I'm wondering how much the added unsprung weight of a 12 bolt/s60/9" changes the handling of the car. It is primarily a street car but I will be pushing it pretty hard on road courses and autocross, nothing competitive.

 

You dont need it.


The 10 bolt can take plenty of road course abuse.

 

I was originally intending to build up the 10 bolt to handle a heads/cam ls1 build. I now have the opportunity to get a ls7 for core price. I don't know that I will trust a 10 bolt behind a ls7.

 

When I got my S60, it definitely changed how the car handled. I need new shocks to really control it now. I plan on upgrading my worn out Koni SA to fresh DA units here. All things being equal the car will like to oversteer a little harder and when it does it "pendulums". I mean when it does oversteer it’s harder to pull back. I actually can get some extra lift throttle oversteer too. Granted this only really shows at low speed for me. Once I lowered my car and didn't get new DA konis it accentuated it.

The pluses, with the extra weight, it really hooks and drives off the corner. Its unsprung, which sucks over bumps, but it doesn't hurt the CG much since it’s so low. It’s super strong; I snapped 3 10 bolt diffs and 1 LSD before I got my S60 with 4/11s. 2 were 3.42 and 1 was a 4.10 so that was a grenade in the first place. No issues with the S60, but extra gear noise. I haven’t worried about shifting hard since I bought it, I am low 400s at the wheel now. But most of the miles on mine were at 370 or so.

My car definitely feels like more of a drag car than a handling car post S60. But if I upgraded my suspension to match, I bet it would be back to the canyon carver it was.

 

So the added weight just makes it oversteer a bit more? That seems well worth the extra strength, especially once the ls7 goes in and it'll oversteer everywhere anyway.

And of course I just bought new sa konis when I thought I'd be staying ls1.

How are the 4:10/11 on the track? I may be able to pick up a 12 bolt with 4:10s soon.

 

Correct, more oversteer for sure (i would rather have over than under myself) if you have SAs already and they are fresh I would call strano and see if he recommends a differant spring now based on the S60? that might be a cheaper option than going DA in the back.

As far as 4.10s, they are way more fun. But i normaly do 1st-3rd-5th because the gears are so short around town. on the throttle first only good for dragstrip launches or starting donuts. 2nd, 3rd and 4th are now nice and close and you can really just stay in 2nd and 3rd when haling. From a roll its a much closer ration between changes so you can boil it better. I do have a top speed issue post change and I get a wierd vibration over 135mph now. We think its a drive shaft issue, but TBD. For autocross work, its nice as I just use 2nd gear now. Before it was alot of 1-2nd gear changes.

Negative is highway speeds actually turn some RPMs now. lame for gas mileage, but i rarely downshift to make a light pass in traffic anymore. Before I always had to do to 6->4th for any momentum.

 

Good read -- I've had some of the same questions. As for now, my 10 bolt is holding up to 450 rwhp /410 rwtq OK on the track well however I believe that's because I don't dump the clutch on launches when driving on the street.

As for the 4.10's...I'm currently running 4.10's in the rear and they feel GREAT on the street and the car pulls hard 1st through 4th, however they are definitely a limiting factor on top speed and it's frustrating at times to have to deal with extra shifts.

As for results, I've run some of the same tracks with both 3.90's and 4.10's and my times were better with the 3.90's. Road Atlanta is a higher top speed track so it isn't a huge surprise the 3.90's would favor that, however I was surprised to see the car run faster at the more technical (lower top speeds) Atlanta Motorsports Park track.

Since you're looking at the LS7, I don't believe you'll have any shortage of torque to help push you along with a taller rear gear.

 

If you are thinking of getting another rear end, why not get a ford 9". They are light strong and you can have multiple centers so you can have different ratios for different uses. If you have the coin, the DSE quads link is nice. Getting rid of leaf springs and going to coil overs will significantly reduce weight and make the car more adjustable.

 

I think the OP has a 4th gen. I'm the dinosaur with the leaf spring car.

 

Yes I have a 4th gen. As for the 9" I would really like to get a fabbed 9" but that's way more than I can spend on a rear end. I'm only doing the ls7 swap because I got a really good deal on it.

I've been in between going 3:73 or 4:10 for a while now. Leaning more toward 4:10 just because 3:73 would barely be an upgrade over stock 3:42. It'll see Road America the most though so top speed might not be a bad thing to have.

I have yet to do any track time in the car so I most likely wouldn't even notice if the springs aren't working with the added weight.