GM 6L80 transmission behind a 512"

These questions are for a street/strip application.

Is the 6L80 a better choice than a 727 to run behind a 512" motor?

Is it a good idea or not even needed or beneficial?

"Is OD good?"
Do you even have to ask?

You want to compare a 6-speed to a 3-speed?

If you can figure out how to get it mounted behind your engine then it will be one of the best things you can do for your car. I'd love to have a 5 or 6 speed auto in my car. I have a 5 speed manual trans and it is clunky and noisy. I'd love to have a modern auto.

An A500/518 with OD and Lockup is about as close as you can come to a "5"-speed transmission with 'usable' Mopar stuff.
But since you need an adapter anyway with a bigblock, the choice might be moot.

Well, plenty of guys run a Powerglide...

Anyone have an opinion on this adapter plate? Would it work on the 6L80?

I know nothing about this...

http://www.tciauto.com/tc/383-440-chrysler-to-chevy-transmission-adapter-kit-6-holehtml/

Doesnt look like it will work.

http://news.compperformance.com/Instructions/149260.pdf

It's a street/strip car - unless (and even with) GV a PG is very limited in SLR vs. RPM in OD.
Ideally, you want a trans that keeps your existing axle ratio (save $$) and has deep enough OD to slow the engine down, and still enough 1st X axle for a decent launch and traffic. The ratio "spread" (first to last) should be at least 3:1, I have 4:1, 6 speeds are even larger.
My factory (non-MoPar) is:
1 2.804:1
2 1.531:1
3 1.00:1
OD .705:1
axle 3.77:1
SLR (overall torque multiplication) 10.6:1 + stall ratio, equal to 727 with 4.33 axle.
With 26.6" tire, 90 mph is 3,000 RPM

Not sure how much advantage in 6L80 vs 4L80, but certainly more complex, heavier, possibly more floor, X-member work.

I understand about four of those words

More ratios + OD sounds like a winner to me, especially if 1st is a deeper ratio; then you have pretty much a gear for every occasion. Not that you need to spin a 512; so the OD is probably of more value than a deep 1st gear.
4L80s are probably smaller, and from what I've read any of the OD automatics, even the Mopar version, are going to require some floor or crossmember surgery, or both.
Nice things about a GV OD unit are easier installation and being bulletproof (at least in my experience in my Dually - 24 years & still excellent).

What axle ratio do you have now/anticipate installing?
Divide 10 by that number to get a useful 1st gear suitable for both strong launch and good manners in low speed traffic.
How fast does your cam need to spin to get torque? This is related to your minimum cruising RPM, you can figure this from your tire OD, axle, and OD ratio if any.

The 6L80 looks like a good choice, it has a much stronger 1st gear than the TH400 (will pull a really tall axle ratio), and deeper OD than 4L80, GV etc.
1 4.027:1
2 2.364:1
3 1.532:1
4 1.152:1
5 .852:1
OD .667:1
Spread is huge at 6:1

200 lb worth of transmission This honker is BIG! Nearly as big as an Allison.

Do a little reading first before drooling too hard. The 6L80E has no bands, just clutches. Shifting from one gear to another involves releasing one clutch while simultaneously engaging another clutch. All the timing is done by electronics.
It sounds wonderfully complicated to me.

http://www.superchevy.com/how-to/transmission/1103gmhtp-circle-d-6l80e-transmission-upgrades/

BUT, it can be done! You may just not like the way it has to be done. http://www.zerogravityperformance.com/pr...0e-6l90e-6l50e/

R.

I would go with a 4L80E there has been much development of the 4L80E - yeah it only has 3 gears and an a OD - but it is well proven in the High Performance big power arena - Rossler offeres a bunch of gear ratios and internal parts all the way to some pretty impressive complete transmissions - Reid makes an aftermarket case and there is now a 6 speed conversion now avaialble for the 4L80E

Heck, even a well-built 200R4 will live behind most RB motors if you don't beat them on the track every weekend. For street strip usage with power below 1000hp a Stage 3 200R4 will work fine.

No need to use an oversized plate to mount one either. Use an SFI rated bellhousing like the one I use on my 408" Magnum(382 hp & 525ft lbs at the wheels). It's only a Stage 2 model with a 3800 rpm stall/ lock-up converter, but its the best transmission I've ever driven. The gear spread is awesome!

If you do want a race only version, leave off the lock-up and call Lonnie at Extreme Automatics. He will build you a bigger transmission that will live under those conditions too.