Enlightenment

[YTNUKLR]

not a very good power to weight ratio though

[RWebb]

thanks for the bump - but substantive posts would be appreciated


surely this thread is more useful than threads on overcoats and fat bimbos/broken windshields....

[Flieger]

I, too, have thought about what a carbon fiber 911 tub would be like.

I think Aluminum would be easier to do but the design would need finite elemeny analysis on a computer to see how the loss of rigidity would affect the structural integrity. A roll cage would be a must, Aluminum tubes should be fine, however.

The standard steel tub can probably be lightened significantly if the chassis is seam-welded. Then holes can be drilled in strategic areas of the flat sheet metal without loosing much of the shear strength from the stock chassis. Those few spot welds make the chassis much weaker than it could be for the same mass of metal.

I like the idea of the Aluminum tube frame -ala 935,917.

I also am very interested in using Aluminum S calipers front and rear.

[RWebb]

seam welding makes sense to me.



For general perusal, here is an interesting thread on Early 911S bbs
http://www.early911sregistry.org/forum/showthread.php?t=24160


Scroll down to the two posts by TRE Cup (Dave B.) - he lists some ideas and suggests that a final wt. of only 1,500 lbs. could be achieved.

[petevb]

Originally Posted by RWebb

seam welding makes sense to me.

For general perusal, here is an interesting thread on Early 911S bbs
http://www.early911sregistry.org/forum/showthread.php?t=24160

Scroll down to the two posts by TRE Cup (Dave B.) - he lists some ideas and suggests that a final wt. of only 1,500 lbs. could be achieved.

I agree in that I'm sure 1500 or even less is possible... I'm also sure, though, that the lightest 911 you can make isn't the best. You end up making so many compromises (smaller brakes, less stiffness, smaller wheels, etc) that it ends up hurting you overall. Unwritten, I think, is the "lightest 911 that you'd want to drive". That's still awfully vague...

I found that the lightest 911 I wanted to make was much heavier than I'd expected- around 2100 lbs. Because most of the extra weight actually made the car faster...

One sacrilegious parting thought- the lightest 911 you can make isn't: it's a 912.

[Flieger]

The only 4 cylinder motor that revs with the sound and soul of a 911 flat 6 is the Fuhrmann 4 cammer.

[YTNUKLR]

One HUGE difference:






5-Main Bearing Crankshaft. Displacements from 2.0 up to 2.7L. Turbo-capable, of course, aluminum case, 911 oil pump, ....wicked. More "912" than 911, but this would certainly bring you into 1650# territory, pretty easily I think (and the weight distribution would be better).

S-brakes at all four corners is perfectly adequate for a Light car.

Aluminum is sometimes confused as being flexier than steel. It is not. Aluminum has a higher stiffness-to-weight ratio than steel (about 5%), but a lower yield strength and less resistance to fatigue (bending). No doubt you could save a lot of weight with aluminum beams as monocoque-stiffening members (see Audi A8--full Al-unibody).

Dymag wheels: Any size you want, Mag spokes with Carbon Fiber rims.

[rfloz]

WEVO makes a 5# flywheel and the requisite 5.5" clutch just has to be lighter than most other options. Well, direct drive ala dirt track usage would be lighter.

Which begs the still unanswered question - what is the purpose of this mythical beast? If street use, good luck; it won't fit any known race class, so maybe track rat or open class hillclimber?

[911pcars]

"Aluminum is sometimes confused as being flexier than steel. It is not. Aluminum has a higher stiffness-to-weight ratio than steel (about 5%), but a lower yield strength and less resistance to fatigue (bending). No doubt you could save a lot of weight with aluminum beams as monocoque-stiffening members (see Audi A8--full Al-unibody)."

A SAE paper analyzes and makes the case for al. as a replacement mat'l for steel here:

http://www.sae.org/technical/papers/2006-01-0708

Anybody got $11 to see the full report?

Part of their summary:
"Aluminum is sometimes confused as being flexier than steel. It is not. Aluminum has a higher stiffness-to-weight ratio than steel (about 5%), but a lower yield strength and less resistance to fatigue (bending). No doubt you could save a lot of weight with aluminum beams as monocoque-stiffening members (see Audi A8--full Al-unibody)."

I have no doubt. However, doing this for a 911 isn't just a replication of the existing steel unit panels with aluminum versions and expecting the same or even higher level of rigidity. In this thread, I don't hear the realization of the level of complexity and expertise required to design and engineer, much less produce sheet metal stampings (in whatever material) to create a new-type 911 chassis. I suspect the cost/benefit would be in the order of $1000's/lb. of weight savings. Money is better wasted fabricating replacement parts in titanium, magnesium castings and state-of-the-art resins.

I wonder how much Lotus spent to create their alloy chassis?
http://www.sandsmuseum.com/cars/elise/information/technical/asauto.html

or this paper on lightweight chassis manuf. and their thoughts on cyclic fatique (steel vs. aluminum):
http://www.entrepreneur.com/tradejournals/article/135661316.html

Sherwood

[RWebb]

The purpose of this mythical beast is to serve as a conceptual prototype (and to attract posters to a thread that is more technical and 911 based, than the current overalls and broken glass/call girl threads...).

I find it a LOT cheaper to work things out on paper than in metal. For one thing, a fairly simple quantification exercise can show whether something is worth pursuing or not. Sherwood's comments on the difficulty in building a new unit body is a case in point.

But so far only the chassis and brakes have really been mentioned.

I would like to see a lighter weight engine carrier for example...

[911pcars]

Originally Posted by RWebb

The purpose of this mythical beast is to serve as a conceptual prototype (and to attract posters to a thread that is more technical and 911 based, than the current overalls and broken glass/call girl threads...).

I find it a LOT cheaper to work things out on paper than in metal. For one thing, a fairly simple quantification exercise can show whether something is worth pursuing or not. Sherwood's comments on the difficulty in building a new unit body is a case in point.

But so far only the chassis and brakes have really been mentioned.

I would like to see a lighter weight engine carrier for example...

"I would like to see a lighter weight engine carrier for example..."

Drilling the factory steel engine carrier (cross bar) removes weight. Reinforcing it so it doesn't collapse adds weight. Net gain: zero

Replacement with aluminum: Susceptible to fatigue. Unknown life-cycle before failure. Net gain: less weight or added frictional loss from engine contacting pavement.

Replacement with stainless steel: Any significant weight loss?

Replacement with Ti: Some weight savings offset by cost of material and fabrication. Is cost a consideration?

The actual engine carrier (between cross bar and engine) has been commercially replicated by a machined aluminum piece. Net loss of a few oz.

Sherwood

[afterburn 549]

As far as I know to use true state of the composites , one needs a big oven (autoclave ) funny how that worked out..
At any rate back in the day, we made wings and things out of graphite's and carbon fiber and the like, Not with styrene resin
So ..true C.F. can be spendy...

[petevb]

I think an outlaw hill climb car is a nice mental target, or perhaps a similar hill climb class with restricted displacement. No rules, but obviously you wouldn't do things that would hurt performance.

Various grades of aluminum are either slightly stiffer or slightly less stiff on a pound for pound basis than various steels. That difference gets lost in the noise when you realize that if you leave the geometry the same and make the car weigh 2/3 as much it will also be 2/3 as stiff. To take advantage of aluminum you need to change the geometry of the chassis, and the best way to do that is to add either very tall boxed rocker, a large closed center tunnel, or a well designed roll cage (effectively making very tall sills and turning the car into something more like a tube frame).

Carbon blows away aluminum on a stiffness to weight ratio basis even if it's not autoclaved. Good vacuum bagging with good resin to fiber ratio makes excellent parts if you have the skill. It's fairly easy to make simpler geometries such as flatter panels. It bonds to steel well.

I think there is a good argument to be made for swiss-cheesing the chassis and bonding in carbon fiber stress panels in place instead. You would simply extend what's already done with the larger panels (roof, etc) to smaller ones like the fender wells, floor pan, rear seat area, nose clip, etc. You'd do a lightweight cage with thin wall tube, and where it makes sense you'd look at replacing the existing structure entirely (full tube frame), especially in areas like the rear torsion bar carrier, etc. The cage would probably be steel rather than aluminum so that you could weld it to what steel from the original body was left. Similar to this, but going further and without trying to retain any stock metal:

We calculate that the bonded carbon roof here actually adds significant stiffness:


I think you'd end up stiffer than the original car and 100-200 lbs lighter depending on how far you went. A skilled person could do it in the garage, though the time commitment would be very significant.

Things like the engine carrier, while obvious, are just not heavy enough to move the needle much. All the metal around and behind it that it bolts to probably weighs 10x as much... 1400-1500 lbs is a nice target I think for a narrow body car on small tires.

[RWebb]

I like that CF rear fender - how much weight did that save?

One nice thing about the engine carrier -- it could be made in the aftermarket and then simply swapped in to replace the stock one. The value of removing some wt. is enhanced since it is at the extreme rear of the car. I've never seen an accurate wt. posted for that item, and I forgot to weigh mine...

Jim Sims posted the idea of bonding in carbon fiber stress panels on the Stiffness thread...
http://forums.pelicanparts.com/porsche-911-technical-forum/259557-structural-reinforcement-post3195258.html#post3195258

[petevb]

Originally Posted by RWebb

I like that CF rear fender - how much weight did that save?

I don't have the delta here, but they were 3 lbs each, reinforced on the front to take cone hits, etc. Here was what it looked like from the inside, giving you an idea of how much metal is removed:


The carbon parts were roof, hood, left and right rear fenders, front bumper, rear bumper, rear deck lid- total weight was 35 lbs without paint. The stock hood weighed 44 lbs alone. The front fenders are fiberglass- a little heavier than carbon, but weight up front isn't the end of the world...

[Flieger]

Are the adapters for the S calipers in the rear currently in production?

How much do the adapters weigh?

Can normal 8x16 inch Fuchs fit them?

[911pcars]

Originally Posted by Flieger

Are the adapters for the S calipers in the rear currently in production?

How much do the adapters weigh?

Can normal 8x16 inch Fuchs fit them?

With al S calipers all around, your brake balance won't be right.

Sherwood

[YTNUKLR]

The car we used them on had a dual master cylinder pedal cluster. A brake bias adjustment would be necessary if you didn't have a dual master pedal.

The adapters..something like 7-9oz. each. They are in production if you request them

[Ole Petter]

Oakley Design has made a GT2 with a carbon-fiber roll cage... They also have CF wheels! They claim a steel cage is 60 kg and the CF one is 12. This cage is TÜF approved and FIA approval is coming, they say. This will possibly give the go ahead for CF rollcages in the near future - that is a nice weight saving.

In his book, Bruce Anderson claims that an oil cooler on the pressure-side of the dry sump is much more effective than that on the scavenge-side. Maybe it could be possible to take advantage of that, and even reduce the oil-capasity of the engine somewhat? That would mean a smaller oil-tank, less oil and no oil-lines and front cooler...?

[RWebb]

besides the link above ("Drill Baby, Drill") on the Larousse S-T, that was posted at the Early 911S bbs, there are some other potentially useful threads - all have accurate wt.s:

438 lbs gone in 5 days - My Build Story
- Shakin' Joe's wt. removal program on a heavy G50 bumper car

THE WEIGHTS - RSA Panel vs CF Panel vs Stock Panel
- wt. impact of removing bumper car map pockets, etc.

Yet Another Boring Hot Rod Rgruppe Car - Part V, Exterior & Paint
- using FG body panels on my '73 longhood (early car)

http://www.penaltykicker.com/911/data/
- downloadable files with weight data and comparisons. My Word (*.doc) comparison table also gives the link to Jim Calzia's wt. data. There is also a list of magazine articles of interest. I've updated both files and should post the revised versions... of course, there are lots of things I should do...