motownZ

well seen this on a GMHT mag before but heard this in the pits today at track saying it made him slower. is it bc the mass weight or is this false?


but i do know it will make it stronger..

chad3113

iTrader: (1)

I know when you move to a bigger rear, you lose a few hp...i guess "technically" it will make you slower, but it may be hard to tell.

MeentSS02

iTrader: (11)

Yes...it will make you way slower. Stay away from them. I think if anything, we should be working to find a replacement rear that is lighter than even the 10-bolt. Then our cars would be super fast. Yeah.

chicane

Only the ego will be slower...

purdueranger

iTrader: (11)

if you can launch harder on sticky tires, it guess it will slow you down.

SuperSlow02

iTrader: (16)

it shouldnt matter, because your not replacing the damn thing every 6 months. And if it made it slower, add more power

N4cer

iTrader: (11)

I think a good rear made me faster, because I'm not scared to give it all it's got. 9" for th win.

LS1Silverado05

iTrader: (41)

With the same ratio etc....yes....the parasitic loss would be greater....but I would assume your loss of speed to be trivial.

themadspoon

iTrader: (7)

Idk if you would notice it but there would be a little more rotating mass due to the larger parts so i guess in theory it could make you a little slower but i dont think it would be noticable

N4cer

iTrader: (11)

There's no denying that there is parasitic drivetrain loss when using a bigger rear. That's basic high school physics. But as said, it'll allow you to run *****-out and feel good about it. So the loss is negated.

motownZ

sorry, for the thread just saw it in a old magazinze article "FSC" on one of there cars running 7.94 then 8.06 , i know... not a big deal,

just wanted to see how commin this was,

N4cer

iTrader: (11)

Are you talking before/after rear upgrade? You haven't specified what is strange about this.

BlackScreaminMachine

iTrader: (17)

If your making no more engine power and the 60 foot doesnt decrease then yes, you will go slower.

A 12 bolt with everything is about 60 pounds static weight increase and the parts inside weigh more.

To give a reference, my old LT1 in my sig....

Ran 12.08X on a 2000 stall, 10 botl, 3.23 gears on nittos at 113, No suspension at the time, I installed the rear, the 3" steel DS and had 3.42's and the car's best time was 12.4XX at 110 mph, and with a 2500 stall and MT ET street radials, I ended up bogging to a 1.9X 60 foot vs 1.7's I ran on the nitto..

Upon getting the car dynoed and converter locked the car needs a 3500 stall, Both runs were on a hot cam.

10 bolt rears = Borrowed time when your hitting 1.7's or better, a 12 ensures reliability at the cost of some power and more weight.

THe same rule applies to a 4L60e vs 4L80e/TH400, you will lose alot of power but you got reliability on your side now.

N4cer

iTrader: (11)

Why are we discussing a weaker 12-bolt instead of a stronger 9" anyway?

NHRAMAN

iTrader: (1)

My wife says my 9" makes me sloooooow.

95 Z28

iTrader: (21)

It's gobbling up power while making your car faster...interesting huh? If your driving/racing style stays the exact same before and after the rear end swap, it's safe to say you won't go noticeably faster. But why would you not launch the **** out of your car if you had a 9"/12 bolt and decently built drivetrain?

thndrracer

iTrader: (5)

i hear barowed time on the 7.5. how fast do you need to be with an a4 to break one? i run a 150 kit(and probally use it more than i should) and drive on dr`s every day so far the only thing going bad is the trans. i know that the m6`s break them with ease

chicane

Wow... I feel dumber after reading all of this.

A 12 bolt is 60+ pounds heavier ?? Its weaker ?? And... it has measureable parasitic loss ??

Where do you guys come up with this **** ??

N4cer

iTrader: (11)

It IS heavier than a stock rear end.
It IS weaker than a 9".
It DOES have parasitic loss that can be easily measured.
So yeah, if you aren't understanding that, you might be as dumb as you say you feel. LOL! Seriously, what part don't you get?

chicane

Sure it heavier... but 60+ pounds ?? Go weight the difference between the two and get back to me.

Weaker than a 9" ?? In what variety ?? The problem with most in this forum is that they have no real experience with either differential. You make a phone call, a crate shows up at your doorstep and you install it. Then... at some time you come back and complain about god knows what. The fact of the matter is that I have seen 12 bolts take the same abuse as a 9"... when dealing with equal to or respective costs. There is nothing wrong with a 12 bolt and there is nothing wrong with a 9"... but when weight and money become the main factor for use, only then does it make a real difference. An inexperienced driver with a heavy street car can and will brake anything. But if you give an experienced driver twice the power... why is it that he can make it live ?? (Id say Moser has a lot to do with it... but that isnt really "PC" around here).

Parasitic loss. Please show me some kind of emperical data to quantify this 'easily measured' phenomenon. Have you actually measured anything off of a differential before (besides the price tag maybe) ?? And please, spare me with the high school physics line... rudimentry physics just scratchs the surface. How about this... Do you think it is possible that a 9" can be made to be a fair percentile more efficient than that of a 12 bolt or a 7.5"... even thought the pinion centerline difference is the main reason in this arguement itself ??

Ok... /soapbox.

I have never heard more complaining or unsupported theories in my life... than I have on this one single forum alone. In fact... in the industry, this forum specifically is affectionately refered as the "bitch" site. But, just to give you a little on my back ground and experience to support my opinion, I have been in the differential drivetrain engineering business for 18+ years doing these sorts of things that are being discussed for private professional motorsports teams as well as the "Big Three". I guess it makes me stupid that I constantly observe some that come here, blurt out some kind of speculative non-sense without providing any kind of evidence to back it up... and think its written in stone.

I just want some facts. That's all...