Setting Your C4 Up for Auto-X
Thread Starter
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
I'm bringing back an oldie but a goodie!
I have an 89 FE1 car that I installed a 32/24 sway bar combo on a few years ago along with Bilstein sport shocks. The car is also lowered. The improvements were very good and it doesn't push bad during the occasional autox's I've done. I scored a NYU spring today off an 88 Z51 and was wondering if used with the FHA (93.1) front spring, if I am going to be neutral, slightly oversteer or lots of oversteer. This total package is almost identical to a 92 Z07 other than my front spring being 93.1 vs 90.1 and my front bar being 32 vs 30. I'm still going to look for a front FHB Z51/Z07 spring but was wondering if this setup will be good in the mean time. Thanks folks!
I have an 89 FE1 car that I installed a 32/24 sway bar combo on a few years ago along with Bilstein sport shocks. The car is also lowered. The improvements were very good and it doesn't push bad during the occasional autox's I've done. I scored a NYU spring today off an 88 Z51 and was wondering if used with the FHA (93.1) front spring, if I am going to be neutral, slightly oversteer or lots of oversteer. This total package is almost identical to a 92 Z07 other than my front spring being 93.1 vs 90.1 and my front bar being 32 vs 30. I'm still going to look for a front FHB Z51/Z07 spring but was wondering if this setup will be good in the mean time. Thanks folks!
Don't forget the front sway can be "salted to taste" to get the car where you want it. I prefer a car that is just barely pushy.
Racer
Joined: Feb 2012
Posts: 442
Likes: 3
From: Hendersonville TN
I would have thought that stiffening the rear with the spring would loosen it a bit thus reducing some of the push I have now. Can you explain how it'll cause a touch more push? I'm running the "what you do to one end effects the other" scenario through my head trying to understand. I too prefer a pinch of push vs oversteer. Thanks for your help! I think I'll go ahead and put the spring in and see how it feels. When you say I can salt to taste on the front bar, do you mean by swapping it out or shimming it, etc?
Last edited by HandsomeMike; Jul 7, 2016 at 08:53 PM.
Thread Starter
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
I would have thought that stiffening the rear with the spring would loosen it a bit thus reducing some of the push I have now. Can you explain how it'll cause a touch more push? I'm running the "what you do to one end effects the other" scenario through my head trying to understand. I too prefer a pinch of push vs oversteer. Thanks for your help! I think I'll go ahead and put the spring in and see how it feels. When you say I can salt to taste on the front bar, do you mean by swapping it out or shimming it, etc?
Yeah, FE1 stuff with the 32/combination, then you put the rear NYU spring on WITHOUT changing the front.
It might be ok, but I suspect it will be loose. Too much rear stiffness compared to the front but you DO have a larger front bar so....who knows.
Now the 93.1 AND the NYU bar, yes that would be a good close to Z07 combination.
Shimming front bar mounts.
Racer
Joined: Feb 2012
Posts: 442
Likes: 3
From: Hendersonville TN
I agree, the 93.1 front spring I have now with NYU rear, bilstein sports and 32/24 bars should get me pretty balanced and make me essentially a Z07 car suspension wise. That and a proper autox alignment should satisfy me for at least a year before I start wanting to mess with something else! Thanks for your input!
Safety Car
Joined: Nov 2009
Posts: 3,973
Likes: 341
From: Adelaide South Australia
I'm bringing back an oldie but a goodie!
I have an 89 FE1 car that I installed a 32/24 sway bar combo on a few years ago along with Bilstein sport shocks. The car is also lowered. The improvements were very good and it doesn't push bad during the occasional autox's I've done. I scored a NYU spring today off an 88 Z51 and was wondering if used with the FHA (93.1) front spring, if I am going to be neutral, slightly oversteer or lots of oversteer. This total package is almost identical to a 92 Z07 other than my front spring being 93.1 vs 90.1 and my front bar being 32 vs 30. I'm still going to look for a front FHB Z51/Z07 spring but was wondering if this setup will be good in the mean time. Thanks folks!
I have an 89 FE1 car that I installed a 32/24 sway bar combo on a few years ago along with Bilstein sport shocks. The car is also lowered. The improvements were very good and it doesn't push bad during the occasional autox's I've done. I scored a NYU spring today off an 88 Z51 and was wondering if used with the FHA (93.1) front spring, if I am going to be neutral, slightly oversteer or lots of oversteer. This total package is almost identical to a 92 Z07 other than my front spring being 93.1 vs 90.1 and my front bar being 32 vs 30. I'm still going to look for a front FHB Z51/Z07 spring but was wondering if this setup will be good in the mean time. Thanks folks!
the 32 front sway bar is 2mm larger than any z51 so that could give an understeer tendancy, but can be tuned out with tire pressures.
My prediction would be that combo would work fine.
https://www.corvetteforum.com/forums...84-96-z51.html
Racer
Joined: Feb 2012
Posts: 442
Likes: 3
From: Hendersonville TN
Thanks blackozvet. I'm pretty pumped to see how it handles after install.
A FHA / NYU combination is pretty close to a Z07/Z51 combo.
the 32 front sway bar is 2mm larger than any z51 so that could give an understeer tendancy, but can be tuned out with tire pressures.
My prediction would be that combo would work fine.
https://www.corvetteforum.com/forums...84-96-z51.html
the 32 front sway bar is 2mm larger than any z51 so that could give an understeer tendancy, but can be tuned out with tire pressures.
My prediction would be that combo would work fine.
https://www.corvetteforum.com/forums...84-96-z51.html
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Safety Car
Joined: Nov 2009
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From: Adelaide South Australia
Max G’s
Joined: Nov 2008
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From: Monroe OH
NCM Sinkhole Donor
Handsome- here is my $.02. First, if you are going to Autox the car you will want to have a touch of oversteer to rotate around decreasing radius corners and tight 180 degree corners. Second, with the car lowered, you could be bottoming the shocks out on the front. With a lowered C4 look for C3 front shocks; they have the same mounts as the C4 on the front. I would work toward getting adjustable shocks next, preferably double, but Koni Sports are pretty nice too. Once you get the new spring in, have the car aligned and corner balanced. Lastly, the most important suspension component is tires; get some good tires for the class you want to run. Just research and see what the faster cars or the National guys are running. HAVE FUN
Tech Contributor
Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Tom, and this is in all due respect, I agree but I disagree. Roll stiffness has the MOST to do with it. You are correct. However, Solofast, was THERE back in the day, and they tried a 84Z51 rear spring and their car jacked, BAD. I'd contact him for a full explanation. I have my saved messages with him somewhere. I can tell you this even with the softer 85-95 Z07/Z51 rear spring and 24mm rear bar, its very easy to get too much rear roll stiffness and the car gets snappy loose very quickly.
The other thing your forgetting is that the C4 and earlier Corvettes have a FIXED length upper control arm. The rear tires DO NOT stay level with the road like C5 and up. There is camber change with suspension travel, has to be with the fixed shaft. This is kept to a low level thanks to the low pivot swing axle design of the C4. Which got lower in 88 with the new mount for the rear lower control arm.
That being said, C4's have a very good rear suspension just not as good as newer cars, but much better than its peers or past sports cars that had basic swing axles. Which jack like a SOB.
I'm no expert in suspension dynamics but I know what works and doesn't. The 84 Z51 spring would work just fine with a front to match. If you put it in my car, it would totally UN-driveable.
The other thing your forgetting is that the C4 and earlier Corvettes have a FIXED length upper control arm. The rear tires DO NOT stay level with the road like C5 and up. There is camber change with suspension travel, has to be with the fixed shaft. This is kept to a low level thanks to the low pivot swing axle design of the C4. Which got lower in 88 with the new mount for the rear lower control arm.
That being said, C4's have a very good rear suspension just not as good as newer cars, but much better than its peers or past sports cars that had basic swing axles. Which jack like a SOB.
I'm no expert in suspension dynamics but I know what works and doesn't. The 84 Z51 spring would work just fine with a front to match. If you put it in my car, it would totally UN-driveable.
FWIW, I'm running the '84 Z51 rear suspension in both my '84 and my '69. I like the handling (I do mostly track days, and autocross on rare occasions), and the ride is quite acceptable to me.
Safety Car
Joined: Nov 2009
Posts: 3,973
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From: Adelaide South Australia
Handsome- here is my $.02. First, if you are going to Autox the car you will want to have a touch of oversteer to rotate around decreasing radius corners and tight 180 degree corners. Second, with the car lowered, you could be bottoming the shocks out on the front. With a lowered C4 look for C3 front shocks; they have the same mounts as the C4 on the front. I would work toward getting adjustable shocks next, preferably double, but Koni Sports are pretty nice too. Once you get the new spring in, have the car aligned and corner balanced. Lastly, the most important suspension component is tires; get some good tires for the class you want to run. Just research and see what the faster cars or the National guys are running. HAVE FUN
in this pic with a couple of typical c4 shocks you can see the effective shaft length can be quite a bit different too.
Last edited by blackozvet; Jul 10, 2016 at 04:36 AM.
Racer
Joined: Feb 2012
Posts: 442
Likes: 3
From: Hendersonville TN
Thanks for the info guys. I'm just an occasional autox'er not looking to win my regional championship. I want to be competitive when I do race but overall just want a great handling Vette. I race in CAM class and was 8th out of 13 the last time out (beat a Viper by .1!). I won't be changing out the Bilstein sports that I bought new and put in a few years ago. The NYU rear spring is going in tomorrow. My neighbor who owns a shop and is also a Vette fan (he has a built C6 GS) is taking care of the job. This will conclude my suspension upgrades other than getting a more aggressive alignment. Tires are Continental Extreme DW. I'll go softer once these wear out. Next up, long tube headers!
Racer
Joined: Feb 2012
Posts: 442
Likes: 3
From: Hendersonville TN
It's was raining when I picked up the Red Dragon from the shop today so I didn't get to drive it hard to feel the difference the spring made. That and the passenger rear is much higher than the driver side so I need to adjust it. Can't tell by looking but I measured from floor to frame on each side. Hoping to have an update for you guys about handling changes on Friday. Just driving home though cruising in a straight line it does feel noticeably more planted and solid.
Safety Car
Joined: Nov 2009
Posts: 3,973
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From: Adelaide South Australia
measure from the jacking points (you will see the little indicators in the plastic) to the ground. make sure you measure from the steel behind the plastic.
that will give you a basis to see where your chassis heights are.
good luck with your autocross !
that will give you a basis to see where your chassis heights are.
good luck with your autocross !
Racer
Joined: Feb 2012
Posts: 442
Likes: 3
From: Hendersonville TN
I adjusted the ride height yesterday using the jacking points as references (metal frame). It was way off! I then drove the car and made a few entry and exits from my steep driveway at different angles to make the suspension travel through its full geometry.
The HPDE will be on the race track, not an autocross. I have autocrossed on their autocross pad though and it is sooo nice and smooth!
The HPDE will be on the race track, not an autocross. I have autocrossed on their autocross pad though and it is sooo nice and smooth!
Safety Car
Joined: Nov 2009
Posts: 3,973
Likes: 341
From: Adelaide South Australia
its tough to get some level measurements with a leaf front, do you have the longer bolts in the rear ?
thats where coilovers are so good, its a dream to adjust the chassis wherever you want it.
thats where coilovers are so good, its a dream to adjust the chassis wherever you want it.