar moment(which is a major determinant of dynamic behavior) depends on the mass and the length of the lever arm from that particular mass and the CoM. The lever arm from CoM to the front is longer than the lever arm from CoM to the rear, meaning a kg lost at the front bumper has a larger effect than a kg lost at the rear bumper. Correspondingly weight lost from the roof has the least effect because it's moment arm is so short and weight lost from the seats is almost the least effective. Taking honors for least important is the transmission case which is right at the CoM.

There is nothing inherently bad about a 40/60 wt distribution compared to a 45/55, You just drive the car a little differently, w/ these cars the throttle and brakes are more important than weight distribution, gas is glue for the rear and the brake pedal is glue for the front end as long as the tires grip isn't exceeded and these days it's easier to over-tire a 911 than to under-tire one

[Reiver]

Have at it...you can always add a bit back up front if you have an issue but I doubt you will...I am down to 2300 lbs fully wet with an '83 SC coupe....I did lose the sunroof/bumpers/AC and a great deal more but it is a street car that occasionally see's 120ish....never noted any poor handling or lift.
I do have a glass Duck and SCRS bumper that is less of a front air dam that the stock SC....I don't note any difference tho.

[70SWT]

I have a 930 front lip on the car, and will keep that and the stock front bumper. My feeling was that this would be a good combo with a ducktail for the occasional DE event. Maybe the simple decklid (while light) will not be the best way to go.

[70SWT]

Originally Posted by Carbster09

...Lexan side and rear windows would offer a good level of weight for cost!

Removing the rear targa glass in favor of the SWT kit should drop a fair bit of weight in this case....that is one huge, heavy piece of glass way up high out back.

[Bill Douglas]

You could lose the fan blower motor and swap in SSIs and Dansk for q bit of weight loss from BEHIND the back wheels.

[70SWT]

Originally Posted by Bill Douglas

You could lose the fan blower motor and swap in SSIs and Dansk for q bit of weight loss from BEHIND the back wheels.

How did I forget - I added swapping out for a lighter exhaust to the list above.

[RWebb]

the guy who did the documented wt. loss on a bumper car was screen name Joe maybe ShakinJoe, IIRC

he used a scale/balance for HVAC work so pretty accurate wts.

[Sebscst]

I’ve gotten my car drastically light and still very streetable (2080# fully wet). Here is what I’ve learned about my car. When I have a full tank (custom 25 gallon ) through 1/2 tank the car drives great at all speeds. I’ve had it up to 130 no handling problems. But once it starts to get light on fuel I can feel the front end lift and it is more of a handful above 90. I’m going to install a front splitter and see if I can add more downforce on the front. It has a 964 spoiler but I can’t tell the difference when it’s up or down so there’s definitely plenty of weight in the back.

[70SWT]

Originally Posted by Sebscst

...I can feel the front end lift and it is more of a handful above 90...

This has been my experience in multiple air-cooled 911s I've owned too; the front end becomes noticeably light the faster you go.

Feeling that light front end sensation when cornering is thrilling - fighting the natural urge to lift the throttle...still, improving F/R distribution while lightening seems, at worst, harmless, and most likely, beneficial if aero has already been addressed.

[Bill Verburg]

At speed aero is more significant than weight, the faster you go the more so

here are the drag and lift curves for a '73 w/ & w/o '73RS aero

and here is for the'74 up

964




964RS




993RS


993RS/CS

[70SWT]

Cool material. Reminds me of the old C&D article reviewing the 74 911 that was dredged up recently:

[AG81]

I am addicted to reading Bill's post. He really has the data. Awesome.

[Bill Douglas]

My SC, no wing, front chin spoiler, slightly low stance, feels decidedly firm and stable at speed. I've taken curves at 100mph and it felt fine, and have done 135mph on the straights - felt great.

I probably get less turbulent air going under the car than the average 911.

[Bill Verburg]

The problem area for 911s is more at the rear due to the shape of the car and slope of the rear top surface these contribute to instability at speed particularly in a cross wind

On the original B series cars wind tunnel testing @ 230kph showed front lift at 815N rear lift @1113n what is rarely discussed is the effect of a cross wind on these #s, w/ a 22.5° yaw angle lift in front rose to equal that in back , at angles > 22.5° front lift was larger. This puts the center of pressure way out in front ~80cm ahead of the wheel base center. The net effect is that though the forces are equal the action or effect is still 85% on the rear. The early factory effort to quell this by placing 11 to 22kg of lead in the front bumper corners was a help but not a cure, later efforts to move weight forward also helped but didn't cure the issue.

The real cure was from longer wheel base,
aero aids particularly in front that matched weight and lift
staggered wheel and tire fitments