"Lightweight " 911

[911nut]

In my never-ending quest to find the best performance bang for the buck I've been considering lightweight body panels for my SC when I re-paint it sometime next year. The issue here is would a reduction of 100 pounds be worth pursuing? Would it make a noticeable difference in performance or not? Would the money be better applied to engine mods?

[pwd72s]

"The issue here is would a reduction of 100 pounds be worth pursuing? Would it make a noticeable difference in performance or not? Would the money be better applied to engine mods?"

Or...Jenny Craig? In my case, she'd be the cheaper option.

[tmctguer]

keep in mind, i'm fresh out of getting my STS license from POC, so i may not be the best person to ask.

100 lb reduction is like not having 2/3's of a driving instructor in your. in my limited track experience, an instructor in the car would cost approx. 1 second of lap time, assuming you weren't actually faster whe n following his advice while in the car with you.

is it safe to assume you already have racing seats, minimal remaining interior, roll cage, trick suspension, etc? if you have, then you can't shed that kind of weight many more ways.

[island911]

You should also consider the tweeking needed to get the replacement carbon to come close to the right shape.

. . .This has the best carbon job I've seen. . .but I could still tell.

[epbrown]

I seem to recall some formula, probably posted here by some HP junkie like Juan, that removing that 100 lbs. weight would the same as adding about 25hp. Noticeable, but not dramatic, I'd think. That is a cool way to increase performance, though; after all, what makes the '73 RS such a beast isn't the 210 hp engine, but the 2145 lb weight giving it ~10 lbs/bhp, almost as good as a '79 turbo! Which reminds me - I don't see a reference for the weight of the 1974 RSR turbo, which had 480 bhp - anyone remember offhand?

Emanuel

[Clark Griswald]

That's an improvement in power to weight of about 4%. So you could have achieved similar acceleration improvement by boosting HP by a similar amount. But, with the weight reduction you are also improving braking and cornering capability.

Is it worth it? Depends. You didn't tell us what you have already done to the car or how you use it.

Fiber / carbon body panels are not cheap when you consider the cost of painting, labor and the reduced life of the panel vs. steel. There are certainly more cost effective ways to get 100 lbs out of the car. Maybe you've already taken these other steps and you are looking to go to the next level. Or maybe not.

[89911]

I've done some research on fiberglass/kevlar body panels for a track car conversions and came upon a few points. The carbon kevlar they use for these is not the same as the race cars. The process used for the competition cars involves numerous expensive processes to get it to the level needed for these cars. People confuse this with the material advertised by parts manufactures and it is not the same. For most common needs, I would go with fiberglass. It proven over time.

[cstreit]

I agree on the Carbon vs. Fiberglass thing. Also remember that Fiberglass is repairable, Carbon is not. Carbon, if exposed to sunlight, will degrade, fiberglass not nearly as much.

As for reducing weight vs. adding HP, remember that while power to weight may be the same for either, braking will be improved by reduction in weight and reduced by adding HP.

[NYSCAR]

Also remember reducing weight provides the equivelant effect of increasing torque across the powerband, as opposed to many power enhancements result in a torque increase on a portion of the power band.

Brad

[911nut]

Thanks to all that offered information and advice. I have no plans to autocross my SC yet. I was just trying to think of a more cost-effective way to improve performance rather than to spend $10K on engine mods.

[cegerer]

".... rather than to spend $10K on engine mods.

Have you considered spending a few thousand on gearbox mods instead? That's what I'm considering. Install gear ratios to reduce the top speed from 145MPH+ down to a more useable 120MPH. They say it's like adding 50HP! -- Curt

[tobluforu]

Last summer I took my car apart for a repaint. No windows, bumpers, rocker panels, or hoods. No door panels, rubber or latches. I drove the car up my street w\ski goggles and could not believe how much quicker it was. What a rattle bucket it was with bungie cords holding the doors closed and no rubber. The looks I got were well worth it.

[Jack Olsen]

911nut, it looks like this is for a street car. And further, it looks like it's for a street car that you're willing to part with some dollars for the sake of new paint making it look better.

If all of that is correct, then I'd stay away from carbon fiber or fiberglass. Both of them are hard to paint well, hard to match (color-wise) to the steel parts, and the new look from the new paint is going to be less durable (in terms of hairline cracks, crazing, etc.).

Unless your car is white, it's going to start looking lousy a lot sooner, which can be heartbreaking, after dropping $3k-$11k on paint. With dark colors, it can be worse, since fiberglass starts to soften at 140 degrees. Porsche solved the problem (somewhat) by making all the Carrera RS's white, since it's an easier color to match and it doesn't get as hot when you park it in the sun. But for the sake of a few pounds on a street car, I'd say the hassle and expense of fiberglass isn't worth it.

Fitting fiberglass doors is its own nightmare, too.

[911pcars]

See what Jim Calzia did to lighten his early 911 race car at:

http://www.early911sregistry.org/jCalzia.html

After all was said and done it stood at around 1700+ lbs. What is amazing is the meticulous recording of this data while building his project. I believe you'll also see an earlier version of Jack's car on the site (pre 3.6). It was nice then too.

Sherwood Lee
http://members.rennlist.org/911pcars

[89911]

The last post failed to mention what he spent. I think it was close to $150,000? Correct me if I'm wrong.

[speeder]

"100 lbs. = 25hp???" With all due respect, this is a very wet dream. If I put a couple of 250lb. football players in my car+ me, it should then have zero h.p. and lose race w/ five yearold on razor-scooter.

Read post on 1988 clubsport test; Porsche removes 156lbs. from production car by removing things like rear seats and passenger sun-visor(??), 0-60 does not improve. Maybe if they took off that other visor, but then you drive into tree w/ extra h.p.

YES, lighter is better;(especially for braking/handling), but on a car the weight/power of 911, it MIGHT be noticable on ass-dyno in 100 lb. increments, probably not on stopwatch. Turn on the A/C on the other hand, (5-10hp?), that is measurable both ways.

[911pcars]

"Porsche removes 156lbs. from production car by removing things like rear seats and passenger sun-visor(??), 0-60 does not improve."

I recall this comparison was between two different cars when they made this observation. This conclusion and comparision would be valid if they took the weight off of the same car. Try this at home. Invite a friend (about 156 lbs) over for a 0-60mph timed ride, then politely ask him to leave and perform the 0-60 mph test again. Might as well do a 60-0 mph test too. Do this several times, different days, locations, times and ambient temperatures just to reduce variables. Thank your friend for his patience and apolgize for wasting his time. Tell us if there was any difference.

To confirm this, I tested my car. Result: It's a lot slower with my wife's steely gaze from the passenger seat.

Sherwood Lee
http://members.rennlist.org/911pcars

[Rich911E]

IMHO, the most cost effective performance modifications you can make are to the driver and not the car.

I think it speaks for itself that a lighter car is faster than a heavier one, both in acceleration, cornering and braking. It is simple physics that with less mass, there is less force required to move it (F=ma). The fact that Porsche spent so much time lightening their production race cars (e.g., 911R) that it is certainly worth the effort. The old rule used to be 100 lbs was worth about a tenth of a second in the 0-60 time

I would suggest spending as little as possible to lighten the car by removing extra stuff (the little stuff really adds up like rear seat backs, floor mats, spare tire, etc.) and spending your money on driving lessons. I am sure that you will find a lot more speed in your car by attending a series of racing schools than all of the plastic body panels would ever give you. Just analyze at the results from your local PCA autocross/time trial and you will see just how much variation there is with exactly the same car. Go to an autocross or track event and have one of the instructors drive your car for a while. When your times are close to his/hers, then you will have wrung all there is out of the existing set-up and it is time to look for more speed.

I used to think driving schools were expensive, but after taking the 3 day Bondurant course, the local 3 day PCA course and a 3 day BMW school at the Nurburgring (Nordschliefe), I feel my money was very well spent and I know that I have a long way to go before I am driving my car to its limit. Plus, your knowledge translates into any car you drive -- sort of like portable horsepower!

Just my thoughts.

Rich

[cegerer]

In the Speedvision GT Series last year they indicated that the Honda NSX had been given a weight penalty of 100lbs. This was based on the theory that every 10 pounds = 3 horsepower. Sounds like alot, but that's what they use.

I also seem to remember an old rule-of-thumb in drag racing that every 100 pounds less in weight = 1/10 of a second in the 1/4 mile?? -- Curt

[cegerer]

In the Speedvision GT Series last year they indicated that the Honda NSX had been given a weight penalty of 100lbs. This was based on the theory that every 10 pounds = 3 horsepower. Sounds like alot, but that's what they use.

I also seem to remember an old rule-of-thumb in drag racing that every 100 pounds less in weight = 1/10 of a second in the 1/4 mile?? -- Curt