Steve91T

Man what a great day. I've changed almost everything possible over the past 4 years since the car was last on track. I didn't know what to expect. I was just hoping the car wouldn't break. Not only did the car hold together, I was one of the fastest cars out there. I was very happy.

Anyway. I'd like some opinions. Here's some information on what I've done.

Weight reduction 3400 lbs with me in it. No ABS
Bone stock junkyard LT1
Coilover fronts
750 front 250 rear
35mm front bar. 21mm rear bar
C5 front brakes
Carbotech XP20 front. AX6 rear pads
Stock LT1 rear brakes
Stock rear end. Stock torque arm
Rear control arm relocation brackets
Nitto NT01 tires.
Blainfab lexan spoiler




I used my iPhone and harrys lap timer for video. The mount wasn't very secure, so the video is a little shakey, but you get the point. I didn't have time to mount my GoPro. Sorry.

Here's a good video of one of my better laps. The car was a little loose and I was having a hard time putting the power down.


Another big problem that I have is one I didn't expect. Tons of axle hop. I felt like a had way too much rear brake. It was a real handful. I was being as gentle as I could and even with that, I could feel the rear end starting to shimmy. If I increased braking at that point at all, or wasn't 100% perfect with a downshift, it would hop. I've never had it this bad before. I used to be able to threshold brake with zero problems with hop, unless I wasn't smooth.

I hopped the axle pretty bad going into turn 14 in this next video. You can see it was the downshift that did it. Also I couldn't put the power down out of 12.



So during lunch I decided to change the rear sway bar. I had a 21mm on the car but brought the 19mm with me. So I threw the car on the lift and changed it out.




Have I mentioned I love that lift!!!

Back out on the track the car felt much better. I couldn't believe how much more traction I had out of the corners. The car also felt much more balanced. I was really happy with how the car was performing at that point.

So this brings me to my last video. I was only a few laps into my second to last session of the day. The car was handling awesome.....until it decided it had enough. Luckily, I got it on video.



I went into the kink the same way I had been all day. Except this time I had major understeer. It came out of nowhere. Notice the two previous right handlers I was pulling over 1g. Everything was completely normal. Then I go into the kink and I only managed .8g. There was no tire noise, no vibration, nothing. When I jumped off the gas the car didn't even try to rotate.

So I go into the pits, check the car over and head back out a few minutes later. There was absolutely nothing wrong with the car. I honestly thought I must have screwed up. So I had back out and I'm taking it really easy. The first right turn I come to I damn near went off again. Same thing. Major understeer to the right only. It felt like I was spraying oil on the left front tire. So I come back in and really check everything over. I found nothing. By this point a bunch of people were taking to me who saw me go sailing off the track. They couldn't find anything either. Our best guess was I just overheated the left front. I let the car cool down for an hour and a half and took it out for the last session of the day. Same exact thing.

The tire looks fine. I didn't pull it off or anything yet. I just loaded the car on the trailer and went straight to my brothers house and drank his beer. I'll pull the wheel tomorrow and see how it looks.

What could cause this? The aligns my looks fine. Everything under the car appeared just fine. It's so bad that I honestly expected to see a broken tie rod or something. Car still tracks straight....just will not turn right.


Anyway, any and all opinions are recommended!

nitroheadz28

iTrader: (3)

I really enjoyed the write up and vids, thanks for posting!!

What have you done for weight reduction?

JD_AMG

What shocks are you running?
Sounds like something is bent...

Steve91T

Glad you enjoyed it.

Let's see. Some things of the top of my head...
AC
Cruise
Airbags
Radio/speakers
Carpet and all sound material
Back seats along with rear seat belts
Drilled the spot welds for all interior brackets they aren't used anymore.

I think those are the big things. Nothing crazy, but it made a big difference. The car is still street legal, so I can only go so far.


Koni's front, bilsteins rear.

Idk. What could have possibly bent going down a straight? Tomorrow I'm putting the street wheels and tires on, so I'll see if that solves it.

Any ideas on the brake hop?

madmike9396

iTrader: (29)

Damn that looks like a blast!

JD_AMG

Check to see if a shock is blown or something too.
Check to see if a relocation bracket is bent or broken.
Common for our cars when there is too much rear brake. Run stock brake pads in the rear, ditch the relocation brackets and a full length adjustable torque arm may help as well.

FASTFATBOY

iTrader: (23)

Keep the rear lower control arm parallel to the ground, if it needs the brackets to accomplish this, keep them.

Is your steering wheel straight? Was it straight to begin the weekend?

On going off the track, my Z28 did that to me at Barber, It appears to me you turned in too early, got on the gas early and pushed the front. You changed the rear swaybar to get more rear grip, you put a push in the car along with it under power.


I hate vids like this because you can't learn anything from them, you can't see what the driver is doing.

Watch me at 20:25 It baffled me until I watched the vid, I turned in too early then tried to fix it with hot tires. The front end felt like it was on ice, no response at all.






The brake hop is due to the harsh downshift with the rear brakes on the threshold.

Put a good posi unit in the car like a Detroit TruTrac and put the bigger rear bar back on.

Nice smooth driving, you need a vid camera mounted similar to mine so you can see what you are doing in the car.

Steve91T

JD...

I've never had a problem with AX6's before, but I guess with all of the changes, they are too much now. I'll put cheap pads on next time.

The relocation brackets are welded on and are a must. My control arms were at about a 30 degree angle because my car is so low.

Ive got a full length tunnel mount torque arm going on when I change engines. (Current exhaust is in the way)

Steve91T

Yeah I hate that camera angle. I wanted telemetry though. I have a GoPro but I just ran out of time to mount it. Next time I'll have both cameras going.

I just don't get why I have so much rear braking. I've run that rear pad a ton and have never had a problem. I was no where near the threshold of the front tires...ever. Maybe all the changes I've made now require less pad on the rear. I'm going to change my pads before going back out.

About the understeer. After I went off and went back to the pits, I also thought that I did just what you said. But even hours later I actually almost went off the track running only 50%. I have zero grip on the left front. So bad I parked the car for my last session. No joke, I nearly went off at 30 MPH. I expected to find something with the rear sway bar that I just swapped, but it's all tight. I'll put the car on the lift and see what I see. I'm swapping to the street tires also. The dudes at the track think that my 6 yr old (but only used twice) tires are to blame.

A posi is definitely on the list. What something like that cost to buy and install? I'm going to keep the 21mm bar. But I have to say, it felt a lot more neutral with the 19. Maybe it actually was just because I wasn't lighting the right rear up all the time.

FASTFATBOY

iTrader: (23)

I ran a stock torque arm.

I ran Hawk HP+ and HPS on the rear with good success. It's not the pad so much as you need to heel/toe the car or learn how to rev match the clutch. The harsh downshift is whats doing it. Why does the trans sound so bad on the downshift? Why is it so harsh?

I got good at easing out on the clutch in the brake zone late to get the car downshifted, I am just now learning heel/toe.

Steve91T

For reference, the axle hop video I posted was the lap before I went off at the kink.

FASTFATBOY

iTrader: (23)

I'd never run a tire over 2 years old again, almost cost me big at Barber this year.

If you know how to work on cars a posi isn't bad. Take the stock one out, put the new one in and check backlash before and after, if it's close run it.

FASTFATBOY

iTrader: (23)

Is the rear end making funny noises? Does the car drag the inside tire on turns in gravel?

Possibly damaged or locked up the posi, this would cause the car to push really bad if it did. Wheel hop is really hard on the rear end.

Steve91T

No my heal toe downshifts aren't harsh. Very smooth actually. I know in that video the downshift is what set it off, I probably didn't time it 100% perfect.

I've fracked this car for many years, although I just made a ton of changes. I know what a bad downshift does. This is different. Like I said, I can hop the axle with no downshift, just very very smooth application of brake. I could feel the rear dancing around as the rear tires started to loose grip. If I asked any more of the brakes, the reads would start to lock and hop the axle.

Are you hearing the engine match rev on the downshift?

FASTFATBOY

iTrader: (23)

I hear what sounds like a crash box trans, Nascar style down shift...a bang on the down shift.

Steve91T

Yeah I didn't know track tires have a 2 yr shelf life. I know now.

You know I haven't driven the car with no helmet. I'll check it out. I never thought to check the posi for damage. Thanks for the tip.

FASTFATBOY

iTrader: (23)

Listen to your vid, its a loud clunk or a low bang I hear in the brake zone.

Steve91T

Yeah I just did. There's decal pop out the exhaust, but I think you're hearing the engine when I blip the throttle.

Steve91T

1:36 and 1:37 of the first video is a good one. Two low speed downshifts. That's the engine blip you're hearing.

STFU racing

iTrader: (13)

I know I had a lot of issues with brake hop in AutoX. Swapping to a full length torque arm helped tremendously. I'll be putting a more aggressive pad on the front vs rear and hopfully clear most of it out this year.

sorry I have no advice on anything else. Never done a road course.