964 vs 993, a systems analysis

[Bill Verburg]

The question often arises, "Which is better?" or "Which should I buy?"

so a comparison broken down by sub sytems seems to be in order. i want to concentrate on the sport versions, just because thats what i'm interested in.

Body
The most obvious difference is in the body contours. This is a very personal issue some like the older more upright visage represented by the 964 others the more fluid sensous nature of the 993.
A few very nice examples of 964RS








A few very nice 993RS

[herman maire]

Bill,

This is all great info, thanks. I was reading in a older porsche magazine where they compared the 964RS and the 993RS and there feed back was that the 964 gave a more connected feel. Do you think its because off all the rubber in the control arms in the back or the lack of power steering in the 964?

I have never driven a 964 and I have very little seat time in my 993 before I tore it apart since it was 100% stock.

[herman maire]

Found the link I was looking for... its a pdf file

http://www.porsche964.co.uk/rev_rep/gt/GT_964RS%20and%20993RSeb.pdf

[Bill Verburg]

Aero



Transmission
964 5 speed w/ available 40% & 20/100 lsd option
993 6 speed w/ available 22/40 or 25/65 or 40/65 lsd option

stock 964 gearing is arguably better for sporting use but can certainly stand improvement, US 993s suffer from very tall gearing
Here's a comparison of most of the factory gearing



Engine management
964 and '94, '95 US cars & all n/a RoW cars use Bosch 55pin OBD1 compliant DME & main harness, 993 version is v2.1 and adds 64kbyte of data memory, hot film mass air-flow sensor & a throttle potentiometer. A single oxygen sensor is used w/ this system

993tt and US '96 - '98 versions use an OBD2 compliant, 88 pin DME a& harness, v M5.2. 4 oxygen sensors are used w/ this system, 2 pre cat and 2 post cat.



Oil cooling
both have a single large ducted oil cooler w/ a multispeed fan in the right front, this cooler is adequate for most purposes but both can benefit from adding a second coler in the left front.

Rear suspension & brakes
all n/a 964 including RS use 299x24mm rear rotors, 964 t uses 299x28mm. All use 1 of 3 versions of the small body 4 piston axial mount calipers using the same ~98x44mm pad as the front small body(also the same as 930 f/r)

993 n/a use the same size 299x24mm rotor(w/ a slightly different o/s) and small body 4 piston caliper w/ 98x44mm pad, 993RS & tt use a 322x28mm rotor w/ an axial mount version of the medium/large 4 piston caliper using the ~132x48mm pad


rear suspension, part 2
one of the biggest differences between 864 and 993 is found here
964 rear uses a semi trailing arm rear suspension not unlike that used on older 911s, it uses a coil over shock rather than torsion bars. I has the advantage of simplicity


993 uses a sophisticated(and expensive) multi link design







Facts

[Bill Verburg]

Originally Posted by herman maire

Found the link I was looking for... its a pdf file

http://www.porsche964.co.uk/rev_rep/gt/GT_964RS%20and%20993RSeb.pdf

Good one!

[Bill Verburg]

Originally Posted by Herman Maire

Bill,

This is all great info, thanks. I was reading in a older Porsche magazine where they compared the 964RS and the 993RS and there feed back was that the 964 gave a more connected feel. Do you think its because off all the rubber in the control arms in the back or the lack of power steering in the 964?

I have never driven a 964 and I have very little seat time in my 993 before I tore it apart since it was 100% stock.

The 964RS and 993RS both have harder rubber in the trailing A arm bush, but not the leading. Both have monoball top mounts. Factory alignment and spec on 993 is sportier, springs have similar rates, 964RS is progressive and 993RS linear.

The big difference is the lack of power steering. I can only assume that the "live" feel of the non assisted steering writhing in the testers hands is what sold them.

Anecdotally, the comments on 964 are usually along the lines of, it feels more stiffly sprung, more direct

I have quite a few of those magazine comparisons, i'll have to dig them out and add snippets to this thread.

[Bill Verburg]

Exhaust
964 uses a very inefficient x-over system, the right bank cylinders merge and x-over to the left where they further merge w/ the left bank cylinders


993 uses a relatively efficient system where the banks are separated untill coming together in a mixing chamber in the cat, 2 large mufflers effectively quite the exhaust while still providing good flow

[Bill Verburg]

Front suspension and brakes
Some big differences here
964 uses steel uprights, normal versions have axial mount small body 4 piston calipers w/ ~98x44mm pads. RS and turbo use steel axial mount uprights w/ either medium/ large or large(aka Big Red) size, 4 piston calipers using either ~132x48mm pads for the medium large and ~132x58mm pads for the large size calipers. n/a use 298x28mm rotors, turbo and RS use 322x32mm 1 piece rotors

993 use aluminum radial mount uprights on all models, RS & GT2 use special versions w/ short steering arms to deal w/ bump steer on lowered cars. brakes on n/a models use a version of the medium/large 4 piston caliper using the same ~132x48mm pads as on 964t & 964RS w/ 1 piece 304x32mm rotors, RS, tt and street GT2 use the large 4 piston calipers(aka Big red) w/ 2 piece 322x32mm rotors.

964 steel uprights top, 993RS aluminum bottom


964RS steel uprights



993 n/a aluminum uprights


stock 964 front


stock 993 front


964RS/t front(the black one not the red one)


993RS/tt front





993 uses increased caster, increased track(by 25mm), incresed negative scrub radius(10mm), all give a "sportier" feel to the front end

Steering
Both 964 and 993 have power assisted steering, however 964RSA and RS manual racks are available
steering ratios
911 is ~3 turns lock to lock, non assisted
964 is ~2.81 turns lock to lock, assisted
993 & 993GT2EVO is ~2.47 turns lock to lock (2.73 for 993RS), assisted
964 manual ~2.6

the rubber "cushion"in the stock 993 tie rod is harder than in the 964 and the RS is harder yet.


ABS
both 964 and 993 base models use pretty much the same 3 channel ABS w/ rear pressure limiters(aka p/v). 993 M220 option adds 4 channel ABS w/ dual pressure limiters

Master cylinder & boost
964 n/a use a vacuum actuated 20.6mm m/c and 8" vacuum can w/ a boost ratio of 3, 964RS and 964t use electro-hydraulic boost systems RS w/ a 25.4mm m/c and a boost ratio of 3.6, 964 t w/a 23.8mm m/c and a boost ratio of 4.8

993n/a use a vacuum system w/ a 23.8mm m/c and 9" vac can and boost ratio of 3.15. 993RS and tt use the electro-hydraulic boost system w/ a 25.4 mm m/c and boost ratio of 3.6

Wheels and tires
964 front can use from 6x16 w/ to 8x18 wheels w/ 225/40 to 235/40 tires, though the latter get very tight, the lower the car the tighter it gets oem RS came w/ 7.5x17ET55 & 205/50x17 tires

993 front is very comfortable w/ 8x18 & 225/40 or 235/40 tires even at very low ride heights oem RS came w/ 8x8ET52 & 225/40x18 tires

964 rear can use from 7x16 to 10x18 w/ 265/35 tires though again the rear is very tight, largest factory fitment was 9.5x18 on n/b and 10x18 on w/b. oem RS came w/ 9x17ET55 & 255/40x17

993 rear has much more room 10x18 w/ 265/35 are a very comfortable fit even on very low cars

[jbkeir]

Interesting read Bill, thanks for taking the time and putting together this comparison!

[Bill Verburg]

It's a work in progress and will be edited and expanded. Feel free to contribute.

[iangray100]

This thread is quite interesting......obviously the 964 wins as thats what I drive

[Bill Verburg]

Patterns inherent in 964 suspension travel





993 patterns

[petevb]

Bill,

Very nice graphs of the suspension movement. Can you help translate a little?

The top graphs both show the front suspension, while the bottoms show the rear?

On the vertical axis, the positive numbers (mm) mean that the wheel in going up into the wheel well?

On the horizontal axis, vorspur (toe in) being to the left of the center axis (negative) means the toe is actually toe out?

The difference between Vorspur and Sturz on the 993 seems difficult to determine by the line weight, at least on my monitor?

Great info, as always- thanks.

-Pete

[Bill Verburg]

The top graphs both show the front suspension, while the bottoms show the rear?

correct

On the vertical axis, the positive numbers (mm) mean that the wheel in going up into the wheel well?

correct, you can confirm because you know camber goes more (+) when the wheel drops

On the horizontal axis, vorspur (toe in) being to the left of the center axis (negative) means the toe is actually toe out?

yes, again knowing that a little (-) static toe is used in front and a little (+) toe is used in back helps top orient your perspective

The difference between Vorspur and Sturz on the 993 seems difficult to determine by the line weight, at least on my monitor?

Yes, the 964 data is far more usable. All pro teams and many of the more serious amateurs do their own. All you need is a few hours on a good alignment machine, there are some computerized apps but paper, pencil and Excel are all you really need to record and view the data


To me the most interesting item is the roll center height, especially the large variance on 964 rear

[petevb]

Thanks for the clarification.

I'd always been under the impression that the 993's rear suspension was designed to create more camber gain than earlier cars. If I'm reading this correctly, however, the 993 actually gains less camber than the 964 for a given deflection. I've never seen this type of graph for a 911, but I believe the rear camber gain is near identical to the 964. Hmmm...

The big difference I notice between the 993 and 964 looks like the toe at the rear- the 964 tries to maintain a relatively consistent toe (in), while the 993 toes in on compression but toes out when it unloads. I understand this is to create a 4 wheel steering effect in cornering (the rear turns into the corner), but it would seem to create instability under braking, when the rear would toe out. But the 993 has a collapsible link that comes into play under braking and corrects for this? Thus the theory is that recreating the 993's camber and toe curve on an earlier car wouldn't help unless it also had a collapsing link?

Very interesting stuff...

[Bill Verburg]

Originally Posted by petevb

Thanks for the clarification.

I'd always been under the impression that the 993's rear suspension was designed to create more camber gain than earlier cars. If I'm reading this correctly, however, the 993 actually gains less camber than the 964 for a given deflection. I've never seen this type of graph for a 911, but I believe the rear camber gain is near identical to the 964. Hmmm...

The big difference I notice between the 993 and 964 looks like the toe at the rear- the 964 tries to maintain a relatively consistent toe (in), while the 993 toes in on compression but toes out when it unloads. I understand this is to create a 4 wheel steering effect in cornering (the rear turns into the corner), but it would seem to create instability under braking, when the rear would toe out. But the 993 has a collapsible link that comes into play under braking and corrects for this? Thus the theory is that recreating the 993's camber and toe curve on an earlier car wouldn't help unless it also had a collapsing link?

Very interesting stuff... [/QUOTE]

Both 993 and 964 use a a derivative of the Weissach axle first introduced on 928. The 993 has a 5 link design where 4 links are solid and 1, the kinematic toe, is elastic. On the 964 W/ this type of axle, under cornering the outer wheel assumes a toe in and the inner assumes a toe out attitude reducing the slip angles that the tire runs at and thus increasing cornerning potential. This is the opposite of what a solidly fixed suspension does.

In the front they both also use differentially elastic bushes to help eliminate bump kickback.

The whole point of most any suspension is usually to minimise camber and track variations. The best at doing that is unequal length A arms ala 959, struts are among the worst.



964 rear achieves the Weissach effect from differentially elastic bushings in the back as well as the front. But even w/ this design camber and toe variations are interdependant

[dad911]

Bill, so for a track-only 964, would it be a mistake to replace the rubber bushings with Spherical Bearings?

[Bill Verburg]

Originally Posted by dad911

Bill, so for a track-only 964, would it be a mistake to replace the rubber bushings with Spherical Bearings?

Not at all. On a track car you want to tell the car where to go not the other way around.

On a track car you would want to limit suspension travel vertically, longitudinally and laterally

[Eric86Red911]

Originally Posted by Bill Verburg

... The 993 has a 5 link design where 4 links are solid and 1, the kinematic toe, is elastic...

The KT link has softer bushings than the others? Even if so, I'm not sure that has an affect on suspension geometry, but I could be wrong. My understanding (from Frere's book) is that the radially soft bushing(s**) in the lower a-arm are what cause the dynamic geometry changes. I don't know the exact affect of the radially soft bushings, but I do know they're there. Perhaps it's to address the toe-out-when-braking problem.

** Frere says that ONE bushing is soft (I forget which), but it looks to me like both are soft.

[Bill Verburg]

Originally Posted by Eric86Red911

The KT link has softer bushings than the others? Even if so, I'm not sure that has an affect on suspension geometry, but I could be wrong. My understanding (from Frere's book) is that the radially soft bushing(s**) in the lower a-arm are what cause the dynamic geometry changes. I don't know the exact affect of the radially soft bushings, but I do know they're there. Perhaps it's to address the toe-out-when-braking problem.

** Frere says that ONE bushing is soft (I forget which), but it looks to me like both are soft.

You can see that from Chicago, eh?? You must have extraordinary vision

Frere(who got his info from the factory) says the same as what I posted, I get my info from the factory training docs.

here's a page


only the KT link(item #5) is particularly elastic.


of course all the bushes are somewhat elastic.