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

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.

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.

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?

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.

Re: POSI vs SPOOL
 

Not allowed stock axles with a spool in NHRA.

Re: POSI vs SPOOL
 

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

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...

Re: POSI vs SPOOL
 

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.

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.

Re: POSI vs SPOOL
 

I have a MW lite-weight steel spool in my Dana 60 and as Ed says, there's a reason. I'm not giving up strength / deflection for a small advantage (if any). But I believe the small engine / no HP car is the one I would use the lite-weight parts on. I've seen some impressive results on a V6 stocker by going this route; especially what I said about slick size.

Re: POSI vs SPOOL
 

I agree about the tires. I can't see lugging those big suckers down the track (SS) if you can hook with smaller, lighter tires.

Re: POSI vs SPOOL
 

What Billy said is the best use of $$ spent. Light wheels and small diameter tires will make a noticeable difference. Since those things have to be purchased anyway, buy what works best. The other lightweight axle parts may or may not make a noticeable difference and cost a lot of money. Loosening the preload on the carrier bearings and pinion bearings makes a noticeable difference, especially in MPH, and just costs time.

If you are going to race a low powered dime rocket, you will be miles ahead to learn how to work on everything - short block assembly, heads, carburetor, suspension, transmission, rear end, brakes, steering. Tweaking here and there, you never know what you will find. Plus, that's where a lot fun and satisfaction is found.

Re: POSI vs SPOOL
 

its call a locker
know many guys using then in stock
i have one in my cyclone for 41 years never, have boken it

Re: POSI vs SPOOL
 

i see to many cars with posi's smoke one wheel in the burn out box , once that happens the rear is done that alone is reason to run a spool gmonde

Re: POSI vs SPOOL
 

The FASTEST rear end is an OPEN rear end. Obviously will not work on a car with good power but for a dime rocket I am thinking of trying something. The problem I have experienced with a open rear is in the water the right rear spins. Then you pull out and stage and leave and the left rear will spin (least amount of traction). The only idea I have come up with is a Open Spool. However since Ed mentioned he wiped the left side splines and that is typically the axle that breaks -- I have to determine if the left or the right axle should be actually engaged??? This is for a combo that can barely do a burnout of course.

Re: POSI vs SPOOL
 

Daran, an open rear wants to spin the right rear tire because of engine torques affect on the axle housing. The rotation of the engine tries to lift the right rear and plant the left rear. to do what you are wanting to do, you would want to engage the left rear.

Re: POSI vs SPOOL
 

Thanks Billy, now I need to see if I can get the Impala to U weight? :) You missed last nights U/SA shootout in Orlando 4 cars 112 degrees alot of fun!!!

Re: POSI vs SPOOL
 

For a low cost, low HP car I would suggest a Locker with 35 spline axles unless it's a stick car. I ran one in my Max Wedge car for a few years and it did well.

JimR

Re: POSI vs SPOOL
 

Man, I love the idea of a one wheel wonder spool. You could run a slick on the drive side and a front runner on the other side. It would take some creative alignment but it might really fly!

Chris Barnes
Wagons of Steel!
Stock 6621

Re: POSI vs SPOOL
 

Yes,I have always wondered about setting up a lower powered car with
a one wheel drive system. I still think I would use matching tires and wheels and just use higher air pressure in the tag along wheel. Also ,but this is just me, I dont like calling alot of attention to stuff that I have on my car.
I am sure people would be scratching their heads if they saw a slick on one side and a lightweight front tire and wheel combo on the other side.
eddie