I have a M6 and thinking about going to auto for more consistant track times. I would like to keep and overdrive for cruises. How much trouble are either one of these in my car? I know I need a controller for the 4L80E.

 

I seem to remember reading that the 4L80E won't fin inside the trans tunnel without mods to the tunnel. The 400 is a good trans, but you'll need to do a crossmember, get the speedo working, etc. Just my $.02 but it seems like a really good peroformance 4L60E should stand up to the power you're making. I just ordered a stage II from Speed Inc., and they even offer a stage III for like $2000. If I recall, a stage I will stand up to 400 RWHP I don't remember the ratings on the stage II and III. The nice part is that you can use all factory parts to put 'em in (vs. going to a 400 or 4L80E).

 

OK, if I go to a 4L60E, will my factory computer be able to control it?

 

Neither will serve your purpose. The 4L80E does not fit and the TH400 does not have an overdrive. If you are wanting to go with an automatic then i suggest 1 of 2 routes. A well built 4L60E will hold up to 450rwhp but after that it is on borrowed time much the same with your six speed and the former 10-bolt. Another option however is the older 200-R4/ 700-R4 series tranmissions. These can be equipped with an overdrive and will be what you are looking for but again these have their downsides( a. they are controlled through vacuum modulation and have to be manually adjusted for shift firmness, shift points and rev limiter, etc. and b. cost the very prettiest of pennies). Hope this helps you get the ball rolling and best of luck.

 

The stock 4L60E in my NA car has held up well,I run a cooler and a Yank 4400.I dont have NOS which would no doubt kill a stock trans in no time flat.

IMHO,if you want a car show,strip/street cruiser go with the 4L60E.The 4L80E is heavy and needs floor mods to fit,the Turbo350/400 has no OD.

I bought a used[less than 2000 miles]Speed Inc Stage 3.The trans is built by Extreme Automatics and I was told I could spray a 150 shot thru the shifts if I so desire.

 

you can buy aftermarket overdrive kits from Gear Vendors for the TH400.