Converting from posi to spool?

GrandSportC3 · Posted: Thu Dec 28, 2006 10:02 am Post subject: Converting from posi to spool?

I'm thinking in converting my rear from a 12-bolt posi (IRS) to a 12-bolt spool (IRS) and I wonder if that would get me a noticeable improvement for my 1/4 mile ET's?
I know that a spool is about 20 lbs lighter than a posi.. That alone should make a difference.. Am I right? If yes, what kind of improvement can I expect. Has anyone here done that and what were the results in your ET?

Big Dave · Posted: Thu Dec 28, 2006 10:23 am Post subject:

I don't think any one else on the board has an IRS that goes drag racing with it. You would need to observe (with a high speed camera played back in slow motion) how your car reacts. If both tires are gripping equally (IRS reacts differently from a live axle as the differential is bolted to the frame) then you would only gain the increase in ET from the sheaded pounds. If the clutch pack allows one wheel to slip more than the other it would effect performance by loosing traction and torque steer would push you towards the tree.

Most racers run spools because they are unbreakable, lighter, and have no possibility of differentiating power out put all of which adds up to consistency.

Big Dave

GrandSportC3 · Posted: Thu Dec 28, 2006 10:28 am Post subject:

jeep_406 · Posted: Thu Dec 28, 2006 5:11 pm Post subject:

If it ain't broke, Don't fix it!!

dawg · Posted: Thu Dec 28, 2006 6:25 pm Post subject:

youll be sorry with a spool on the street

GrandSportC3 · Posted: Thu Dec 28, 2006 6:49 pm Post subject:

GrandSportC3 · Posted: Thu Dec 28, 2006 6:50 pm Post subject:

Brutisgearhead · Posted: Thu Dec 28, 2006 7:18 pm Post subject:

I'v driven my vega on the streets its got a full spool, I havent had any problems while in turns, remember slow and wide.

Paul P · Posted: Thu Dec 28, 2006 7:20 pm Post subject:

If you have the $$ to play I would do it.

af2 · Posted: Thu Dec 28, 2006 7:24 pm Post subject:

GrandSportC3 · Posted: Thu Dec 28, 2006 7:32 pm Post subject:

af2 · Posted: Thu Dec 28, 2006 7:52 pm Post subject:

GrandSportC3 · Posted: Thu Dec 28, 2006 7:58 pm Post subject:

af2 · Posted: Thu Dec 28, 2006 8:17 pm Post subject:

[quote="GrandSportC3"][quote="af2"][quote="GrandSportC3"]

Big Dave · Posted: Thu Dec 28, 2006 8:23 pm Post subject:

If you can afford it go for it. I'm surprised the clutches are still holding. You must have some serious preload on those discs to keep it running pass after pass with slicks on a posi.

The spool is lighter and stronger without the danger of a broken spider gear. I can remember when no one ever broke a ring and pinion because the spider gears shattered first. I don't know if the first posi's came with cast iron gears but the rear behaved as if they were. Of course a lot of that was due to people welling the spider gears in an open rear end because no one could afford a factory posi.

As far as power increases and ET goes it does seem to be an exponential increase, but it is in fact still linear just incrementally slow and exponentially expensive.

Big Dave