I have a 94 caprice classic. it had a 4.3L L99 in it and i swapped it to a 5.7L 350. the car now has 370 hp compared to 200 from before. i need to do my tranny over now because of the power difference. should i rebuilt my 4L60e with heavy duty components or go with a different tranny. also, im worried about my rear end. i want to drive the car and have fun with the extra power (brake stands are a must). should i replace the rear end and if so what gears should i go to? i posted a question about what kind of rear end i have and i got a response that it is probably a 7.5 inch with either 2.73s or 2.93s. and i do not have posi. can this rear end handle this power? if i floored it from a dead stop will i blow my rear end (thats what im worried about)? any advice would be appreciated...o and also should the driveshaft be replaced or is the stock one fine?

I have a 94 caprice classic. it had a 4.3L L99 in it and i swapped it to a 5.7L 350. the car now has 370 hp compared to 200 from before. i need to do my tranny over now because of the power difference. should i rebuilt my 4L60e with heavy duty components or go with a different tranny. also, im worried about my rear end. i want to drive the car and have fun with the extra power (brake stands are a must). should i replace the rear end and if so what gears should i go to? i posted a question about what kind of rear end i have and i got a response that it is probably a 7.5 inch with either 2.73s or 2.93s. and i do not have posi. can this rear end handle this power? if i floored it from a dead stop will i blow my rear end (thats what im worried about)? any advice would be appreciated...o and also should the driveshaft be replaced or is the stock one fine?

I'm pretty sure that it has a 8.5" gear. If it had the L99 in it, it probably has the 3.23 gearing (GU5 on the SPID label on the underside of the decklid).

370HP, is this stock? The LT1 only put out 300HP in the 'Vette, 260HP on the Caprice, is it stock? LT4 was 340 HP.

Stick with the 4L60E, use heavy duty parts.

Been there done that. IF the axle is the 7.5" which it very well could be if it was a civilian car then yeah you need a 8.5" axle and driveshaft.
A Transgo kit with a Vette servo(the servo was stock on all LT1 cars) in the tranny would go a long ways towards helping it, it is the same tranny but setup slightly different for the smaller motor this would correct most of it.

I don't know where you are getting that 370hp number from either as said the b-body LT1 was 260hp 330tq.
Did you reprogram or swap the computer?

Far as blowing the axle you pretty much need traction or severe wheelhop to do that, non-posi traction will not happen.

My car started life as an L99 civi car but today is a low 12 second heads/cam in serious contention for the heads/cam b-body 1/4 mile record and putting more than 370 to the tires roughly 480 at the crank. You have questions ask and I am glad to try to help but I will tell you right now I will not take kindly to folks contradicting me on this subject I only mention that because every time this subject comes up some ignorant goober comes and tries to say something I am saying is wrong and it is not there are a few folks here who can vouch for me and my knowledge level on this subject in particular.

the motor is not a stock 350 it has work done to it. i did replace the computer as well. so if i got an 8.5' rear i should be all set? what kind of gears are in those rear ends? should i change them to taller?

Go to Jegs or Summit and they will have drawings of the diff cover shapes to help you ID your axle. A civi 8.5" in a Caprice is almost always 2.93 but I have heard of at least one case of a civi L99 car getting a 3.23 drum rear, very freak case. The 8.5" is stout, might consider 3.42-3.73 and a posi Eaton or Torsen usually considered better than the stock Auburn.

What has been done to the motor?

i got the motor built at A-1 engines in columbia south carolina. they make a 330 horse power street and strip motor and a 390 horse power high performace engine (both 5.7L 350's). i got the 330 horse motor and had them put a better cam and crank in it. guy who built it said i should be getting at least 370 to the wheels...probly a little less but i know it is much faster than when it had the 4.3L L99 with 200 horse. now i just need to fix the tranny which is slipping and take care of the rear end and driveshaft. anyone know where to get some headers??? had a real hard time finding any that fit

370rwhp is doable, am beyond that myself BUT from what you are saying I say no way in hell are you there not even close. Requires substantial and SKILLED head porting as well as a good cam not likely something off the shelf.

330hp is less than what a stock LT1 will make at the crank with good boltons if that tells you what a joke their engine offering are..

Headers for this application are either a tough fitment or expensive, there are alot of options though.
For serious modification research the impalassforum.com would be a MUCH better place to go, hope to see you there. I have a link in my sig over there which covers all the L99 to LT1 swap stuff.