NVNO1

Hey guys I have a question about my car putting down the power. I have HCI C6Z06 making 553rwhp 500TQ. I was in San Diego last weekend and noticed that when I was full throttle going through the gears the rear end of the would wallow or shift from left to right. It seemed as though it was putting more power to the right wheel then left back and forth like that. Sorry for the horrible description, but it's kind of the only way I can describe it. No noises or anything like that. It was very unnerving however. Had I not eased off the throttle I'm not sure what would have happed as it seemed to get worse the faster I went. I also noticed this at home.
Is the diff too weak and can't handle the extra power? Car only has 7k miles on it and set up perfectly and no issues. I've gone over everything on the car numerous times to make sure everything is tight and is the way it should be.

Unreal

Tires or alignment. Not normal.

Racingswh

What tires and what size?

NVNO1

Tires are new. Alignment is fresh. Tires are 285/35/18 and 345/30/19. I did some more research and some have mentioned the traction control is the problem and can’t keep up. Apparently if the traction control is off no more problem. Can anyone confirm this.

73DBG

Did you see “engine drag mode” on the DIC? That can happen with 345’s in the rear and you still have all the nannies on, tend to agree with Unreal....tires or alignment not saying your diff is fine since I’m just a dude on the forum and haven’t seen the car but I’m making a significant amount more power than you and my differential is holding.....for now lol did you do factory alignment specs? Not sure if what your intended use for the car is or how much more power you plan on making but if you do move up and decide it’s a “straight line” car a custom 4 wheel alignment helped me out, took a while to find a quality shop that new what they were doing and said they align whatever specs I wanted, lots of shops said they would only do factory setting. A more race/track oriented shop with a Hunter touch-less set up is the way to go. Keep us posted man. Are you local to SD? I’ll be moving out there with the next year trying to see who’s in the area with fast vettes, or any I guess....I’m not too picky lol

73DBG

****I don’t want to confirm 100% over the internet but I’ve seen “engine drag mode” making a small pull in 1st or 2nd with the nannies on, never seen it with “all off” now I can’t or couldn’t stay in a pull from 1st or 2nd for long so I can’t compare as to what the rear end would do, I’d image you can make that hit much longer so nothing to give you on comparison as to what the rear does when “engine drag mode” displays and you keep on the gas, I figured this stuff out early on so once I realized why I was getting that display on the DIC I don’t make hits with the nannies on I’ve seen mine do it in competitive driving as well, I usually cruise in that mode but if I’m making test runs or in Mexico it’s all off....and it took me a solid 8 months of feeling the car out before I was comfortable with taking everything off.

Unreal

What are the alignment specs and what tires? Saying new and fresh doesn't help. There are tires that are known for doing this, so if you got a brand new set of those tires, that is the issue. Same with alignment, thats fine that it was done, but doesn't mean it was done for stability putting power down as OEM specs are kind of junk.

Pb82 Ronin

Happened to me when running 345 NTO5R's (drag radials). "Engine drag mode" came on the DIC and the car was literally unstable at freeway speeds. Immediately ditched them for regular 325 NTO5s. All problems went away and the car was fun again.

What tires are you running?

73DBG

I’ve got 345/30/19 NTO5R’s and have been 160+ quite a few times and the car felt pretty damn good, stable and tracked straight. Again I do have a custom 4 wheel alignment and the specs on this alignment are specifically for putting down straight line power and being able to hold straight at 160+ I got help for the best alignment specs to do this from several guys on here. I’m sure Unreal has been went even faster on a drag radial as well. Run down the simplest solutions first and if you do want specs for a better alignment to suit your needs let me know I’ve got mine saved. 🇺🇸

TRSCobra

Sounds like a Michelin pilot super sport problem

Unreal

Was trying to get there without calling out specific tires by name, but since he just said new tires can't really say if it is one of the tires that is known to sway like the PSS.

Premiumspeed

My car did this in second gear when i had Nitto Invo's on the car and traction control off but active handling on. It feels like the rear tires are taking turns losing traction and it's a weird feeling of the rear end switching left and right. I didn't notice this when i turned everything off by holding down the TC button.

I have MP 4s now and haven't noticed this happening, but i always turn TC/AH completely off when i'm going to be laying rubber.

I'm not sure you are experiencing the high speed wobble, this is different IME.

tommyc6z06

also check the rear wheel bearings, in case. Service Bulletin No.: 07-04-95-001A

Michael_D

I have MPSS 19/345's. Never experienced what the OP has, and I am not bashful with the go peddle. I usually disable traction control, but that's it. Sounds more like a mechanical or alignment issue causing this, rather than tire brand.

Lawdogg

Check your upper and lower control arm bushings

NVNO1

Thanks for all the input guys. I will look for the alignment sheet and post up how my car is set. I believe it is set at factory specs. I never new there was a problem with Michelins?? I have super sports. Would it even be possible my lower control arm bushings are bad with only 7k miles on the car? Btw the car never did this when it was stock. Thanks Tommy for the wheel bearing post. One more thing to look at.

Racingswh

The very first thing I would do before you chase anything else is try another set of wheels and tires on the car and see if it still does it.

I went through exactly the same thing and chased every component it could have possibly been on the suspension. It ended up being the tires. Those happened to be Michelin Pilot Sport cups in 345 30-19 on a stock 12 inch wide wheel.

Literally in post number four of my thread back many years ago I think from 2012 it was suggested that I try changing out the wheels and tires and I did not and spent the next 3 weeks trying to diagnose the problem. I should have eliminated it right then and there at the track that day because we had other wheels and tires we could have tried. Live and learn.

jayyyw

this

KnightDriveTV

Definitely strikes me as bushing deflection. Put a gopro under the car with a mount strap and rip it and watch those control arms. Same with the rear tie rod allowing deflection under load. If you're getting dynamic toe changes, the car is going to walk all over the place.

tommyc6z06

actually, I experienced instability at 135+ at Mosport. I had to back out over the undulations up the back straight.
It was incrementally better with the passenger window up, but I’m guessing that my primitive AH, even in competition mode, may not have liked the slight unweighting at high speed over the rises.

Too bad I didn’t think of this at the time, to try switching off altogether.
That, or putting up the driver’s window too. I know 991 GT3s and Turbos have such an aero problem with windows down (they sell air deflectors for their A-pillar area specifically to negate this).

Next chance for me to experiment will only be in August at Watkins Glen...although no such undulations on the back straight there.