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Hi all, i have a 91 that I campaign in the NCCC 1SE/1E class. The car currently has the base FX3 suspension package with the shocks replaced by non adjustable bilstine's (unknown which model at this point). I am currently trying to source all components to switch to a 88-9 Z51 setup. I have a NYU rear spring, and a 30mm front sway bar to go on the car. I have been trying to find a FHB front spring and as some of you know, they are unobtainable. Question is, while I am waiting to find a front spring, if I put the rear spring and front sway bar on how will it affect the handling? I bought this car last fall and haven't done anything to it except swap tires and replace brakes. Currently the car is loose and I am constantly correcting for oversteer whether on street tires(RT615K+) or hoosiers. Also feels like it has quite a bit of body roll. I personally have not taken it in for an alignment to see where it is at or have it setup at all. Car is used both street and autocross.
FHB spring is a little hard to come by. It will be better but still a little funny coming out of the corner. The Z51 26mm rear stabilizer bar should correct roll coming out of corner..
I have a NYU rear spring, and a 30mm front sway bar to go on the car. I have been trying to find a FHB front spring and as some of you know, they are unobtainable.
What's an FHB spring worth? I might be able to pull one out of my garage...
I have an 89 Z51 car that I put coilovers on.
The 90-91 Z07s had a 26mm rear over the 88-89 Z51s' 24mm. Other than that, spring rates were the same for them.
you really need to stiffen the front up first - get the biggest bar you can in the front.
do your class rules dictate what components you can use ?
Both bars and springs must be "stock for class". That means i can run anything that came on 84-91 cars that will fit, except ZR-1. The 30mm bar i already have is the largest one I can put on the front. The rear still has the stock 24mm bar. I've heard the 26mm rear bar wasn't good on these cars and that is why it was only on for 2 years.
Both bars and springs must be "stock for class". That means i can run anything that came on 84-91 cars that will fit, except ZR-1. The 30mm bar i already have is the largest one I can put on the front. The rear still has the stock 24mm bar. I've heard the 26mm rear bar wasn't good on these cars and that is why it was only on for 2 years.
this stock for class rule isnt so good when your trying to track a 30 year old car !
I take it you dont have the 30 mm swaybar on yet ? If not make that your next change. What size swaybar is on the front now ?
If you can get an FHB spring I would grab it while you can.
I was just at Peru for the CAM Challenge. I recognize that control tower! Next time you should come out to that event, because I had the only C4 in the field of 31 Corvettes (CAM-S).
If you don't have the 30mm front bar on yet, do that now for sure. Definitely don't go larger on the rear bar unless/until you get a stiffer front spring. It's hard to know for sure from action pics, but your rear ride height seems a little high. If allowed in the rules, you could lower that and it would help reduce oversteer by lowering the rear roll center. Definitely do get the car aligned, and go for the most negative camber at both ends you can. Pay special attention to rear toe, making sure you don't have toe out. Also make sure your toe links in back are in good shape with no slop that might allow dynamic toe out under braking.
I was just at Peru for the CAM Challenge. I recognize that control tower! Next time you should come out to that event, because I had the only C4 in the field of 31 Corvettes (CAM-S).
If you don't have the 30mm front bar on yet, do that now for sure. Definitely don't go larger on the rear bar unless/until you get a stiffer front spring. It's hard to know for sure from action pics, but your rear ride height seems a little high. If allowed in the rules, you could lower that and it would help reduce oversteer by lowering the rear roll center. Definitely do get the car aligned, and go for the most negative camber at both ends you can. Pay special attention to rear toe, making sure you don't have toe out. Also make sure your toe links in back are in good shape with no slop that might allow dynamic toe out under braking.
I've wanted to do the CAM Challenge there for the past 2 years. However, my club (Michiana Corvette Club) hosts a weekend at Tire Rack that same weekend and I am in charge of tech inspection. I did very well there taking 11 of the 14 overall FTDs for the weekend. I am running for an Indiana Region NCCC Championship this year so I can't miss any events. I have a 71 point lead over my Dad at the moment.
I will be back at Grissom this weekend (Aug25-26) with the Fort Wayne Corvette Club and the Corvette Club of Indiana which they are holding a 14 event weekend. Then back to Tire Rack on Labor Day weekend - 21 events, Grissom on Sept 22-23 - 14 events, parking lot in Indy on Sept 29-30 - 14 events, and finally Grissom on Oct 20-21 - 14 events. Anybody interested can come play with us. You are guaranteed to get 2 runs per event = lots of seat time!!!
I will be running street tires at the Grissom events. I haven't decided if i am going to try to run the Hoosiers at Tire Rack or save them for the Indy event. I don't have much tire left for the rear so it may only last 1 more weekend, or maybe only last one more day. The Indy event is supposed to be a small lot and that is where I have the best chance to take overall FTD.
I guess I will try to put the 30mm front bar on by this weekend. I will see if i can lower the rear any. I have to keep stock hardware and can only lower it with in stock adjustment range.
this stock for class rule isnt so good when your trying to track a 30 year old car !
I take it you dont have the 30 mm swaybar on yet ? If not make that your next change. What size swaybar is on the front now ?
If you can get an FHB spring I would grab it while you can.
The current front bar is 26mm. The rear is 24mm. You can't even order aftermarket as nobody is making a front spring for these cars anymore. VBP went out of business and Hyperco discontinued making them. Stock original parts are all there is for these and the FHB spring is almost a unicorn.
The current front bar is 26mm. The rear is 24mm. You can't even order aftermarket as nobody is making a front spring for these cars anymore. VBP went out of business and Hyperco discontinued making them. Stock original parts are all there is for these and the FHB spring is almost a unicorn.
If your running 26 F and 24 R its no wonder you are experiencing oversteer.
If you can get an FHB spring and a 30 mm bar on the front it will be a different car.
With VBP out of business and Hyperco only offering a rear c4 leaf it doesnt leave much hope for anyone having to run a leaf suspension.
I've wanted to do the CAM Challenge there for the past 2 years. However, my club (Michiana Corvette Club) hosts a weekend at Tire Rack that same weekend and I am in charge of tech inspection. I did very well there taking 11 of the 14 overall FTDs for the weekend. I am running for an Indiana Region NCCC Championship this year so I can't miss any events. I have a 71 point lead over my Dad at the moment.
I will be back at Grissom this weekend (Aug25-26) with the Fort Wayne Corvette Club and the Corvette Club of Indiana which they are holding a 14 event weekend. Then back to Tire Rack on Labor Day weekend - 21 events, Grissom on Sept 22-23 - 14 events, parking lot in Indy on Sept 29-30 - 14 events, and finally Grissom on Oct 20-21 - 14 events. Anybody interested can come play with us. You are guaranteed to get 2 runs per event = lots of seat time!!!
I will be running street tires at the Grissom events. I haven't decided if i am going to try to run the Hoosiers at Tire Rack or save them for the Indy event. I don't have much tire left for the rear so it may only last 1 more weekend, or maybe only last one more day. The Indy event is supposed to be a small lot and that is where I have the best chance to take overall FTD.
Sounds like you're doing really well indeed! For NCCC events, I have only done our local one in the St. Louis area. I would like to get to at least some of the ones at Peru next year, though. I'm really spoiled in having too many autocross opportunities where I live.
FWIW, I'm running the 30mm bar up front on my car, and currently use a 23mm (1984 Z51 only) rear bar. Granted this is in combination with VBP Xtreme springs (1125f/550r), so it isn't a full apples:apples comparison. That set up has just a bit of push at the grippy concrete of Peru, and possibly slightly too neutral on much less grippy asphalt. Or it may be just right - I'm still deciding.
Originally Posted by blackozvet
With VBP out of business and Hyperco only offering a rear c4 leaf it doesnt leave much hope for anyone having to run a leaf suspension.
There may be reason for optimism. It's my understanding that another well established business has the VBP molds and the knowledge for how to use them. So aftermarket springs may be back on the market in a year or so.
Last edited by MatthewMiller; 08-20-2018 at 07:59 AM.
There may be reason for optimism. It's my understanding that another well established business has the VBP molds and the knowledge for how to use them. So aftermarket springs may be back on the market in a year or so.
Thats good news, there must be a few people around who would be keen to get hold of a 1000 - 1200 lb front leaf !
Out with the old (top), in with the new(bottom). Installed the 30mm bar today. Took it for a test drive to the dentist. It seemed to be more stable going around a clover leaf. The real test will be this weekend at Grissom.
Update to changes: So i ran the car at Grissom and at Tire Rack last two weekends. The bigger bar took the car from very loose, to a bit of push. It now pushes when i am braking or on throttle into a corner. If i get into a turn and all i do is get off the throttle, the car is then loose. After talking with 69autoxr at the event, I think i am going to go ahead an put the rear spring i have on and see what it does. Hopefully i can get that done before the next event, but I am going to be pretty busy between now and then.
Update to changes: So i ran the car at Grissom and at Tire Rack last two weekends. The bigger bar took the car from very loose, to a bit of push. It now pushes when i am braking or on throttle into a corner. If i get into a turn and all i do is get off the throttle, the car is then loose. After talking with 69autoxr at the event, I think i am going to go ahead an put the rear spring i have on and see what it does. Hopefully i can get that done before the next event, but I am going to be pretty busy between now and then.
I don't know what the Tire Rack surface is like, but the Grissom site has a lot of grip. The same setup that provides the bit of push you describe above at Grissom will feel a lot more neutral on a less grippy asphalt site IME. The 88+ C4s have a crap ton of anti-dive built into the front geometry, and that's why they push while braking.
It sounds to me like you're a lot closer to the right setup now. You can certainly try that other rear spring - that's a pretty easy swap. Maybe it will be too much, but it can't hurt to experiment. Also, with the setup you have now you should make sure you have all the front negative camber you can run, and you can also play with front and rear toe. A good starting point is probably zero toe front and rear, or maybe a very small amount of toe out in front. The more toe out on either end, the less push you'll have.
Update to changes: So i ran the car at Grissom and at Tire Rack last two weekends. The bigger bar took the car from very loose, to a bit of push. It now pushes when i am braking or on throttle into a corner. If i get into a turn and all i do is get off the throttle, the car is then loose. After talking with 69autoxr at the event, I think i am going to go ahead an put the rear spring i have on and see what it does. Hopefully i can get that done before the next event, but I am going to be pretty busy between now and then.
it sounds like you are on the right path, stiffen the front first and then you tune out the understeer with stiffer rear spring and or swaybar.
08-17-2018, 04:57 PM
C4 Suspension Changes
