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Converting from posi to spool?
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GrandSportC3
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PostPosted: Thu Dec 28, 2006 10:02 am    Post subject: Converting from posi to spool? Reply with quote

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?
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Big Dave
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PostPosted: Thu Dec 28, 2006 10:23 am    Post subject: Reply with quote

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
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GrandSportC3
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PostPosted: Thu Dec 28, 2006 10:28 am    Post subject: Reply with quote

Big Dave wrote:
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


Both tires are hooking consistent.. I've had no issues with one or both tires spinning.. Dead hook every time since I switched to my new Hoosiers...
I also wonder if all of the weight loss can be considered rotating mass?? 20 lbs less rotating mass should get me about .05 off my ET...
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jeep_406
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PostPosted: Thu Dec 28, 2006 5:11 pm    Post subject: Reply with quote

If it ain't broke, Don't fix it!!
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dawg
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PostPosted: Thu Dec 28, 2006 6:25 pm    Post subject: Reply with quote

youll be sorry with a spool on the street
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GrandSportC3
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PostPosted: Thu Dec 28, 2006 6:49 pm    Post subject: Reply with quote

jeep_406 wrote:
If it ain't broke, Don't fix it!!


It's not about fixing anything..it's about getting the maximum out of my setup and 20 lbs less rotating mass should give me a few hundreds at the track...
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GrandSportC3
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PostPosted: Thu Dec 28, 2006 6:50 pm    Post subject: Reply with quote

dawg wrote:
youll be sorry with a spool on the street


I stopped driving the car on the street.. It's a track only vehicle now, therefore I'm not concerned about streetability..
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Brutisgearhead
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PostPosted: Thu Dec 28, 2006 7:18 pm    Post subject: Reply with quote

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.
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Paul P
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PostPosted: Thu Dec 28, 2006 7:20 pm    Post subject: Reply with quote

If you have the $$ to play I would do it.
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af2
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PostPosted: Thu Dec 28, 2006 7:24 pm    Post subject: Reply with quote

GrandSportC3 wrote:
jeep_406 wrote:
If it ain't broke, Don't fix it!!


It's not about fixing anything..it's about getting the maximum out of my setup and 20 lbs less rotating mass should give me a few hundreds at the track...


.05 for $400.00? I don't think so. As Jeep said I am in the same boat and hope it doesn't sink. That number is a wanabe hoax! The further you go to center the less the weight matters! You will never see a .05 by changing it given apples for apples comparison!
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GrandSportC3
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PostPosted: Thu Dec 28, 2006 7:32 pm    Post subject: Reply with quote

af2 wrote:
GrandSportC3 wrote:
jeep_406 wrote:
If it ain't broke, Don't fix it!!


It's not about fixing anything..it's about getting the maximum out of my setup and 20 lbs less rotating mass should give me a few hundreds at the track...


.05 for $400.00? I don't think so. As Jeep said I am in the same boat and hope it doesn't sink. That number is a wanabe hoax! The further you go to center the less the weight matters! You will never see a .05 by changing it given apples for apples comparison!

Actually, the effect of losing weight on the car doesn't change as the car gets faster but the HP needed to take time off the ET gets higher and higher as the car gets faster.. I got over a tenth off my ET with my lightweight front brakes and another tenth with my rear brakes.. Rotating mass has a great effect on the ET..
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af2
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PostPosted: Thu Dec 28, 2006 7:52 pm    Post subject: Reply with quote

GrandSportC3 wrote:
af2 wrote:
GrandSportC3 wrote:
jeep_406 wrote:
If it ain't broke, Don't fix it!!


It's not about fixing anything..it's about getting the maximum out of my setup and 20 lbs less rotating mass should give me a few hundreds at the track...


.05 for $400.00? I don't think so. As Jeep said I am in the same boat and hope it doesn't sink. That number is a wanabe hoax! The further you go to center the less the weight matters! You will never see a .05 by changing it given apples for apples comparison!

Actually, the effect of losing weight on the car doesn't change as the car gets faster but the HP needed to take time off the ET gets higher and higher as the car gets faster.. I got over a tenth off my ET with my lightweight front brakes and another tenth with my rear brakes.. Rotating mass has a great effect on the ET..



You are not talking apples! Front brakes is unsprung Spool is sprung! A total different concept!
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GrandSportC3
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1968 Chevrolet Corvette

PostPosted: Thu Dec 28, 2006 7:58 pm    Post subject: Reply with quote

af2 wrote:
GrandSportC3 wrote:
af2 wrote:
GrandSportC3 wrote:
jeep_406 wrote:
If it ain't broke, Don't fix it!!


It's not about fixing anything..it's about getting the maximum out of my setup and 20 lbs less rotating mass should give me a few hundreds at the track...


.05 for $400.00? I don't think so. As Jeep said I am in the same boat and hope it doesn't sink. That number is a wanabe hoax! The further you go to center the less the weight matters! You will never see a .05 by changing it given apples for apples comparison!

Actually, the effect of losing weight on the car doesn't change as the car gets faster but the HP needed to take time off the ET gets higher and higher as the car gets faster.. I got over a tenth off my ET with my lightweight front brakes and another tenth with my rear brakes.. Rotating mass has a great effect on the ET..



You are not talking apples! Front brakes is unsprung Spool is sprung! A total different concept!

Well, I'll get AT LEAST 2 hundred off my ET. 20 lbs less weight is about 2 hundreds.. but I believe that it'll give me at least 5 hundreds...
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af2
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PostPosted: Thu Dec 28, 2006 8:17 pm    Post subject: Reply with quote

[quote="GrandSportC3"][quote="af2"][quote="GrandSportC3"]
af2 wrote:
GrandSportC3 wrote:
[

Well, I'll get AT LEAST 2 hundred off my ET. 20 lbs less weight is about 2 hundreds.. but I believe that it'll give me at least 5 hundreds...


I am not trying to create a dissension and I am trying to educate! With that said what is the best bang for the buck?
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Big Dave
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PostPosted: Thu Dec 28, 2006 8:23 pm    Post subject: Reply with quote

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
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