Very cool thread!
Best handling C4 ever!
Burning Brakes
Joined: Nov 1999
Posts: 859
Likes: 17
From: Houston TX
1990 Z51 is your best bet. 1991 Z07 has the exact same suspension except shocks are FX3 adjustable. Just as good, they're just more expensive to replace/fix.
1990/91 TPI engines are the same. The reason for the bump in power is the increase in compression over the 89 and previous. (10.25:1 vs.9.5:1)
If I were racing SCCA, I would go with the 90 because you can revalve the billsteins to whatever you want and there isn't much anybody can do about it. Take the shims out of the front spring mount and the car will sit lower in the front. And while running 315s out back is beneficial there is something to be said for being able to rotate your race tires for the best tire life.
And like somebody already said, ZR1s have terrible suspension for autocrossing...
1990/91 TPI engines are the same. The reason for the bump in power is the increase in compression over the 89 and previous. (10.25:1 vs.9.5:1)
If I were racing SCCA, I would go with the 90 because you can revalve the billsteins to whatever you want and there isn't much anybody can do about it. Take the shims out of the front spring mount and the car will sit lower in the front. And while running 315s out back is beneficial there is something to be said for being able to rotate your race tires for the best tire life.
And like somebody already said, ZR1s have terrible suspension for autocrossing...
Le Mans Master
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From: The Old Dominion
Le Mans Master
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The 90 Z51 has th stiffest springs from the factory ans handles great. I think it would be your best bet!
Melting Slicks
Joined: Oct 2006
Posts: 2,238
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From: College Station TX
89-91 Z51/Z07 had the same springs, which were all softer than the '84 Z51 (which probably isn't a bad thing).
Max G’s
Joined: Nov 2008
Posts: 2,751
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From: Monroe OH
NCM Sinkhole Donor
Paul,
Surprised nobody has told you the best set up for any car for autox or road race is the DRIVER. That being said, I have a 91 Coupe with a 6spd for sale. Click on my picture to see the car and you can see all the specs in the C4's 4 sale section.
Surprised nobody has told you the best set up for any car for autox or road race is the DRIVER. That being said, I have a 91 Coupe with a 6spd for sale. Click on my picture to see the car and you can see all the specs in the C4's 4 sale section.
Last edited by l98tpi; Jun 22, 2009 at 03:43 PM.
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Max G’s
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From: Monroe OH
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1991 Covette Coupe, L98 250hp/350lbft, ZF 6spd, 3.45 Ratio, Dana 44 Rear, Sport Seats, AM/FM Cassette Bose, Hard Top and Glass Top, Red Exterior with Black Interior, Stock SawBlade Wheels with Newer Tires, Fresh Tune Up this Spring with AC/Delco Parts, this Vette is STOCK, NO MODS with less than 107,000 miles. Asking $7,900.
Thread Starter
Advanced
Joined: Dec 2007
Posts: 58
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From: Austin TX
Word. I have been autocrossing my '68 Camaro for about a year and half now. I consistenty beat the folks who show up to run their C5 and C6s on street tires. Have even beat C5 Z06 on occasion. Needless to say i have a lot of mods in the car--probably at this point you could buy a C5 Z06 for less than what i have in the Camaro. I also occasionally AutoX my '01 WS6. Just looking for an affordable project, thought a C4 would be fun.
Safety Car
Joined: Feb 2000
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From: Austin Texas
That said, your driving style will need to change based on the car you have. You'll find the limits to where the car can go based on your skills as a driver. The 1991 Z07 package is killer...I was spanking cars in Group 2 with nothing but a poly suspension upgrade (since the bushings wore out from too much aggressive driving) and everyone else had engine/suspension mods. The Z07 rewards a smooth driver with very fast times and loads of grip.
Max G’s
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From: Monroe OH
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Safety Car
Joined: Feb 2000
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From: Austin Texas
In the first few years you could only order it as a MN6 so mine also has the 3:45 rear end with the ZF6.
Safety Car
Joined: Jul 2001
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From: Detroit's West Side MI
Why would you want the ZF6 tranny? You only need the lower gears in Auto-X and it is extremely heavy.
Did the '89 cars have the ZF6 or the 4+3? I know the 4+3 sucks in general, but isn't it better for AX? Unless of course that means you only get the 3.07 rear gear...what a conundrum.
Did the '89 cars have the ZF6 or the 4+3? I know the 4+3 sucks in general, but isn't it better for AX? Unless of course that means you only get the 3.07 rear gear...what a conundrum.
Burning Brakes
Joined: Aug 2005
Posts: 1,172
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From: '88 TPI L98/HotCam Powell, Ohio
Why would you want the ZF6 tranny? You only need the lower gears in Auto-X and it is extremely heavy.
Did the '89 cars have the ZF6 or the 4+3? I know the 4+3 sucks in general, but isn't it better for AX? Unless of course that means you only get the 3.07 rear gear...what a conundrum.
Did the '89 cars have the ZF6 or the 4+3? I know the 4+3 sucks in general, but isn't it better for AX? Unless of course that means you only get the 3.07 rear gear...what a conundrum.
'88 was the last year for the 4+3 (it came w/ the 3.07). The '89 has the 3.54 w/ the ZF.
Race Director
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Drifting
Joined: Mar 2009
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From: East Wenatchee (2hours from n e where) WA
Can anybody tell us what the suspension geometry improvements were in the later L98/C4 cars and if the improved parts can be fitted to the early L98/C4?. I was looking for a LT1 car but this thread has caused me to reconsider. The light weight of the early C4 is important. Also very important to me is the fact that Washington state does not smog test cars older than 25 years. This would be a big advantage for a mid 80's C4.
Safety Car
Joined: Feb 2000
Posts: 4,564
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From: Austin Texas
Can anybody tell us what the suspension geometry improvements were in the later L98/C4 cars and if the improved parts can be fitted to the early L98/C4?. I was looking for a LT1 car but this thread has caused me to reconsider. The light weight of the early C4 is important. Also very important to me is the fact that Washington state does not smog test cars older than 25 years. This would be a big advantage for a mid 80's C4.
I know they changed up some other geometry stuff as well. Just minor tweaks to make the contact patch under deflection better. I don't think you can change the parts out though...there is a reason they have early C4 and late C4 as different parts when you order them...
Drifting
Joined: Mar 2009
Posts: 1,253
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From: East Wenatchee (2hours from n e where) WA
I know that the offset is different on those cars...makes it so you can slide the 315's on the rear and have them inside the wheel wells.
I know they changed up some other geometry stuff as well. Just minor tweaks to make the contact patch under deflection better. I don't think you can change the parts out though...there is a reason they have early C4 and late C4 as different parts when you order them...
I know they changed up some other geometry stuff as well. Just minor tweaks to make the contact patch under deflection better. I don't think you can change the parts out though...there is a reason they have early C4 and late C4 as different parts when you order them...
I am also really interested in the small improvements in scrub radi, bump, ect that took place as the early C4's evolved. Sometimes a mix and match of spindles control arm tie rods ect can help a early platform.