ltborg

Well, I've been a Corvette owner and member of this forum for roughly ten years. Since I'm starting to get more and more questions about my car and autocross, I figured I would just post a build thread. I've gotten so much from this forum, it's about time I worked to give back. The car is always a work in progress, so I will try to keep things updated here. I'll try to briefly cover the details of the AS (A Stock) build as well as the current B-Street setup.

I bought my 2004 Corvette coupe in 2011, sight unseen from a dealer in Missouri who had it on eBay. Since it went to Solo Nationals for the first time in 2011, it has been on two different front sway bars, three brands of tires, four different tire size combinations, three different brands of shocks, two different sets of wheel sizes, and has spent more time on the dynos (engine and shock) than most SP cars.

2011 Solo Nationals
Finishing Position - 1st (driven by Dave Ogburn), 9th (driven by me)
Shocks - Pfadt Sport Shocks on nearly full stiff
Bar - Pfadt C5Z SS bar on full soft
Tires - Hoosier A6 (275/40R17 front, 295/30R18 rear)
Wheels - GM Magnesiums (17x8.5 front, 18x9.5 rear)
Engine - Corsa titanium exhaust with mufflers, green air filter, NGK plugs, Granatelli wires
Misc - Teamtech Harnesses and BK Harness Bar
Notes - Car was first driven on at the National TNT course on the Wednesday the day before Nationals.

2012 Solo Nationals
Finishing Position - 1st (driven by me), 10th (driven by Scott Hurley)
Shocks - Koni 3013s at roughly eight sweeps front and five sweeps rear
Bar - Strano 33mm hollow, stiff setting
Tires - Goodyear Eagle RS/AC (275/40R17 front, 275/35R18 rear)
Wheels - GM Magnesiums (17x8.5 front, 18x9.5 rear)
Engine - Corsa titanium exhaust with mufflers, green air filter, Brisk plugs, Granatelli wires

2013 Solo Nationals
Finishing Position - 2nd (driven by me), 3rd (driven by Josh Pu'u)
Shocks - MCS doubles, 11/9 front at 175 psi, 9/10 rear at 175 psi
Bar - Strano 33mm hollow, stiff setting
Tires - Hoosier A6 (295/35R17 front, 315/30R18 rear)
Wheels - GM Magnesiums (17x8.5 front, 18x9.5 rear)
Engine - Corsa titanium exhaust without mufflers, green air filter, Brisk plugs, Granatelli wires

2014 College Station Setup
Finishing Position - 1st (driven by me - 2nd in PAX), 3rd (driven by Jerry Centanni)
Shocks - MCS doubles, 6/7 front at 155 psi, 4/7 rear at 130 psi)
Bar - Strano 33mm hollow, stiff setting
Tires - Hankook R-S3 version 1 (255/35R18 front, 275/35R18 rear)
Wheels - Reproduction C6 18x8.5 front, GM C5 thin spoke 18x9.5 rear
Engine - Corsa titanium exhaust without mufflers, green air filter, Brisk plugs, Granatelli wires

In the 2013 trim, the car weighs 3080 lbs. I run 100 octane and am at peak wheel numbers of 331 HP and 341 ft-lbs. The average torque available from 2500-5500 (the engine range during typical autocrosses) is 329.9 ft-lbs (96.9% of peak). For the record, LGM did say that this car is one of the strongest stock LS1's they have seen (the first dyno session I had with them, they verified it was the stock tune).

The engine is the reason I picked the coupe over the FRC. I am almost as light and have a ton more torque with a little more power. Running with the roof out also helps with power application on corner exit. I have tested roof in versus roof out three times and was 0.3-0.5 seconds faster on a 30 second course each time with the roof out.

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Background

To start with, I think some background is in order. While some people already know this, I still get questioned about it and want to make sure I fully disclose all my info, so here is my background. I have worked as a professional test driver for a tire company for the past six years. I went to Virginia Tech where I earned both my BS and MS in Mechanical Engineering. During that time I was involved with the Formula SAE team, as a member during my undergrad years and as a teacher during graduate school. My master's thesis covered a finite element modeling approach to analyzing the FSAE suspension under a variety of loading conditions and discussed how the various assumptions being made at the time affected the suspension member loads and compliances. I've been autocrossing in some form or another for ten years, always in Corvettes. I say all of this because I always seem to get questions about how I got where I am. Unfortunately I didn't just wake up one day and decide I knew all about cars and could suddenly drive fast.

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B-Street

Since it's 2014 and I am getting a ton of questions about the street tire setup, I'll go into more detail on it. In changing from R-Comps to street tires, I did nothing other than change the damping on the car to run the street tires at the A&M Tour. I was probably overdamped on race tires to begin with, so if you account for that, the changes really weren't all that significant. I chose to run the 18" wheels in the front for a larger selection of tire sizes and to increase the stiffness in the front by decreasing the sidewall height. Unlike on Hoosiers, I was putting blankets on the tires while everyone else was spraying their's down with cold water. Heat isn't always a bad thing.

I actually liked the Hankooks on the car. It was loose, especially on entry, before I made some damping adjustments to finish on the settings listed in the 2014 specs above. It's still loose, as you can see in the videos below, but it's definitely drivable and responsive. The car is certainly not as easy to drive as it was on the Goodyear or Hoosier R-Comps, but it seems to be rotating very well. While it obviously doesn't have the grip it use to, it turns very well and there is no waiting on the front, which suits my driving style. I was pleasantly surprised by the power-on capabilities of the street tires. All this said, I have not tested any different street tires on this car and there may or may not be gains to be had from changing brands/sizes/etc. As an unsponsored amateur racer, the Hankook contingency definitely played a factor in my decision to run them.

This was my first attempt at setting up the car for street tires, so there is definitely some work to do, but it is pretty close as it sits. My alignment settings (for all years) are basically an average of what you see on this forum. I'm at about -2.2 front camber, -1.4 rear, with as much caster as I could get (I think it was about 6.2 on both sides). I run 1/8" toe out front and 1/8" toe in rear. Pressures on the Hankooks were 31 front, 30 rear, which I know is lower than most people suggestion, but the car has good camber curves and I want to maximize mechanical grip, even if it comes at the expense of response and feel. Ride height is about 0.5 turns up from the bottom in the front, and probably around 5 turns up from the lowest in the rear. I set the rear by roughing in the rake, then adjust at the site based on oversteer. If it's sudden and quick, it's probably hitting the bump stops, so I raise the rear ride height slightly to correct this.

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The College Station Tour

I feel that I drove very well at the College Station Tour. I usually don't get the adrenaline shakes unless I actually drive very well. I got them last weekend.

Class Results
PAX Results

While it is just one data point (and my first event on street tires) I was third in PAX on day 1 and first on day 2. I finished second in PAX overall. This was the best PAX finish I have ever had in national level competition.




I posted the Day 1, Run 2 video to show what can happen when you overdrive the car. I was trying VERY hard on this run and driving more like I wanted to. Clearly, it was too much for the setup and I had to back it down on Run 3. The car was much better after the adjustments going into Day 2 and overall, I think the car is pretty good. I don't think there is a ton more pace to be gained from any of the tuning I have yet to do. That said, I still want to try some things with the tires (like 285s in the rear, even though it hurts the gearing), and can probably make it more drivable with some additional damper tuning. As it sits thoughts, it was a pretty fun drive.

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Hopefully this post (and future ones in this thread) will answer most of the questions people have. I'll do my best to keep this thread updated as I move forward this season. My hope is that putting this information out there will encourage people to bring their cars out to events in the SSR, AS, and BS classes. If anyone has anything they want to ask, please feel free to do so. I'm always happy to share.

-Lane

JRL

Great write up/information/driving . Thanks for sharing

The grip of today's street tires is impressive.


------
John

talon95

Yea, thanks for all the info. Your videos remind me of when I was running those tires a couple of years ago though. Lots of corrections with the wheel. I could go pretty fast with them, but it was more of a challenge to keep the car pointed in the right direction. Not just when trying to put power down, but on entry too. The car was just always a little too twitchy on them and I ended up running quite a bit higher shock settings in the front relative to the rear compared to my A6 setup (same as you I believe).

Are you going to try to take more of that loseness out of the car?? I never was sure if I just needed to drive to it, or maybe try an even bigger front bar or shocks with a bigger adjustement range (I just have Koni singles). I had used most of my shock adjustment already.

gunluvS14

wow great thread, thanks for all the info!

ltborg

I hate waiting on the car to turn. I'd rather maintenance some entry oversteer to get the car rotated sooner and back on the power. The overall balance is close enough, I don't want to bind the car up more with a stiffer front bar. I'll probably continue to use the damping to try and make the entry oversteer more progressive. I don't really mind entry oversteer, I just don't want to be getting large, quick slides. The Hankooks felt progressive enough that I think just some damping should take care of things. Ideally though, I would find a way to increase the rear capacity and get a little more pace out of the car. I still need to try pressure adjustments, but I am probably near the max grip levels I'm going to get.

brenb

For Sale 89 z51/6speed




This is going to be a rough year.

ltborg

Judging by this photo from Day 1, I could reduce the dive to keep some weight on the rears and kill some of the entry oversteer. I didn't think it would dive that badly on street tires.

ltborg

But you've got better gearing and more front wheel. The spec curb weight on the car is something over 3200 lbs. A well driven C4 will probably be closer than you think.

brenb

The weight difference is really shocking. I'm hoping that one of us had bum scales. :eeps:

For reference, my car weighed 3240 lbs. in impound at nationals in ~2004.

Wow, yeah it looks like it's sitting firmly on the front air dam.

ltborg

I used calibrated scales, but they were meant for larger weights so only read in 10 lbs increments. It could be that it is nearly 5 lbs per corner additional, putting me at 3100 even. Keep in mind, that was with race levels on all fluids (gas, washer fluid, etc), on race wheels and tires (both of which are much lighter than stock), and without the roof.

briannutter1

Nice vids! Any thoughts on setting the rear bar?

ltborg

You can only change one bar in Street. I run an aftermarket front bar so the rear bar is stock.

froggy47

Nice post, thanks.

For the MCS settings, I assume the higher numbers are compression & lower rebound?

To understand the settings better what are the full & sweeps on the shock from full soft to full hard comp/rebound?

I am tuning some JRI da's now and trying to understand (learn) the process.



Are you doing San Diego tour/pro?

ltborg

No SD Tour for me, that's too long a haul to be in the budget.

You are correct on the comp/rebound info. MCS uses 0 as the lowest setting and then runs up from there. The compression has 15 settings (so 0-14) and the rebound has 16 (0-15). That means I'm on the low side of middle for the compression and about middle for rebound. However, these are most likely going to change...

froggy47

Thanks, that helps. My rebound range is 14 sweeps and compression is 30 sweeps.



I lost the back to a small power on (full) oversteer last Sunday.

I think I nedd a little less rear compression and (maybe ) a little less rebound. I know there is more to the issue (rear toe and tire pressure) whick I am addressing, but is that the right way to go on shocks?

West lot is old low grip bumpy asphalt with on/off camber elevation chgs depending on the course.

ltborg

I'm no damping expert, but I think it depends on what the car is doing overall. Assuming the steady state balance is decent (ex. balance on a skid pad), then you can start getting into the dampers. If the car is too tight or loose steady state, there's no point in messing with damping until that is fixed.

As for a power on oversteer issue, decreasing rear compression is one way to do that. I would make sure you aren't running too low or too high of a tire pressure. Too low and the tire will roll onto the sidewall rubber, which would cause snap oversteer, too high and there is just no grip available. Assuming inflations, rear camber, and rear toe are reasonable, I would try dropping rear compression as you suggested.

gunluvS14

Hey Lane, do you mind post picture of your harness and harness bar layout? I assume you still have factory seat in your car, I'm curious what I can do without cutting holes through my stock seat.

ltborg

I don't have a harness or bar in the car. It's not legal with the roof out and I'd rather have the extra pace. I just use the ratcheting feature on the stock belt. That's part of the reason I lean so much in my videos. That's something I'm trying to work on eliminating.

I'm pretty tall and most of it is in the torso, so when I did run a harness, I just ran it around the seat. The BK bar captures the shoulder belts to prevent them from sliding around and that seemed to help. The Teamtech harness also had a chest strap to help keep the shoulder belts in place.

froggy47

Thanks, I think steady state (skidpad) is good, but I don't really have access to one. Since I put the new shocks on I did up the tire pressure 1 psi all around, but I am going to try going back down 1 psi in the rear.

ltborg

Assuming you don't go too low and roll the tire onto the sidewall rubber, that will help a little. I'm usually between 1 and 3 psi higher front than rear, but it definitely depends on tire brand and size.