What's the diameter of the rotor going to be? I think that even a 5/8 MC is going to be to big with that setup. The Volvo is a 1.5in 4-piston in the front (as John mentioned) with a 10.4in rotor. Un-boosted, it's doable, but not ideal (5/8in MC and 4-4.5 pedal ratio). Like you have to really stomp on it, but that's just from personal experience DD'ing a car with a blown out booster for a few months... |
Pete Pete Remner Super Moderator Location: Cleveland, Ohio Join Date: 01/11/2006 Age: Midlife Crisis Posts: 2,022 |
9". It's a goofy rotor where the ID of the friction surface is smaller than the OD of the hub. It's real close to full pad contact if I just set the caliper down until it barely cleared the hub, maybe 8mm of overhang, but if I cut a little bit out of the bottom/outer face it will clear the hub even better and only leave a couple mm of overhang, which I'd prefer since then you get no lip on the outside of the rotor. Clearing wheel is no problem, heck it would clear even if I didn't sit the caliper down more, and the 4-pot barely sticks out past the hub face so clearing spokes is also a non issue.
That's off in the distant future, though, after we get our machine shop setup again. I'd like to flycut the calipers rather than hand-booger them, and I'm patient. Note that I've already modified the brake pedal for 7:1. I *get* that leverage and hydraulic multiplication have two separate feel effects, more leverage over the master gives you more control even if the end multiplication from pedal to brake pad ends up being the same. (Kind of like a quick rack and a 350mm steering wheel vs. 6 turns lock to lock and as doorknob, I guess) The other thing I consider, is I've customers with manual brakes, 1" bore masters, and 1.75" 4-pots over little 10" drag rotors, and the braking feels better than my power brakes. So I do have some faith that pad composition and proper leverage are worth a lot. Or I could say fark it, and blow another $400 and get one of these things: http://www.ebay.com/itm/MAZDA-MX5-HYDRAULIC-BIAS-BOX-KIT-B-WITH-LINES-CMB6331-KIT-LINES-/282084767188?hash=item41ad8ff5d4:g:nooAAOSwwo1XdRzb&vxp=mtr which I'm considering for the bridge ported RX-7 because it kind of IS "that kind" of car... Pete Remner Cleveland, Ohio 1984 RX-7 (rallycross thing) 1978 Silence is golden, but duct tape is silver. Edited 3 time(s). Last edit at 09/06/2017 07:19PM by Pete. |
john vanlandingham John Vanlandingham Infallible Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
Other readers..I invented the RX7 caliper and big 740 rotors on 240 spindle 13 years ago and it is a reduction of 19, sumpin percent in hydraulic are versus stock Volvo calipers.. ALL the drivers I know who actually have driven rallies--in contrast to those who haven't driven rallies, ALL agree its insuffient force to lock even at Grass-o-cross speeds.. Believe them or believe Cult-person, your choice. But we tried it cause it cost us under $15 and it was not good. Guys, this brake sizing shit is one of those horses that hets pounded to death again and again.. If you're not like some people who even though they have never driven a single event or maybe done 4 over 15 years and yet you feel compelled to offer advice on how well things work, fine go discuss and figure out with your favorite on-line calculator....and fap to your hearts content. But there is an alternate method and that called empirical engineering.. What is the "industry standard" for car this (or that weight) and use and surface? We can look things up...So a 2080lb for Escort in Group 4 spec---which is a good enough car to win overall today used Nice 4 piston AP calipers with 4 x 1.5" or 38mm pistons..front and 2 x 1.5" pistons rear.. Thats with front pads about 100mm long.. Now Pete's looking at some junk that is significantly smaller--because second hand?---so that makes for problems... But at least knowing the "industry standard" one can do some areas and juggle some per centages and make a better stab--a half educated guess. Pete you have some second hand calipers lined up for cheep cheep? John Vanlandingham Sleezattle, WA, USA Vive le Prole-le-ralliat www.rallyrace.net/jvab CALL +1 206 431-9696 Remember! Pacific Standard Time is 3 hours behind Eastern Standard Time. |
Pete Pete Remner Super Moderator Location: Cleveland, Ohio Join Date: 01/11/2006 Age: Midlife Crisis Posts: 2,022 |
No, I have some calipers I was going to run on something else and now they're just laying around. Brand new, marked down from $125ea to $25ea at Summit. Buy first, ask questions later, you know? Like the RCI camlock 6-points that I grabbed for $50 each...
I'm not worried about braking at rallycrosses, I don't hardly ever use the brakes at those except for a little weight transfer, it's faster to just pitch sideways and let sliding slow you down, which also conveniently gets you pointed in the right direction to power out of a corner. Slow down from 60 to 30 real quick when you pitch sideways on dirt/clay, and if you're going slower than that then you don't need to slow down anyway... 'Sides, this car probably won't ever really get used for that, it seems like to be successful in the classes it's legal for, you need way more power and fresh tires all the time. Not 160hp and 15 year old Silverstones. So, just a street toy, something fun to drive that isn't a pain in the ass to live with. Pete Remner Cleveland, Ohio 1984 RX-7 (rallycross thing) 1978 Silence is golden, but duct tape is silver. Edited 1 time(s). Last edit at 09/06/2017 08:31PM by Pete. |
DanielSL Daniel Mega Moderator Location: Vero Beach, Florida Join Date: 03/02/2016 Age: Possibly Wise Posts: 338 Rally Car: 2005 VW Mk. 4 Golf GTI 1.8T |
Be careful Pete. Buying first and asking questions later is my usual way of doing things. And we all know how that turns out around here. But hey... I've learned to stop doing that, so I guess my wife is right. I am trainable... on some things. |
Pete Pete Remner Super Moderator Location: Cleveland, Ohio Join Date: 01/11/2006 Age: Midlife Crisis Posts: 2,022 |
I have a garage and a basement and a storage locker full of buy first ask questions later. When a deal comes up, grab it!
My Volvo is now riding on springs I grabbed over ten years ago that were new takeoffs from an '04 Camry. Somehow they fit just right and have the right rate and ride height I want. This is a bad precedent for hoarders. Anyway, I know this is for a street car and not a stage rally car, but I ask these questions here because there seems to be a lot more practical knowledge regarding braking *here* than at any other site I frequent... more builders and did-ers (it's like do-ers, but with more experience). Pete Remner Cleveland, Ohio 1984 RX-7 (rallycross thing) 1978 Silence is golden, but duct tape is silver. |
Pete Pete Remner Super Moderator Location: Cleveland, Ohio Join Date: 01/11/2006 Age: Midlife Crisis Posts: 2,022 |
Then I discover that this exists:
http://www.wilwood.com/Pedals/PedalProd.aspx?itemno=340-4630 Neeeet. Balance bar attached to a remote mountable bracket with a built in 1.48:1 ratio lever. That will turn a 4.5:1 pedal into a 6.66:1 pedal. Be simple to knock up a strong bracket that attaches this to the firewall. Already have a .700 and a .750 master, as well as a .625 for the handbrake, to replace the .700 already there. Pete Remner Cleveland, Ohio 1984 RX-7 (rallycross thing) 1978 Silence is golden, but duct tape is silver. |
john vanlandingham John Vanlandingham Infallible Moderator Location: Ford Asylum, Sleezattle, WA Join Date: 12/20/2005 Age: Fossilized Posts: 14,152 Rally Car: Saab 96 V4 |
Niice John Vanlandingham Sleezattle, WA, USA Vive le Prole-le-ralliat www.rallyrace.net/jvab CALL +1 206 431-9696 Remember! Pacific Standard Time is 3 hours behind Eastern Standard Time. |