Dissappointing autox with the LS Z

[heavy85]

Here's the short version of my story ... recent history anyway. 240Z. Had an L6 with tripples, etc that ran well. Usually about a second shy of fasted time of the day and actually got FTD once. Running FP, slicks, etc. So then came the 1.5 year journey to LS land. During that time I also cut out the old, cracked subframe and installed full length subframe. Also welded in tubes from the rockers to the T/C bucket & the upper frame horn. Also welded tubes from the towers to the firewall. Also turned the crossmember into a k-member. The swaybar mounts were badly ripped out so they were also fixed and then some. So in other words the front end was stiffened up a LOT and the swaybar now actually mounts to something substantial. On the rear all I did was weld a rollbar tube between the towers. So now it is all but uncontrollable. Yeah part of that is the LS power and getting used to it (already switched back to the 3.7 from the 3.9 but didn't help much) but something else is just way out of balance. Running 225F/250R, big front bar, no rear bar (this is actually another change as of T&T a couple weeks ago to attempt to get the power down - was running medium size rear bar). This is a street/track car so I drive there and change tires so nothing crazy for spring rates. Today I was 4 ... count them FOUR ... seconds back on a 50 second track to the sames cars I was competing within a second of before on a typical 60 second track. I obviously need to double check the alignment to make sure somethings not jacked. Slow corner and any throttle the front end just washes out. Mid speed corners and any throttle the back end snaps around NOW. Fast corners it just dances like it's on ice. This sucks ... but at least the LS1 still puts a smile on my face every time it fires up and the power is just silly really.

 

Cameron

 

PS: Lost the fifth and best run at the end due to puff of oil smoke inside the car ... freaked me out ... turned out to be the stupid oil pressure idiot light sender which I had to then replace in the Autozone parking lot in lieu of trophies.

[260DET]

Others will have more experience with your type of engine/chassis combo but I know that it does not take much to bring on the sort of handling you describe with a S30. Obviously check wheel alignment, bit of toe out on the front. Dampers may now benefit from heavier valving, up the spring rates a bit to take advantage of the stiffer chassis.

 

But it may not take much to improve it a lot, start with the obvious things.

[BillZ260]

Sounds exactly like my first solo run a month ago. I don't have runs to compare with but I'm sure my tires are old, and could use some alignment tuning too.

[katman]

Well the obvious problem would be too much front roll stiffness. Less obvious possibilities: Not enough front bump on the shocks, not enough front bump travel, not enough front camber or toe out. Corner exit understeer caused by onset of throttle is usually standard corner entry understeer exacerbated by onset of throttle, so I suspect unless you don't have enough low speed front shiock rebound you've probably got plain ole slow corner understeer. Front roll stiffness has increased a lot by your own description, so that's proly it. What tires are you running, what camber, what toe, what shocks?

[carusoracer]

Here's the short version of my story ... recent history anyway. 240Z. Had an L6 with tripples, etc that ran well. Usually about a second shy of fasted time of the day and actually got FTD once. Running FP, slicks, etc. So then came the 1.5 year journey to LS land. During that time I also cut out the old, cracked subframe and installed full length subframe. Also welded in tubes from the rockers to the T/C bucket & the upper frame horn. Also welded tubes from the towers to the firewall. Also turned the crossmember into a k-member. The swaybar mounts were badly ripped out so they were also fixed and then some. So in other words the front end was stiffened up a LOT and the swaybar now actually mounts to something substantial. On the rear all I did was weld a rollbar tube between the towers. So now it is all but uncontrollable. Yeah part of that is the LS power and getting used to it (already switched back to the 3.7 from the 3.9 but didn't help much) but something else is just way out of balance. Running 225F/250R, big front bar, no rear bar (this is actually another change as of T&T a couple weeks ago to attempt to get the power down - was running medium size rear bar). This is a street/track car so I drive there and change tires so nothing crazy for spring rates. Today I was 4 ... count them FOUR ... seconds back on a 50 second track to the sames cars I was competing within a second of before on a typical 60 second track. I obviously need to double check the alignment to make sure somethings not jacked. Slow corner and any throttle the front end just washes out. Mid speed corners and any throttle the back end snaps around NOW. Fast corners it just dances like it's on ice. This sucks ... but at least the LS1 still puts a smile on my face every time it fires up and the power is just silly really.

 

Cameron

 

PS: Lost the fifth and best run at the end due to puff of oil smoke inside the car ... freaked me out ... turned out to be the stupid oil pressure idiot light sender which I had to then replace in the Autozone parking lot in lieu of trophies.

 

 

What are your alignment specs and what size tires and rims are you using.

Also what brand and model of tire are you using?

 

If you were on slicks were they real slicks ie no hologram or groove on the tire or are they Autox compound radials , ie Kumho 710's or Hoosier A6's

 

I would not stagger front to rear wheels in AutoX and with the power you are putting out I would want to be on 16x10's Fr &RR.

 

Depending on your tire I would look hard at camber plates on under the shock tower adjusters so you do not have to cut. You need at least 1.5 degrees of camber in the front and 1.8 rear with 1/4 Toe out Fr and 1/4 Toe in for the rear if you are using A6's or 710's. About 28F 26R psi check your sidewall rollover.

 

Good luck

 

BTW, with out a LSD you would be wasting your tires. I make a huge difference and a must to AutoX.

 

Is your 3:90 a R180 or R200?

[JMortensen]

You mean to say you changed everything and didn't have a winner straight out of the box?

 

I think katman is onto something. Your front bar can now do it's job as it is supposed to, so its like you've added a gigantic front bar compared to the old setup. It's kind of like me testing the bar strength on my workbench. The workbench seemed fairly solid but I was losing 3/4 of the spring rate of the bar through the bench. On top of that you removed the rear bar. So your roll stiffness when compared front to rear is way off from what it was before. I like the suggestion of toe in out back for the power oversteer, but I think you're going to have to do something else to get your balance back. Either put the rear bar back on or put a smaller bar in front and run stiffer springs to help with the body roll.

[evildky]

I believe all the FP champs are running 400 lb springs, I am running 440 front and 250 rear on my L28ET powered car, I tried 440 rears and found I had practiaclly no straight line traction, the softer rear really helped me to put the power down, I'm also running 17x12's in back and 17x11 up front with lots of camber

[heavy85]

Well the obvious problem would be too much front roll stiffness. Less obvious possibilities: Not enough front bump on the shocks, not enough front bump travel, not enough front camber or toe out. Corner exit understeer caused by onset of throttle is usually standard corner entry understeer exacerbated by onset of throttle, so I suspect unless you don't have enough low speed front shiock rebound you've probably got plain ole slow corner understeer. Front roll stiffness has increased a lot by your own description, so that's proly it. What tires are you running, what camber, what toe, what shocks?

 

9.5" FA Hoosier slicks R35 compound on 15x10 rims. Front camber little over 2 deg, rear camber a little less than 2 degrees but right before the race I discovered the left rear was a little over 2. Koni single adjustables (the new versions) which are only two years old with maybe 12 autocrosses and a couple thousand street miles. Front a bit of toe out the rear a bit of toe in - before the race I measured like a half inch toe in and set it back out but was not able to get a real good after measurement but still some toe in. Next thing I will do is obviously verify the exact settings including see if one of the coilovers moved. Oh also forgot I changed from high 2 to low 2 deg camber on the front because before I was wearing the inside of the tires. I now have a pyrometer and the temps are even with the low 2 setting but never measured temps before. Maybe I need to add the half degree of camber back in as this was my first race with the reduced front camber? So what's the best way to deal with the increased front roll stiffness ... I thought it would be good to stiffen the chassis now just need to figure out how to deal with it?

 

About the wicked on throttle oversteer in mid to high speed slight curves - any idea on that one? I went from 3.9 to 3.7 gears (clutch type Nissan R200 LSD) which didn't really help. Anytime I'm just slightly turned and hit the throttle the back just snaps sideways in a very uncontrolled manner. Realize some of it is just the power but it feels really jacked as much and how quickly it goes. Also seems the rear always wants to go to the right.

 

Due to this being a street/track car I didn't really want to go too crazy with springrates but maybe go a little higher if that would really help. I live in the midwest where the roads are really crappy.

 

Jon - I've been running rear toe in for a long time which really helped the unstable braking where the rear used to dance around. I removed the rear bar to help soften it with the idea to get more traction - this seemed to have contributed to the low speed corner exit understeer.

 

Thanks

Cameron

[katman]

Okay, now we're getting somewhere. Take some front bar out. Is that the bias ply or the radial slick? The bias ply's run bigger slip angles and with power on it's not unusual for the rear to feel like its stepping out. I wouldn't expect any meaningful tire temps from an autox run. We're gonna need a skidpad or real track. Camber's sound about right, with that wide a tire. Also sounds like you need to confirm your alignment settings. I think the 1/4 in/outs mentioned by carusoracer is excessive- I don't like dragging tires around, rather make it handle properly with about 1/32 toe in out back and 1/8-3/16 tops toe out in front (road race I don't exceed 1/8, for autox slow corner turn in 3/16 should do it). Get back to us after you're rechecked your alignments. Got corner weights? How exactly did you check your tire temps, what kind of probe, what order, how deep?

 

I'm not a big fan of big springs on an autox car. Parking lots tend to be bumpier than real tracks, plus in your case you have to drive it to and from. Plus, softer springs are easier to drive fast sooner, even though big springs may be slightly faster eventually. In other words, you get 4 minutes of race time, you need to be hooked into the car in the first 15 seconds. A softer car will be easier to figure out. Autox is 95% driver anyway, so there. Are you sure you have enough suspension travel everywhere?

 

When you say "dances like its on ice", what you mean exactly? Just the snap oversteer, or is it chattering across the bumps, is it oscillating between oversteer and understeer, or what?

[JMortensen]

I've been convinced through talking to a number of people who know better than I do that the way to go for a race car is stiffer springs and no rear bar. If you aren't going to do that because it's still a street car, then you're going to need the rear bar to balance what is going on in the front. More rear toe in than you currently have might help. Fix the front toe, go 1/4" toe out for autox. I used to adjust one tie rod and I had a street mark and a track mark, which made it really easy to adjust back and forth at the track. You can do the same with your camber plates so that you don't burn your street tires off. A lot of the guys in OR are running really stiff springs (over 500 in/lbs) and are able to put the power down, which leads me to believe that running 400/250 is not necessary.

 

You might also look at 74_5.0L_Z's suspension motion ratio sticky, download the weight transfer spreadsheet and work it out that way. At least with the spreadsheet you're dealing with numbers and not individuals' opinions. They give a suggestion for the "magic number" you're looking for, but then suggest that you can tailor it to suit your driving style. Might get you in the ballpark and you'd be surprised how much a SMALL change to the roll center makes.

 

On the tire temps I'd try and keep the insides 10-20 degrees hotter than the outsides if possible.

[260DET]

I've been convinced through talking to a number of people who know better than I do that the way to go for a race car is stiffer springs and no rear bar..........................................................................................

 

Particularly when you have a powerful engine, at least for circuit work, I have no autocross experience.

 

Case in point. Friend of mine has a nothing special daily driver S30 with a stiffened body and a heavy but fairly powerful Ford Falcon straight six engine. Since we fitted a 25mm front bar and removed the rear he has been cleaning up nearly everything on wheels, including the usual big dollar Euro pretenders.

 

Car pushes a bit in the high speed corners but he drives around that, importantly the corner exits are great so he carries good speed onto the straight bits.

[heavy85]

Is that the bias ply or the radial slick? ... Got corner weights? ... How exactly did you check your tire temps, what kind of probe, what order, how deep? ... Are you sure you have enough suspension travel everywhere? ... When you say "dances like its on ice", what you mean exactly? Just the snap oversteer, or is it chattering across the bumps, is it oscillating between oversteer and understeer, or what?

 

Bias ply. No corner weights but I'm trying to hunt down some scales. Pyrometer is a Longacre probe. Just standard low end one. Probe is about 3/16" long and I stick it all the way in. It blips high then within a few seconds settles down about 10 deg lower than the instantaneous peak. Only used it twice and I can't really figure out the tricks so any help would be appreciated. No idea if I have enough travel but I've not done anything to my knowledge to affect that from before. Dances like anytime I hit the throttle the rear end steps out and the whole car just gets badly unsettled. Really hard to go through a couple of offsets in a row without it wanting to pendulum back and forth eventually trying to rip the wheel out of my hand. No chattering. Maybe I just need a throttle stop

 

No smoking gun yet. Camber LF 2.25 deg, LR 2.125 deg, RF 2.125 deg, RR 1.75 deg. Front 1/8" toe out, rear 3/16" toe in. Toe was checked quickly with two boards and a tape measure so they are approximate but directionally correct. Since it's a compromised street/track car I know it'll never really be competitive in EM (or before in FP for that matter). Before I was usually in the top 10 out of 80 in indexed time but never even close to a threat for index fast time. I'm an above average driver but nothing special really just trying to keep up with the SS cars with the good drivers (almost always fastest on index and raw). Agree it's mostly driver but right now it's all I can do to hold on. Will keep digging and look closer at the coilover heights tomorrow.

 

Thanks

Cameron

[EMWHYR0HEN]

I hope I don't run into anything worse than what have encountered when I finish...

 

Like Jon mentioned, you can't just expect your car to handle well after extensive changes like you have done. It's ALL about the fine tuning and experimenting.

 

Keep at it Cameron, you'l figure it out.

[jt1]

Do you have sufficent gas pedal travel? With a fairly high hp car, I think it's important to roll in and out of the throttle smoothly. This is a lot easier if you have as much pedal travel as possible. The stock pedal has a pretty high ratio, and if the engine linkage isn't compatible you can wind up with some pretty quick transitions.

 

jt

[katman]

I've been convinced through talking to a number of people who know better than I do that the way to go for a race car is stiffer springs and no rear bar. If you aren't going to do that because it's still a street car, then you're going to need the rear bar to balance what is going on in the front. More rear toe in than you currently have might help. Fix the front toe, go 1/4" toe out for autox. I used to adjust one tie rod and I had a street mark and a track mark, which made it really easy to adjust back and forth at the track. You can do the same with your camber plates so that you don't burn your street tires off. A lot of the guys in OR are running really stiff springs (over 500 in/lbs) and are able to put the power down, which leads me to believe that running 400/250 is not necessary.

 

You might also look at 74_5.0L_Z's suspension motion ratio sticky, download the weight transfer spreadsheet and work it out that way. At least with the spreadsheet you're dealing with numbers and not individuals' opinions. They give a suggestion for the "magic number" you're looking for, but then suggest that you can tailor it to suit your driving style. Might get you in the ballpark and you'd be surprised how much a SMALL change to the roll center makes.

 

On the tire temps I'd try and keep the insides 10-20 degrees hotter than the outsides if possible.

 

Tire temps - totally agree, Hoosiers like a little camber thrust.

 

Small changes in roll center make a big difference [in front/rear balance, and hence front to back spring ratios and sway bar choices] - absolutely true.

 

1/4 toe, Jon and I will continue to respectfully disagree on this by about 1/16, but what's a 16th among friends?

 

Stiffer springs and no rear bar- agrees with my road race experience on mostly southeast tracks. However, IMHO we want as much spring as the bumps and shocks will allow, with about 400 being the upper limit for a series 1 chassis with front strut bar but no cage forward of the firewall (ITS spec, basically). Beyond 400 we started going backwards, although possible to go higher in an EP car where the cage can go forward of the firewall. Up above 200-250 and you're beyond the capability of almost all off-the-shelf shocks, and "twitchyness", skating, and other unwanted hair trigger responses are likely. Again, IMHO, roll bars are for trim only, and you only need one so save the weght, UNLESS you are spring limited because of bumps/shocks/street ride desires so you use two big bars to limit roll whilst maintaining some resemblence of kidney health.

[johnc]

If the car feels like its dancing or skatey, I would check ride height. It sounds like your roll centers have gone underground and the car won't roll and take a bite.

 

How tall are your tires?

What's your ride height front and rear (measured at the rocker panels)?

[JMortensen]

Again, IMHO, roll bars are for trim only, and you only need one so save the weght, UNLESS you are spring limited because of bumps/shocks/street ride desires so you use two big bars to limit roll whilst maintaining some resemblence of kidney health.

I think that with 9.5" slicks and 200ish lb springs, he is right at this point. Stiffer springs would be better than the rear bar, but running a smaller front bar with those tires and springs is going to leave him scraping the door handles.

[tube80z]

About the wicked on throttle oversteer in mid to high speed slight curves - any idea on that one? I went from 3.9 to 3.7 gears (clutch type Nissan R200 LSD) which didn't really help. Anytime I'm just slightly turned and hit the throttle the back just snaps sideways in a very uncontrolled manner. Realize some of it is just the power but it feels really jacked as much and how quickly it goes. Also seems the rear always wants to go to the right.

 

You've gotten a lot of advice in the thread but there are a couple of areas that haven't been mentioned. How calibrated is your right foot? Still L6 or V8. Why I ask is that the first time I drove friends similar car I had very similar issues. I chose to go a gear higher and found that worked for me.

 

You have to remember that the LS1 has about twice the torque of an L6. With your really soft springs when you step on the gas it's going to use a lot of travel. Are you bottoming (use zip ties to see). Pictures of video of the car in action will help a lot too. Some of the power on oversteer could be the rear squatting and the nose raising.

 

Check your tires. Have you cooked the centers out of them. Big power can do this pretty quickly if you're not careful. Handling will become evil with the centers gone.

 

Good luck, I personally feel your car is too soft to make this combo work.

 

Cary

[heavy85]

If the car feels like its dancing or skatey, I would check ride height. It sounds like your roll centers have gone underground and the car won't roll and take a bite.

 

How tall are your tires?

What's your ride height front and rear (measured at the rocker panels)?

 

With the 24" diameter street tires the front is 5 7/8" to the flat edge of the bottom of the rocker (not the bottom of the flange) and the rear is 6". I also run 1" 'bumpsteer' spacers in the front as well as moved the inner pivot up ~3/4" to attempt to keep favorable camber with the low ride. The LCA point down a few degrees at static ride height. Race tires are 22.5" diameter.

 

Thing I keep scratching my head about is I used to be fast with this basic set-up other than the increased chassis stiffness and gobs more power. Seems doom and gloom from everyones comments but I used to be fast (did I already say that???). Would a stiffer chassis and more power alone throw everything so far off to where I can't recover without taking it off the street ... thats hard to swallow. To answer Cary the rear tires look fine - same as the fronts. Calibrated? Right is GO right .... seriously I need to work on this.

 

My thoughts based on everyones posts which I really appreciate:

 

- Add more front camber maybe up to 2 3/4 deg if I can

- Fix rear toe (was shooting for 1/8" in anyway just missed it)

- Take LR camber down to match RR ... maybe even less

- Add back rear bar

- Learn how to drive it ... dammit I used to be fast

 

Other thoughts under consideration:

 

- Try a stock front bar since I have one

- How much spring would I have to add to make a difference and which way would I bias them - more front or more rear? The Koni's being the newer style SA are suppose to support 300 lb if I remember correctly. Not sure how much that would affect the kidneys though.

- Put the 3.5 rear in it since I have one

 

That about summarize it or did I miss something?

 

Cameron

[johnc]

Stop focusing on how your old car drove - its irrelevant. You cannot compare how your old car handled with how the car performs today. Based on your description of how messed up the chassis was, there's no consistent baseline to compare from. You didn't know if your fast times came from the suspension, chassis flex, or your adaptations to a funky car. Focus on what you have, not what you had.

 

Here are my suggestions for when you run the race tires (22.5" tall):

 

Drop the front ride height to 5".

Drop the rear ride height to 5.5".

Increase front toe-out to 3/16 - 1/4".

Put in as much positive caster as you can get.

Set front camber in the 2 to 2.5 negative range.

Set rear camber in the 1.5 to 2 negative range.

Set rear toe-in to 1/8".

Up your spring rates at least 33% (300F, 250R maybe).

Run a 25mm (1") front bar but have a 23mm (7/8") bar ready just in case.

Leave the rear bar off but have a 17mm (5/8") bar ready just in case.

Make the front track 1/2 to 1" wider then the rear.

Adjust the throttle linkage to be as long and linear as possible.

 

Remember, the older you get the faster you was. Right now it doesn't matter how fast you was.