Which Transmission Should I Choose?
 

I am getting ready to do an LS swap on my 92 RS. I have decided to to go with the LS3 crate motor from Chevy Performance. I am also upgrading to a Mosser 12 Bolt rear-end since the stock isn't nearly strong enough for the motor. I was going to convert the car to a manual transmission but I have decided to stick with an automatic. I am trying to see what my options as far as automatic transmissions go. I know a lot of people on here like to go with the 4L60e but I don't know if it will be strong enough for the LS3 motor. It will be putting about 520 or so HP and it looks like its a little above the 4L60e's limit. The 700R4 is obviously out of the question.

So any suggestions would be much appreciated.

BTW, I did see that Monster Transmissions had a 4L60e that was capable of handling the power I want to put though it but I have heard from numerous users here to avoid them with a 10ft pole.

Re: Which Transmission Should I Choose?
 

What auto trans came in cars that came from the factory with the LS3?

Whatever it is, it's "strong" enough that the car mfr warrantied it.

Start there. Work towards "better" once you have a starting baseline.

Re: Which Transmission Should I Choose?
 

The LS3 is usually backed by a 6L50, 6L80, or 6l90 auto transmission. The only problem is that they will not fit into 3rd gen F-bodies without major fabrication. The 4L70e looks like it's the best candidate but the main question I now have is where is the best place to purchase one from?

I want to avoid Mad Dog because I have heard nothing but bad things about them. I'm open to buying a used one and rebuilding it if anyone here knows a good place to buy a used 4L70e. I have checked area scrap yards and have had no luck.

Re: Which Transmission Should I Choose?
 

In the GM codes, the meaning of the model # are:

1st digit - # of gears
2nd letter - configuration (L=longitudinal, T = transverse)
3rd & 4th digits - some sort of arbitrary "relative" torque "rating"

So, in general, if you look at the "rating" part, a 60 is "rated" (whatever that means...) for "more" than a 50, a 70 for still more, etc.

The 4L60E, 65E, and 70E are all pretty much the same. The difference between the 60 and 65 is one planetary set. Not sure exactly what the 70 has different but it's a similarly small detail.

Best place to find em these days is trucks. The 60 & 65E come in half-tons, and the 70E comes in Escalades and Denalis and similar up-model large ones with the 6.0, something like 07 up. You'll need to get a 2WD one, and put a Camaro/Firebird extension housing on it. Not sure if that's possible: at some point they changed the way it bolts to the case, not sure whether there's any ext hsgs available that have the same bolt pattern as the newer transmissions. If not you might be looking at an aftermarket crossmember and torque arm instead.

I'd suggest picking up a junkyard one and rebuilding it yourself. There's plenty of resources to help you out. Watch the videos by transmissionbench on youtube; ProBuilt has a video and tech support for his customers as well; and there's others too. Learn all you can and you should be able to handle it.

Re: Which Transmission Should I Choose?
 

It's just sheetmetal.

Go for the 6L80E

Re: Which Transmission Should I Choose?
 

I appreciate all of the input from everyone. I keep going back and forth on sticking with an automatic or converting over to a manual. I read the T56 swap thread and the manual swap doesn't seem as hard as I thought it was.

Really the only thing preventing me from wanting to convert to a manual is the fact that I live in an area with the worst traffic in the nation. Driving stick on an open highway, fun. Driving stick in 2 hours of stop and go traffic, you can skip leg day at the gym.

I did post in the classifieds section that I'm looking for a used T56 so if anyone knows where to find one or is trying to sell one, let me know. There aren't many for sale on ebay and craigslist where as there are a ton on 4L60e trannies for sale.

Re: Which Transmission Should I Choose?
 

I'd give RPM transmission a call. The transmissions are kinda pricey but they hold up to HUGE power. They have 5 different 4L60E's you can choose from..anywhere from $2000 to $5400. The shop car they have runs high 8's on spray and there's a level X 4L60E in it. Give them a call and tell them what your goals are and they'll hook you up with the answers your lookin' for.http://www.rpmtransmissions.com/page11.html