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99 z28 q's

This is a discussion on 99 z28 q's within the General Help forums, part of the LSx Technical Help Section category; hey im new here. i have a 99 z28 that is stock as far as i know. i bought it ...

  1. #1
    trance_addict
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    99 z28 q's

    hey im new here.

    i have a 99 z28 that is stock as far as i know. i bought it used from some one on autotrader. i had it checked out at the dealer first though. rydell chevy ran a diagnostic on the car and said it was ok.

    i have raced it a bit on the street but never what i did today. today was the first day i took it to the track. my best time was 14.4.

    on the way back i took a stealth and a late 90's mustang goin 120-140 for about 40 miles on the fwy. at one point the car went side to side and scared the **** out of me. my friend said it was speed-wobble.

    my questions:
    is my time good for being stock
    why did that speed-wobble happen
    what can i do to prevent it from happening again
    what is the most bang for my buck horsepower gain
    why will my car not drive straight even after an allignment

  2. #2
    Senior Member
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    Check the rear suspension/chassis components. Panhard bar, torque arm, lower control arms, anti-sway bars, etc. Something is worn, loose, missing, or broken.

    Don't drive it anywhere until you get it looked at.

    If you don't have SFCs, get them now.

  3. #3
    Senior Member
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    Oh, and you have no business attempting speeds like that with original components. Shocks wear out, bushings wear out, and unless your tires are new/only a few years old w/low miles, you're asking for trouble.

    When you wreck it, can I have your tail light assemblies? I wanna put strobes in 'em...

  4. #4
    trance_addict
    Guest
    what a nice sentiment. thanks...


    what are sfc's and i do actually need new shocks. any particular ones i should get

  5. #5
    Senior Member Hurley711's Avatar
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    414 RWHP 395 RWTQ
    00 Black Ram Air Trans Am

    Get some weld in SFC...Sub Frame Connectors, they stiffen the ride on your car and help prevent the underside from twisting and turning. Also look into some Bilstein HD shocks all the way around. They made a HUGE diff. in my cars handling. Stock shocks are crap crap crap. As far as 14.4, that's pretty horrible, most LS1's run in the mid 13's stock with some hitting low 13's with good drivers. This is assuming you are racing at sea level. 14.4 leaves ALOT of room for improvement. As far as perf. mods, what do you have? M6 A4? Usual first mods are lid, FRA!, headers , cam...etc. a stall convertor if you are an A4, possibly gears if you have a M6. What kinda tires are you running also and what is your $$$ budget?, just make sure you keep up with the supporting suspension mods like SFC and LCA..Lower Control Arms, a nice Torque Arm, panhard rod so that the car can handle the extra power you are putting down.

  6. #6
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    Quote Originally Posted by trance_addict
    what a nice sentiment. thanks...


    what are sfc's and i do actually need new shocks. any particular ones i should get
    Yeh - you're right (sorry). However, I'd still be REAL careful because what you describe is an accident waiting to happen.

    Subframe connectors tie the front subframe to the rear, taking stress off the unibody. That was my first mod (I did the SLP bolt-on and am very pleased with them). You'll get an argument over which is better (bolt-on vs weld on), but if I feel the need, I can always weld them.

    Shocks. Like anything else, you get what you pay for. SLP still offers OEM DeCarbon for very little $$$. The Bilstein shocks were an SLP option, and they're next up the line. I have no experience with the adjustable shocks, but the top of the line (IMHO) are Koni.

    Seriously, my $$$ went for suspension/chassis mods first thing. Next were little things to help the car run cooler (160 T-stat, fan switch, auto trans cooler). Next up will be brakes and then I'll start looking at power upgrades.

    Best wishes, good luck, and PLEASE be careful out there.

  7. #7
    Senior Member SeVeReDiStOrTiOn's Avatar
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    05 Wrangler
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    Quote Originally Posted by trance_addict

    on the way back i took a stealth and a late 90's mustang goin 120-140 for about 40 miles on the fwy. at one point the car went side to side and scared the **** out of me.
    my questions:
    is my time good for being stock
    why did that speed-wobble happen
    what can i do to prevent it from happening again
    what is the most bang for my buck horsepower gain
    why will my car not drive straight even after an allignment
    well for one, going 140 on a public highway is moronic...not only can you kill yourself and someone else but your shit will get impounded

    your time blows...what was your 60' time, you probably need to work on the launch.

    Welcome to the world of F-bodies...they tend to follow the road like a mofo, so get used to it. New tires will help a lot, along with what everyone else has mentioned. Not going 140 on jacked up roads will help also.

    Do a good tune up on it first...best bang for the buck is headers and rear gears....but start off with a air lid and a catback and the free mods....then SFC's...then i'd get headers...ls6 intake manifold....port your throttle body...stall(auto)...tune....my .02

  8. #8
    Senior Member SeVeReDiStOrTiOn's Avatar
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    05 Wrangler
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    Quote Originally Posted by trance_addict
    i do actually need new shocks. any particular ones i should get
    Check to see if their leaking first...if their not then odds are their still good. Either that or their so shot that there's no fluid left. How does it ride? Check to see what the rebound is....anything more than a bounce and a half is bad IMO

  9. #9
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    Sebring Silver
    98 Z28

    Quote Originally Posted by SeVeReDiStOrTiOn
    well for one, going 140 on a public highway is moronic...not only can you kill yourself and someone else but your shit will get impounded

    i hope i don't get caught doing it but i regularly hit 130+ without any problems . but these are wide 4-6 lane hywy's . an di also have alot of high speed driving experience....not that i am saying it is ok. i don't notice any shimmy shake or anything, i might as well be doing 55. i also found out that the needle does go about an inch past 155...lol. and the car still felt strong!!! sorry but you can't do that on the track. maybe at the speedway

    the only thing that sucks is the brake fade after slowing down from a run like that....so i make sure to allow cool down times...and i am also very on top of my maintenance including eagle f1 gs d3's, and i always keep a good eye on my brakes etc.....also my car has the usual safety upgrades
    i can't skydive anymore so i just stick my head out the window at 130 mph....hehehe

  10. #10
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    What elevations is the track you ran at?

  11. #11
    car enthusiast djvaly's Avatar
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    some info on calculating HP, and my bolts on mods below:
    A4 TA, substract 18% to 20% from the engine hp and you get hp to the rear wheel.
    The M6 are said to be about 16% power loss..
    so let's take my '99 A4 TA which claims 305hp to engine. That means
    305-(305*0.18) = 304-54.9 = 250.1rwhp as stock engine.

    my Mods:
    I've got bolt on mods, lid and filter (5rwhp), SLP cold air induction kit (8rwhp), smooth bellow (5rwhp), Gratenelli MAF (5rwhp), 160F thermo, cat back Corsa (15rwhp), HyperTech Programer II (10rwhp), ASP Underdrive Pulley(12rwhp).

    This dynoed the car at 315wrhp. so all those bolts on gave me only about 60-65 rwhp gain which is just about right. I did spent $850 on the Corsa, then $250 on the HPP3, and then another $300-$400 on the rest, about $1500 total which is about right for 60rwhp gain. If you were to spend $2000 on new head cyclinder it would bump you 50-60rwhp so I think I made a pretty good investment so far on the bolt ons.

    My next move is to get jet-hot long tube haders and Y pipe which will add 20-25rwhp and then
    get ls6 manifold intake adding another 10rwhp. And when I get $2-3k aside next year I can get the
    head/cam package Patriot stage III probably which will get me in the 420rwhp with a nice tune.

    PS. I did get the Eibach Pro kit lowering 1.25, it looks great.. use the stock shocks as you won't bottom out with this unless you go with 2inches springs.
    If you lower your ride and want to do LT headers and Y pipe later, you can still do it just stay away from the SLP brand since they will eat an additional 1-1.5 inch into the clearance and may scrape/bottom out every now and then.

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