Good times. It was a long drive from Asheville but it was the last time it'll have stock seats and stock front spring rates so we wanted to enjoy a nice roadtrip in it. If you're not using Waze on roadtrips you're doing it wrong, by the way. You'll also notice the Hankook RS3 tread pattern in the 2nd shot, I ordered those the week before the 24 hr and got them mounted up since the Rivals from last year were toast. Good thing too since it rained most of the drive down there. These will be the tires I run at least until July, then I will either get more Hankooks for Nats or try a different tire if there is a new hot option- lots of interesting things in the pipeline right now. These are the generally accepted best option for C5s at this point in time so it seemed like a safe bet for me. There was also the 285/30-18 Dunlop Z2 SS, but I wanted more sidewall height to be able to put down power better. I was considering the Z2's on the front wheels and RS-3s on the rear but then you lose the chance for Hankook contingency. It turned out that I got probably the last or 2nd to last set of these in the country, since Tire Rack was sold out of them only a few days after I received mine. Very glad I didn't wait to buy them since the next batch doesn't come in until April 30th. Hankook is always spotty on tire availability so if you know you want some and they are available now, buy them now!
Moving on, I also installed an MGW shifter and billet lower box before Daytona. Wow, what a nice upgrade. Before, the trans never really wanted to go into 1st or reverse and the throws were long and somewhat vague. Now the gear engagement is very positive and mechanical. Takes more effort but it is a rewarding experience to shift. It's like shaking hands with Optimus Prime if you can imagine that.
Finished off the beautiful MGW shifter with a machined Delrin shift knob in the C5.R style, big improvement over the awkward stock shift knob.
Once we got back it was time for the serious work to begin. Put the front up on jack stands and removed all 4 front control arms to send to Van Steel for Delrin bushings. They press out the old bushings, clean the arms, and then jig them up and ream out the bushing bores to receive precisely machined Delrin pieces. Comparable to spherical bearings in terms of stiffness, but Delrin is not metallic so it's allowed in the rules for ST classes. Why not polyurethane? Poly bushings, while stiffer than the stock rubber ones, still allow the bushings to deflect some amount which causes unwanted toe and camber changes throughout a corner. They also need to be greased fairly often, whereas Delrin lasts several years (at least) without requiring any service at all. Some cars need to run poly or rubber bushings at some joints to allow for multi-axis rotation but the Corvette doesn't need it. You can't adjust caster easily with Delrin bushings but the stock caster is set to 7-8 degrees which is plenty. The Delrin allows you to take advantage of the well-designed suspension geometry while limiting deflection under load for better performance. You can also run less static negative camber since the rubber isn't moving around causing your wheel to go further towards positive camber. Less static negative camber means better braking performance with the front wheels and better acceleration with the rear. Here's the front all taken apart, was surprisingly straightforward to do:
Also with the front control arms off, the leaf spring is completely exposed and easy to swap. I took the opportunity and replaced the stock fiberglass Z51/Z06 526 lb rate leaf with a Hyperco 634 lb spring (20.7% increase). They call it the "HPT" spring. You can also tell it's higher rate than the Z06 spring since it has so much less arch:
Another cool thing are the ride height adjusters on the Hyperco spring- Delrin pads (can you tell I like Delrin) that have a lower stack height than the rubber pads on the GM springs, allowing for a lower ride height (if you can run that low and not bottom out your shocks or go into a bad bump steer range).
I should probably also talk about why I chose this spring compared to some other ones on the market like VB&P. First, VB&P rates their springs differently from GM so you can't really tell what your rate increase is. Also, they don't come with the lower height Delrin adjusters, and lastly they are more expensive and you can't get them from Sam Strano (of stranoparts.com). As far as the HPT vs the slightly lower rate HPS spring, my philosophy is that at this stage it's okay to make big changes since I am going to be retuning and relearning everything anyways. Plus the car was very loose with square tires and I like a car that is biased more towards stability (understeer), since I can be more aggressive with the throttle. I usually underdrive corner entrances so if I can stand on the gas at or before the apex it means I don't lose as much time to people that carry more speed into the corner. Plus with a powerful RWD car you want most of your roll stiffness to be up front in order to put down power better. Think of a trophy truck, how the rear end just squats and hooks up and the truck catapults off even on very low grip surfaces. Speaking of trophy trucks, if you haven't seen the BJ Baldwin video (Recoil 2) where he drives through (over?) Ensenada, Mexico, you should check it out, good lesson on well setup long travel suspension setups. The combo of the 33mm sway bar and the 20% front spring rate increase might mean I went too far, but I can easily go to a 30mm front sway bar or a size higher rear sway bar to balance things out. Strano makes a nice tubular 1" 3-way adjustable rear sway that could end up being just the trick.
Speaking of trophy trucks:
How's that for a roll stiffness distribution!!! I think Robby Gordon set up his Stadium Super Trucks to lift front wheels that high because it looks cool, but still I bet it has great traction since that inside rear tire is extremely planted.
Continuing with the spring rate discussion, it is also worth considering that the venerable Danny Popp sets up C5Z's for SSP autocross with higher rate front leafs and stock rears. Not sure on what sway bars he uses though. I'd really like to know his suspension setup that he won the Optima USCA last year with since he was on street tires, but I have been unable to find anything other than the fact he was sponsored by JRi so was probably running their shocks.
Should have the Delrin-ified control arms back next week so we can take a look at those, and hopefully some good news on shocks as well.
No comments:
Post a Comment