POSI vs SPOOL

House of Darts · 07-27-2011, 11:56 PM

Is there any HP to be found by using a posi over a spool? 8 3/4 rear with a Stocker 318 2v. Stock axle over the HD units? Thanks

Jeff Lee · 07-28-2011, 03:57 AM

The performance gain will be in using the lightest weight parts you can put in the rear; from slick to slick. That includes the wheels and possibly using a lighter slick by going smaller in both width and diameter and adjusting the gear ratio as needed. And since there won't be much power, I would suggest a light-weight aluminum spool. Since this would be the lightest, that answer's the question on the posi unit. And I would find the lightest wheels available and no wider than 8". Personally I would be looking at 7" wheels with 8" slicks and running Cal-Track bars, springs & shocks. And you can also get away with a small diameter / thin wall / lite driveshaft.

Jim Kaekel · 07-28-2011, 07:30 AM

I would not run a posi in a race car. You can never assure that equal power is being delivered to both wheels. I ran one years ago when I first started racing and the most common problem I had was unequal wheel speeds in the water box.

Adger Smith · 07-28-2011, 08:42 AM

Way back in the real early 70's I ran a 69 Z-28 in stock. Remember this is with 7" tires. We noticed the et's would vary just a little with the posi. I think that was slip, but the posi always ran more MPH. So we didn't cheat with the spool. We did break a lot of spider gears and cross shafts until I shimmed the clutch pack extra tight and ran the service pack HD springs. The stock springs would come out and be bowed (if they werent chewed up) like the forces of RPM got to them. I think the extra MPH was due to the slip in the posi when there was un even tire growth. Most of the time I ran the Firestone tire on a skinny wheel and they grew a bunch. The only problem we had with axle's was the outer beraring going out and chewing up the hardened surface of the axle. We had a side gear or two break and chew up the axle splines. I think the Mopar axel bearings are not like the Chevy 12 bolt and you would not have that problem. You would not have the problem of the axels floating side to side and breaking the spiders and cross shaft. I had to do alot of work and buy alot of parts to keep the posi alive. With the rules today I agree with the statement about what weighs less...besides, a lite spool is trouble free.
Dwight, What did you guys do?

Billy Nees · 07-28-2011, 09:53 AM

Ahh, the age old question, the spool for less rotating mass or the posi for less frictional losses. I'd love to see someone do a "back to back" test on them at the track. It's kind of hard to do with a GM rear.

Harry 6674 · 07-28-2011, 10:15 AM

Not allowed stock axles with a spool in NHRA.

Dwight Southerland · 07-28-2011, 11:21 AM

Quote:

Originally Posted by Billy Nees

Ahh, the age old question, the spool for less rotating mass or the posi for less frictional losses. I'd love to see someone do a "back to back" test on them at the track. It's kind of hard to do with a GM rear.

We did it twice years ago and concluded that the posi was a bit faster, but no quicker.

When I first put my '67 Z28 together in 1980, I tried to run the posi and spent way too much time and $$ trying to make it live. Lot's of dollars to Tom's Differentials and heat treating facilities. Worth about 15 runs before something would break. Building your own is necessary to insure the clutches work correctly.

The best approach would be what Jeff says. Rifle-drilled or small diameter axles, aluminum spool, micro-ed gears, loose bearings, light wheels and tires. MHO

Knocky · 07-28-2011, 11:45 AM

I also asked my chassis shop about spool vs posi and they said they just use spools in their race cars...

Billy Nees · 07-28-2011, 01:17 PM

Quote:

Originally Posted by Dwight Southerland

We did it twice years ago and concluded that the posi was a bit faster, but no quicker.

The best approach would be what Jeff says. Rifle-drilled or small diameter axles, aluminum spool, micro-ed gears, loose bearings, light wheels and tires. MHO

I guess what it all comes down to is if it's a high powered car go for all of the tricks. If it's a "dime rocket" with no power and an automatic (and I'm guessing that the combo that started the thread is) then there are lots of better places to spend your money like really light wheels and tires and the correct size header.

Ed Wright · 07-28-2011, 09:49 PM

I did back-to-back Aluminium spool versus Strange light weight spool in my car with a 12 bolt rear, saw zero. Only lost a couple of lbs. Didn't pull it back out. Should have before Memphis nats in '08. Cleaned the pass side splines out on the starting line, 1st round. Won't run one again. Just my experience. Yours may vary.

07-27-2011, 11:56 PM	#1
House of Darts Member Join Date: Mar 2007 Posts: 346 Likes: 19 Liked 20 Times in 15 Posts	POSI vs SPOOL Is there any HP to be found by using a posi over a spool? 8 3/4 rear with a Stocker 318 2v. Stock axle over the HD units? Thanks

07-28-2011, 03:57 AM	#2
Jeff Lee VIP Member Join Date: Jul 2007 Location: Anthem, Arizona Posts: 2,766 Likes: 0 Liked 3 Times in 3 Posts	Re: POSI vs SPOOL The performance gain will be in using the lightest weight parts you can put in the rear; from slick to slick. That includes the wheels and possibly using a lighter slick by going smaller in both width and diameter and adjusting the gear ratio as needed. And since there won't be much power, I would suggest a light-weight aluminum spool. Since this would be the lightest, that answer's the question on the posi unit. And I would find the lightest wheels available and no wider than 8". Personally I would be looking at 7" wheels with 8" slicks and running Cal-Track bars, springs & shocks. And you can also get away with a small diameter / thin wall / lite driveshaft. __________________ Jeff Lee 7494 D/S '70 AMX

07-28-2011, 07:30 AM	#3
Jim Kaekel VIP Member Join Date: Jul 2002 Location: Michigan Posts: 1,227 Likes: 133 Liked 531 Times in 108 Posts	Re: POSI vs SPOOL I would not run a posi in a race car. You can never assure that equal power is being delivered to both wheels. I ran one years ago when I first started racing and the most common problem I had was unequal wheel speeds in the water box. __________________ Jim Kaekel 3836 STK

07-28-2011, 08:42 AM	#4
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: POSI vs SPOOL Way back in the real early 70's I ran a 69 Z-28 in stock. Remember this is with 7" tires. We noticed the et's would vary just a little with the posi. I think that was slip, but the posi always ran more MPH. So we didn't cheat with the spool. We did break a lot of spider gears and cross shafts until I shimmed the clutch pack extra tight and ran the service pack HD springs. The stock springs would come out and be bowed (if they werent chewed up) like the forces of RPM got to them. I think the extra MPH was due to the slip in the posi when there was un even tire growth. Most of the time I ran the Firestone tire on a skinny wheel and they grew a bunch. The only problem we had with axle's was the outer beraring going out and chewing up the hardened surface of the axle. We had a side gear or two break and chew up the axle splines. I think the Mopar axel bearings are not like the Chevy 12 bolt and you would not have that problem. You would not have the problem of the axels floating side to side and breaking the spiders and cross shaft. I had to do alot of work and buy alot of parts to keep the posi alive. With the rules today I agree with the statement about what weighs less...besides, a lite spool is trouble free. Dwight, What did you guys do? __________________ Adger Smith (Former SS) Last edited by Adger Smith; 07-28-2011 at 08:48 AM. Reason: sp

07-28-2011, 09:53 AM	#5
Billy Nees VIP Member Join Date: Oct 2002 Location: On a hilltop in Pa. Posts: 4,493 Likes: 3,595 Liked 7,724 Times in 1,738 Posts	Re: POSI vs SPOOL Ahh, the age old question, the spool for less rotating mass or the posi for less frictional losses. I'd love to see someone do a "back to back" test on them at the track. It's kind of hard to do with a GM rear. __________________ Billy Nees 1188 STK, SS I'm not spending 100K to win 2K

07-28-2011, 10:15 AM	#6
Harry 6674 Senior Member Join Date: Dec 2006 Posts: 589 Likes: 0 Liked 0 Times in 0 Posts	Re: POSI vs SPOOL Not allowed stock axles with a spool in NHRA.

07-28-2011, 11:45 AM	#8
Knocky Junior Member Join Date: Sep 2010 Posts: 32 Likes: 0 Liked 0 Times in 0 Posts	Re: POSI vs SPOOL I also asked my chassis shop about spool vs posi and they said they just use spools in their race cars... Last edited by Knocky; 07-28-2011 at 03:34 PM.

07-28-2011, 09:49 PM	#10
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: POSI vs SPOOL I did back-to-back Aluminium spool versus Strange light weight spool in my car with a 12 bolt rear, saw zero. Only lost a couple of lbs. Didn't pull it back out. Should have before Memphis nats in '08. Cleaned the pass side splines out on the starting line, 1st round. Won't run one again. Just my experience. Yours may vary. __________________ Ed Wright 4156 SS/JA