GM 6L80 transmission behind a 512"
#2540498
08/23/18 04:17 PM
08/23/18 04:17 PM
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crankn101
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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?
Last edited by crankn101; 08/23/18 04:20 PM.
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Re: GM 6L80 transmission behind a 512"
[Re: crankn101]
#2540524
08/23/18 05:37 PM
08/23/18 05:37 PM
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polyspheric
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"Is OD good?" Do you even have to ask?
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Re: GM 6L80 transmission behind a 512"
[Re: crankn101]
#2540525
08/23/18 05:38 PM
08/23/18 05:38 PM
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John_Kunkel
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You want to compare a 6-speed to a 3-speed?
The INTERNET, the MISinformation superhighway
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Re: GM 6L80 transmission behind a 512"
[Re: polyspheric]
#2541052
08/24/18 09:52 PM
08/24/18 09:52 PM
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crankn101
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"Is OD good?" Do you even have to ask? Well, plenty of guys run a Powerglide...
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Re: GM 6L80 transmission behind a 512"
[Re: AndyF]
#2541053
08/24/18 09:53 PM
08/24/18 09:53 PM
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crankn101
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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. 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/
Last edited by crankn101; 08/24/18 09:54 PM.
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Re: GM 6L80 transmission behind a 512"
[Re: crankn101]
#2541056
08/24/18 10:05 PM
08/24/18 10:05 PM
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Re: GM 6L80 transmission behind a 512"
[Re: crankn101]
#2541068
08/24/18 10:52 PM
08/24/18 10:52 PM
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polyspheric
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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 $$) and has deep enough OD to slow the engine down, and still enough 1st X axle for a decent launch and traffic. The ratio "spread" (first to last) should be at least 3:1, I have 4:1, 6 speeds are even larger. My factory (non-MoPar) is: 1 2.804:1 2 1.531:1 3 1.00:1 OD .705:1 axle 3.77:1 SLR (overall torque multiplication) 10.6:1 + stall ratio, equal to 727 with 4.33 axle. With 26.6" tire, 90 mph is 3,000 RPM
Not sure how much advantage in 6L80 vs 4L80, but certainly more complex, heavier, possibly more floor, X-member work.
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Re: GM 6L80 transmission behind a 512"
[Re: polyspheric]
#2541074
08/24/18 11:10 PM
08/24/18 11:10 PM
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crankn101
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It's a street/strip car - unless (and even with) GV a PG is very limited in SLR vs. RPM in OD. Ideally, you want a trans that keeps your existing axle ratio (save $$) 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
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Re: GM 6L80 transmission behind a 512"
[Re: crankn101]
#2541089
08/25/18 12:10 AM
08/25/18 12:10 AM
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polyspheric
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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
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Re: GM 6L80 transmission behind a 512"
[Re: crankn101]
#2542879
08/29/18 02:56 AM
08/29/18 02:56 AM
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jbc426
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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.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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