POSI vs SPOOL

[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.

[Harry 6674]

Not allowed stock axles with a spool in NHRA.

[Dwight Southerland]

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]

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

[Billy Nees]

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]

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.

[Jeff Lee]

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.

[Ed Wright]

Originally Posted by Jeff Lee

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.

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.

[Dwight Southerland]

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.