So my 71 camaro went 11.3 @122 on a 100 hit with my 468 and richmond 5 speed and a 10 bolt 3.08 with half a posi. I bought a moser 12 bolt with a 3.90 gear after alot of saving bull**** paychecks and i built my own TH400 with the tranny shops manager over my shoulder. My auto shop and his tranny shop are in the same building and we do favors, (Joe is a great guy). So i fire the car up and out of some stroke of gods hand an auto trans really works??? I built it, it doesn't slip and i still have no clue how this compilation of **** actually puts power to the output shaft...? Anyway my lack of a higher knowledge isn't the question at hand. Why did my car run 11.6 at 119 with the auto setup and a way bigger gear. I expected MPH to drop due to the gear however ET should have picked up a lil. My 60 was 1 tenth faster but ET dropped .3 WTF?

 

Your gearing actually wasn't that bad with the 5 speed if it had the typical 3.25 1st, direct 5th. You basically had a 4 speed with an extra 5th, except you had the equivalent of od in direct 5th due to the 3.08 gear. 3.25 x 3.08 = 10.01. 2.48 x 3.90 = 9.672.

TH400 and torque converter are going to eat more hp than a manual =lower mph. And if your converter has higher stall it's going to slip more on the top end. Your cam might have also liked the smaller drops in rpm with the manual. The wider drops of the 400 gearing might have pulled the cam out of it's sweet spot. That's all I can come up with.

 

after i put a cam in my monte 305 ss I relized I needed a stall. It would push against the brake do to higher Ideal rpm. I went from a stock convertor to a 2500 stall. the car was alot better but ran the same et with a .1 quicker 60 foot? A long time friend talked me into trying a diiferent convertor. It came out sent it out and they "loosened it up". the problem I had was it is to tight for my application lack of low rpm torque. So I learned something new. A convertor for a more than mild app like something in the low 11's like your should be on the more custom side becuse convertors are like choosing cams.


On a side note did the sound of your car change with the auto swap? I sear my friends ls1 changed and so did my v8 ranger when I went from auto to stick.

 

First thing I'd check is your 60 foot time. How much of the .3 is in the 60 foot? Any of it? Steeper gear might mean you're now breaking traction off the line where you used to be right on the edge of it.

Agreed the TH-400 is a power hog. And your fresh 12 bolt is probably eating a fair bit more power than the little 10 bolt did. I could attribute much of that loss to the new drivetrain (certainly the MPH, but I wouldn't have expected to lose so much off the ET).