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Poor-sha, Tried mine last weekend at Eagles Canyon Raceway, I think there going to be the cats meow. I also finally set the shock stop travel so maybe I will quit buying finder liners :-)
I think my spring rates were about 784 front and 732 rear, but my memory is a bit fuzzy on the exactness,
Will be going to COTA the end of the month so I should be able to have some decent info if anybody is interested. Maybe we should start a new thread on the subject, dont mean to hijack this one
Operations
Yeah we really should start a new thread on the Tractive coilovers and another on the ice mode issue so they don't get lost in here.
My understanding is your car has 140 front and 130 rear. I believe that is kg/cm so that works out to roughly to 784/728 lb/in. Unfortunately we were still waiting on a shipment of springs to come in so I'm going for a very unconventional 110 front/130 rear. I'm going to run the big GS Z07 from bar so this is at least the same basic thought process as the GS Z07 did with leafs. I figure my car is much lighter up front than yours with it being NA and no additional cooling so we'll see how it does this weekend,
Sorry to drop a few details and disappear but I've been pretty slammed lately. I did get the car out to the track last weekend and learned a few things. The car was very loose out of the box and I clearly botched the toe as the car was slightly pulling to the left. Putting the rear Hotchkis bar at full soft helped but it was still loose at turn-in and on exit. I tried making small changes to the front toe and kept driving the car but it would not put power down at all and while it was stupid fast in a straight line I was tip-toeing around the corners. Best lap I could muster was a 1:20 (I hit 1:14's end of last year).
By lunch on day 2 I had corded the LR tire so I put a new set of scrubs on. The fronts were the same size but the rears I had on were 325/680-18 Pirelli DHD2 whereas what I was putting on now were 315/680-18 Pirelli DH. The car was 100X better with the tire change and would finally put some power down, although still not as well as I would have liked. I spent the session just getting settled in the car and this ended up being my last session but I still was able to improve 3 seconds on my lap times from earlier in the day.
For those of you interested in just listening to the music of a built 427 LT1 and a sequential transmission I posted up a video of the last session here:
I thought for sure that I had a bad set of tires but I was researching the Pirelli slicks and found this little gem of info in one of their documents on the web. Care to guess how my tires were mounted? Not the way the picture shows. So if you are running the DHD2 and think you can flip the tires to improve wear know that it may cause some really bad handling. This also might explain why I had such a poor experience with the 325/660-18 when I tried it a few years back.
While mounting my tires correctly will definitely improve things I don't think the experiment with softer springs is working out. I have the ride height set even at the chassis (more to follow) with 250 lbs of ballast in the driver seat and if you look at the data it's interesting that the car seems pretty neutral in left turns but loose in right turns. This chart shows yaw rate overlaid with steering angle, as well as throttle and brake at the bottom. If you overlay them right the yaw and steering traces will match up when the car is neutral. If you have more yaw than steering the car is loose, if you have more steering than yaw the car is understeering. Note that I am filtering the steering and yaw rate when not in a corner and also doing a bit of a moving average filter to smooth out the lines.
This is likely because the front springs are too soft which wasn't unexpected. When I got the car home I put the strings back on to fix the toe issue. I'll be back at Summit Point middle of next week to see how that does and at this point I won't have time to swap the springs. I do have a set of 140 front springs on the way which is what @Operations is running and if I am feeling ambitious I might try to swap them while I'm there and give it a go. My gut is saying that the 140 front springs and putting the sway bar back to the middle will be the hot ticket.
Next post I'll back track and cover the changes I made to the car.
Time to backup and talk about the suspension changes in the off season. Given the changes in weight to this car I don't think any of the factory leaf spring options are a good fit. Now that DSC Sport has a coilover package for the Tractive shocks it was time to pull the leaf springs and go coil over. I was pretty limited in spring rates as the springs they had ordered were stuck on a ship outside the port and we wanted to test whether lighter springs in the front than rear would work so we ended up with 110 kb/cm front and 130 kg/cm rear (About 616/718 in in/lb). I also put the adjustable rear Hotchkis bar back on and decided to keep the big front GS Z07 bar since on paper it looks to be the same spec as the Hotchkis front and I haven't been able to get a front bar from anyone.
Removing the leafs was a bit of a pain but installing the coilovers was super easy. In the fronts I ended up removing the bolts holding the rear leg of the UCA and loosening the front to allow me to swing the UCA out of the way and slide the coilover in to place. I didn't need to do this in the rear.
I didn't have good ride height data at the chassis so I started by taking the stock measurements I had at the fenders and dropping the car about 1/2". I then measured the actual chassis height at the front and rear cross-member and evened up the car with 250 lbs of ballast (I'm a big guy). The ride heights ended up at 124mm front and 131mm rear at these locations (I painted the spots I measure red). After that I aligned the car with camber -2.7/-2.1, toe 1mm in front and 4mm in rear, rear caster at 0.8 laid back.
So that your vehicle has a perfect balance
You must be on the scales,
Setting filled with tank and you are also in the car
Stabi front and rear dismantle one side
Then you make with thread a perfect base with 50.00
This is the best base
After that you make the geometry
Sean, the pull that car has in the upper RPM is crazy, it must feel amazing. Thank you for the updates.
Originally Posted by Racingswh
I can't believe how quick it is. Already serious MPH by start finish going on to reach 165 MPH at the brake zone into T1. WOW!!
I have to say that I am genuinely intimidated by how fast this car is. That 165 on the straight was with me braking way early, short-shifting, and tip-toeing through T10. Katech built a monster motor, that's for sure.
Hey Poor-sha, good job I watched first 3/5 of at session, from the beginning...as you build up speed gradually, you get to know the telemetry - I used different sections of the telemetry to analaze on different laps, really make use of the data. Very interesting, top of the line implementation as you hone the setup - very cool. Nice
I have to say that I am genuinely intimidated by how fast this car is. That 165 on the straight was with me braking way early, short-shifting, and tip-toeing through T10. Katech built a monster motor, that's for sure.
As you know once dialed in you will see 90 + mph min speeds in T10. I suspect that results in 170 mph front straight speeds.
My prediction is that you will get this car in the 1:12's soon enough and will work on it from there. Such an amazing car!!
BTW when you said the best you could muster was a 1:20 what did you mean? At 13:36 you click off a 1:17.48 and ran many laps in the 1:17's in the 2nd half of the session.
As you know once dialed in you will see 90 + mph min speeds in T10. I suspect that results in 170 mph front straight speeds.
My prediction is that you will get this car in the 1:12's soon enough and will work on it from there. Such an amazing car!!
BTW when you said the best you could muster was a 1:20 what did you mean? At 13:36 you click off a 1:17.48 and ran many laps in the 1:17's in the 2nd half of the session.
I didn't post the previous sessions on the old tires. Those were the ones where I could barely turn a 1:20 lap.
Circle back on the brake booster hard peddle issue I'm having (and a few others) seems to be mostly for those who have gone with AP Racing Brakes or similar, and left foot braking or going from 100% throttle to 100% instantly the brake vacuum is lacking in that the peddle feels very hard for a moment before the vacuum assistance catches up. Although what I have described may not be technically accurate, it is accurate from the viewpoint of what it "feels like" is happing.
I reached out to Mark Stielo at GM for some ideas on the matter, right off the bat he told me to add a vacuum reservoir. So we purchased one from Summit Racing HERE and mounted it where the windshield washer bottle was. Extended a 3/4" hose up and "T" in between the pump and booster, we will see how this turns out at COTA at the end of the month.
I also also poked around the online GM parts and saw that there are two different vacuum pump part numbers Part Number:20981800 is for FE3, FE4 Corvette without soft ride $179, and Part Number:22990902 is for FE1, FE2 Corvette with soft ride, I will use my ZR1 VIN and find out that pump part number, I bet its the 20981800, and that should help sort that out, my Z06 is a non Z07 I bet it is the other p/n.
If this turns out to be the case I will order the (I'm calling it) CCB Vacuum Pump.
Operations
We did swap out the Vac pump for the a race pump, when we went out to test we were also testing out our 2650R, cam, ported heads etc at the same time, the change made 850/800rw, but on track we started blowing a ton of oil through the PCV, we tried various catch cans and re plumbing the lines, but it volume of oil under WOT was to great for any of our solutions to work. We ran compression checks and found no issues there. On the last track test I took Sergio from LG as a passenger to watch the gauges and his laptop with HP tuners. He saw my dash oil pressure dip really low, so we killed the engine and was towed in. Pulled the engine, only then did we find a piston broken, that cylinder was also really worn. Likely the piston was damaged a while back when the Callaway SC cooling brick failed and flooded the right cylinders with water. Unknown to anyone because it ran fine before turning it off a week prior, upon trying to start the engine we must of cracked the piston due to being it was hydrolocked, all we know is it would not turn over. Long story short, it took a 0.010 over bore to clean up the worn cylinder, we ordered new pistons from Racetec, going on six weeks now waiting on them, then sending them on to Swain Tech for coating. So the Race vac pump test in inconclusive for now.
Damn, that sucks, hopefully the pistons come in soon and you can get back up and running. What race vacuum pump did you install and did you install the vac surge tank too or decide not to due to the race vac pump? Thanks for the reply.
Damn, that sucks, hopefully the pistons come in soon and you can get back up and running. What race vacuum pump did you install and did you install the vac surge tank too or decide not to due to the race vac pump? Thanks for the reply.
LG ordered the pump, I dont know the brand or part number at this point, and yes we did have a surge tank.
On my car I've been focused on getting the handling where I want it. I think my problem is coming down to front/rear roll rates and the C7 seems very sensitive to this. I ended up making a spreadsheet with various bar/spring rates and comparing different stock and aftermarket combos. Looking at the spreadsheet the GS Z07 and Z06/7 both have the same magic ratio of front/rear roll stiffness to weight. Last time I went out I used 140/120 springs (F/R), the stock Z06/7 front bar, and the Hotchkis rear bar on full soft. According to the spreadsheet this was very close to the "magic ratio".
The car was pretty good with this setup but I am still having a hard time putting power down. I know that car has more power and lower gearing but just looking at the longitudinal Gs of past cars I should be able to put more power down. The one interesting tidbit I've found comparing the data from various setups is that my current setup seems to be unloading the inside rear wheel more than other setups. I need to figure out why as I suspect that is the cause of my power down issues.
Thanks for the update Sean, I didn't mean to hijack your thread. The spreadsheet is very helpful, thank you for making it. Hopefully you get the car sorted to your liking soon, I've enjoyed following along and have learned a lot.
On my car I've been focused on getting the handling where I want it. I think my problem is coming down to front/rear roll rates and the C7 seems very sensitive to this. I ended up making a spreadsheet with various bar/spring rates and comparing different stock and aftermarket combos. Looking at the spreadsheet the GS Z07 and Z06/7 both have the same magic ratio of front/rear roll stiffness to weight. Last time I went out I used 140/120 springs (F/R), the stock Z06/7 front bar, and the Hotchkis rear bar on full soft. According to the spreadsheet this was very close to the "magic ratio".
The car was pretty good with this setup but I am still having a hard time putting power down. I know that car has more power and lower gearing but just looking at the longitudinal Gs of past cars I should be able to put more power down. The one interesting tidbit I've found comparing the data from various setups is that my current setup seems to be unloading the inside rear wheel more than other setups. I need to figure out why as I suspect that is the cause of my power down issues.
Last year when Randy Pobst drove my car at COTA, that was his big compliant was corner exit power down was poop,(he is good friends with Mike at DSC) he said Mike could fix most of that with the tuning of the DSC. I know you have dug quite a bit in to the DSC tuning yourself, have you talked to Mike about the problem with laying down power?
My last trip to COTA was a bust as I mentioned in another post, but it was my first chance to try the Coilover conversion, and Mike was working with LG on the programing. The car felt really good, power laid down better from corner exit then it ever has, and I got the electronic shock STOP travel to limit the tires from rubbing the liners for the first time ever! It was so awesome not having to buy another set.
I thought you got the coilover conversion too? Did I miss that in your earlier post?
03-09-2021, 07:58 PM
