Slotting strut towers?

I've had my LS swapped RX-7 out to two autocross events now and it's too understeery. My proposed fix is 1) more camber and 2) more tire. Current tire setup is 225 45 17 front 255 40 17 rear Azenis RT615K on 8" and 9" wide wheels, respectively, and I'm pretty well maxed out on what I can fit up front between the spring perches and fenders. Current alignment is as follows:

Car is on Racing Beat springs, KYB shocks, and ST sway bars (though I should note those first two events were with the ST front bar and stock rear.) Also running eccentric bolts in the lower strut mounting holes, which are adjusted about as far as they can go before running the tire into the spring perch. 

Ultimately, I'd love a set of Ground Control coilovers and camber adjusters, but that's just not in the budget right now, so I'm going to slot the upper strut mount holes instead. I'm hoping to get to <-1.5 degrees of camber or better on the front, which should help grip in and of itself, and as a bonus hopefully allow enough clearance for more tire.

I have some questions for those of you who may have tried this in the past. How are you marking your slots, or is eyeballing good enough? Should I think about reinforcing the strut towers afterwards? Will this hold adjustment adequately? Should I go straight in towards the engine, or would I benefit in adding some caster as well by angling back towards the fire wall?

Following this thread for advice.

Your lower eccentric bolts are maxed until the tire hits the strut and you only have .65deg of camber?

I'd probably go back to a stock rear bar or no rear bar at the same time.  And obviously address the small front tire issue when you have the opportunity.

How much room is there between the spring and the inside of the tower?  Besides tire/wheel clearance, that's the other reason coil-overs have narrow springs.

For example, my '06 MCS has Ireland Engineering fixed camber plates with JCW (essentially stock) springs.  The plates give about 1.5 deg of camber.  I've installed a few of these in friends' cars over the years.  On a couple of them, the springs would rub the tower sheet metal.

In reply to ProDarwin :

I've got maybe 1/4" of clearance, at best, and thats with a 6mm spacer. Wheels are 35mm offset, probably should have gone lower. Something will probably have to give between the fender and spring eventually in regards to tire fitment. 

Will definitely go to stock or no rear bar before the next event. The big bar was just going to be a bandaid for the last event, until I had time to mess with the strut towers, but a dead battery kept it at home anyways. 

In reply to Ian F :

Theres room. Not a ton, but enough to gain a worthwhile amount of adjustment. I can probably do better on maximizing the factory tolerances elsewhere too.

Add more caster too if you can.  That'll reduce understeer too.

An old trick that gets some gain.

Loosen suspension parts.

Push , shove.

 tighten

Offset bushings available?

More front spring and or more front bar is always a possibility too. On paper stiffening the front is supposed to induce understeer but that's not always the case. My autocross s2000 had front springs that are roughly 3x stiffer than stock and an adjustable sway bar that's currently 4x stiffer than factory and it behaves beautifully. No push at all and telepathic steering.

I decided just to start messing with it. Stuck a level between each opposing set of bolts and used a protractor to mark a line at a 20 degree angle back towards the fire wall for a little caster gain too. Pulled the drivers side strut off and went to town with the rat tail file and was left with this. Went just shy of 3/16" or so for now.

Another complication I hadn't thought about was the rubber lip on top of the strut mounts, which interfered with the strut tower before I could gain much movement.

I tried grinding the lip flush on a spare I had laying around, to see how well it looked like it would hold up as well as to test fitment. I think this would be a viable solution, but a 1/8" or so spacer might be a better option than hacking good parts up.

That's as far as I got for tonight. Tomorrow I'll throw it all back together and see what camber and caster it yields.

I don't know what you're running for front suspension, but if you're on the stock arms and ball joints, you can unbolt the ball joints and slot the holes on them.

Success! This...

...yielded this!

Gained a bit of tire clearance too.

Definitely pleased! Need to find some 1/8" thick cutting boards or aluminum sheet to make spacers for the strut mounts, since the lip is just kinda shoved over and squished down for now. Now its time to take it all back apart and do the other side too.

The larger rear tires are not helping.  A lot!

225 is enough tire all around on these cars unless drag racing.

Don't worry about that rubber lip.  Mine has been gone for years for the same reason.

Did you know that the strut tops are eccentric?  You rotate the 4 bolt holes to gain camber and castor.

Whiteline makes lower control arm bushings that help with camber and castor as well.

I would also check the rear end.  Minimal toe is desired to get these cars to rotate.  Actually, it looks like you are good there.

Try 245 all the way around if you can.  Also, 17s seem to make the cars handle worse.  When the car is lowered enough to look good on 17s, the control arm is NOT level in the front and it exaggerates the poor geometry of the strut front end.

But damn, do those wheels look good!

Running the 225/255 setup can work, it'll just take different suspension tuning than a square setup (so it loads up the rear tires more and doesn't understeer). 

In reply to wvumtnbkr :

Yea, the staggered setup is definitely the bigger issue here, and something is going to need to be done about that sooner or later. My thinking was to add camber, because slotting strut towers is essentially free aside from my time and camber is definitely needed anyways, then assess how much additional tire clearance that buys me and react accordingly.

I think what I'm leaning towards doing is picking up some 245s to throw on the existing front wheels and hope that they fit. That would get me pretty close to a square setup. Per the specs on Tire Rack's website, a 245 45 17 Azenis looks to be 0.7" wider and 0.6" taller than what's on there now, which, eyeballing things last night, I think could fit with a bit more spacer and, at worst, a slight fender roll. I think two tires is about as much as I can stomach to replace with <1000 miles and not even a proper heat cycle on the current set (only 16 auto x runs so far, all in ~60 degree rainy conditions) and I like the Enkeis too much to ditch them yet  

I did know that the strut mounts are eccentric, although it's funny you mention that as I was questioning the other night whether or not I had the driver's side flipped. Didn't think about it until after it was off, and the passenger side was right, but I remember being able to get at least 1/4 degree more on the passenger side when I did the last alignment - thinking that may have been why. 

If you can get 245s up front, that'll definitely help.  Otherwise, try for more caster.  That'll help plant the front tires better in a turn and put more cornering load onto the rears (at the expense of more issues with unweighting the inside rear in tight turns).