M3hunter

My '11 GT has manual transmission with the 3.73 gear, lowered with Steeda Sport springs, KONI STRT, squared 275/40R19 Michelin PSS mounted on Brembo pkg. 19X9 wheels. I already measured the rear and is almost 2" at both sides, the lowering did not affected is centered.

When I power shift the car, the rear of the GT jumps to the right (I think this happens when 2nd. gear goes in hard).
Any idea what might be causing this to happen? I think that I noticed this since my '11 GT was new before the mods.

Also I'm curious, twice I have gone head to head with different newer 5.0 with 420hp compared to mine (412hp), and in both occasion, they left me behind by one car distance. Is it really an advantage to have 8 hp more?

berzerk_1980

Not sure about the jumping.

Are we taking about a quarter mile race? I have heard that 3.73s are not optimal for drag racing because it requires an extra shift. You might be up against automatics or manuals with a lower rear gear ratio.

lakeguy77

Someone may want to correct me on this one but when the rear breaks loose, the design of the diff causes the right rear wheel to lose traction first before the LSD sorts it and shifts power, that's why you get that feeling of "jumping" to the right. Watching drag launches of these cars, when the tires lose traction on hard shifts, the tail always scoots right.

As for the 8hp difference...do you know what rear end those other cars have? Like was said, with the short 3.73's they're going to shift less often if they have a taller ratio, though you'll have better acceleration between shifts. But unless your shifts are utterly perfect they may have the advantage. Tires can also play a role. Do they have better quality tires so they get a cleaner launch? Suspension mods/rear geometry (ex. lowered without relocation brackets) they might put their power down better if their setup is better.

Unless you're comparing two absolutely identical cars (one a 412hp car, one a 420), same tire make and wear, same setup, same mileage, same fuel and passenger load, all other factors will make a much bigger difference than that 8hp, including driver skill.

berzerk_1980

Please pardon the Corvette forum link, but I think this is a sensible explanation.

http://www.corvetteforum.com/forums/...eleration.html

Tldr; driveshaft torque.

By the way, are we talking about a clutch diff or a torsen on your car?

ford4v429

when car was lowered, were control arm bolt loosened and retightened with car sitting loaded at new ride height? if not loosened, the center bushing/rubber can act like a torsion bar affecting spring rate- the car will usually still sit level as most of the weight is up front with a massive swaybar- making the car twist difficult, even if load on rear tires is different... the bushings can tear loose from the rubber if too much torque on them, they were made more for operating 'neutral' than as a torsion device- might be worth a check.

reaction torque will always plant the drivers rear harder/lift the passenger rear, but its usually not that noticeable. powershifting my 06, theres a very slight squirm, usually rear moves to the right, but its barely noticeable...some racers put a airbag on right rear to launch straighter, but really think its more of a wheelie leveling thing, not something most would worry about

M3hunter

Yes I think I have to shift more with the 3.73 gear. I have Michelin PSS tires, probably other tires hook better in straight line acceleration. For general driving they are great.
No I did not lose and tightened them after I lowered car.