Educate me on brake options!
10-17-2018, 07:04 PM
#1
Rennlist Member
Thread Starter
Educate me on brake options!
I've done lots of searching and reading, and I'm still a bit confused. I seem to find a lot of conflicting information
1991 964. Have factory brakes and looking to upgrade. The car isn't tracked and even through hard pushing through the twistys, I never have any brake fade.
It has the 2 pot rear calipers, which just look so tiny. The upgrade is mostly for cosmetics.
What are my options? Can I get the larger 4 pot rears? Do I need to change the proportioning valve or no? Any other ideas?
Is there any real improvement with the 4 pot rears that would also justify doing it?
If yes - what am I exactly looking for and where's the best place to get them? I don't want to spend an arm and a leg on doing it but since I am planning on powdercoating and rebuilding the brakes this winter, I might as well upgrade if I can.
Thanks in advance
1991 964. Have factory brakes and looking to upgrade. The car isn't tracked and even through hard pushing through the twistys, I never have any brake fade.
It has the 2 pot rear calipers, which just look so tiny. The upgrade is mostly for cosmetics.
What are my options? Can I get the larger 4 pot rears? Do I need to change the proportioning valve or no? Any other ideas?
Is there any real improvement with the 4 pot rears that would also justify doing it?
If yes - what am I exactly looking for and where's the best place to get them? I don't want to spend an arm and a leg on doing it but since I am planning on powdercoating and rebuilding the brakes this winter, I might as well upgrade if I can.
Thanks in advance
10-17-2018, 07:19 PM
#2
Rennlist Member
get 92+ rears + pads
put in 92+ proportion valve
Benefit? Heat management. You probably won't notice a difference on the street. Unless your wheels get too hot to touch you're not using your brakes much and very well may never notice it. And if you have smoking brakes on the street you'll probably get thrown in jail soon.
I think the 4 piston rears do look 'better'.
put in 92+ proportion valve
Benefit? Heat management. You probably won't notice a difference on the street. Unless your wheels get too hot to touch you're not using your brakes much and very well may never notice it. And if you have smoking brakes on the street you'll probably get thrown in jail soon.
I think the 4 piston rears do look 'better'.
10-17-2018, 07:21 PM
#3
Rennlist Member
The technical questions have all been answered here and on the Pelicanparts forum. Look for Bill's responses and discussion.
Regarding source for the 4 pods, I went to a dismantler and had them completely rebuilt by GoldLine Brakes outside Seattle. No affiliation but they were fantastic. If you want to powder coat them anyway, that would be one way to go. GoldLine will paint them in any color you want.
Regarding source for the 4 pods, I went to a dismantler and had them completely rebuilt by GoldLine Brakes outside Seattle. No affiliation but they were fantastic. If you want to powder coat them anyway, that would be one way to go. GoldLine will paint them in any color you want.
10-17-2018, 09:50 PM
#4
Three Wheelin'
You might want to consider the negative impact of the additional weight (larger caliper & larger rotor). This is trading performance for aesthetics.
10-18-2018, 12:00 AM
#5
I’m in the same boat and I do think there is as advantage to the later caliper if you take into account that the original tire that the system was designed for was a 225 and that most have gone up to 255 which means that more rear bias is appropriate.
Pete
Pete
10-18-2018, 01:05 AM
#6
Banned
I just picked up a set of 4 piston rear calipers for my 90 c2. I will be installing along with stoptech slotted rotors and ferodo 2500 pads on all 4 corners. I plan to gut the proportion valve based Bill’s recommendation.
the benefit of the 4 piston rear calipers is heat management and wider selection of matching front and rear pads. Not many pad options for the 2 piston rear calipers.
the benefit of the 4 piston rear calipers is heat management and wider selection of matching front and rear pads. Not many pad options for the 2 piston rear calipers.
10-18-2018, 09:01 AM
#7
Rennlist Member
Originally Posted by -nick
You might want to consider the negative impact of the additional weight (larger caliper & larger rotor). This is trading performance for aesthetics.
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10-18-2018, 10:42 AM
#8
Rennlist Member
I just picked up a set of 4 piston rear calipers for my 90 c2. I will be installing along with stoptech slotted rotors and ferodo 2500 pads on all 4 corners. I plan to gut the proportion valve based Bill’s recommendation.
the benefit of the 4 piston rear calipers is heat management and wider selection of matching front and rear pads. Not many pad options for the 2 piston rear calipers.
the benefit of the 4 piston rear calipers is heat management and wider selection of matching front and rear pads. Not many pad options for the 2 piston rear calipers.
FYI I installed Stoptech slotted rotors on my sons Audi. I Like the rotors however if you let the car sit for any period of time they rust badly and cause raised areas around the slots. It got so bad after 5 weeks of the car sitting outside I had to ditch them and buy factory. If the car sits inside or is driven regularly you should be fine. Although factory rotors aren't all the expensive and last a lot longer.
10-18-2018, 12:04 PM
#9
Banned
FYI I installed Stoptech slotted rotors on my sons Audi. I Like the rotors however if you let the car sit for any period of time they rust badly and cause raised areas around the slots. It got so bad after 5 weeks of the car sitting outside I had to ditch them and buy factory. If the car sits inside or is driven regularly you should be fine. Although factory rotors aren't all the expensive and last a lot longer.
10-18-2018, 12:32 PM
#10
Rennlist Member
"race" rotors typically don't have the coatings on them to minimize corrosion. I have brembo and the ones on my 964 are coated and don't corrode like the ones on my RS which are full race rotors. Its not bad, but I try to avoid spraying them when washing the car (ie wheels off for wash).
10-18-2018, 01:12 PM
#11
Three Wheelin'
Sorry, I read the original post as "brake upgrade" not just 4-pot rear caliper upgrade 
Big reds/etc add quite a few pounds of unsprung rotating mass. You are definitely correct, swapping the 2-pot rears to 4 has no ill effects. Carry on...!
Big reds/etc add quite a few pounds of unsprung rotating mass. You are definitely correct, swapping the 2-pot rears to 4 has no ill effects. Carry on...!The weight difference for the calipers is negligible and the rotors are the same. I would be very surprised if you could feel the difference in weight. One of my old 2 pods was sticking so rather than rebuild the original I upgraded to 4 pods in the back for the reasons stated above.
10-18-2018, 02:00 PM
#12
Technical Guru
Rennlist Member
Rennlist Member
The Stoptech hubs are coated and fine. It is the actual slot on the disc.
10-18-2018, 03:35 PM
#14
Rennlist Member
Thread Starter
This is perfect, thanks guys. I was really looking for the 'coles notes' version.
I do run a 265 tire in the rear (and the brand fits wider than most, so it's closer to 275) so I'm sure there will be some benefit as well.
boostedt0y - where did you get the 4 pot calipers from? Or anyone else have recommendations? Or what I should look to pay approx?
I found some 964 turbo rear calipers for sale - could those work?
I do run a 265 tire in the rear (and the brand fits wider than most, so it's closer to 275) so I'm sure there will be some benefit as well.
boostedt0y - where did you get the 4 pot calipers from? Or anyone else have recommendations? Or what I should look to pay approx?
I found some 964 turbo rear calipers for sale - could those work?
10-18-2018, 06:12 PM
#15
ideally you would want bias to be < 1.5 and > 1.425, and then not use a p/v or at least use the least intrusive one that you can get away w/. This will depend on how the car is setup,
to use more rear the car needs to be
stiffer
have an effective lsd
good tire bias
All stock 964 are fairly heavily front biased, factory removed the p/v for racing use in the Cups
The following is @70bar line pressure, a fairly hard stop, but line pressures to ~ 100bar can be seen, All on stock rotors, only the Cups use bigger rotors and then only in front
964 Cup bias is 1.713 w/ 2381NM front & 1390NM rear no p/v
964 4/4 bias is 1.889w/ 2203NM front &1167NM rear (no p/v) This goes to 3.498 w/ 2203NM front and 630NM rear when the stock 55bar p/v is in place
964 4/2 bias is 1.643 w/ 2203NM front &1341NM rear (no p/v) This goes to 3.042 w/ 2203NM front and 724NM rear when the stock 40bar p/v is in place
As you can see bias is worse w/ 4/4 than w/ 4/2 and all are are too much front,
reasons to go to 4/4: looks, uses same pad f/r, longer rear pad life
use stock front and a stock normal 993 rear
964 4/993 4 bias is 1.547w/ 2203NM front &1424NM rear (no p/v) This goes to 2.865 w/ 2203NM front and 769NM rear when the stock 55bar p/v is in place
to use more rear the car needs to be
stiffer
have an effective lsd
good tire bias
All stock 964 are fairly heavily front biased, factory removed the p/v for racing use in the Cups
The following is @70bar line pressure, a fairly hard stop, but line pressures to ~ 100bar can be seen, All on stock rotors, only the Cups use bigger rotors and then only in front
964 Cup bias is 1.713 w/ 2381NM front & 1390NM rear no p/v
964 4/4 bias is 1.889w/ 2203NM front &1167NM rear (no p/v) This goes to 3.498 w/ 2203NM front and 630NM rear when the stock 55bar p/v is in place
964 4/2 bias is 1.643 w/ 2203NM front &1341NM rear (no p/v) This goes to 3.042 w/ 2203NM front and 724NM rear when the stock 40bar p/v is in place
As you can see bias is worse w/ 4/4 than w/ 4/2 and all are are too much front,
reasons to go to 4/4: looks, uses same pad f/r, longer rear pad life
use stock front and a stock normal 993 rear
964 4/993 4 bias is 1.547w/ 2203NM front &1424NM rear (no p/v) This goes to 2.865 w/ 2203NM front and 769NM rear when the stock 55bar p/v is in place