Ideally it would be both light and rigid (DUH!) but lightness wins in my book. Starting with an early chassis gives a 100-200lbs advantage out of the box. The better handling afforded by a more rigid chassis isn't worth much if the other car is 200lbs lighter (and all else the same)!

I'm biased as the owner of a non-sunroof early coupe but it is significantly lighter in full street trim (2150#) than a stripped 964 (even the heavily lightened versions are 2400#!). Do the same techniques to an early chassis and you'll have it at closer to 2000#.

In addition to the added rigidity of the 964 chassis you also have added mass due to crash worthiness. Safety adds weight.

If you're building a street car - lightness isn't as critical. You can afford a couple hundred lbs of dead weight. If you want the 'ultimate' street car, go lighter to start with and you can add creature comforts instead of stripping them all out. Think of it this way: you could take an early chassis, add a 3.6L, good stereo, A/C, lightweight carpet, door panels and sound insulation. Or, take a 964 and strip all that stuff out. In the end you may have the same power/weight ratio, balance, etc. but one is much more comfortable on the street. If the 964 is marginally faster - who cares, it is a street car and you can't exploit that very small difference on the street anyway. Oh, and the early car hotrod will always be worth more than the stripped 964 not to mention look much cooler. :)

Comfort and usability? We are talking about sports cars here, right? Comfort was not high on the list of things the OP wanted out of the car. Then again, the car I am talking about is not uncomfortable to drive for long distances.

In my experience, the extra rigidity of the 964, however much it is, does not offer enough handling improvements to overcome the extra weight.

Take a '73 RS clone with a 3.6L and a 964 RS America, both well setup. Which car is more fun to drive? Which would go faster at the local autocross? Which would be the best handling? Which would more enjoyable overall?

My answer is the '73 RS clone with the 3.6L. It would be a rocket ship compared to the RS America.

Maybe you would want a nice comfy car. Maybe a soft 964 C2 or C4 would suit your needs. I don't think that is what the OP was looking for.

Scott

This is turning into a great thread, with lots of good info, advice and opinions, but it is a little short on actual examples......come on....show me what you have done to achieve the perfect balance. I'd like to see actual examples, including pix and specs of your "street rod". Include as much info as you want, describe your decision making process, handling/weight/suspension vs. comfort/driveability, and the results, subjective and otherwise. Where are the hot rodders??....show me your stuff. Show me good examples of the what and the why!

Regards,

Al

A rigid chassis makes for better tunabilty of the suspension. It will respond more sensitively to changes. The rigid chassis removes an unknown-rate, undampened spring from the equation. It allows for more extreme biases of roll stiffness distribution. I would say that this tunability means better handling and a better real world lap time.

the thing is, the perfect balance depends on the driver and the road being driven on. (for the 911s)

That is, on a perfectly smooth road, a very stiff suspension is great. As the road gets bumpier the suspension needs to become more compliant. -think go-kart vs rally car.

If you want the best, you will be looking to active suspension. And there again, the 'best hot-rodder' seem to be Porsche engineers. Although, the Porsche Active Stability Management (PASM) actively controls only the damping component -- w/ only slow acting change capability for the (air)springs. (maybe that's changed by now - dunno)

All other things being equal, you are right. But all other things, specifically weight, are not equal.

Scott

We have about as much consensus here as a room full of economists. It all depends on what you want, and what you are willing to sacrifice. Me? I just love a lightweight, tossable 911. Think of a go-cart coupe with license plates. Something done on a 964 platform would probably perform better overall......certainly have more power......and I suppose could be very light, but would be a bit more expensive than I would want to tackle.

Good luck in your decision-making. Fortunately (or perhaps unfortunately), the Porsche 911 is almost certainly the most widely hot-rodded car in automotive history. There is virtually nothing about these cars you cannot learn here, at this site, likely in minutes, and the various parts and options are nearly endless.

Having said that, I will make one more stab at selling my suggestion. Buy a decent but tired 1969-1989 911 (or 912 for that matter), take the whole darned thing apart, deal with engine/transmission/chassis issues, and reassemble using only the parts necessary to drive the thing down the street. Choose a known-balanced system of torsion/sway/shocks and freshen every suspension bushing. You'll really enjoy driving the outcome.

Or better yet. Buy someone's completed project.

Ok, you asked….I will comment on my process up to this point. My car will be street driven 90% of the time….it is not my daily driver it will be a fun 911 “hot-rod”. I was really after modern high-end sports car performance in a vintage 911 chassis, vintage looks, feel and fun….dialed up to 10+.

Here is my list of priorities for my project in descending order:

1) Speed/acceleration
2) Handling
3) Looks, feel, sound, etc.
4) Comfort

It seems to be widely accepted that weight is the first consideration to achieving a high performance 911. Power to weight is a big factor and played a major role in my decision to use a 1976 chassis. Also, the fringe benefits of lightness are that there is less mass to throw into turns or slow down when braking. That said a light car seemed to be necessary to achieve my goals.

I stripped the car to the bone and I am reluctantly adding back in “comfort”, light weight sound deadening will be used on floorboards, and the rear seat area. All metal body (except bumpers), real glass, stripped down heating system, no cage.
As to suspension and handling, I went back and forth and asked some of the best both on and off forum. All basically agree that the handling of the car is one of the most subjective systems. I think this is the main reason the debate rages on, weight vs. rigidity, TB vs. coil-over, etc. My feeling is that few have driven, let alone built, enough cars to really comment on what the “best” setup is, as this is also subjective to the driver. I have also found that budget will dictate MANY decisions about what we use on our cars.

I have found that the people that I respect have a”formula” based on your budget….the first question is ALWAYS how much do you want to spend. Next is to define your goals/use…..then a plan can be developed. In my case I have a 930 engine and trans to stuff into the 911 chassis as well.

My total suspension build including coil-over conversions and bracing is about $10k. This also includes some proprietary mods to the front struts. The shop that is building my car is primarily a race shop, so the coil-overs are his “formula” to create a very good handling car. The suspension will also be easy and relatively cheap to “tune” based on MY impressions once I have driven it a while. I have also been told that the coil-overs will help a great deal with keeping the car on the road, power to the ground, predictable handling, etc (in addition to proper wheel widths and tires) as we will be running about 400hp to the rear wheels.

I have not discussed weight distribution at length with my builder. He has commented that the battery placement on the stock cars is “not good” and he I don’t see many areas where this can be affected. He advises moving the battery be to an area behind the front wheels. One of the coolest mods I have seen for this is moving the oil tank to the smugglers box, this is not cheap and obviously requires re-plumbing the car.

So my simple answer to the question is weight first….then suspension components…then weight distribution……and then comfort;)

Good catch Mr. Webb, after reading your post I went back to look at my notes and I was wrong, the DELTA was not for bare tubs as I had remembered. So as you suggested something in the 40-60 lbs. range sounds more like it.

While your goal is laudable, almost all your criteria are subjective - handling, comfort, driveability, e.g., all vary with the eye of the beholder.

My <2500# (a/c, stereo, etc., etc., etc., delete) 911 w/ 22/29 torsion bars, 22/21 anti-sway bars and 245/315 17 R tires seems a near perfect driver to me.:D My wife is less enthusiastic. In fact, she calls it an oxcart and refuses to ride in it.

So, who's right?

You could, at a not insignificant cost, build a sub 2000# street legal 911. With moderate torsion bars and sways and 50-60 series tires, it would handle and ride reasonably well. Of course, it would have no HVAC and conversation would have to wait for rest stops. After you took your earplugs out. Works for me (except that cost part). Would it work for you?

My car, although street legal and street driven, is heavily biased toward auto-cross. I like to think it handles very well. Comfort, not so much. But, I don't mind.

So, what are you willing to give up? A/C? Stereo? Your hearing? Your kidneys?

Have you ridden in many hot-rodded 911s? If not, round some up in your area and try it. Ask the owners what they have done (and not done).

Good luck in your quest.

Bob,

Excellent post! You make very good observations and points.

Scott

Ergo my suggestion. Let's get together, drink beer until we can't stop giggling, then take our 911's out on some twisty roads and test their limits. Okay, I'm kidding about the beer part. Sort of. But seriously, you could certainly take my car for a spin, as a data point.

I used to have some files posted that summarizes about 20 cars, including Jack Olson's.

as others have implied you need to be more specific about what you want.

BTW - Ghost - I don't think you will achieve modern levels of sports car performance or feel, even given your extensive work. The geometries are just not up to it. BUT, you will get a very fun and high level car. My goal was a light wt. high perf. car that was FUN to drive, and that I could feel the road in, with that old-timey religion of feel. My testing on a familar, known road, back to back with a Boxster S, and a stock suspensioned '75 911 (a bit more motorvated than stock) was described in the Yet Another Rgruppe Suspension link I posted.

Don't be afraid of stock suspension. I rebuilt my 86 Carrera to stock specs with new shocks, lowered ride height, LSD diff, 7&9's, and 205/245 MPSC's.

Was faster than a lot of cars on the track and probably could not have been much faster on the back roads if it had a stiffer suspension.

I left the spare wheel, jack, tools, and cat at home which saved about 70lbs.

A stiffer suspension is more predictable in transition. However, if you have the tires and camber they can have very close to the same speed potential.

Weight does not have to be equal. If the track is really tight and point and shoot is the fastest way round, then you should make the car oversteer even if it means carrying a small weight penalty for rigidity. Just carry a gallon less fuel. I think weight in the chassis is about the best definition of useful weight. If the driver is comfortable, he will reach a greater percentage of the car's capabilities. The better handling balance, just like weight distribution and moment of inertia, will result in a faster lap time and can overcome a moderate weight disadvantage.

That pretty much describes my car although I currently have no side windows or windscreen wipers. The car is not sub-2000 pounds but then again, I have a roll cage- which is good for rigidity so I am willing to put up with the mass. ;) The Engineer in me would rather have it fully welded into the suspension pickup points, and seam-weld the chassis.

But the C2 is not at a moderate weight disadvantage. Nor is the rigidity difference great enough in practice to make a significant enough difference to overcome the weight penalty.

The tighter the track, the more the extra weight hurts.......

Scott

Randy, where are these files you talk about?

um.. they're gone - I guess he got tired of hosting

one is a MS Word file with a table & footnotes - the table lays out some light wt. cars by P AG - 911R, RS, etc. & what they did to get there; also include Jim Calzia's car (in it's original purple form).

it has a list of magazine articles & etc. and some info on other noteworthy sports purpose builds (hot rod outlaw modded 911s)

the other file is my MS Excel sheet of the accurate wt. of various components, stock & otherwise, includes the table that Jim used to have posted or still does - it is in different sheets, so not sure if it can be posted in Google docs

anybody that wants to tell me an EASY & QUICK way to stick them up on comcast.net, fire away...

Well said, Jim,....:) :) :)

While there are many good suggestions here and several examples of each person's idea of perfection as well as opinions, the key aspect in Al's request for input is context (which oftentimes get lost in such passionate discussions).

Streetability both defines and excludes many things in order to make the a car tolerable for long stretches and thats something not important for track use or racing. Certainly, everyone's tolerances for NVH vary widely and one man's tea is another man's poison.

When I talk with a customer, the first thing I ask (after the budget question) is to define the "Mission" and purpose of the project and outline what one is willing to tolerate so I can design and spec the car successfully.

Balancing weight objectives with NVH is one of the major challenges we face when modifying these cars for the street.

I present for your consideration, "The Hooligan":

http://forums.pelicanparts.com/uploa...1293591197.jpg

1973 non-sunroof coupe, powered by a 1987 3.2. 915 tranny with 7:31 ring & pinion, Quaife limited slip diff. 23/31 torsion bars. 7 & 9 x 16 Fuchs for street tires, 17" Fikse wheels with Hoosiers for Autocrossing.

Most of the decisions on this car were guided by whatever used parts I could scrounge up. Really! The only new parts are the torsion bars, lightweight clutch & flywheel, Elephant Racing's finned oil cooler lines and cooler, and the SSI headers w/Triad West muffler. Everything else came from the '87 Targa parts car, John Walker's swap meet, and a couple tidbits that were advertised for sale here at Pelican. It weighs about 2200 lbs, and is an absolute Hoot to drive.

Personally, I like the clean, understated look, so it has no tail or graphics, not even the hood crest. Almost the stealth hot-rod. Racing seats and five-point harnesses are a give-away that the car is not stock. Most people would never recognize the rear flares that do not belong on an original example.

Can't think of much I'd do differently if I did it again. Silver was the original color, but so many Porsches leave the factory in Silver now that its kind of generic. Maybe I'd go with a different color.

Other than that, It's about perfect. I'm very pleased that the big torsion bars are not too stiff for the street.

The car is still not complete. Some interior parts are still sitting in boxes, a few trim bits are still missing, and the windshield wipers still have not been reinstalled. Once the car would move under it's own power again, its been more fun to drive the snot out of it than finish the details.

great read...
after this thread, i figure at worst i'll keep throwing stuff out and make it lighter, then hand it over to someone who knows what they're doing to spec the suspension to complement it.

Now that is darn near perfect. That thing will run circles around a C2!

Scott

Nice
 

That's more like it. That is very, very nice. Very clean machine. I'm thinking that a 3.2 may be a great choice for an early car,. I.E. more go, but relatively easy to install. Your torsion bars seem a bit heavy for a street rod, more focused on the auto crossing side., but do they work well on the street too? I have to say that your car, from the power/handling details to the understated aspect of your car........no graphics, etc. is well thought out. i like it a lot.

Regards,
Al

I guess I’ll join the “…room full of economists ….” :D

Al,

Your reaction to ‘The Hooligan’ gives us some direction to extend that effort.

Pelican Dantilla doesn’t say if he completely stripped the undercoat/sound deadening but that would be #1 in my book. As noted above, this allows chassis welding and reinforcement. Additional benefits are the ability to repair rust that every 911 has and prevent any future corrosion. If noise reduction is part of the plan, it can be accomplished with more modern material (at lighter weight).

I notice stock rear quarter-bumpers and license panel. Even the FG replacement seem to be heavier than necessary in my view. The ‘stock’ appearance can be maintained with chrome plating and black decals (not tape). TRE’s nice alu deck lid would be a proper addition.


Back to ‘theory’ and more opinion.

Mass and polar moment have been reasonably discussed. Only touched on is the height of the center-of-gravity (CG).

In the early ‘70s, Porsche took a very lightweight 911 coupe and built a variable CG test vehicle. There is a Christophorus article about ’71.

This had a 1’ lead cube mounted on a vertical track through the horizontal center, next to driver and extending down through the tunnel and pan and up to just under the roof. You could crank the track to move the lead cube vertically. I drove this car around the skid pad at Weissach in August ’74.

This was able to change the overall vertical CG of the 911 about 3”. This 3” difference in CG had the same skid-pad effect as the difference between Michelin XWX street tires and Dunlop race tires of the day. That is a BIG change.

It is not possible to lower the CG of a street 911 by 3” but the Porsche made the point.


Another is the ratio of unsprung weight to the ‘reaction mass’ of the car. As the car gets lighter, the unsprung weight has more (usually detrimental) effect. If you are going to spend hard earned $/#, this is the place.

Note that Porsche went to the effort (and weight penalty) to install weights in the front bumper of the SWB 911. This was ‘fixed’ with the two batteries starting in ’69. Note that the dual batteries are located as far to the front corners as possible and the mass of the battery is firmly strapped to the chassis. This adds to the ‘reaction mass’ of the chassis for the front suspension to act against.

Porsche thought so much of attempting to move mass to the front that they put the (935) oil tank in front. In my opinion that was somewhat mis-directed as I could turn on the low oil pressure warning light during hard braking. Better is the GT2/3 oil tank at the engine cooler location – at least it is farther forward and smaller than the RR fender.

For street, there is no substitute for displacement. Bigger is better. Hi-rev, peaky hp is of little use. High CR also is very desirable but must be tempered with fuel availability. ‘Knock sensing’ will be of help.

I agree that carburetors are lightweight and you can have all the other fuel components on the front suspension cross member. There are great power and drivability benefits from FI. It seems light weight ITB and EFI is the most desirable solution.

For street use, I like stock (quiet) exhaust. The weight is of concern.

I have a philosophy of ‘things’: If it isn’t there, it doesn’t weigh anything, didn’t cost anything, can’t fail and isn’t in the way of something important.

Interior falls into this category. For street use, a bare chassis interior is not appropriate. A solution is interior-appearing stitched black Nomex attached with glue or Velcro. The weight penalty is not much more than a good driver’s suit. There is also some (slight?) sound attenuation.


Steve (and others) touch on an important point; this is a street car. Safety from attack by SUV is critically important. Doors with side bars should not be replaced with FG or CF. There is a lot more. While a 911 like this will never be as ‘safe’ as a new 997 coupe, you want to not spend hospital time as light-weight penalty.

My 2¢

Best,
Grady

PS: Randy, I recall those figures. Can you find them and post them here?
I put stuff on Pelican (rather than link) because Wayne seems to be very intent on preserving the database. Other sites (like the recent ‘upgrade’ to EarlyS) loose archived information.
G.

Yes.
Road noise and vibration/harshness will fatigue anyone. In my case, I have a 50 minute commute to get to the twisty roads that I like to drive. If I'm driving a 2100 lb. 911 with no A/C (wind noise with the windows down in a 911 at e-way speeds is deafening), sound deadening and stiff suspension, I won't feel like doing much driving when I arrive at my stomping grounds.
My 964 Turbo is harsh on rough roads and loud with it's sport muffler. It's not at the limit of comfort and usability for me, but I couldn't see myself using it as a daily driver, either.
In the end it's really a matter of personal preference.

Ok, I will play too. Here is my rat rod, The Beast. To quote a past instructor, “Looks like a turd but fast as $hit!”

http://forums.pelicanparts.com/uploa...1293636744.jpg

I built the car with a couple of things in mind; cheap, light and fast. I wanted a street legal track car and I did not care about aesthetics. I have hit curbs, guard rails and trees and simply use wal-mart spray paint to touch up. Maybe one day I will get a nice paint job, but for now she serves her purpose well.

~$12k invested
<2150 lbs wet and ~200 hp
Stock 3.0 with early exhaust (just added webers but not tuned yet)
Carrera front and rear brakes
Carrera front and rear suspension
Bilsteins
22/28 torsion bars
19 adj sway bars
15x7 fuchs with 225.50.15 Khumo on all 4 corners

I chose a stock 3.0 because it would be nice on the street and the track, and should last a loooong time. Eventual plans include cams and pistons.

I wanted the same size tires all around so I could rotate for even wear. For more street use I would probably go with different tires.

The suspension is not *too* bad on the street and awesome on the track. I would not change a thing for canyon carver duty.

The biggest issue on the street is the noise. Eventually this will be track only, but if not, I would add in some sound deadening in the rear seat area. I would also add a radio, a glove box, and some carpeting.

If I had to do it over again, I would probably start with a ’74 – ’77. Not too much heavier and I would feel better about customizing. But overall I think I achieved EXACTLY what I was going for.

Great posts by the gurus, Grady and Steve W...

I recently did a light weight battery on my 89 3.2, 18 lbs vs about 40lbs. Now thanks to Grady, I'm wondering if I did the right thing. Seems Porsche sweats the details more than most people will ever know.

Back to the OP, what's you're budget? Let's get this project buttoned down or at least headed in the right direction. :D

If Porsche had access to lightweight batteries, I think they would have used them. In fact, I think you can order a lightweight batter option on a new car.
Again, light beats balance - but if you have to add weight (such as a battery) it is smart to do so at the opposite end of the engine. BMW does it (battery in the far rear corner), Porsche does it, etc. They don't add weight if they don't have to. The only exception I've known is the early SWB 911's trying to tame handling as a temporary measure until they changed the wheel base and put the batteries in the far front corners.

Grady,
Thanks for checking in. I have added my questions and/or comments...highlighted below.

Al

The ultimate handling capability of a car is determined by the CG height, mass, polar moment of inertia, and track width. These are the main criteria that will dictate the limits of how well a car can me made to handle.

The CG height determines how much weight transfer there is during cornering. A lower CG means there is less weight transfer to the outer tires and you will get more out of the inside tires during hard cornering. A tire with 500lb of vertical load applied might provide 500lb of lateral cornering force but the same tire with 1000lb of vertical load applied might only provide 900lb of lateral force. Reducing weight transfer tends to keep the tires closer to their sweet spot.

A lower CG also reduces the stiffness required of sway bars required to limit body roll, assuming the CG is lowered in a way that doesn't kill the suspension geometry (lowered by reducing mass, raising spindles, etc...). Reducing the sway bar stiffness makes the suspension more independent.

Increasing the track width also reduces sway bar requirements and the weight transfer so the ultimate would be to lower the CG height AND increase the track.

I believe the polar moment of inertia has been discussed in detail.

These are the characteristics that dictate the limits of a platform and from there it boils down to tuning (spring rates, shocks, sway bars, chassis stiffness, etc...). If you want to get more out of your car without spending a lot of money you could lower it slightly and increase the track width by adding wheel spacers. Don't go off the deep end though because these will affect the suspension geometry. Things that will lower the CG are reducing weight that is high in the car. Change out side and rear windows for polycarbonate, get rid of the sun roof, fiberglass hood and deck lid, etc...

Grady,

Isn't the low oil pressure warning problem you experienced with the 935 more a result of improper implementation than an invalid concept?

Scott

There is a lot of really good info in this thread. I think it also shows that the key is to have a really clear vision of your goals and aim for a cohesive car where things work together as a whole. And also, to be sure that you understand what your own goals and limits are and that they may be different than someone else's. For example, I spent much of my adult life with a track oriented motorcycle as my primary transportation. In my world my 911, which is a very light '74 with a 3.6, stiff suspension, no sound deadening materials, no stereo, Recaros's and harnesses, etc. is a luxury ride that I would happily drive cross country. YMMV. Having said that, I also have a great A/C system, because I hate being too hot and it's worth the weight to me. Most people I'm guessing would have different priorities.

If there is anything perhaps controversial that I could add, it's that I think some people buy 911's and then try to turn them into something they are not. Sure, a "perfect" car has 50-50 weight distribution, fast shifting tranny, etc. But a 911 will never be that. I embrace the fact that the pivot point of a 911 is so far removed from the CG, making your right foot an integral part of the steering. I don't worry very much about weight distribution as it's a battle I can never win. But adding lightness, as Colin Chapman said, pays dividends in handling, braking, acceleration and so on.

Configuring a 911 to your desires is no different than any other project. The first thing you do is to clearly define exactly what it is your are hoping to achieve. Then execute to that vision and don't get distracted along the way. It's easy to miss the forest for the trees when you are reading forums and buying parts here or on ebay or whatever. Do the research, talk to people, most importantly be honest with yourself and don't be swayed by people with strong opinions that have different goals than you do.

TIRES! :)

BK911,

How did you achieve <2000 pounds wet? :eek:

This is a great setup, 73 911 with 3.2 Motronic. I have a friend with this same setup but he kept the 15" rims, the car is a 'Sleeper' it screams. I must agree this is a very great setup for the money.

It is ALL about you budget. You can just approximate it to the nearest $50,000 and that will give people a clue as to what you can afford.

One of the points that seems to get overlooked a lot-Grady referred to it-is the problem of changing the ratio of sprung to unsprung weight. If you lighten the car significantly but then add bigger (heavier) wheels and tires, plus bigger (heavier) brakes the ride and handling are both going to suffer.

My bad. I just looked at the corner balance sheet. It was 2300# with 150# on the drivers seat, so 2150 #. I remembered the 2150# but forgot that was already subtracting out the 150#.

Good catch.

Right, but good tires on a car with a high CG will not perform as well as good tires on the same car with a low CG, with all else being equal.