Camera's 818C

Nice Vid on your tires and track time. I put this Walmart yoga mat 10,000 street miles back and it has held up for 4 years now, Thin and makes the wells quiet, pleased with durability and light weight too:

Wal Mart Brand: “Athletic Works” 68” L x 24 “ W x 3mm Black CL3792B

Searching on line 4 years since then... I didn't get a hit on the part number but search Walmart for this - it sure looks like the same stuff in a gray color. Image of material matches mine too:

Athletic Works PVC Yoga Mat, 3mm, Dark Gray, 68inx24in

Mounted it with this adhesive, which I used on my whole build. Never have had any problem with this stuff - top notch:

https://www.dltcorporation.com/produ...-2065c-1qt.htm

But I read good about this easier to get too:

https://www.homedepot.com/p/DAP-Weld...0272/100125525

Nice recap video.

I had 2 set of RT660's (just switched to V730's). At the track, I was looking for 27 psi hot. So, 37/42 seems really high, especially on our light cars. There's always the disclaimer that tracks and autocrosses are hugely different.

If you're getting uneven wear on the outside edges, at least on the rears, it's super easy to tune for it by dialing in more negative camber. I increase rear camber at the track by 2 full turns of the linkage adjustment, then put it back for the drive home. Fronts are more difficult to adjust camber, so I don't mess with it. But, I'm usually not trying to improve front grip or tire wear, so it's not an issue.

I'll be doing my first autocross next weekend at Crows Landing, CA.

Thanks for the tips and links Art. I'm sold on that mat being a good cover, but I've been wondering if I want to cover the rivets in the wheel wells. Might make it harder to remove the wheel wells if I need to make a repair.

Dave, that's why I thought it was worth mentioning my tire pressures. They seem high but anything less was scrubbing my sidewalls. I started at 36psi all around thinking I would slowly lower pressures, but that's not how it played out. I'm glad to hear you mention camber because I think that's playing a bigger role now. I only have -0.5 degree on the rears which worked great on my old summer tires that had less grip. I think the new RT660's have so much more lateral grip that now my car is actually leaning and my tires are flexing/rolling. I agree I could benefit from more camber now, I'll add some to the rear like you suggested. My car currently handles close to neutral, but with slight oversteer. So adding a little grip in the rear should only help.

Let me know how your autocross goes. I'm curious to see what you think.

As long as your rivets are along the perimeter, just cover a little less width so you can still see them. 90% less noise probably. I used screws for all that and left the edge of the mat covering them but not glued - the mat could flap but has not worn away so must not be doing much in the wind.

Good idea Art

Quote:

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Originally Posted by mcamera

Thanks for the tips and links Art. I'm sold on that mat being a good cover, but I've been wondering if I want to cover the rivets in the wheel wells. Might make it harder to remove the wheel wells if I need to make a repair.

Dave, that's why I thought it was worth mentioning my tire pressures. They seem high but anything less was scrubbing my sidewalls. I started at 36psi all around thinking I would slowly lower pressures, but that's not how it played out. I'm glad to hear you mention camber because I think that's playing a bigger role now. I only have -0.5 degree on the rears which worked great on my old summer tires that had less grip. I think the new RT660's have so much more lateral grip that now my car is actually leaning and my tires are flexing/rolling. I agree I could benefit from more camber now, I'll add some to the rear like you suggested. My car currently handles close to neutral, but with slight oversteer. So adding a little grip in the rear should only help.

Let me know how your autocross goes. I'm curious to see what you think.

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I did my first autocross today. The participants were all in which is awesome! I met a National Champion and a guy that's been auto crossing since the 70's. I respect the skill needed to be smooth and fast. Some amazing cars and huge tow rigs. Nice social aspect to it. I worked a corner with a nice guy and fellow first timer that just got his 4C. A great way to get to push the limits of almost any car with very low risk and very low bearers to entry (seems all you really need is a car and helmet). But, to be honest and with respect, not my thing. I did 10 - 37 second runs on a practice course and 5 - 63 second competition runs and never got out of second gear (only 4 of us newbies on the practice course - everyone else did just the 5 competition runs). Notwithstanding it just being fun to be at a car event, it's just hard to wrap my head around spending the better part of a day for 11 minutes of track time (most participants only got 5 minutes).

I'm happy there are options for everyone to find their car thing be it wheel to wheel race series, drag racing, drifting, time trials, autocross, HPDE, shows, rallies, rock crawling, whatever. I'm glad I finally got the opportunity to try an autocross, but I'll be sticking to HPDE track days with my 818 and 24 Hours of Lemons racing.

BTW, I also have about 0.5 degrees of rear negative camber for street driving. 1.5 turns of more negative camber on the rear camber adjustment and about 20psi front and 24psi rears (hot) gave me the best tire wear read on my V730 tires.

I can see how autocross would feel like a poor compromise for a full track but there's a huge convenience to it. I have 12 events less than 10 minutes from my house. I don't need to have a truck and trailer to get my car to a track 2 hours away. I just drive to the event, pay $45, race, and drive home. I agree it's not a lot of seat time but it's a different kind of challenge. Like qualifying vs racing. It also allows me to try new mods/setup changes without ruining a $300 track day. I would pay double if I could just show up for my heat and leave though because like you mentioned it takes up most of the day for very little racing.

I looked at the inside tread of my rear tires and 1" of it still looks brand new. It's never touched the pavement, even after an aggressive track day. So I turned my camber links 1 full turn which I measured as an extra -1deg of camber. So -1.5deg total now on the rear. A quick drive on the street felt much sharper and it was harder to break the tires loose, but I'll confirm this week at autocross.

Attachment 200251 Attachment 200252

They set up a long competition course and had a smaller practice course that was bigger than the courses I see set up on my track days complete with timing which cost an extra $20 (on top of $70) to have access to it. I'm thinking I could not show up for the competition and get 50+ laps in on the practice course. Wish I thought of that on Sunday. That would be worth the hour's drive to get there.

That would be more worth it. Give you time to learn the course and try to squeeze every last tenth out of your time!

I think if you go to an Autocross with drive time in your head as a metric, yeah it's going to be a huge disappointment. Think of it more like a social event, like a cars and coffee but you get to have some friendly competition at the same time.

There's also something to be said of getting out there and putting down a quick time in 4 or 5 runs on a course you've never seen before, drives you to better understand how your car handles instead of having memorized braking zones and lines on known tracks.

Also the cost. It's like 45 bucks where I live, on 2 day events with a class or Test/Tune on Saturday it's $80. If you live close it's really low barrier to drive there in you car, compete with good confidence that your car will be drivable to get home, all on the same tank of gas.

https://youtu.be/e59jho6G4zY

I keep looking for bottlenecks on my car to make it faster at the track and this one seems like such a basic oversight. I've been watching the outside shoulder of my tires to dial in pressures and maximize my contact patch, but I didn't realize how much of the inside shoulder had ZERO contact with the ground.

It's hard to see at the track and I figured -0.5 degrees of camber on my rear wheels would be.... 0.5 degree past horizontal... favoring the inside of the tire slightly. I never thought I'd be adding a bunch of camber to improve straight line traction!

Obviously if I add too much camber I'll start lifting the outside shoulder and could reduce my contact patch in a straight line. However, what I'm seeing at the track is that I'm still overworking the outside shoulder vs the inside shoulder. Just have to find the sweet spot.

Fighting the same battle over here but embarrassing myself in EM instead of XB ��

I added a downright irresponsible amount of rear toe in and it made the car SO much more stable. If you're spinning look at that.

Quote:

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Originally Posted by lpmagruder

I think if you go to an Autocross with drive time in your head as a metric, yeah it's going to be a huge disappointment. Think of it more like a social event, like a cars and coffee but you get to have some friendly competition at the same time.

There's also something to be said of getting out there and putting down a quick time in 4 or 5 runs on a course you've never seen before, drives you to better understand how your car handles instead of having memorized braking zones and lines on known tracks.

Also the cost. It's like 45 bucks where I live, on 2 day events with a class or Test/Tune on Saturday it's $80. If you live close it's really low barrier to drive there in you car, compete with good confidence that your car will be drivable to get home, all on the same tank of gas.

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The idea that pretty much anyone in any car can have fun at an autocross at a low cost and with minimal risk to self and car is great! There are most defiantly differences between auto cross and HPDE. Pros and cons that everyone will weigh differently including drive time and cost being big ones. Seems autocross is burning $10 bills and HPDE burns $100 bills (and that's if nothing blows up). So yep, there is that. But, there are many similarities too including the social aspect of it and "understanding how your car handles" by pushing it and yourself to the limit. Ultimately, both are fun - pick your poison (or do both)! Golf... that's something I just don't get.

Haha golf is paying $50 for a 4hr nature walk, where you yell and curse the whole time. Unfortunately I know this all to well.

Quote:

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Originally Posted by mcamera

Haha golf is paying $50 for a 4hr nature walk, where you yell and curse the whole time. Unfortunately I know this all to well.

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Golf: Whack.... "****!"

Car: "****!"... Whack

Last Saturday my son's buddies organized his bachelor party and I was invited. The first event was indoor electric go karts and it was vicious.

https://www.k1speed.com/

Steering is exceedingly heavy. You can't spin the wheels, and with rear brakes only, there is no understeer. Too much brake will cause oversteer. With equal power passing requires a strong offence. Sliding can be a defensive maneuver at the cost of lap time. Speaking of cost: about $26 for a ten lap session. I was arm/hand sore the next day.
It resembles a very tight autocross but either someone is humiliating you in real time or someone is all over your butt.
BTW the next sporting event was axe throwing. I do not endorse that as entertainment YMMV.
jim

Got a check engine light yesterday during my last autocross run. I think one of my TGV's is stuck. I put this off for 4 years but it might be time to look at options.

Attachment 202102

https://youtu.be/g5IctlXyeu0

Wow, that's a lot of rear pressure!

I'm using a different tire but I'm seeing pretty good usage of the entire tire at autocross with 25 psi and just a degree of camber. I wonder what's so different between our cars, it doesn't seem like tire selection would make that drastic of a difference.

I'm using 235/40/17 Zeknova RS606 (go on, get your laughs out now, I'll get better tires next time) in the rear.

I'm curious what size and brand tires you have.

I'm really don't know what pressures I should be running on my low sidewall tires. 215/35R18 Pilot Sport 4S on Enkei 8" and 255/35R18 PS 4S on Enkei 9.5". Haven't made it to autocross or HPDE yet - just canyon roads and I am not an experienced high performance driver. This is my first sports car - and it's a monster! I've run 32lbs and as low as 24lbs and I haven't really been able to see any difference, but then it's hard to corner near limits when I don't know what those are. With 100' drop offs and canyon walls, I'm nervous to push it. Not the same thing as hitting cones! I've squeaked the outside front a few times. Felt like it was kind of skipping a little but not really sliding. I only broke the rear loose once cornering, but that was into a surprise tight downhill switchback and braking pretty hard to keep from hitting the mountain. I didn't have any time or room to countersteer, just had to get it stopped and take a breath. Easy enough to break the back end loose accelerating from a turn at a stoplight tho. ;-)

Ed

Quote:

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Originally Posted by lpmagruder

Wow, that's a lot of rear pressure!

I'm using a different tire but I'm seeing pretty good usage of the entire tire at autocross with 25 psi and just a degree of camber. I wonder what's so different between our cars, it doesn't seem like tire selection would make that drastic of a difference.

I'm using 235/40/17 Zeknova RS606 (go on, get your laughs out now, I'll get better tires next time) in the rear.

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Lol I've never head of those but after looking they should be pretty grippy with a 140 tread wear rating. I'm using Falken Azenis RT660 tires. Another guy in my class with an MR2 (mid engine, similar weight) said he was at 36psi on his old RT660's. Even less pressure on his new Bridgestone RE-71's. My rear tires are 255/35/18 which I think are lower profile than his tires.

Mine are also a lot wider and slightly lower profile than your 235's. More grip = more leaning = able to use more camber. 1 degree of camber was better for my old 500TW tires that didn't grip nearly as much (so my car didn't lean as hard). Maybe the sidewall stiffness is that big of a difference between your Zeknova's and my Falkens? The track surface might also be grippier asphalt vs concrete.

The first time I ran these Falkens I started at 36psi and the tire wore all the way down below the indicator on my outer sidewall. No way I can lower my pressure right now.

Quote:

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Originally Posted by Bicyclops

I'm curious what size and brand tires you have.

I'm really don't know what pressures I should be running on my low sidewall tires. 215/35R18 Pilot Sport 4S on Enkei 8" and 255/35R18 PS 4S on Enkei 9.5". Haven't made it to autocross or HPDE yet - just canyon roads and I am not an experienced high performance driver. This is my first sports car - and it's a monster! I've run 32lbs and as low as 24lbs and I haven't really been able to see any difference, but then it's hard to corner near limits when I don't know what those are. With 100' drop offs and canyon walls, I'm nervous to push it. Not the same thing as hitting cones! I've squeaked the outside front a few times. Felt like it was kind of skipping a little but not really sliding. I only broke the rear loose once cornering, but that was into a surprise tight downhill switchback and braking pretty hard to keep from hitting the mountain. I didn't have any time or room to countersteer, just had to get it stopped and take a breath. Easy enough to break the back end loose accelerating from a turn at a stoplight tho. ;-)

Ed

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Running on the street will be different than at a track and you're smart to not push it 100%! I wouldn't recommend super low pressures on the street. I haven't run your tire before but 24psi sounds way too low. You might crack a rim on a pothole or rough bridge crossing (ask me how I know lol). You generally want higher pressures ~35-40psi to give your tire strength for rough roads and to protect your rims. You will sacrifice a little tire contact/grip though.

On the track you can push the car a lot harder and lower pressures to maximize contact though. I use chalk on the shoulder of the tire to see how much of the tire I'm using during my autocross runs. It's a cheap/easy way to start optimizing your tire contact at the track. You can see in my video there's a triangle on the sidewall of my tire. You don't want your tire to wear below the tip of that triangle or you'll start using the sidewall of the tire which isn't designed to touch the ground. It also means your tire is too soft (underinflated) and flexing a lot!

What is your rear toe-in setting? Could it be that toe-in is fighting you somehow?

For tire pressure at track days (30 minutes runs with 60 minute rest between runs. We start at 20psi all around. then adjust between each segment to get even tire temps across each tire. Never more than a pound or two.
Below is a chart I kept of alignments. Ours is the last column.


Attachment 202422

Quote:

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Originally Posted by Bob_n_Cincy

For tire pressure at track days (30 minutes runs with 60 minute rest between runs. We start at 20psi all around. then adjust between each segment to get even tire temps across each tire. Never more than a pound or two.

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Pretty similar for me, tho I've only done a few track days. I've followed a few of these racing guys and used modest camber and tire pressure. I get it that autocross is very different with cold traction being so important.
I picked up an IR gun and measured pretty consistent temps across the width of the tires; a little higher on the left side on a predominately right turn track.
Anybody using data like that?

I was at 0.2 degrees rear toe in before I increased my camber from -0.5 to -2.5 degrees.

At autocross this weekend I lowered my pressures even though last time I tried it started to wear down below my sidewall indicator. It immediately wore down into the indicator, but my time was faster. So I dropped another 2 psi. It didn't wear much further but my time was faster again. So I dropped 2 psi again. The wear had plateaued but my time was even faster.

I started the day at 37 front / 40 rear. I ended the day at 33 front / 34 rear and placing in the top 20 for the first time.

The tires felt squishy at times and the rear hopped several times around a long sweeper, but faster times are hard to argue with.

Attachment 202539 Attachment 202540

https://youtu.be/S2j5L-SZ2q4

https://youtu.be/8fN_ohGMEqg

Years ago I did exhaust development on my motorcycle in an attempt to reduce backpressure. Sound was not a priority. These days there are more baffling configurations to evaluate.
Anyway I had a non-destructive method of measuring exhaust options.
With a flow bench as inspiration, I used my shop vac to draw air through the mufflers or blow through them
A simple monometer between the shop vac and muffler measured static pressure. More drop = more restriction. This method can be used for intake systems as well.
I went on to measure dynamic pressure for air speed with a pitot to develop air boxes and ram-air at 150MPH.
Not as interesting but entertaining was measuring air flow in lawn mower decks.
Water and jet pumps are similar just alternative equations and math.
jim

It doesn't surprise me that you are having trouble with boost control and detonation uncatted. Everything I have read says don't unrestrict your exhaust or even your induction without a tune. Even just shortening the exhaust from the WRX long pipe setup has to be doing something. My 02 donor had a little downturn right behind it's downpipe and a pretty bad hitch in it's giggyup. Might have benifited from a tune, but I just drove it for a couple of months and cut it into pieces.

Ah, exhaust noise vs power. I go carted my car on the 818 adapter and stock catted downpipe. I had lowered the transmission mount for better lubrication and I didn't like the idea of where I would have to cut the bumper so I fabricated my own exhaust. I was given an aftermarket downpipe with a nice bellmouth and 3" piping by somebody who wasn't going to use it. I cut and modified it to run a pipe straight out the back of the car centered vertically in the lower cutout of the bumper and off to the right side. Talk about loud! I can't speak to horsepower on that version as I was running on a base tune which called for zero boost. I only got about the 12psi that the wastegate spring provided. I bought a Magnaflow straight through muffler with a 7" long body - not a lot of room back there and welded that in exiting in the same location. Still pretty damned loud and now had an annoying drone especially when letting off in the 4-5k RPM range. I bought a Car Chemistry 3 disc insert and stuffed it into the tailpipe. Much quieter and the drone was pretty much gone. Still sounded healthy but I didn't need earplugs anymore. Seriously - it made my ears ring more than my usual tinnitus. Still on the basemap tune.

I took it to my tuner and he said that it would cost a bunch of horsepower. The way the CC inserts are supposed to go in puts the can opener cuts towards the airflow which, he said, would effectively reduce the diameter of the pipe to that of the inner tube of the insert because of turbulence. I decided to turn it around to reduce that scooping effect. In the process of removing it using a slide hammer I beat the **** out of the inner baffle and tube. I then cut it off making it a 2 disc insert and put it back in backwards, reasoning that it might not be quite as restrictive that way.

Back for my tuning appointment, he was unable to fit his O2 probe into the baffle and removed it for the tune. I don't know how he has any hearing left after running it in his closed dyno booth with no ear protection, but I guess that's his problem. Anyway, he got 310 whp out if it on 91 octane pump gas and 386 on E85. He then stuck the baffle back in and ran it, probably just so he could prove to me how right he was about the power loss. It cost 24 hp.

Exhaust restriction is a thing. When you think about it, the guys who claim no power loss from these baffles (with V8s) and even that it has more low end torque are not mounting them behind turbos where every bit of restriction really shows up. Did I pull the baffle out when I got home? Nope. First, I like that I don't cringe and hurt from the exhaust note. Second, I like the way it sounds - it makes me feel like I'm in a British sports car on a B road. Third, 362whp is absolutely nuts in this light car. 290hp would be way plenty and that's probably what it will do on pump gas. It isn't going to overboost with the baffle in and it's already tuned for when I pull it out for HPDE in the fall. I am running it on the ethanol. It's cheaper at the pump and oh so much fun!

Ed

I had a similar but different experience with a stock setup with just the catted downpipe and no muffler. After a track day last month I found the cat guts completely gone. Since it degraded and left the chat over some period, I didn't notice it being louder until unloading and backing in the garage. And definitely noticed the whistling.
Going easy around town no one seems to notice. Concerned about local track limits, we measure 94db at 10 yards under full boost and acceleration.
I haven't noticed any power changes, but as noted, I'm full stock ('06 STI), no tune.
For now, it's enough power; I'm still getting a handle on the thing at the track. All the years of traction control meant it was disconcerting to feel the rear start to break loose in a fast corner at top of 4th. (Time for aero I think)
A bit later I want to go your route and add boost, so I'll be watching how this evolves.

Jim, I used to do similar tests when I designed airboxes for the big 3 (Chrysler, Chevy, Ford). The air filter was the single biggest restriction, which is partially why filters have such a large area compared to the cross sectional area of the ducts. Didn't do any ram air work like you though. That could make things more interesting. No surprise that the cat is a restriction since it's just a thick filter for the exhaust. The honeycomb is so dense you can barely see through it.

Ed, yeah I expected some problems but wanted to test the sound before committing to a tune with a catless pipe. Glad I checked, the car was too boomy at low rpms and too loud at WOT for me. With just the cat on my car the sound is louder than a typical car but reasonable for a sports car. Still get some turbo whistling too which I like. I agree with you, some car guys will always say louder is better but there's a point where it makes driving more annoying than fun. Your setup sounds potent! You have plenty of power on tap even with your baffle in. I was trying to maximize my stock setup (235whp) / improve boost response for autocross, but this was not the way to do it for me. Now my thinking moves to a mild turbo upgrade with an electronic boost solenoid. Again, trying to maximize response and mid range power for autocross.

Driveslikejehu, that was one of my concerns too. I think I would have blown past sound. A stock STi engine still has plenty of power in these cars. I took a similar path in leaving my engine stock for 2 years (with just a tune). It was nice to learn how to drive the car first. I'm just now looking for more power because I think my driving is finally good enough to benefit from it. Tuning the stock engine was a huge improvement by itself. I didn't make much bigger peak numbers (+15whp), but my low and mid range torque grew a LOT (+60wtq). Made the car more responsive and I have way more useable power. Dyno pic below.

Attachment 202806

Looks to me like you would benefit from a flatter torque curve. It's probably a function of your uneven boost control. I was told that I'm doing ~28psi on ethanol, much less I imagine on pump gas. I haven't been able to look at my boost gauge when I have my foot in it - too busy trying not to die. ;-)

Ed
Attachment 202809

The blue curves at top are 75% ethanol. As you can see, my torque is pretty much there from about 3500 and falls off slowly with either fuel. I was told that most of the benefits are available above ~40% and that it'll run fine up to 100%. I'm currently at 80%. Incidentally, he also said that first starts in cold weather might take some cranking which in summertime SoCal isn't a thing. We'll have to see how it shakes out come winter.

Attachment 203394

This weekend I had another great outing at autocross. I finished 2nd in my class and 17th out of 92 cars overall. I beat the class leader but I'll likely end up in 3rd for the year. Too little too late, but not bad for a pretty basic 818 build (tuned stock engine, upgraded front LCA's, and 200TW tires (215/255). A lot of my improvement has come from fine tuning my setup and learning to drive better.

As the autocross season winds down I'm starting to plan my winter upgrades. The most impactful but expensive upgrade I'm looking at is wider wheels/tires. Which requires new rear trailing arms but I can't find any info if aftermarket trailing arms give more tire clearance. I know the VCP trailing arms allowed up to 9.5" wheels but it looks like VCP has closed. The Cusco and Mooresport (MSI) arms don't mention anything about allowing wider wheels. Does anybody know if these (or any other arms) allow wider wheels?

https://www.flatironstuning.com/666-474-t
https://shop.mooresport.com/shop/msi...orrection-2576

I'm also looking at replacing the 17yr old rubber bushings on the rear trailing arms and lateral links. As I've improved the grip on my car, it sometimes hops around fast sweeping turns and exiting sharp corners. I don't think the old/squishy bushings are helping this. I like the stiffer STI Group N bushings instead of polyurethane mounts since they're maintenance free, won't squeak, and still offer a little compliance and isolation from NVH.

My TGV's are also throwing engine codes every couple weeks so I'll be replacing those with deletes this winter. Since the car will already need to be retuned, I'm also going to do an electronic boost control solenoid to improve my power band. Still debating on a mild turbo upgrade (VF48 HF or TD05-20G) while I'm getting tuned. I would want it to remain quick spooling for autocross, but hopefully power wouldn't die off at 4500rpm. The stock turbo has actually been great for autocross. Great response and low to mid power.

mcam,
My previously unfinished 2014 kit has 255/35-18 Yokos on FFR? 18X8.5 wheels.
It came with FI/Cusco Trailing Arms and Lateral Arms. (4)
As I bought it there was less than 0.25 sidewall to TA clearance. I installed 1.5in wheel spacers for 1.625 clearance.

I am going to Acura J-V6 and control arm suspension so this stuff is available. I prefer selling as a package.
jim

Attachment 203410

Attachment 203411

I used something like the Godspeed arms and some adjustable lateral arms. Search "02 wrx adjustable trailing arms" or similar and you'll get a bunch of hits. I had to cheat all the spacers to the outside to move the arms inboard and get as much wheel clearance as possible. Had to cheat the spacers on the arm that goes up to the firewall too. I used 12mm wheel spacers with 9.5" Enkei wheels w/45mm offset. I wound up bending the arms a little bit more with a Harbor Fright hydraulic pipe bender to get just a little more clearance. I have 255/35 R18 Pilot sport 4S. The closest approach to the trailing arm is right at the rim. I think I could get maybe even 275s on there, but I'll need to wear these ones out first and so far, it doesn't seem like I need more tire.

From the pix, it looks like the Cusco ones are roomier than what I started with, but pricier too.

Ed

The VCP arms it turns out are simply the Godspeed trailing arms with a relief welded into them. I bought the Godspeed arms first and needed more space so then I ordered the VCP arms. When I received them I was able to compare the two and see the VCP arms were the same, but modified to allow for more space. You could do the same cut and weld in a relief or have someone do it for you. I am fitting 265s on a 9.5” wheel with 10mm spacers.

Attachment 203519

Thanks for the info. I currently have 255/35/18 tires in the rear. 8.5" wheels with a 45 offset, and use a 5mm spacer to clear the stock trailing arm. I've had no issues with clearance to the fenders either. Good to know the vcp arms are modified Godspeed arms. Wasn't sure if those cheap arms would be reliable but lots of people have run the VCP arms. Might need to cheat the spacers like you mentioned with any of the arms if I want to go to 275 or 285 tires. Going to be tight!

https://youtu.be/83btfOvF250

I noticed something this weekend when checking my tire clearances. My rear tires (255/35-18) are already rubbing my wheel liner. My driver side ride height is much lower than my passenger side as a result of corner balancing so it's rubbing worse. I also think I've been hitting the bump stop on the driver side with as much rubbing as I'm seeing. That might be part of the reason I've felt the car hopping around high speed sweepers. My driver side shock is getting maxed out (instantly going super stiff) while the passenger side shock has a larger working range. Putting the rear wheels in very different, uneven conditions.

DRIVER
4.1" ride height
2" tire to liner clearance
1.75" shock travel before it hits the bump stop
Attachment 203883

PASSENGER
4.75" ride height
3" tire to liner clearance
2.5" shock travel before it hits the bump stop
Attachment 203884

My thoughts:
1) I could raise the car to give more clearance. I won't do this because it'll hurt performance, look worse, and my rear passenger shock is already maxed out.

2) I could add weight to the rear passenger corner and rebalance the car. This might allow me to reduce the height on the passenger side, which could level the body more and put the rear wheels in a more similar condition to each other. I'm about 30lbs underweight for my class so I'm not against adding weight, but this will likely just make the passenger side rub more like the driver side.

3) I need stiffer springs. This will reduce suspension travel, stop me from hitting the bump stop, reduce rubbing, and keep my tires closer to their nominal alignment where they have the most consistent contact patch. I think this is necessary to not only fix my current condition, but to allow for more improvements at autocross. It wouldn't be smart to put wider tires on the back right now which would take up more room and add more grip (more stress on the suspension) until I fix this issue first. Looks like the ride is going to get a little stiffer this winter.

If you are using the supplied ffr Koni shocks, they are only vaguely adjustable and difficult to adjust damping. May I suggest the QA-1 shocks? They are externally adjustable, so no need to remove and disassemble in order to change damping and they offer a double adjustable for both compression and rebound. A bit pricey but for what you are doing, I think a worthwhile consideration.