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

[Steve@Rennsport]

Originally Posted by al lkosmal

I am primarily interested in street car solutions,......

We have about as much consensus here as a room full of economists

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.

[Dantilla]

Originally Posted by al lkosmal

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!

I present for your consideration, "The Hooligan":



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.

[clutch-monkey]

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.

[winders]

Originally Posted by Dantilla

I present for your consideration, "The Hooligan":

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

Scott

[al lkosmal]

Originally Posted by Dantilla

I present for your consideration, "The Hooligan":



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.

.

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

[Grady Clay]

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

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.

[911nut]

Originally Posted by winders

Comfort and usability? We are talking about sports cars here, right?

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.

[BK911]

Originally Posted by al lkosmal

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

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!”



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.

[AlfonsoR]

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.

[PropellerHead]

Originally Posted by AlfonsoR

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.

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.

[al lkosmal]

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

Al

Originally Posted by Grady Clay

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).

There are obvious benefits to removing the undercoating, as you point out above, including added lightness, but since the weight is so low down on the chassis, does removing it have any significant effect on the handling? I.E. why is it #1 in your book?

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.

These changes focus on the rear end, including weight reduction up fairly high on the rear end. I would think that this is big bang for the buck. Removal of weight, resulting in forward weight distribution....and a bit of effect on the CG.


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.

You bring a unique perspective to the festivities..........by having theory and opinion backed up by hands on experience of the finest kind.

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.

I have been experimenting with a few different induction configurations, from carbs to MFI. I love the obvious benefits of carbs and MFI, but I am currently working on a ITB/EFI/Megasquirt system. The benefits of carbs and MFI, with modern engine management flexibility, i.E. the ability to tune/datalog with my laptop. I plan to implement this system on my street rod.

YouTube - Porsche EFI kit - fire up

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

I have tried almost every configuration and I keep coming back to 2 in - 1 out.

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.

I like the less is more approach, but I will probably keep a bit more creature comforts and sound attenuation on the floor......I like to be able to hear the engine sounds, but not the road noise.....I'm getting fussy as I get older.

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.

I agree....I don't want to have my personal weight removed....permanently

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.

[Bullet Bob]

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...

[winders]

Originally Posted by Grady Clay

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.

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

[AirKuhl]

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.

[Flieger]

Originally Posted by Bullet Bob

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.

TIRES!

BK911,

How did you achieve <2000 pounds wet?

[scarceller]

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.

Originally Posted by Dantilla

I present for your consideration, "The Hooligan":



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.

[RWebb]

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.

[davidbir]

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.

[BK911]

Originally Posted by Flieger

TIRES!

BK911,

How did you achieve <2000 pounds wet?

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.

[Bullet Bob]

Originally Posted by Flieger

TIRES!

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.