STi brakes, the brute force way!

[sperry]

So, I was fed up with the brakes on my SVX... not just with the poor pedal feel, but also with the lack of heat capacity (I'm an SCCA driving instructor, so every now and then the SVX sees the race track, and I get one or two good stops out of the car before the pads are faded). Sure, the brakes are adequate for driving around on the street... but I've seen the light with my StopTechs on my WRX, and I want that on the SVX too.

Additionally, and probably a big contributor to the poor brake feel on my SVX, my wheel bearings are on their way out. I've to the point where I'm getting quite a bit of brake drag as well as pad knock-back due to the bearing flex, so I decided to kill two birds with one stone. The stone in this case is a pair of StopTech 328x28 brakes for a WRX mounted on a set of '07 STi knuckles and hubs adapted to the SVX.

The STi knuckles are pretty close in shape to the SVX, but they're not straight bolt in. So far, I haven't sorted out all the issues quite yet, but I have made a bunch of progress. Here are all the issues as I see them, and my solution so far:

1) Suspension upright mounting - the spacing between the holes on the SVX uprights is just a little tighter than on the STi. One solution would be converting to STi suspension, but that just pushes the problem out to the top-hats and there's of course the whole strut length deal. I'm choosing just to slot the lower hole on the knuckle enough to allow the stock suspension to bolt up. This also leaves me the option of switching to STi struts in the future.

2) Ball-Joints - the SVX uses an inverted (when compared to the STi) ball-joint that is attached to the LCA with three bolts. This is a pretty different design than the STi... but it actually works in our favor. After taking a bunch of measurements, it is actually pretty simple to build a ball-joint adapter that will bolt to the SVX's LCA and hold an STi ball-joint. The best part is that because of the difference in ball-joint angles between the two knuckles, the STi adapter is actually *simpler* than the existing SVX ball-joint part. Here's my design for the part... I haven't gotten around to fabricating it yet... I'm torn between trying to do it myself, or finding a machinist to make it for me. The only hard part is drilling the proper bevel for the ball-joint... it's a weird angle and needs to be pretty accurate to ensure the ball-joint mounts without any slop.



The adapter is made from a simple piece of hot-rolled 3"x.5" flat bar, with the ball-joint mount section made from stacking the bar at double thickness. Certainly a lot easier than my first design that was going to cost like $200 each to be made at eMachineShop.com out of a big old solid CnC'd block of steel. Once again, it's just figuring out how to get a good angle on that ball-joint socket that's kept me from cutting this in my garage.

3) ABS sensor - the ABS sensor on the SVX is much longer than the one on the STi as it pokes horizontally through the knuckle to read the tone wheel mounted on the back of the hub. The STi's ABS sensor points at the tone wheel mounted on the axle itself. The good news is that the tooth count on both tone wheels is exactly the same... so the hall-effect sensors will see the same number of pulses per rotation of the wheel whether or not its coming from the hub or the axle. So, I've decided I'm going to put STi front axles on my car to match the knuckles/hubs. The good news again is that converting the SVX transmission to accept the STi axles is just a matter of two new oil seals. Just pop out the stub-axles, swap the oil seals for the slightly larger STi seals, and pop in the STi axles. Or at least it's that simple in my head... we'll see once I get the seals I ordered and actually try it. The big down side of this is the cost of STi axles... list price is north of $400 *each*. At that price, I'll bet many folks would rather just go without ABS. Like I said, this is definitely the "brute force" means to big brakes. Finally, in order to get the SVX ABS sensors to bolt into the STi knuckles, I'm going to have to fab a riser of sorts. I'm willing to be a set of STi ABS sensors would splice in, but I'm going to try to reuse the SVX's parts first on this one.

4) The brakes - after all, that's the whole point of this, right? Obviously, once you've got STi knuckles and hubs on the car, any brakes that work on the STi will work. Having raced with StopTechs for the last 5 years or so, I'm a huge fan of their brakes. IMO, you get the same quality brakes as the *race* Brembos at the same price as the street Brembos. I ended up grabbing a set of the WRX 328x28mm StopTechs from someone on NASIOC. I expect the brake bias shift to the front won't be so bad if I use the slightly smaller WRX BBK over the STi BBK. The only caveat is to make sure you get the rotors with the dual bolt pattern, or you'll be visiting the machine shop to get the rotors drilled.

5) Wheels - you're going to need some big wheels. Once again, anything that fits the STi. Unfortunately for me, I have an awesome set of 17x9 Enkie RPF1's that I absolutely *love* on the SVX. The problem is that they don't clear the big brakes. In fact that's why they're on my SVX, since I originally bought them for my race car, but ended up putting them on the SVX when I found out they wouldn't clear the StopTechs. So now I'm selling my wheels... however, another option I'm considering is to slap a 15mm spacer in there up front, which should give me the clearance I need, plus it should help handling a touch by taking away a little of the understeer. I figure, with the massive new unit bearings up front, I can probably get away with a 9" wide rim with the equivalent of a +30 offset, as long as I'm not rubbing the fenders. I certainly wouldn't recommend it on the stock bearings.

6) Suspension Geometry - I wonder what the end result will be. I did try to do my due diligence, and took a bunch of photo graphs to compare the angles between the two knuckles. The angle between the hub face and upright is the same between the two. The angle of the ball joints is the same once you switch to a flat mount as diagrammed above. But there is a slight difference in the axis point on the ball-joint because the SVX is inverted vs the STi. The steering arms are the same length and height. I'm pretty convinced the geometry will be nearly identical after the swap... but there is always the off chance of introducing some bumpsteer if the LCA angle and tierod angles are off from each other. Then again, it's probably not any worse than the scrub angle I'm going to get from running the wide tires.

So, in summary, I think this is doable... to the point where I've already bought a stack of parts. Once I get everything assembled, I'll take some pictures and post up all the additional problems I encounter, hopefully with their solutions as well.

Then of course, there's the whole rear brakes to worry about. Perhaps I'll start looking at that after/if I get a 6MT and R180 back there... some STi rear knuckles and 2-pot brakes would be nice.