Forgive a newbie, but Im needing to know something. And two days of searching hasnt helped.

Ive got a 1991 Firebird, thats gonna get a 95 LT1 (from a Vette) swapped in next year. Itll have the 4L60E, and Im going to try and get a posi (maybe a 1LE) with 3.42 gears in also. And Im going to try to get a 150hp nitrous kit. The LT will be fresh but stock, except with forged pistons, as Im having it rebuilt. And If im lucky maybe even some drag radials (275/60s). This is if all goes well, but thats the plan.

So my question is, the 1/4 mile calculators say I should be well into the 12s with this, on spray, and deep into the 13s without. Is anybody here running this combo? And does that sound about right? Im guessing the car weighs about 3700 lbs. Its a base model, with only power windows, T-tops, and A/C.

 

Umm dude.. 3700lbs for a mostly stripper '91 Firebird? Not a chance. Closer to 3,000. Maybe 3300 or so. But ya 13's w/ a stock healthy LT1 and a *cough* Piece of **** *cough* 4l60e in that car sounds in the 13's alright. I'd go posi without a DOUBT if budget allows it.

 

I was pretty sure its close to 3600 lbs, so I went higher, just in case. Itll be lighter with the aluminum heads, but Id never think its a 3300 lbs.

I went 4L60e because I didnt want the headache of trying to make the 700r work. Id rather have a t-56, but it is what it is.

 

Sounds like it is going to be a cool conversion. Once money becomes available down the road, you might want to look into a higher stall converter and a tranny cooler. That will really wake up your automatic. A limited slip differential and better gears is a good step as well. If you plan on doing some bigger upgrades down the road though, that factory rear might not be up to the task. Just some food for thought. Good luck with the project, keep us posted.

 

Third gens are extremely light. I think 3600lbs is even pushing it. That's closer to what convertables weighed man.
The 4l60e is a gay transmission because it has some nasty dead-spots, and they are prone to going early-on. A t56 would be the best route, but theres a lot of modifying stupid stuff.

 

I figured the 4L60 would be better than having to rig my 700r to work.

And im going to weigh the car after the engine install. I have a friend at work with 4 corner scales, she said I could use them. Im hoping with the fresh engine, and rebuilt tranny, maybe a gear, and posi, or locker, and some spray itll go 12s. If its that light, I might have to hit it with a 175 or 200 shot, and shoot for an 11. Well see if the rearend starts making noise first.

Ive got a grudge match coming up, and Id like to hammer a point home.

 

this site has some good technical data

http://www.thirdgen.org/tech-data

you will be fine with that trans, although it may need a rebuild and like stated a good stall and converter are highly recomended

 

The trans is freshly rebuilt, with a new, but stock converter. And Im on thirdgen, thanks. I ask alot of stuff over there, but they can be **** sometimes.

 

first off the car will weigh around 3300-3600 lbs. stock cars we scale are 3400-3700 depending on year and motor combo. v6's run over 3300 lbs. the 4l60e is a great transmission and has the good piston in the vettes. to really take advantage of the trans you need a tuning software that will allow you to change pressures,shift times,tcc application. you can do a lot with tuning. i would recommend a 2500stall and a good cooler. you can adjust the converter to lock up at lower speeds to make sure it doesn't slip.
with a converter you should be in the low 13's . on spray you should be able to hit high 11's. that is only if your tune is on and car hooks.

 

Low 12's should be easy on the hose,especially a 150 hit. I'd do a 3000 stall minimum along with those 275/60's. Try the Hoosier Drag Radials in that size on an 8-9" rim.