Bowtieman4life

iTrader: (1)

I like the sturdiness but the handling has suffered and it feels like it has a fat arz. I like being able to run ET Streets at the track but haven't been there in a year. I am looking for a more corner friendly setup. I have QA1's and stock springs that I am willing to replace. Should I dump the 12 bolt and install my stock rear? I'm pretty much sick of 4.11 for the street. All smoke and no go.

Plz no filler post. I want ideas from guys that have made the change or have assisted in it not from guys that heard something or read a post.

Thx ahead of time.

96lt1m6

iTrader: (31)

the rear axle has nothing to do with the cornering ability,10 bolt,12 bolt,9",should not make any difference in this situation.
your cornering ability is all tire and suspension,you can use the qa1's if you set the settings to stiff mode,front and rear swaybars are both in and you have good bushings in them.as for the gear ratio,4.10 give you a much more aggressive launch thats the reason for blowing the street tires away so if you swapped back to a 3.42 it would not be as violent coming out of the hole as well as corners.it would be beneficial for you to keep the stronger rear end in your car,sell the stock 10 bolt and get 3.42s installed in the 12 bolt.you did not mention the size of wheel and tire combo you are using for cornering/handling.
a few other things to check would be;
1.check youe pinion angle,drag racing is usually -2*/ - 2.5*.stock is 0/1.5*+.
2.if you have lca relocators remove them
3.make sure your panhard bar bushings are in good condition.

HPP

That is really not true. I'm not sure where you get that idea.

Formula 1 cars have super trick differentials that are the result of massive R&D budgets. And OEMs like Ferrari and BMW are putting versions of the computer controlled differentials in their high performance street vehicles.

Neither BMW nor Ferrari are known for drag racing at all.

Logically, they would not bother with putting F1 diffs in their cars if it didn't help handling. Nor, for that matter, would F1 diffs be anything special.

The wrong diff can make a car reluctant to turn in off power, and push under power.

I don't intend to speak for anyone else on this forum, but I found a quote that is a useful example, pointing out that there certainly is something to be gained in handling from the right choice of diffs -

Also, a drag shock, no matter how stiffly it's set, will never be "good" (in an absolute sense) for handling.

Plus, eliminating the suspension (by going SUPER stiff) isn't the be all-end all to handling. It's possible to get both superb handling and a good, comfortable (if firm) ride. BMW is a great example of that as well (M3).

Foxxtron

iTrader: (1)

I have previously installed a 12-bolt because of all of the paranoia across the board from mostly lemmings who "read, see, and hear" most of the supposed absolute needs for a 12-bolt, and my lap times paid the price. A 12-bolt vs. a 10-bolt yields approx. 36lbs. more unsprung weight. That doesn't seem like much, however the more unsprung weight there is present, the more difficulty the suspension has time to react quickly and the solid rear axle is already a lot of unsprung weight to begin with. This was with the combination of shocks, springs, swaybars, and tyres that was yielding significant improvements than before.

If you are pulling lots of 4500 to 5000 rpm burnouts, I could see why you would need a 12-bolt, but if you're not, then why?

SJM Manufacturing Inc

iTrader: (5)

Fox,
You're completely correct. Unsprung weight plays a significant roll regarding handling characteristics. Dampening needs are altered among other areas. Change to a heavier rear-end i.e. 9-bolt or similar design, you amplify problems. Though you can increase performance by altering your spring-rate, dampeners and sway bar, the weight will still be there. I try to explain this quite often when discussing rear-end choices and wheel choices. Many think that “just 5 lbs difference per wheel really is no big deal”…”why bother spending slightly more money on your Bogart wheels when I can get a set of inexpensive weld wheels for drag racing.” Additional wheel-hop among other concerns arises…

Since you seem to want a RR setup…additionally, another way to overcome some of the added weight would be lighten up other areas of unsprung weight. I.E. wheels. Many folks use very heavy wheels with very heavy tires...this creates more headaches. Take our RR wheels, a typical design F-body wheel will weigh ~17lbs whereas take-off wheels can be up to 25lbs!! A lighter wheel will oscillate quicker reacting faster on bumps and imperfections in the road...which results in better handling and performance.

I’m not sure your answer is to remove the rear since your stock rear is quite weak. You could have lightened it up by considering removal of ABS components. Certainly this is not going to drop 25lbs but every pound does help. You could consider lighter suspension components, our LCA’s are ~2lb 11oz whereas stockers are ~6 lbs…there another bit of unsprung weight that you are helping offset the rear. A spool would be great as they are much lighter then stock…BUT that doesn’t work to well for the RR setup that you seem to want over drag racing.

At any event, above is some food for thought.
Good luck with your decisions,

DONAIMIAN

iTrader: (18)

I would start with shocks. Also, what swaybars are on the car?

jmilz28

iTrader: (13)

Smooth roads - 12 bolt will handle beautifully with the right components. It's then the roads get rough that IRS and lighter axles start to demonstrate superiority.

Foxxtron

iTrader: (1)

As compared to a 10-bolt or lighter solid rear axle, it won't. The unsprung weight still added 10th's of seconds to my turns, because the axle will still move laterally in a turn. I already had (still have) revalvable shocks to adjust compression (Koni DA's on one trial, and the current revalvable Bilstein ASNs that the G2 CO's use), used different spring rates, using the same aluminium control arms with rod ends, and the same lightweight track wheels fitted with at least the most suitable tyres for the task, and still had problems with the rear.

Depends on what type of IRS and how it's designed. If it's a swing arm, trailing arm, or even semi-trailing arm, there are still problems with yielding a considerable amount of unsprung weight (sometimes not much better than a solid rear axle). Even though some retrofitted uneven length double wishbone suspensions can yield much less unsprung weight, they usually add considerable added sprung weight to a rear car that was originally designed for a solid rear axle. Now a properly designed uneven length double wishbone or muti link rear suspension with little unsprung mass combined with proper spring rates and valvings yields a good responsive rear end with a decent amount of camber control on turns and over bumps.

If it was sprung weight, it wouldn't be much of a problem, however even 10lbs. unsprung weight can still make a world of difference with suspension reaction, regardless of solid rear or IRS, or roads with or without bumps. Quite a long time ago when I asked this on the forum, either LG or Louis stated that even the smallest amount of unsprung weight added to the already unsprung laden rear end can considerably hinder performance, even on smooth roads.

jmilz28

iTrader: (13)

Great info, thanks Foxx!

Foxxtron

iTrader: (1)

No problem, and thank you for being objective.

Bowtieman4life

iTrader: (1)

Thx for the info guys. I can tell you from experience that the my car handled better with the ten bolt. I was hoping I could make some changes and compensate for the 12 bolt weight but it doesn't seem realistic. I think I will sell the 12 bolt and install my 10 bolt again. The quarter mile thing is getting old, especially with an M6. Thx again and any additional info is greatly appreciated.