NTMD8R

OK, I've been Autocrossing for over 35 years, with a variety of Corvettes.

I've been pretty good too.
But this 2014 Z51 of mine is starting to annoy me.
I have made changes in accordance with my experience with C2, C5, C6 suspensions, and have been quite successful with those models.

But, this mother will NOT turn in, and it is still "tail-happy".

So... EXPERTS... what have I done wrong, and what can I do to fix things.

2014 Z51 MN7 with MRC
I have gone with wider wheels.... 10x19 front, 11x20 rear.
Toyo R888 tires... 295x30x19 front, 315x30x20 rear.

I installed LG Motorsports C7 sway bars... bigger front and rear.
Alignment.... -2.5 camber, 1/8" toe out front both sides.
-2.0 camber, 1/8" toe in rear both sides.

With this setup, it was VERY "tail-happy".... the rear comes out like crazy... entering a corner.

So, replace the rear bar with the stock Z51 rear bar.
Rear still comes out like crazy.... entering a corner.

But, with all this, I still could not get the front to stick while entering/transitioning a corner... it still slides out.

So I have completely removed the rear bar.
It still won't corner... slides out.... and it is still somewhat "tail happy".

Today running with Porsche club (PCA), a 2013 Grand Sport running Toyo R888 tires puts 2 seconds on me. And 5 Porsches also beat my time.
I don't mind getting beat, but I am really upset with the way the car handles..... not turning in (sliding out on turns... entry, apex, and exit),
and oversteering when I try to get on it.

Yes, it could be my style... I am aggressive.
Yes, enter slow and come out fast..... and I do know to "feather" the car.

But a base GS should not be 2 seconds faster.

So what do I do to make a C7 Z51 with MRC handle like it was on rails... for Autocross.... forget track days. What should this suspension be to do this ?

Cost is a minor object... but let's hear it all, and I'll see what I can do.
Next Autocross is this Saturday May 28.

Thanks in advance

Bill Dearborn

Sounds to me you have to get back to a known baseline. Put it back to stock and see how it handles now and then add your changes back in starting with tire pressures and then alignment. I know it is a PIA to put it back to stock but that is probably the best way to attack the issue. It probably would help if you could get another C7 autocrossser to drive the car and see what they think.

The other thing you need to think about is how the eDiff affects the cornering. It works differently than a regular LSD and you may need to change your driving style to make the best use of it.

Bill

QKSLVRZ

A "problem" is that you did a lot of stuff that changes the balance.

Did you lower the front? Is it possible it's bottoming out?

And do you have someplace you can use as a skid pad, so you can measure G load, and balance?

Magister Ludi

What PTM mode are you running in?

NTMD8R

Bill,
I was thinking of going back to the stock sway bars, just to see what happens.
That's probably the best way to settle this out.
I do know that stiffer suspension for Track is not what is needed for Autocross.
Perhaps the LG front bar is just too much.

You mentioned that the eDiff is different..... can you explain how, and how it works differently ?

And to QKSLVRZ, I did lower it all around, but have put it back to stock height.
The wider wheels/tires caused a major rub on the inner fender lips with it lowered.

LUDI,
I put it into Track mode, and turn OFF Traction control and Active Handling.
If I use the secondary choice with "Track", and go with "Race",
it really interferes with the acceleration... lag, bog, etc.
In fact a course worker told me that he saw a 3 foot flame come out of my exhaust
last time I tried that.

I might have to go back to the original wheels, if I revert back to the OEM sway bars,
since I might be having tire rub again.

By the way that GS has R888 tires on it also.
Also, in other events (SCCA), there is a C5 which also runs circles around me...
It has a huge front spring, stock sway bars, and Bridgestone RE-71R tires.

And those frigging Miatas...... get the momentum up and then hang on....
again running Bridgestone RE-71R tires.

And I have a 2015 C7 Z51, Auto, with MRC that also is spanking me somewhat.
He put smaller wheels on (18,19), those frigging RE-71R tires.

Jeeeezzzzz

AND0

One thing to consider, transitions are affected mostly by shock tuning. Perhaps MRC "TRACK" mode simply slows down the shocks too much, inhibiting weight transfer so it doesn't stick on turn in. Maybe try some different drive modes and get more shock action.

NTMD8R

Thanks guys.
Yeah, I might try a less stiff setting for the shocks, and see what it does.

B Stead... I have them at 32 cold square now.
I've been using R888 tires for about 6 years now, so I know what they like.
And, I'd like to stay with the OEM size wheels (19, 20).
I have already bought wider ones.
But, I could consider the Base version wheels (18, 19)... and this means new tires too.

NTMD8R

Come on..... anyone else ?

How do I make this into a "Killer" autocross car ????

I appreciate all input/suggestions.

AUTO_X_AL

Well, I have a MR 15 with about -3.0 in the front and -2.0 in the back. I run 18/19's with RE71R's.

Take the thing back to stock, get some re71's. Keep a good alignment on it. Run 29 psi in the front and 26 in the rear. Most importantly, DONT drive over the front tires. I run 255's in the front and have learned to drive around them. I drove a lighter car with 315 A6's square for years. If I can learn to drive these front tires, anyone can.

Don't forget, the MR car has a much softer spring than a non mr Z51. Manage the body motion and don't fight it constantly.

formula80_ca

Hi Gary,

Your C7 set-up is a little different than mine, but I'm willing to try your car and give you any feedback I can. I promise not to put it into the blueberry field. Save me a pit spot next to you this Saturday and we can talk about it.

JiminVirginia

I wish I could offer more than sympathy.

I had a BMW M Coupe a few years ago with springs, shocks, a sway bar, an alignment, and it was awful: wouldn't turn in, and it over steered on corner exit. Odd thing was that it felt perfect in spirited street circumstances, when it was being driven like 85 percent. Maybe there was a clue in that, but I never figured it out despite tinkering. Why was that last 15 percent so different that the handling just fell apart?

Gave up and sold the car to a non-autocrosser.

Anyway, going back to the stock front bar seems like a sensible, low cost next step.

Jim

NTMD8R

Update....
OK, back to OEM sway bars.
Saturday... The weather was HOT... 34 deg C.
Tried 32 lbs and 32 lbs (front/rear) pressure.
Didn't really make much difference... still "kicks out" when trying to accelerate out of a curve/turn.
Tried 25 lbs and 25 lbs (front/rear) pressure
No different.
A friend drove it (he is a really great autocrosser with his C4 ZR1).
His remarks at the end was "This car is EVIL". You just can't put the power down
when coming out of a corner... the back end just comes loose.

So.... Sunday.... let's try something a little different.
The weather again was HOT... 34 deg C.

38 lbs cold in rears, 33 lbs cold in fronts.
Migawd... what a difference.
It turns in quite well, and I CAN put moderate power down
when coming out of a turn.
I wasn't fastest, but I was among the top 5 or 6.

So, I seem to be moving in the right direction.
Now, to improve things (I want to put FULL power down when coming out of a turn),
what should I try ?
Back to a stiffer front bar ?

Or ?????

hamburgerman

Lower the rear a half turn and add more toe in. SSR and AS guys run about 11/32 toe in the rear. Bring Toe plates and wrenches to add toe in and lower the rear ride hight. Write down all changes in a log. If it sucks just reset the setting.

AUTO_X_AL

Toe is on Cams and will effect camber so no matter how many marks you make, you can't revert it because it's not a normal toe link.

I ran in the rain this weekend and my passenger was astounded that we could still put power down.

I never run my tires over 30 and I always stagger it more in the front by 2-3 lbs.

rustyguns

I put my money on that electronically controlled rear end. have it checked!

rustyguns

scrubs baby! scrubs!!

http://wwetteforum.com/forums/autocrossing-and-roadracing-classifieds/3832990-fs-hoosier-r7-a7s-in-315-and-255-a.html

NTMD8R

rustyguns,
excuse my ignorance, but the e-Diff....

How is it different than a "normal" LSD ?

How can I have it checked ?,
and what do "they" check for ?

And can it be fixed if something is wrong ?

rustyguns

very good questions, wish i could help but I am a C5 guy, I just know GM is pretty famous for throwing new technology on the market that has not been completely proven. of course that is pretty impossible lol

But if you have had good experienced drivers test your car and they say its scary, i think it is more than your suspension or brakes or tires. you just are not that modified to make the car .. scary.

I would ask those questions in a new thread, good Luck!

NTMD8R

Well, Dammit..... now 2 people have mentioned the ELSD.

So I've spent a lot of effort in researching it, and I found a few things out.

We originally used to run with our Magride set to "Track",
and then the secondary setting to "Race".
(only Z51 with Magride has this capability to make these settings changes)
But I always felt it "hampered" our ability to put full power down,
especially when exiting a corner... it would "bog" somewhat.
So, we have been turning all the "nannies" off, for the last 8 months or more.

Now, in researching the ELSD, it will manage (control) engine speed, brakes, etc.
to ensure the car turns in smoothly and quickly, and it allows full power
when it determines the car will not become a monster to manage, allowing the best exit speed out of a corner.

Dammit.... this is my problem... I can't exit out of a corner... it gets "tail happy" (oversteers).

So maybe we have to learn to drive the car with this ELSD enabled, and learn to
use it so we get the best performance.

Maybe by turning everything off, we were causing the problem.

So, this Sunday, we will give it another try... using the ELSD and its associated "nannies".

I'll update how things went.

doclex

Is that less or more 2-3 psi in the front?