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New project for me, yet another 993 RS Clone for you :-(

 
Old 11-02-2011, 09:49 AM
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Originally Posted by Cupcar View Post
You are correct if one wants to copy an RS braking system exactly, and I considered a C4 initially for this. However, if one uses a C4 chassis, then one is subjected to the draconian potential maintenance costs if any of the electro-hydraulic boost system components fail; the pressure pump, master cylinder or booster are all well over $1000 each as you know, not to mention that if one is going to go the full RS conversion route, both the booster and master cylinder have to be changed to R$ parts on a C4 anyway.

The RS system is heavy with all this equipment and bigger rear discs and calipers.

At the front the calipers I am using are 928 GTS front calipers (which are identical to RS "Big Red" in size) that have been flipped to work in a 911 chassis, they match the color and Porsche font of the stock C2 rear caliper. Both the RS and GTS caliper have the identical piston sizes as a stock C2, so there will be no change here in hydraulic force ratio to the master cylinder. The mechanical force ratio of the 322 versus the 304 mm disc is +7.2%; it is not exactly related to radius since the Big Red pad is closer to the disc center.

At the rear I plan to use stock C2 brakes with the backing plates removed.

So the only difference from a stock C2 braking system will be a slight increase in brake torque distribution forward do to the the larger front discs; the hydraulic ratios will all stay the same. I plan to switch to 60 BAR proportioning valves from a Turbo to shift brake torque toward the rear.

This system I will have when will be identical in thermal capacity - same rotor sizes, piston sizes and pad sizes - to the one I had on my 964 Cup and this was plenty adequate for my use.

Cheap, light and effective, and in my experience big enough.
The vacuum system certainly has merit, they use it on all subsequent models, the one thing i'd like is a 25.4mm m/c for it to get a better pedal, it would be a lot easier to operate the brake and gas w/ one foot w/ a higher harder pedal.
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Old 11-02-2011, 10:08 AM
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Originally Posted by 77'3.6vram View Post
Bill ,why don't you like the Turbo rear brakes.I feel as if the bigger calipers are not as responsive(do not bite as well)on the non-boosted 2wd car.Maybe I am lazy but I feel as if I have to put too much force on the brakes to get them to respond.Is there a problem with my setup?Thanks-Michael
Here are some brake torque ratios taking into account hydraulics(23.8mm m/c & calipers as speced), rotor size, effect of p/v and actual pad swept area(effective rotor size) all are normalized to the same m/c line pressure, f/r pressures are in newtons, second # is the f/r ratio
993RS(w/ 23.8mm m/c)
3319/2328 1.48

993(w/ 23.8mm m/c)
3209/2001 1.604

993tt(w/ 23.8mm m/c)
3319/1662 1.997

Bobs(w/ 23.8mm m/c) a change in p/vs will change these #'s
3319/2001 1.637

the traditional 911 ratio thru '83 as done above was always 1.491

the 993Rs and t have the same brake setup except for p/v and rear piston size, RS is 30/36 tt is 28/28

the tt is way too front biased for my taste, modern trends in brake design put as much load on the back as can be managed the RS does that but it does help a lot to have a low, stiff car w/ an effective lsd, you can further tune bias w/ pads, Pagid RS 19 f/r was good but lacked front bite, Pagid RS 29/19 is a bit too much front for my taste, so next season i'll try RS29/RS29. Several other experienced/respected 993 drivers like the PFC line but I haven't used them yet.
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Old 11-02-2011, 10:42 AM
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Thank you for the education.I started my RS clone as a exterior project.Over the past three years I wanted to do everything mechanical.I am not a "track guy" and I clearly have been given some bad advice along the way.I have changed wrenches four times while doing the conversion.I moved from South Florida to CT in the time frame.It's probably me,but,I have run into some less than honest shops in south western CT.It seems as if all the mechanics in the area believe they are "Porsche gurus" and deserve to be paid CEO wages.The stories are unique but each ends with an act of dishonesty or incompetence ending with a ridiculous bill and subsequent run in with local law enforcement.I have been told that it is the look on my face that brings out the worst in people.Never had these issues in Florida.In any case I will now call Sonnen and order part numbers 99335242580 and 99335242680.Thanks again for the education.You guys have forgotten what I will never know about these cars.
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Old 11-02-2011, 11:45 AM
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Originally Posted by 77'3.6vram View Post
Thank you for the education.I started my RS clone as a exterior project.Over the past three years I wanted to do everything mechanical.I am not a "track guy" and I clearly have been given some bad advice along the way.I have changed wrenches four times while doing the conversion.I moved from South Florida to CT in the time frame.It's probably me,but,I have run into some less than honest shops in south western CT.It seems as if all the mechanics in the area believe they are "Porsche gurus" and deserve to be paid CEO wages.The stories are unique but each ends with an act of dishonesty or incompetence ending with a ridiculous bill and subsequent run in with local law enforcement.I have been told that it is the look on my face that brings out the worst in people.Never had these issues in Florida.In any case I will now call Sonnen and order part numbers 99335242580 and 99335242680.Thanks again for the education.You guys have forgotten what I will never know about these cars.
just a suggestion

Dan Jacobs, "Hairy Dog Garage" might be a good place for you to go
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Old 11-02-2011, 12:01 PM
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I run RS brakes all around on my car and have never been wanting in regards to pedal feel, my brake pedal is high and hard. Pads and fluid make a huge difference to the pedal feel.

I run Pagid Blacks front and rear and Endless fluid, anyone who drives my car is amazed at the pedal feel and easy of heel and toeing...

While I was waiting for my RS rear calipers to arrive I did run with RS Fronts and stock C2 rears, this was not a great setup, way too much front bias, causing the car to nosedive under braking rather than braking flatter with the proper rear calipers.
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Old 11-02-2011, 12:22 PM
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Bill, Donna does not like me.Work quality was great but she got into a "thing" with Dan for quoting me 12 hrs labor to install a LWF on my TT.She insisted it was 16 to 18 hrs.She was using fact.labor hours for a 4wd 964.I went from being her favorite new customer in 2010 to being bared from the premises.Donna should stay at home.She does not like nor understand her job.
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Old 11-02-2011, 12:26 PM
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Originally Posted by trophy View Post
I run RS brakes all around on my car and have never been wanting in regards to pedal feel, my brake pedal is high and hard. Pads and fluid make a huge difference to the pedal feel.

I run Pagid Blacks front and rear and Endless fluid, anyone who drives my car is amazed at the pedal feel and easy of heel and toeing...

While I was waiting for my RS rear calipers to arrive I did run with RS Fronts and stock C2 rears, this was not a great setup, way too much front bias, causing the car to nosedive under braking rather than braking flatter with the proper rear calipers.
I have to disagree w/ you about brake fluid being a major contributor to pedal feel, the primary contributors to pedal feel are slave master ratio and mechanical stiffness of the component parts in the pedal mechanism and attachment points.

If you ever drove a car w/ the 25.4mm m/c pushing Big Reds like Bobs old RS, then you'd know what a really good pedal feels like. The 23.8 is ok but there is room for improvement.

Based on steering rack, spring/shock choice and brake setup, Bob appears to be setting this car up to feel/drive similar to his RS, I'm in awe of the work done so far
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Old 11-02-2011, 12:32 PM
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I suggest you try some of the Endless Fluid.... It can and does make a difference. Compress-ability or lack there of is a factor.

I'll do you a deal, buy some and try it if it doesn't improve your brake feel, I will pay for your fluid, deal?

I have driven both 993 RSCS and 993 Cup cars and do agree the pedal feel is excellent, and do agree that there is room for improvement from the 23.8mm master.

Bob is doing some pretty nice work here, I hope to see the finished product one day in a visit to Ca...
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Old 11-02-2011, 01:31 PM
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Thanks, guys. I like this brake discussion.

My Cup had great pedal feel, I also installed the race part fluid line that Porsche made to eliminate the proportioning valve altogether.

In the end, I will probably eliminate the valve in my semi-clone car here as well.

I like Bill's list of brake torque ratios over the years. Since improved grip increases front weight transfer, my thought was that Porsche has moved bias to the front because of the improvement in tires over the years.

I did toy with the thought of eliminating the assist altogether and using the Fabcar dual mastercylinder kit. I figured the brake pedal would feel about like it did in the olden 911 days when we used a 23.8 mm Mercedes master cylinder to replace the stock 19.04 mm part. If I could just get the weight down to 2400#'s or less...
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Old 11-02-2011, 03:43 PM
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Originally Posted by trophy View Post
I suggest you try some of the Endless Fluid.... It can and does make a difference. Compress-ability or lack there of is a factor.

I'll do you a deal, buy some and try it if it doesn't improve your brake feel, I will pay for your fluid, deal?

I have driven both 993 RSCS and 993 Cup cars and do agree the pedal feel is excellent, and do agree that there is room for improvement from the 23.8mm master.

Bob is doing some pretty nice work here, I hope to see the finished product one day in a visit to Ca...
hint: all brake fluid is incompressible, that's one of the big reasons it's used as brake fluid, the biggest difference between one brand and another is the wet/dry boiling points
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Old 11-02-2011, 03:47 PM
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Originally Posted by Cupcar View Post
Thanks, guys. I like this brake discussion.

My Cup had great pedal feel, I also installed the race part fluid line that Porsche made to eliminate the proportioning valve altogether.

In the end, I will probably eliminate the valve in my semi-clone car here as well.

I like Bill's list of brake torque ratios over the years. Since improved grip increases front weight transfer, my thought was that Porsche has moved bias to the front because of the improvement in tires over the years.

I did toy with the thought of eliminating the assist altogether and using the Fabcar dual mastercylinder kit. I figured the brake pedal would feel about like it did in the olden 911 days when we used a 23.8 mm Mercedes master cylinder to replace the stock 19.04 mm part. If I could just get the weight down to 2400#'s or less...
more front bias seems to be used on Porsche's AWD cars

for rwd you want to offload as much of the load to the rear as is possible it lets the front run cooler and gets the big rear tires w/ less camber help stop the car. The latest and greatest 997RSR's run ~1.5 w/ cockpit adjustable twin masters, also cockpit adjustable sways
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Old 11-04-2011, 06:13 PM
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Brake bias is not a fixed thing, it changes with tires, coefficient of friction to the road (wet pavement), fuel load, passenger load, changes in CG (lowered car), etc. the bias chosen is a compromise at best.
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Old 11-04-2011, 06:21 PM
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Update. Got tired of suspension stuff, so moved on to some other projects.

Here I have removed radio, airbags and airbag dash. Euro RS trim pieces fit nicely to replace airbag bottom and I found the holes are already drilled. It looks like I can install an ashtray even. Ashtray ordered, we will see. Otherwise a bracket for center piece will have to be made. Plan is RS interior carpet and door panels with Recaro buckets.




RS water bottle installed and waiting for wiring.

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Old 11-04-2011, 07:58 PM
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Originally Posted by Cupcar View Post
Brake bias is not a fixed thing, it changes with tires, coefficient of friction to the road (wet pavement), fuel load, passenger load, changes in CG (lowered car), etc. the bias chosen is a compromise at best.
i'd rephrase that, bias is fixed by the system parameters, but ideal bias changes dynamicly due to both environmental factors and vehicle dynamics
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Old 11-04-2011, 08:00 PM
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Originally Posted by Cupcar View Post
Update. Got tired of suspension stuff, so moved on to some other projects.

Here I have removed radio, airbags and airbag dash. Euro RS trim pieces fit nicely to replace airbag bottom and I found the holes are already drilled. It looks like I can install an ashtray even. Ashtray ordered, we will see. Otherwise a bracket for center piece will have to be made. Plan is RS interior carpet and door panels with Recaro buckets.




RS water bottle installed and waiting for wiring.

One of the things I wish I had done while it was all apart like that is relocate the OBD port to a more convenient location.
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