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Brake bias calculations 931-951 OEM/Volvo/Brembo...
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1559
Location: MI

PostPosted: Wed Jun 24, 2015 3:54 am    Post subject: Brake bias calculations 931-951 OEM/Volvo/Brembo... Reply with quote

Thanks for the numbers I couldn't find...
FIXED I THINK FOR CALCULATING PISTON AREA ONLY ON ONE SIDE OF CALIPERS WITH PISTONS ON BOTH SIDES VS ALL PISTONS ON BOTH SIDES


PISTONS..

931 master cylinder = 2X 23mm pistons = 415.27 mm2 surface area total per piston (X2)

951 master cylinder = 19mm rear 23mm front = 283.4 mm2 rear 415.27 mm2 front

My new Volvo front calipers = 4X 38mm pistons = 2267 mm2 surface area per side of caliper

931 rear calipers = 36mm = 1017.4 mm2

931 front calipers = 54mm = 2289 mm2

924 4 lug fronts = 48mm = 1808 mm2 (can be fitted to 931 rear)

951 brembos front = 2X 36mm + 2X 40mm = 2273.4 mm2 surface area total per side of caliper/slave (near as makes no difference the same effective size as volvo calipers )

951 brembos rear = 2X 20mm + 2X 30mm = 1020.5 mm2 surface area total per side of caliper/slave


SLAVE/MASTER RATIOS

4 pot Front = 10.95:1 .091 slave/master ratio... Applies to any combination of 931/951 master and front Brembos/Volvo 4 pots as they are effectively the same..

951 rear = 7.2:1 .139 slave/master ratio... The number I should be shooting for I think.?.?.

Rear 931 master with 951 brembos = 2.46:1 slave/master ratio (same either way with brake split)

Front 931 OEM = 5.51:1 .181 slave/master ratio

Rear 931 OEM = 2.45:1 .408 slave/master ratio

924 4 lug fronts on 931 rear = 4.35/.230 slave/master ratio

FRONT/REAR BIAS RATIOS

951 OEM front/rear bias = .091/.139 1.53:1 ratio (My goal? about 1.5:1 ratio?)

931 OEM front/rear bias = .181/.408 2.25:1 ratio

931 master 4 pot front/OEM rear = .0704/.408 5.8:1 ratio

924 4 lug fronts on 931 rear w/4 pot front on 931 master = .0704/.230 3.27:1 ratio (still way too much front bias)

931 master 4 pot front/951 brembo rear = .0704/.204 2.9:1 ratio (would need bias proportioning valve to turn rears down?)

951 master, Volvo 4 pot front, brembo rear = Hey!! the same as 951..

928 86- VIN#F 92GS8 61000 - model year 87: Front Caliper 42mm and 36mm
Rear Caliper 30mm and 28mm
88 Front Caliper 44mm and 36mm
Rear Caliper 30mm and 28mm

930 and Carrera Turbo look: Front calipers: all 38mm pistons
Rear Calipers: all 30mm pistons

944 Turbo:

Front Calipers:
'86 Turbo 38mm and 36mm
'87-88 Turbo 40mm and 36mm
'88 Turbo S 44mm and 36mm
'89 944 S2 up to VIN # >> 94KN4 51880 40mm and 36mm

Rear Calipers:
'86-88 Turbo and Turbo S 30mm and 28mm
'89 S2 up to VIN #>>94KN4 51880 30mm and 28mm

CAUTION.. MAY ALL BE COMPLETELY WRONG[/b]
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Last edited by Fasteddie313 on Thu Jun 25, 2015 1:35 pm; edited 16 times in total
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motormouth  



Joined: 28 Feb 2010
Posts: 113
Location: Canton

PostPosted: Wed Jun 24, 2015 4:08 am    Post subject: Reply with quote

Make a spreadsheet. I would wager Dan has already made one up with every possible brake combination for a 924 lol
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1559
Location: MI

PostPosted: Wed Jun 24, 2015 5:16 am    Post subject: Reply with quote

motormouth wrote:
Make a spreadsheet.


Not my area of expertise, feel free..

motormouth wrote:
I would wager Dan has already made one up with every possible brake combination for a 924 lol


I searched my a** off and can't even find OEM 931 slave piston diameters much less a compilation of "exhausted research"..
I was able to find the 931 and 951 master sizes and Brembo/Volvo slave sizes, all the rest of the math is mine..

BTW so everyone knows what I'm talking about here, the Volvo calipers are supposed to bolt right up to 5 lug non-brembo cars, they fit 91 Volvo's from 1975-1987 so they are easy to get, and CHEAP, real cheap.. This exact pictured pair are on there way to me freshly refurbished with pads for UNDER $80 shipped.. Amazing value IMO..


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gegge  



Joined: 27 Jul 2007
Posts: 1025
Location: Sweden

PostPosted: Wed Jun 24, 2015 7:18 am    Post subject: Reply with quote

931 front calipers = floating single pistonequals 2x54mm

931 rear calipers = floating single piston equals 2x36mm

Is it Volvo-Girling calipers for non-vented rotors?
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924 turbo -81 Carrera GT clone LSD Coilovers
924 -85 DP kit, BBS RS, M030 and tuned engine
924s -86 Black on black with low ET "Phonies"
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fiat22turbo  



Joined: 18 Jan 2006
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Location: Portland, OR

PostPosted: Wed Jun 24, 2015 7:23 am    Post subject: Reply with quote

There were different sizes for the 928/951/968 calipers depending on the options and years, etc.
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1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1559
Location: MI

PostPosted: Wed Jun 24, 2015 9:23 am    Post subject: Reply with quote

gegge wrote:
931 front calipers = floating single piston equals 2x54mm

931 rear calipers = floating single piston equals 2x36mm

Is it Volvo-Girling calipers for non-vented rotors?


Thank you very much for the numbers.. I'm super busy and just stopped to eat, I'll calc them later today prolly.. My IC just came in the mail and it's in, mounts done, looks amazing, 1 more intake hose clamp, J-pipe, WG, Exhaust and it's alive.. Prolly not alive today..

I think I read something along the lines of "lucas-girling" but I'm not real sure of anything... Like another member posted in a super old thread, "if there Volve 4 pots are off an old Volvo with 2 brake line connections you really cant go wrong".. Also something like "up until ABS"..
Seeing as they fit so many Volvos from such a large time span I think the odds are astronomical that you could pick up the wrong ones, they look the same, I sure hope they bolt on when they get here, I'll surely let you all know.. ETA thursday 25th but so was the IC and its here already..

fiat22turbo wrote:
There were different sizes for the 928/951/968 calipers depending on the options and years, etc.


Oh.. Which ones do I have numbers for then? The thread said "951 brembos" iirc..
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Wed Jun 24, 2015 1:49 pm    Post subject: Reply with quote

OK I finished the numbers and it leaves me with an insane .0352/.408 11.6:1 front bias just putting 4 pots on the front of OEM 931 stuff.. Pretty much putting the biggest with the smallest... bad..

What am I to do?
Anyone know a good way of getting big in the back without Brembo price? What fits?
A proportioning valve to the front is a bad idea correct? idk..

sounds like 48mm 4 lug fronts work on 5 lug rears swapping just the piston/cylinder.. Still too small but half way there..

Looks like I just need rear 951 Brembos and a proportioning valve (great $$$)...

What should I expect to pay for said rear brembos? Maybe I'll still find an easier solution..
a 52mm single piston rear slave would put me in the same boat as brembo rears, that sounds findable.. Or 36mm twin piston rears..
Wonder if there is a way to get my 54mm front 931ncalipers on my rear, that would be awesome and work perfect..
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Last edited by Fasteddie313 on Wed Jun 24, 2015 3:02 pm; edited 1 time in total
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fiat22turbo  



Joined: 18 Jan 2006
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Location: Portland, OR

PostPosted: Wed Jun 24, 2015 2:59 pm    Post subject: Reply with quote

the V8 944 guys figured out how to adapt RX-7 front calipers to the rear.

Check the 944 V8 forums over on Texas Performance Concepts.

Also the commonly found Porsche 944 Brembos share the mounting pattern front and rear.
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1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Wed Jun 24, 2015 3:24 pm    Post subject: Reply with quote

fiat22turbo wrote:
the V8 944 guys figured out how to adapt RX-7 front calipers to the rear.

Check the 944 V8 forums over on Texas Performance Concepts.



Looked, have to make adaptor plates, adaptor plates would be my very last resort..

fiat22turbo wrote:


Also the commonly found Porsche 944 Brembos share the mounting pattern front and rear.


Does that mean that ANY 944 4 pot calipers will solve my rears problem and just turn them down with a valve? What about disk height/thickness problems?
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ideola  



Joined: 01 Oct 2004
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PostPosted: Thu Jun 25, 2015 1:46 am    Post subject: Reply with quote

Just an FYI, regarding 951 Brembos, I believe that in order to mount them on the steel trailing arms, you need to use some washers / spacers for them to seat correctly, or possibly to space them correctly relative to the rotor.

Also, don't forget that the early 924/931 4-wheel disc setup was an X-split. When doing the kind of thing you're attempting, you will need to re-plumb the brake lines for a front-rear split.
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Thu Jun 25, 2015 2:24 am    Post subject: Reply with quote

Would I want to separate the masters front and rear to have 2 separate systems or would connecting both rears do the trick?

like..
2 rear lines T to 1, 1 line to proportioning valve, 1 line off proportioning valve T back to 2 rear lines... Easy... Masters linked at T to rears effectively turning it into 1 big master to all 4 brakes...

Or a lot of new lines masters separate..
1 Master T direct to fronts, Other master to proportioning valve then T to rears... Masters completely separate..

Or linked masters right at the get go...
Both masters to 4 way split, 1 direct T to fronts, 1 to valve then T to rears..

Linking the masters would equalize the performance of the 2 and act like 1 big master pushing all 4 brakes, but would do away with the fail safe of having 2 separate brake systems in case 1 fails the other would still operate like the DOT wants...

I'm guessing separate is the correct answer due to safety "if" this "if" that stuff.. How do racers run theres?
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ideola  



Joined: 01 Oct 2004
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PostPosted: Thu Jun 25, 2015 3:45 am    Post subject: Reply with quote

I don't follow you.

The stock setup on 944-onward was one chamber of the master for fronts, one chamber for rears. The chamber for front on most cars I've seen has two separate lines, one to each front brake; I believe this is merely for ease of plumbing, there's nothing wrong with teeing the fronts, but the cylinder two ports for the fronts. The rears are tee'd under the car. I don't see any reason to do anything otherwise unless you're building a ten-tenths race car where you would have an adjustable brake bias valve in the cockpit so you could adapt for changing conditions, as described here: http://www.924board.org/viewtopic.php?t=27181
and here: http://www.924board.org/viewtopic.php?p=256394#256394
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15 981 GTS | 88 924S SE | 82 931 Holbert | 82 931 Rallye | 81 937 | 81 Euro 931 | 81 Weissach | 80 US 928 | 80 US 931 '941' | 80 US 931 | 80 931 GTR | 79 Sebring | 78 D-Prod Replica | 78 w/D-Prod kit | 78 Poli-Form | 78 Limited Edition | 77 Martini
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 1559
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PostPosted: Thu Jun 25, 2015 4:00 am    Post subject: Reply with quote

Yup, going for adjustable brake bias valve in cockpit because its only a little extra $20-$30 and massive cool factor even if not needed..

All this big brakes stuff is mostly just for massive cool factor anyway, It gives me that funny feeling... I think it'll all squeeze under $200 and that's worth it for that alone..

CÚdric wrote:
Rasta Monsta wrote:
Hilariously, if you put good pads on the factory calipers you get plenty of stop...the brakes on my race car will displace your organs.


+1!


I agree, this is merely for personal satisfaction and I'm not afraid to admit it..

You have your nice paint/seats/pretty things, I want big breaks, FMIC, cold ram air, permanent CIS testor, custom stuff..
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nickthompson  



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PostPosted: Thu Jun 25, 2015 9:05 am    Post subject: Reply with quote

If you are going though this much trouble why not ditch CIS?
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Fasteddie313  



Joined: 29 Sep 2013
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Location: MI

PostPosted: Thu Jun 25, 2015 11:32 am    Post subject: Reply with quote

nickthompson wrote:
If you are going though this much trouble why not ditch CIS?


Haven't decided.. I kind of like CIS, like it has a soul and may be plenty for me...

Thats too expensive of a project for now anyway, CIS will get me to the end of my turbocharger, so to gain much more stand alone vs CIS I would need a bigger turbo too, I'll be plenty busy just adjusting and tweaking what I have for a while..

I'd pretty much need another junk 924 to mock up an EFI project on, no sense in doing just a piece, that stage would look something like..
VEMS, Garrett, custom exhaust manni, custom intake manni or ITB's, etc.. May as well do all that in one go if I was to.

I may never go that far, I think I can approach 1 bar boost right now pretty much and that may be enough, I really like how original and tastefully modified it is the way it is now as far as the engine goes..

Engine will need refreshed someday with some light internal mods of course, like non-interference w/VW flats, bore, O-ring, cooling mods, replace slightly worn cam prolly with original grind, maybe bigger valve springs and lighter buckets if I decide I want more revs.. Thats more reliability/bulletproofing upgrades than power IMO but I'll use up the one I have first..

Big FMIC, Bigger boost (with a knob), Bigger brakes (with a knob), the next things aren't power related besides FMIC sprayer but that's easy fast and free prolly..

Do the suspension with bilsteins all the way around if I can lower a bit on em if not Konis, dual rate front adjustable coilovers, not sure on rear springs yet, lowered a bit, I like my strange looking forged fuchs wheels they stay, Might turn out some better bushings here and there myself or buy them, that's enough there prolly..

Squeeze in G31 2nd synchro fix somewhere, maybe swap around some gear ratios while I'm at that idk yet, I can see the G31 in the house on a coffee table for a winter, maybe buying a 928 trans or something for parts to get gears and a 2nd synchro would be the way to go there, IDK I haven't researched that completely yet, I may just buy a single synchro and go..

Then maybe pretty things like fix my drivers seat in some fashion or swap to sports seats or something, new dash cover, shorter shifter, custom pedal faces, make the interior look nicer, details.

Then body, maybe euro bumpers and the cool rear under spoiler thing, new hatch, shave side markers, remove belt trim, paint it some color, paint color doesn't even cross my mind yet that's so far down the road..

Will need more stickers eventually, Bilstein, Stahlwille, german go fast stuff idk..

Don't want to go widebody, I like the 931 lines, if I wanted widebody I'd buy a wide body..

Plenty of things to do next to keep me busy and broke besides more more more motor..
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