350 trans vs 400 trans

in 79 was the 350 the stock trans for the trans am??

found out today my trans am as a 350 trans in it not a 400 learned that when the new seal kit dint work anyways was thinkin about trying to find a 400.how well does a 350 trans work on a 4000 pound car and 450 foot pounds of torque on the 1/4 mile?would I be better off trying to find a 400?would it perform better?
thanks  

350 would be standard in a 79, don't think they put 400 in them after about 74. A good quality 350 would stand up to that for a few years, but you would never have a problem with  400. I put a 400 in my 68 and it run's in the mid 10's. Been in there for 14 years and only had it rebuilt once, and it didnt' really need it, but it was a good deal and insurance policy.

If you decide on aa 400, you will need to move you crossmemeber back a couple of inches and shorten your driveshaaft a couple also, the yoke is different too. Convertor will work on both unless the 350 is a lockup.  

You also need to figure out a different way for the kickdown to be hooked up. The 350 uses a cable from the transmission to the carb. The 400 has an electronic switch inside the transmission and a switch connected to the accelerator pedel. You will need to fabricate a bracket on the carburator for the switch since the 350 transmissions don't have the provision for the pedel switch. Personally, a well built 350 from someone one knows what they are doing with heavy duty parts will make you quite happy without the alterations you would have to make for the 400.
I have both, and can't say I prefer one over the other - they both kick butt.  

I agree with Brazil both work well if built right.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Thanks eveyone for the great advise seems  I will still with the good ole 350 its been rebuilt 4000 miles ago and the trans oil is reder then red just woried as alot of the seals were leaken so we droped it to replace to find out the dip stick was way to high the lip was about 3 inches to high cuasing the previous owner to over fill it and im hopin thats why the trans is leakin and not becuase it was poorly put back together

ONE more question how can you tell if its a lock up or noun lock up?
thanks  

Lock up trans will have a electrical plug in on the drives side just above the pan  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

Pontiacman8, Will you give us all a quick lesson on exactly what a lockup vs. a non-lockup transmission actually means. I'm sure there are a lot of folks out there who really don't know, like...umm....Brazil?  

Lock up trans. have lockup converters some have 2nd,3rd gear lock up and some just 3rd gear lock up now the lock up converter was designed for gas mileage it actually locks the converter so it is like a direct drive so slippage will not happen were on a non lock up it will.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

I see what your saying, but it's still a bit confusing why some cars would have one or the other. Aside from gas milage what would be the better choice in a street Trans Am? Is it more important in race cars?  

Well if you were to put a aftermarket stall converter on the lock up trans. it's going to cost you a lot more then the non lock up for racing you would want a non lock up.
On the street I would say either trans but the lock up will give a little better gas mileage.
I have a lock up trans in my regal and it works great for what I use it for used to race it and run it on the street.  
professional hi-performance engine builder

Horsepower sells engines and torque wins races

I see. Auto transmissions have always been a mystery to me - it's the one thing I always have to depend on someone else to work on!
thanks