How do you keep the C3 from getting light above 120mph?
10-04-2012, 08:31 PM
#142
Tech Contributor
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i would keep the front vents open. i would not think you would get much lift there, but the flow of air to the radiator on theses C3's sucks... That's what I've always heard, but I've run several track days with temps between 95 and 101 degrees and this thing doesn't overheat. I credit the DeWitt radiator and a decent ignition curve.
your belly pan... AMAZING..
Thanks!
i want one....did you ever to the pressure testing?
your belly pan... AMAZING..
Thanks!
i want one....did you ever to the pressure testing?
10-05-2012, 06:33 PM
#143
Le Mans Master
I'm still having hand sweets..... The streets of willow are fast enough.... But I really want to do more big track... But I just don't like the way she feels above 120... What I like the least is the steering wheel feel up there... I have rack and pinion, but I was wandering if anyone ever put a shock like system on ther r&p like I see on some other stock autos? It would help keep the steering more solid at high speeds????
FWIW, at the other end of the scale, after having had them on a couple of ~50,000# motorcoaches I can highly recommend steering dampeners/stabilizers for those such applications.
10-05-2012, 10:26 PM
#144
Race Director
Thread Starter
I did some part time instructing with the SCCA back in the 90's and I had my students put a piece of 1 inch tape on the windshield below eye level then told them to not look below the tape going into a corner especially turn 8 on the big track which helped them "look through" the corner. I learned the hard way by following one of my competitors through the corner during my first race. I let off going in and he didn't. I had another 2 miles to think about how I was going to keep my foot down through that corner on the next lap 
. I am happy to report I stayed on his "ash" the whole race ...till I went off in turn 9...but "that's racing"...
p.s. I forgot to tell you I would be happy to take your car on the big track to help sort it out...
. I am happy to report I stayed on his "ash" the whole race ...till I went off in turn 9...but "that's racing"...p.s. I forgot to tell you I would be happy to take your car on the big track to help sort it out...
I'm running behind on that. The suspension and exhaust changes, along with finally building an air box for the cowl induction have eaten into my free time. I still need to make some sort of in-car mount for the pressure gauge so I can read it while driving. In addition to the aero type pressure measurements I'm kind of interested in what sort of (minor) pressures exist in the airbox, and the pressure drop across the stock air filter versus the well known aftermarket filter.
I'd have a hard time advising to install a steering dampener as a bandaid against high-speed instability in a sports/racing car, at least until exhausting all other available fixes. Besides, it would tend to further isolate one from road feedback (as does power steering), which is the opposite of what you should want when on track. I'd put your effort into improving your aero as well as mechanical setup rather than into masking the issue, as that could give you a false sense of security.
FWIW, at the other end of the scale, after having had them on a couple of ~50,000# motorcoaches I can highly recommend steering dampeners/stabilizers for those such applications.
FWIW, at the other end of the scale, after having had them on a couple of ~50,000# motorcoaches I can highly recommend steering dampeners/stabilizers for those such applications.
another member was posting something about,,,,,,,mmmmmm...forgot what its called now...but the faster you go, the less the steering assist works... i would like that. adaptive steering????
10-05-2012, 10:36 PM
#145
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10-05-2012, 11:09 PM
#146
Race Director
Mine is very stable at 120mph, I attribute it to rake, the front is lower than the back and the rubber "spoiler" only 2-3 inches above the pavement, which probably gets less and less the faster I go and design of the front end not allowing much air under the car at speed and creating a downforce the way it was designed. Take a look at an 80-82 under the front
Last edited by MotorHead; 10-05-2012 at 11:11 PM.
10-06-2012, 10:18 PM
#149
Le Mans Master
http://forums.corvetteforum.com/c3-g...-steering.html
Assuming we're only going this fast on tracks and closed circuits, IMCO it's worth pointing out that one can easily take mechanical setup too far towards the stable/comfy end of the scale (including with caster) only to end up with a less nimble car and measurably slower lap times. Not saying you should just learn to cope with a diabolical machine if there's something actually wrong, but do keep in mind that even a well sorted race car will tend to scare the crap out of you when you start pressing hard enough to call it racing.
As long as the suspension is doing its job well at lower speeds (<90) and isn't, in and of itself, creating an instability at speed, I'd suggest the focus should remain on aero to address any true high-speed issues.
10-08-2012, 12:24 PM
#151
Race Director
Thread Starter
Front 63 - 82 Corvette*****Daily Driver****Advanced Street****Autocross Baseline***** Track Baseline
Toe 1/32" in *****0" *****3/16 out******** 0-1/16 out
Camber 0° neg ********.25° neg *******1.5-2° neg****** 1-2° neg
Caster 2.75° pos****** 2.75° pos *****2.75°***** pos 2.75° pos
Caster (w offset a-arms) 4.75° pos 4.75° pos 4-4.75° pos 4-4.75° pos
Rear 63 - 82 Corvette Daily Driver Advanced Street Autocross Baseline Track Baseline
Toe 1/8" in 1/8" in 1/8"-1/4" in 1/8"-1/4" in
Toe 1/32" in *****0" *****3/16 out******** 0-1/16 out
Camber 0° neg ********.25° neg *******1.5-2° neg****** 1-2° neg
Caster 2.75° pos****** 2.75° pos *****2.75°***** pos 2.75° pos
Caster (w offset a-arms) 4.75° pos 4.75° pos 4-4.75° pos 4-4.75° pos
Rear 63 - 82 Corvette Daily Driver Advanced Street Autocross Baseline Track Baseline
Toe 1/8" in 1/8" in 1/8"-1/4" in 1/8"-1/4" in
Camber 0° neg .50° neg .75-1.5° neg .75-1.5° neg
1. OK, that's a different technology than the dampener/stabilizer type I thought you were talking about. I believe you're referring to this...
http://forums.corvetteforum.com/c3-g...-steering.html
Assuming we're only going this fast on tracks and closed circuits, IMCO it's worth pointing out that one can easily take mechanical setup too far towards the stable/comfy end of the scale (including with caster) only to end up with a less nimble car and measurably slower lap times. Not saying you should just learn to cope with a diabolical machine if there's something actually wrong, but do keep in mind that even a well sorted race car will tend to scare the crap out of you when you start pressing hard enough to call it racing.
2. As long as the suspension is doing its job well at lower speeds (<90) and isn't, in and of itself, creating an instability at speed, I'd suggest the focus should remain on aero to address any true high-speed issues.
2. good point.
But, that being said, when the steering gets to feel "light" or "to quick" it helps to add to the non stability feeling on the car.
in the C5, at speeds of 140+, yes the car feels less "solid" to the road, (not to the point of the C3 of course) but none the less, less grounded... But, the steering still has some resistance to it... it feels as if it stays .... wants to stay straighter....
AAAHHHh.... going to lick this if it kills me. still loving that under body pan... and i really want to to a pressure test at speed for under hood psi..... still worried about those block offs for everyday cooling driving.
Now, if there is a low pressure at the hood... back to the hood vents... would not that almost eliminate under hood pressures for a lighter front end?...
Last edited by pauldana; 10-08-2012 at 12:27 PM.
10-08-2012, 03:45 PM
#152
Ive hit 130 on the road course (no more gear left) But I can say there is a big difference compared to nothing.
Look at BeeJays custom Pace car spoiler. I would say his looks the best and is probably the most functional.
Here is mine... The aluminum support rods are "consumables" but the fiberglass will flex enough if you scrape a driveway. The only reason I have scraped my splitter/bent a support rod is because I was forced to enter a driveway at a less than optimal approach angle or I wasnt paying attention and hit a HUGE pot hole. Most speedbumps are no taller than 3" and if they are, they are the speed "humps" that span a further distance so I still wont scrape.
Look at BeeJays custom Pace car spoiler. I would say his looks the best and is probably the most functional.
Here is mine... The aluminum support rods are "consumables" but the fiberglass will flex enough if you scrape a driveway. The only reason I have scraped my splitter/bent a support rod is because I was forced to enter a driveway at a less than optimal approach angle or I wasnt paying attention and hit a HUGE pot hole. Most speedbumps are no taller than 3" and if they are, they are the speed "humps" that span a further distance so I still wont scrape.
10-12-2012, 12:26 PM
#155
I cut the bottom lip off my spoiler and extended down. I also used aluminum that I painted black behind grills and license plate area to keep air from sneaking through. I then covered the holes with aluminum on the bottom side of nose. I have no air coming in through the front and have been 165mph with no issues.
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12-19-2012, 05:17 PM
#156
Le Mans Master
Finished adding the additional bellypan area back to the rear camber links the other week, along with the front suspension geometry change (for reduced camber gain)...
...The geometry change seemed to help also. A little more front grip in the corners (less understeer), and the reduced camber change under hard braking is always a plus.
...The geometry change seemed to help also. A little more front grip in the corners (less understeer), and the reduced camber change under hard braking is always a plus.
IMCO better to address excessive dive with increased anti-dive geometry and/or stiffer front spring rates than to compromise front camber curves and end up needing even more static camber. The other side of the coin is that it's not uncommon to actually increase front camber gain to improve grip during hard cornering. Think about it...
12-20-2012, 11:34 AM
#157
Race Director
Thread Starter
I've meant to respond to the above before now, but had forgotten to get back to this. Anyway, the above begs the question, what are your front spring rates now?
IMCO better to address excessive dive with increased anti-dive geometry and/or stiffer front spring rates than to compromise front camber curves and end up needing even more static camber. The other side of the coin is that it's not uncommon to actually increase front camber gain to improve grip during hard cornering. Think about it...
IMCO better to address excessive dive with increased anti-dive geometry and/or stiffer front spring rates than to compromise front camber curves and end up needing even more static camber. The other side of the coin is that it's not uncommon to actually increase front camber gain to improve grip during hard cornering. Think about it...
spring rates are very important i agree... mine are the #550 front with 1/2 coil cut, and it is my understanding that this brings the spring rate up... to about 600#
this was a major improvement in handling and fast lane transitions. but it also brought the car down 2-3"... so this was a big help also...
12-20-2012, 09:53 PM
#158
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I've meant to respond to the above before now, but had forgotten to get back to this. Anyway, the above begs the question, what are your front spring rates now?
IMCO better to address excessive dive with increased anti-dive geometry and/or stiffer front spring rates than to compromise front camber curves and end up needing even more static camber. The other side of the coin is that it's not uncommon to actually increase front camber gain to improve grip during hard cornering. Think about it...
IMCO better to address excessive dive with increased anti-dive geometry and/or stiffer front spring rates than to compromise front camber curves and end up needing even more static camber. The other side of the coin is that it's not uncommon to actually increase front camber gain to improve grip during hard cornering. Think about it...
My front coilover spring rates are 375#. While that might sound cushy, the wheel rates are higher than they were when I had 550# springs in the car years ago. The coilovers are attached further outboard on C4 LCAs than on C3 LCAs. The present wheel rates are about 20% higher than the old C3 550# setup.
I have anti-dive built into the geometry. It's easily changed with my suspension bracketry if I wish.
I have a decent amount of roll stiffness in the suspension. The F&R spring/wheel rates along with the front sway bar keeps the car very level during cornering. The sway bar attaches close to the end of the LCA, making the effective bar rate higher.
I don't want to bump up the front spring rates any higher. Herb Adams has a point regarding keeping the spring rates reasonable for good road following ability, and then use the sway bar to get the roll resistance you need.
There is camber gain in the suspension, but I reduced it to get a flatter tire footprint under hard braking. My '69 is pretty fast down the straights, so I have to do some pretty stiff braking entering some of the corners.
I'm quite happy with the balance and handling of the car. I'm just trying to improve the braking ability, while still keeping a modest amount of camber gain.
12-21-2012, 02:43 PM
#159
Le Mans Master
With all due respect, I genuinely would appreciate it if you would inquire about what my suspension is, and how the car is handling, before you instruct me on what should be changed on my car.
My front coilover spring rates are 375#. While that might sound cushy, the wheel rates are higher than they were when I had 550# springs in the car years ago. The coilovers are attached further outboard on C4 LCAs than on C3 LCAs. The present wheel rates are about 20% higher than the old C3 550# setup.
I have anti-dive built into the geometry. It's easily changed with my suspension bracketry if I wish.
I have a decent amount of roll stiffness in the suspension. The F&R spring/wheel rates along with the front sway bar keeps the car very level during cornering. The sway bar attaches close to the end of the LCA, making the effective bar rate higher.
I don't want to bump up the front spring rates any higher. Herb Adams has a point regarding keeping the spring rates reasonable for good road following ability, and then use the sway bar to get the roll resistance you need.
There is camber gain in the suspension, but I reduced it to get a flatter tire footprint under hard braking. My '69 is pretty fast down the straights, so I have to do some pretty stiff braking entering some of the corners.
I'm quite happy with the balance and handling of the car. I'm just trying to improve the braking ability, while still keeping a modest amount of camber gain.
My front coilover spring rates are 375#. While that might sound cushy, the wheel rates are higher than they were when I had 550# springs in the car years ago. The coilovers are attached further outboard on C4 LCAs than on C3 LCAs. The present wheel rates are about 20% higher than the old C3 550# setup.
I have anti-dive built into the geometry. It's easily changed with my suspension bracketry if I wish.
I have a decent amount of roll stiffness in the suspension. The F&R spring/wheel rates along with the front sway bar keeps the car very level during cornering. The sway bar attaches close to the end of the LCA, making the effective bar rate higher.
I don't want to bump up the front spring rates any higher. Herb Adams has a point regarding keeping the spring rates reasonable for good road following ability, and then use the sway bar to get the roll resistance you need.
There is camber gain in the suspension, but I reduced it to get a flatter tire footprint under hard braking. My '69 is pretty fast down the straights, so I have to do some pretty stiff braking entering some of the corners.
I'm quite happy with the balance and handling of the car. I'm just trying to improve the braking ability, while still keeping a modest amount of camber gain.
That said, since you've invoked Herb Adams, IMCO it's worth pointing out that readers shouldn't mistake his advice to run the softest practical springs as meaning that they should necessarily run soft springs. Quite often more spring rate IS a good thing. Besides, higher spring rates (where higher spring frequencies are suitable) permit the use of smaller bars (read, "less crutch"); the former of which doesn't increase lateral weight transfer as does the latter.
...but, I digress. A healthy debate between schools of thought regarding springs and bars is best left to threads dedicated to such, suffice it to say that I'm admittedly a tad further away from the BBSS (big bars soft springs) line of thinking than most.
.
Last edited by TheSkunkWorks; 12-21-2012 at 04:11 PM.
