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c4 autocross setups

Old 12-03-2018, 01:35 PM
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ZRConekiller
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Default c4 autocross setups

Hi everyone, I posted over in the zr1 section as well but im looking for what everyone is running as far autocross setups. Car in question is a 90 c4 zr1 yes I know its heavier and not the best platform c4 for auto crossing but they told me my 03 cobra wouldn't be competitive or fun and it was. I am looking to set the car up for BSP, car is bone stock right now and my first round of mods is going to be a big front bar van steel 35mm or equivalent, poly bushings up front possibly custom offset lower control arms, brand new factory style bushings out back and Hoosier a7s in 295 front 315 rear (going on stock wheels this year) . If anyone has any information it would be greatly appreciated thanks!
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Old 12-05-2018, 08:25 AM
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what are you allowed to do in BSP - is that a limited mods class ?

the Vansteel 35 mm is a hollow bar - saves weight but loses a bit of rate. The Vansteel 32 mm solid (early c4) is over 1700 lbs spring rate - if you ask them they will tell you what the 35 mm bar rate is.
For $400 the complete kit with rodends is a pretty good deal I reckon. You will need axle clamps on the sway bar to locate it if you run rodends.
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Old 12-05-2018, 12:15 PM
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Yes, please let us know what the rule restrictions are for BSP, then we can give you some input.

I've done lots of stuff to my 88' and it handles amazing but not sure if my mods would be allowed.
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Old 12-05-2018, 12:39 PM
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BSP in a nutshell r comp tires big sway bars and springs (no coilovers), racing seats, lighter flywheel, any size wheels I want, mild engine modifications, whatever shock setup, small aero (which wont be done just yet), and I cant change any of the multi link suspension to spherical rod ends like banski, also offset poly bushings in the front are allowed no metal bushings though, whatever breaks I wants etc. That's the main points I can remember off the top of my head.
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Old 12-05-2018, 12:54 PM
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Looks like the rules don't allow most of what I have done...

One thing that maybe allowed is global west del-aluminum front control arm bushings, they are not offset. DRM toe rod and trailing arm relocation brackets sound like they may be allowed.

Don't put poly in the stock trailing arms as they move in more than one axis of motion so poly would bind up.

I have stock shocks and springs in my rear and like them, but lots of people like the koni yellow shocks.

The rules sound pretty restrictive.... so another big thing to look at is alignment.

Just a rough place to start would be:

Front:
6 degrees front caster and as much negative camber as possible and a little bit of front toe out.

Rear:
1.5 negative camber, slight rear toe in.

I will say a big benefit of rod ends and and adjustable suspension parts is you can get .uch better alignment specs than a stock ish C4....something to think on just in case you go up in classes in the future.

Other than that just nice sticky tires is all I can think of for now.
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Old 12-05-2018, 12:58 PM
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Forgot to mention the stock ZR1 brakes are probably fine for autocross. But if you want more I hear Wilwood makes some nice kits, or if your on a budget C6 brakes work well too.

Oh and also there is the DRM brake bias spring which adds a little more rear bias to the brakes, its suppose to help a bit
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Old 12-05-2018, 05:24 PM
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B Stock Production. Minimal mods. I thought the C4 was too old for many of the SCCA classes.
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Old 12-05-2018, 08:59 PM
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B street prepared is actually very well suited for a c4,it’s a lot smaller than the newer vettes and the old lt5 makes decent power out of the box with a very long first gear.
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Old 12-06-2018, 10:52 PM
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Originally Posted by blackozvet View Post
For $400 the complete kit with rodends is a pretty good deal I reckon. You will need axle clamps on the sway bar to locate it if you run rodends.
Unfortunately, as the OP noted after you posted this, rod ends aren't allowed in Street Prepared. That does kind of suck for the rear suspension links of C4s. I don't even think he can run rod ends for the swaybar links.

Originally Posted by DMITTZ
One thing that maybe allowed is global west del-aluminum front control arm bushings, they are not offset. DRM toe rod and trailing arm relocation brackets sound like they may be allowed.
Del-A-Lum bushings aren't allowed either, because they replace a lot of the bushing material with metal. So he's stuck with poly or rubber (good luck finding those!) or those new SuperPro bushings for the rear. Offset bushings are allowed if they maintain the stock outer shell and inner sleeve dimensions. OTOH, other suspension relocation like the DRM brackets are not allowed: stock geometry only, except for whatever changes you can finagle out of offset bushing materials.

Other than that, DMITTZ, I agree with all your recommendations. Eventually he's going to want much stiffer springs and a lower ride height, but AFAIK he has to stick with leafs. The ZR1 in 1990 had essentially the same spring rates as the base C4, a 96.2N/mm front and 39.9N/mm rear. So an easy option would be to go to the Z51/Challenge springs at 115.5/57.2 (or 660/326 in Lb/in). The step up would be to scrounge stiffer aftermarket monoleafs, which just got more difficult with the closing down of VB&P. If possible, try to find a used set of VBP Xtreme springs, which allow much higher rates (mine are 1125/550 Lb/in) and fully adjustable ride height. Also, keep monitoring Van Steel (or call and ask them), because I've been advised that they bought the molds from VBP and may start making Xtreme springs.

For swaybars, I think I have the 30mm Z51/Challenge bar on my car right now, and I'm currently using a 23mm 1984 Z51 rear bar. Whether you want way stiffer swaybars will kind of depend on whether you plan to get much stiffer springs or not. If you stick with stock springs or Z51/Challenge springs, you might seriously consider the big Van Steel swaybar combos that blackozvet mentioned, IF they can be used with stock-style end links (I would think they can, but just make sure).

For shocks, Koni is a good choice but another option is Ridetech's HQ series. I agree that stock brakes are just fine for autocross use - just get pads that will take a bit of heat. Believe it or not, I've found that PowerStop z26 pads are fully adequate for my C4 for autocrossing. I have Wilwoods that I would put back on the front for track events, but they aren't needed for autocrosses at all. The DRM bias spring might be pretty useful, as these cars seem heavily biased toward front braking force. I might have to look into that myself.
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Old 12-11-2018, 07:12 PM
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The ZR1s with their heavy motor in front push bad in corners. The bigger front bar you plan on will make this even worse. My dad runs a 90 Z in NCCC group 1/1S (stock class). He tired the bigger bar for one weekend, and immediately took it off because the car wouldn't turn. If anything, plan for a bigger rear bar or stiffer rear spring to loosen the car up a bit. I took his bigger bar and put it on my base model 91. My car was very loose to begin with and the bigger bar swung it to the sightly tight/push side.


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Old 12-12-2018, 12:03 AM
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Originally Posted by vettehardt View Post
The ZR1s with their heavy motor in front push bad in corners. The bigger front bar you plan on will make this even worse. My dad runs a 90 Z in NCCC group 1/1S (stock class). He tired the bigger bar for one weekend, and immediately took it off because the car wouldn't turn. If anything, plan for a bigger rear bar or stiffer rear spring to loosen the car up a bit.
I agree overall, although I think the ZR1 push has as much more more to do with wider rear wheels/tires and wider track as it does extra front motor weight (there's no clear answer to how much more an LT5 weighs than an LT1, but curb weights suggest it is heavier and more of the weight is definitely higher up). One thing I encouraged the OP to do in another thread is go up to 11" wheels in front and run 315s up there. IIRC, he said that would be in the plans eventually, but not at first due to budget. If he did this, it would make a world of difference in getting neutral balance. Getting lots of negative camber up front will, too. So eventually this will come around. My 96 with square 11" wheels, 315 tires, and lots of negative camber is close to neutral with the 30mm front bar and 23mm rear bar (OEM bars). But yeah, he may have some push initially, unless/until he upgrades front wheels and tires. OTOH, if he follows blackozvet's advice and gets both front and rear aftermarket swaybars, it might stay pretty neutral right now. It's hard to say until he tries it.
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Old 12-12-2018, 04:21 AM
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The LT5 engine weighs 596 lbs
The L98 engine weighs 431 lbs
L98 with auto trans is 541 lbs
L98 with ZF6 manual trans is 592 lbs (ZF box is 150 lbs)

so your starting with a 165 lb handicap over the front end
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Old 12-12-2018, 08:37 AM
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Originally Posted by blackozvet View Post
The LT5 engine weighs 596 lbs
The L98 engine weighs 431 lbs
L98 with auto trans is 541 lbs
L98 with ZF6 manual trans is 592 lbs (ZF box is 150 lbs)

so your starting with a 165 lb handicap over the front end
Where did those numbers come from? I'm curious, because there are numbers for each that are all over the map. The all-aluminum LS engine family is usually quoted at around 430lbs, whereas the iron block/head gen-1 Small-Block Chevy (like early L98) is usually quoted at around 570lb. An aluminum-headed L98 should come in around 530lbs or so, and should an LT1 or LT4. but maybe the difference is between a bare long block (light) vs a fully dressed engine (with oil, accessories, exhaust manifolds, etc.). I'm never sure what to believe.

ETA: I've always thought that there had to a difference of ~165lb, like you said, regardless of what the absolute engine weights are, because there's a such a big difference in listed curb weights between an L98 C4 and a ZR1. There's no way that convenience options account for the big difference in curb weights.

Last edited by MatthewMiller; 12-12-2018 at 08:40 AM.
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Old 12-12-2018, 08:41 AM
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Originally Posted by blackozvet View Post
The LT5 engine weighs 596 lbs
The L98 engine weighs 431 lbs
L98 with auto trans is 541 lbs
L98 with ZF6 manual trans is 592 lbs (ZF box is 150 lbs)

so your starting with a 165 lb handicap over the front end
Where did those numbers come from? I'm curious, because there are numbers for each that are all over the map. The all-aluminum LS engine family is usually quoted at around 430lbs, whereas the iron block/head gen-1 Small-Block Chevy (like early L98) is usually quoted at around 570lb. An aluminum-headed L98 should come in around 530lbs or so, and should an LT1 or LT4. but maybe the difference is between a bare long block (light) vs a fully dressed engine (with oil, accessories, exhaust manifolds, etc.). I'm never sure what to believe.

ETA: I've always thought that there must be a difference of ~165lbs, like you said, because there's around that much difference in curb weights between a ZR1 and a regular L98 or LT1 C4.
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Old 12-12-2018, 07:04 PM
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Originally Posted by Kevova View Post
B Stock Production. Minimal mods. I thought the C4 was too old for many of the SCCA classes.
National competition has a 30 year limit, which does not apply to regional. The wording seems to indicate it only applies to street class anyhow, not street prep.
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Old 12-12-2018, 11:14 PM
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Originally Posted by ZRConekiller View Post
B street prepared is actually very well suited for a c4,itís a lot smaller than the newer vettes and the old lt5 makes decent power out of the box with a very long first gear.
i never thought about that, you are right about a long first gear !


it sounds like you are no stranger to autoX - some of the autoX clubs in my area were a little too competitive.

people would get all butthurt if so and so, who doesnt usually beat them, beat them. They would go running to the officials, claiming so and so must have an illegal mod.

they also hated corvettes. Would set the course to not have long straights/ highly technical to benefit the miatas.

they also took pride in setting a minimum of cones to make the course difficult and confusing to see how it went - to make sure the newbz screwed up and the regulars went home with the prizes.....

ok end rant.

yea the zr1 should be awesome and really cool to be competing with that there! Good luck / have fun
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Old 12-13-2018, 02:25 AM
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Originally Posted by MatthewMiller View Post
Where did those numbers come from? I'm curious, because there are numbers for each that are all over the map. The all-aluminum LS engine family is usually quoted at around 430lbs, whereas the iron block/head gen-1 Small-Block Chevy (like early L98) is usually quoted at around 570lb. An aluminum-headed L98 should come in around 530lbs or so, and should an LT1 or LT4. but maybe the difference is between a bare long block (light) vs a fully dressed engine (with oil, accessories, exhaust manifolds, etc.). I'm never sure what to believe.

ETA: I've always thought that there must be a difference of ~165lbs, like you said, because there's around that much difference in curb weights between a ZR1 and a regular L98 or LT1 C4.
A while ago a friend asked me about using an LT5 ZR1 engine in a kit car and wanted to know about the weight differences.
Those numbers are from searching different places around the web, Im pretty sure the LT5 weight is pretty accurate, it comes from GM info on the engine.
As far as accuracy goes, there is always going to be a plus/negative fudge factor involved, taking into account how 'dressed' the engine is.
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Old 12-13-2018, 09:29 AM
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Couple questions what would be the minimum weight for a ZR1? If the FX3 is working why change out shocks?
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Old 12-13-2018, 09:34 AM
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As far as weight im hearing 3200 is achievable with race seats, smaller battery etc... im not changing out the shocks right now they work perfectly fine (have been in performance mode since I have owned it ) well see how the care behaves in the 2019 season. I have some nasty competition my buddy has a well prepped c5 z06 with 315 and 335 hoosiers, another friend with a very well prepped m3 and a pesky Honda civic with one hell of a driver all in all cant wait for next year. I will make a build thread when I start tearing into this thing before spring.
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Old 12-16-2018, 09:16 AM
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What about a carbon fiber hood? Is that allowed?

exotic muscle used to sell one that fit well. Said it was hugely popular wirh zr1 guys
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