Best handling....lightness vs. distribution vs....?

[al lkosmal]

I am seeking out a 911 for my next driver/project. I have typically concentrated on the engine/drive train, because that is what I like to do. I envision that for my next project, I may focus on an long wheel base, longhood (although SC's and even 964's keep distracting me) and shoot for the ultimate street rod.....as it relates to stop, go and balance. The 1st two (stop and go) I can do, but..............what about balance/handling, while retaining occasional long distance drive-ability.

I often hear and/or see people removing parts or swapping out their bumpers for fiberglass, etc. to lighten their 911s. Adding lightness sounds like a good thing, but.... It seems to me that the quest for "lightness" has somewhere along the way, lost any meaning as it relates to weight distribution and balance. I.E. it's turned into bragging rights about what has been done, without any connection to the "why".

I expect that a slightly more systemic approach, perhaps linked to a goal regarding the use of the car, may be more appropriate. I.E. lightness vs, distribution.

So, here are my simple questions, that I'm sure, have a myriad of answers, but.....please tell me what you know.

1. What is the typical weight distribution of the early to mid-year 911s.

2. What would the "best" weight and distribution goal be for a 911 street rod.? (no track...no auto-X...just street rod, twisties carver).

3.) How would you achieve this?

Beyond that simple question, what suspension changes lend themselves well to compensate for the rear end weight bias?

4. ) Torsion bars vs. coil overs?

5. ) wider track/wheels?

6. ) shocks?

6. ) Whatever else I have forgotten, due to sheer ignorance......

It would be great if your advice was based on what you have achieved and experienced with your own cars. I.E. first hand experience/knowledge.


Regards,

Al

[TonyFlaco]

Very sorry I have nothing to contribute to this discussion, but I must say...... I'm really looking forward to the replies on this one.

[Steve@Rennsport]

Originally Posted by al lkosmal

So, here are my simple questions, that I'm sure, have a myriad of answers, but.....please tell me what you know.

Hi Al,

Those are not as "simple" questions as you may think.,....

1. What is the typical weight distribution of the early to mid-year 911s.

2. What would the "best" weight and distribution goal be for a 911 street rod.? (no track...no auto-X...just street rod, twisties carver).

3.) How would you achieve this?

1) Assuming you are referring to LWB cars, its right around 42/58, depending on options.

2) As close to 50/50 as would be possible,...... Seriously, its not easy to move sufficient weight around to make significant changes in the weight distribution without major efforts and expense; i. e., moving the powertrain forward an inch or so. Installing lightweight batteries is a step in the wrong direction.

3) The answer to this truly depends on one's budget.

Beyond that simple question, what suspension changes lend themselves well to compensate for the rear end weight bias?

4. ) Torsion bars vs. coil overs?

5. ) wider track/wheels?

6. ) shocks?

6. ) Whatever else I have forgotten, due to sheer ignorance......

4) Coilovers require a full cage that connects and triangulates all of the suspension pickup points to maintain stiffness and thats not always safe for a street car without a helmet and proper restraints. Torsion bars permit sufficient stiffness for street and moderate track use. Further, torsion bars place their weight at the very bottom of the chassis and thats a plus for CG.

5) This is the key aspect to compensating for a 911's rear engine configuration. As you know, there are many ways to accomplish this.

6) Shocks need to match the spring rates and there are many options including raised-spindle front struts and shorter rear shocks to maintain suspension travel and control roll center location. If one has a real budget, there are ways to make huge differences here both in handling, car control and ride quality. (think Moton's)

This is truly a big subject and difficult to adequately discuss in writing, however I can tell you that with sufficient resources, you can build a car with altered weight distribution and a proper suspension that will put everything else to shame.

As you cogitate all this, you should not forget the effects of Polar Moment of Inertia when deciding where to save weight. Low MoI cars give little warning of their intention to spin; just ask a 914 driver.

[al lkosmal]

Steve,
Yes...the simple part was meant to be tongue in cheek. Thanks for taking the time to reply. It may have been lost in my ramblings, but I am primarily interested in street car solutions, so I appreciate the statement regarding the coilovers, suspension stiffness, etc. This is the first that I've heard that a full cage and full pickup point trangulation is required for coil overs. It seems that these are often applied, without a cage, using cross bracing only. Is this ok for the street, overkill, poser territory........

I never thought of the advantage of torsion bars from a CG standpoint....interesting.

"1) Assuming you are referring to LWB cars, its right around 42/58, depending on options."

"2) As close to 50/50 as would be possible,...... Seriously, its not easy to move sufficient weight around to make significant changes in the weight distribution without major efforts and expense; i. e., moving the powertrain forward an inch or so. Installing lightweight batteries is a step in the wrong direction."


I expect that just going for lightness, without taking the 42/58 distribution into account could result in back-ass-wards or, from a handling standpoint, ass-front-wards results. I've seen a few examples of folks moving the battery to the smugglers box. While this appeals to me from a simplicity standpoint, it seems that you are shifting the weight distribution rearwards, which is counter-intuitive, due to the existing rear weight bias of 911s.

OK......because this is such a big, wide open question, let's narrow it down to actual examples of excellent "street rod" set ups. What did you do to your 911 and why? What are/were the results. Handling, weight distribution, ride quality, etc.

I want pix too

Regards,

Al

[RWebb]

it is not hellishly expensive to take 200 to 300 lbs. out of an early car

Here is what I did re body panels:
Yet Another Boring Hot Rod Rgruppe Car - Part V, Exterior & Paint

you can improve a bit on that making add'l sacrifices in driveability, by using CF race parts instead of cheaper FG parts, and by doing a few other things.

MG case motor, carbs & 901 Mg cases tranny will reduce wt. in the rear also

is this a street car or what?

[Flieger]

I think that the theoretical fastest lap time (for a NON-downforce car) depends primarily on tires, overall mass, center of mass height, and polar moment of inertia, in roughly that order.

I think the best "handling" is very subjective and depends entirely on the driver. The driver will turn his/her fastest laps with a car that he/she is most comfortable with. If that means a high polar moment of inertia, so be it.

For a track car, just remove weight anywhere possible and learn to like the handling that results, be it understeer or oversteer.

Downforce can fix a lot of handling issues in high speed turns, and will significantly lower laps times.

[al lkosmal]

Randy,
Per my original post, I'm thinking street car. I read Part V....most of your weight reduction effort seems to be focused on the rear of the car, which makes perfect sense to me. So, what are the results from a weight distribution standpoint and more importantly......the subjective, drivers, seat of the pants experience.

Regards,
al

[al lkosmal]

Originally Posted by Flieger

I think that the theoretical fastest lap time (for a NON-downforce car) depends primarily on tires, overall mass, center of mass height, and polar moment of inertia, in roughly that order.

I think the best "handling" is very subjective and depends entirely on the driver. The driver will turn his/her fastest laps with a car that he/she is most comfortable with. If that means a high polar moment of inertia, so be it.

For a track car, just remove weight anywhere possible and learn to like the handling that results, be it understeer or oversteer.

Downforce can fix a lot of handling issues in high speed turns, and will significantly lower laps times.

I'm focused on street car mods/results. How is your car set up and what are the results?

Regards,

Al

[RWebb]

al - it feels better - it would be hard for me to say much more with any reliability.

one thing you can do to test - and you DO need to test one trial right after the other is to find yourself a test road (mine is at Yet Another Boring Rgruppe Car – Part II, Suspension
for an example) and then drive it alone and with a 200 lb. companion in the pass. seat.

Pay particular attention to how it feels in the corners and under braking (accel. will be very obvious). That will be less of an effect in some regards compared to removing wt. from the rear.

Yes, I've focused on removing wt. from the rear. It just makes sense. Overall wt. reduction is worthy too, but in terms of $$ or effort, focus on the rear, and focus up high.

You need to think hard about your budget. A guy in NY told me that there are different $$/lb. strata or levels for different racing classes, based on what a win means in that class. He develops light wt. parts for Porsche Racing so...

[BK911]

I have stripped just about everything out of my '73. She is LOUD!! I drive her on the street, but only until my '71 is finished. Then she will be just a DE car. If she was going to remain dual purpose I would sacrifice some rear weight and put some sound deadening back in the rear seat area.

[Steve@Rennsport]

Originally Posted by al lkosmal

Steve,
Yes...the simple part was meant to be tongue in cheek. Thanks for taking the time to reply. It may have been lost in my ramblings, but I am primarily interested in street car solutions, so I appreciate the statement regarding the coilovers, suspension stiffness, etc. This is the first that I've heard that a full cage and full pickup point trangulation is required for coil overs. It seems that these are often applied, without a cage, using cross bracing only. Is this ok for the street, overkill, poser territory........

You'll note that many people who replace torsion bars with coilovers without all the requisite bracing rave about improved ride quality. Thats due to all the flexing in those thin sheet metal areas never meant to support the static & dynamic loads they are now subjected to.

I expect that just going for lightness, without taking the 42/58 distribution into account could result in back-ass-wards or, from a handling standpoint, ass-front-wards results. I've seen a few examples of folks moving the battery to the smugglers box. While this appeals to me from a simplicity standpoint, it seems that you are shifting the weight distribution rearwards, which is counter-intuitive, due to the existing rear weight bias of 911s.

Moving batteries around affects MoI much more than distribution unless its relocated to the cockpit. There are specific reasons for doing that, however those are applicable to certain kinds of race cars, only.

[boba]

I would agree with Steve on the coil overs on a torsion bar car, you might not need a full cage (which is a bad idea on a street car) but you would need bracing and reinforcing. I would also point out that the main advantage of a coil over setup is on a race car where you would be adjusting from track to track. I doubt that you would be making constant suspension setup changes on a street car. You did mention not going just for bragging rights.

The first choice would be the starting platform and I would choose either a 964 if you wanted to take advantages of the stiffer tub, coil overs, creature comforts (that work), and nice drive train. There is alot of weight that can be saved in the interior.

The other direction would be to start with a longhood tub, and my choice would be a'72. I like these since they have the oil tank forward of the rear wheels.

Budget is a major consideration and could impact which platform you start with. Lightening a 964, improving its suspension, and just a bit of tweaking on the motor would yield a fun ride and not brake the bank.

A longhood project done right would be more involved as you would be starting with at least a 37 year old tub. I would take the tub to bare metal, repair any rust, seam weld, and reinforce pickup points. Powder coat the underside, trunk, interior and engine bay rather that going back with undercoat. I would then go back together as light as possible. You need to decide what creature comforts you want (heat/air) and then what drivetrain. For me it would be a ss 2.5/2.8/3.2 with MFI, but budgets do get in the way sometime. If you go for air, you may want to use 2 later front condensers and eliminate the rear. Again as a street ride you may want to up rate the t-bars but not to the max, and match the shocks to the spring rate. With the modern rubber that is available and keeping in mind that you have lightened you should not need to over tire the car. One place to take some meaningful weight out would be the wheels and brakes. We are lucky that the Fuchs are some of the lightest and strongest wheels out there. For the brake package I would recomend two piece disks with AL hats front and rear and delete the stock parking brake. You can then go with a line lock or RSR style e-Brake. For a street car I would stay away from FG fenders and doors, but you could use FG lids.

You could of course do a full strip of a 964 if time and budget were not a limiting factor.

[jmitro]

i agree with Flieger.

i'd go with lightness first; you can dial out any weight distribution issues with suspension setup later. and for a streetcar, it's not going to really matter anyway.

[rfloz]

There's a good article on lightness re Jim Calzia's car in the May 2001 Excellence. While this is a race car, there are many ideas you can apply to a street hot rod.

Beware - the figures he mentions on $/# of weight loss are sobering and these are circa 2000 dollars.


Despite trying to concentrate on rear weight loss on my own car, I currently have a 38/62% f/r balance. Worse, most of the remaining deletable/replaceable items, footwell fans, HVAC stuff in the trunk, smuggler box lid, front bumper and front trunk cover, are in the front.

I have had some understeer issues, but they are exaggerated by a large f/r tire stagger , 245/315, at present. I have been able to tune most of this out with tire pressure adjustments and suspension settings and may go to larger front tires as a further experiment.

Despite some issues, the changes in the car due to weight reduction are all to the good - better acceleration and more "toss-able" handling being the most noticeable.

I got to auto-cross a friend's circa 2000# SC a while ago - what fun. Even with a stock engine, that was the most entertaining car I have ever driven. My car is definitely going to lose more weight!

So, I say go for it!


p.s. - you can get torsion bars that are plenty stiff for the street. Coil-overs are neat and all, but superfluous for a street car, in my opinion.

[JeremyD]

I am right at 42/58 and 2400 lbs. I have a wide body car with 255/315 wheels.

I can tell you that even with a 2.7 the car does not feel heavy or under powered (except on the back straight)

On the street it feels very peppy and tossable. The 87 cabriolet - at 3000 lbs felt almost portly compared.

Just one reference point.

[Bill Verburg]

lightness improves every aspect of perormance

it's amazing how good drivers can use throttle to get a rear weight biased car to rotate, From the way Boxsters and Caymans perform it would appear it's much easier to get a mid engine design to do so

wider track and wider wheels will generally allow for higher g turns

coilovers are generally easier to adjust and can be obtained w/ higher spring rates, but as Steve noted the chassis will need to be reinforced to use them.

If you are looking for a project I see 2 different paths
1) use an early chassis as it can ultimately be lightest, accept the compromises inherent in this choice and go from there, keeping t-bars, stock brakes, 7or 8 x15 front s and 8-9.5 x15 rears
2) use a 964 chassis which will only be a few 100#s heavier if completely stripped and take advantage of the brakes and suspension and wheels/tires available for that package

[RWebb]

also, the 964 unit body is much stiffer

you can get some background info by going to penaltykicker.com and downloading my 2 files there - you could thank the guy that hosts the site too

someone who wanted to expend the effort and money could likely create a street 911 in the 1,600 lb. range...

[Captain Ahab Jr]

As mentioned by Bill V, lightness first as this will improve acceleration, cornering and braking.

If you target all the weight at the rear and high up first this will help move your weight distribution forward too.

Leave front mounted lightweight battery, carbon hood and front fenders last, you may save lots of lbs but you will offset the performance gain by shifting the weight distribution in the wrong direction back towards the rear.

Weight saving also need not cost a lot up to a certain point just look around the car to deciede which parts you can do without.

If you can't remove it from the car, then fit it as low as possible and within the wheel base.

[scarceller]

I own a 84 911 3.2L but recently I've had the opportunity to drive 2 different 73 911s both with Motronic 3.2L motors and I must say this setup really works. I was amazed how nimble this setup is and also because of the 15" rims in the 73 cars the gear ratio is noticeably shorter.

If I ever had the time to build something special it would be an early car like the 73 cars with transplant motor from the 84-89 Carrera or the 964. I saw another early car done with the 964 motor but did not have the chance to drive that setup, but was told the car was extremely quick and would out run any 964 or 993 off the line.

[winders]

I don't get the 964 suggestion. "Lightweight" and "964" are just about mutually exclusive unless you have lots of money and are stripping the car down to nothing.

Get a something prior to '87 as a base. If you have to have coilovers, it will still cost and weigh less than a 964 project.

Scott