[79RedRocket]

Good Morning. I have a 79ss with the 2:56 gears and th350 trans. It does great top end but I would like a little more out of the hole without losing streetability. Would a 700r4 or 200r4 suffice? and where do I get the crossmember to do the swap?

 

[melissadunagan]

Jegs has the crossmember and it is their brand.

 

[Zerberfert]

Swapping gears would help more than swapping trannys. If you drive on the highway a lot do a 2004r/3.23-3.73 swap. Gets a good hole shot and good rpm's on the highway. Don't forget about drive shaft length. Let the guru's chip in but I think its a different length from a Th350 to 2004r not sure about the 700r4.

 

[JKCamino]

Swapping gears would help more than swapping trannys. If you drive on the highway a lot do a 2004r/3.23-3.73 swap. Gets a good hole shot and good rpm's on the highway. Don't forget about drive shaft length. Let the guru's chip in but I think its a different length from a Th350 to 2004r not sure about the 700r4.

you would be correct, the 200r4 and 700r4 are both longer, a crossmember and extension kit are needed i believe, probably easier to change gearing to get a better holeshot

 

[79RedRocket]

Thanks for the info. I will research the rear and see what my options are. I will probably pull one from a junk yard.

 

[elco lover]

Guys im pretty sure th350 and 200r4 are the same length the 700 is longer though.

 

[Wayne Parrish]

The 350 and 2004-r ARE the same. I did this swap and love it !! WP

 

[ccc]

the 700 is 2 3/4 in longer than the 350/200r4.the 200r4 needs a custom crossmember with your original drive shaft and the 700 you can use your existing crossmember and shorten the mount pad about 1 in. to clear the pan,the 700 needs a shorter drive shaft . you can shorten your old one it uses the same yoke for all of the 3 trans.the problem i had when i went to a lower gear with my 700.was i lost 5 mpg going from 342 sto 273 s. it seemed the carb wasnt effiecient at the slow a engine speed and load.2050 rpm at 75 mph.went from 23.6 to 18. it now has efi and is getting 25/26 with the same 273 s

 

[Wayne Parrish]

I am running the 2:73 and 2004-R and threw the computer away,went to vac dist. and had Mountain Man build me a carb and get 25-27 on the road and 18 around town . I would love to have EFI but the pocket book won't stand for it . I built a new mount for mine and it sure isn't hard if you have the equipment. WP

 

[ccc]

do the throttle body efi it isnt as hard on the pocket as mpi

 

[Wayne Parrish]

Thanks and I'll look into that if and when I have Rochester problems

 

[ccc]

i got tired of the carbs.the fi motor starts instantly and runs flawlessly

 

[woody31]

i have a 5.7 tbi -200r4-273 gears in brown lumpy. 18 in town 22-hwy love the swap:beer:

 

[Wayne Parrish]

I know some will not believe it,but my Roch carbed engine starts as quick as any inj engine I have ever seen or heard. Maybe I got a rare one but I think the key is the MtnMan rebuild .I'll guarantee you that its impossible to start any quicker than mine.i'm happy !

 

[Carr7640]

I did the 2004r swap on my 80 I used a crossmember from a Buick. Stationwagon 86 model. Fit great with no extension needed. Just drilled 2 holes at drivers side frame. Single hump but only cost $10.also saw a 88 caprice. With. Same. X member.

 

[Skandolis]

earlier this year, i swapped my fourth gen over to 700r4,)2.73 gears, first and second were amazing, but fuel mileage went way down, 60 mph was around 1100 rpm, (so lugging in fourth at 55 gets old) swapped to 3.73 gears and have never been happier, really woke it up! now with a tbi 350 i get 22-25 mpg around town and way better on the highway.

2.56 gears might not be so bad, but thats still pretty high for an overdrive.

the only things i had to change was driveshaft cut 3 inches, moved crossmember back and drilled new holes(90s blazer trans mount) and on mine had to change kickdown bracket(although it would have been as easy to change kickdown cable instead but i already had the other bracket.)

 

[fauxrs]

earlier this year, i swapped my fourth gen over to 700r4,)2.73 gears, first and second were amazing, but fuel mileage went way down, 60 mph was around 1100 rpm, (so lugging in fourth at 55 gets old) swapped to 3.73 gears and have never been happier, really woke it up! now with a tbi 350 i get 22-25 mpg around town and way better on the highway.

2.56 gears might not be so bad, but thats still pretty high for an overdrive.

the only things i had to change was driveshaft cut 3 inches, moved crossmember back and drilled new holes(90s blazer trans mount) and on mine had to change kickdown bracket(although it would have been as easy to change kickdown cable instead but i already had the other bracket.)

I was thinking along the same lines, the OD in the 700r4 will turn a 2.56:1 gear ratio into something like a 1.7:1 in 4th gear and that is gonna mean its a gear that can only be used going downhill (and depending on the motor) on level roads, but very few motors short of big blocks will have the torque to pull that kind of gear ratio up even the slightest hill.

In my experience about the best rear ratio for these is something in the 3.31 range it gives you good launch gearing without being excessivly low and excellent cruise gearing.

 

[Zerberfert]

That's why I went with 3.23's. It's the perfect gear. Decent launches and 2400rpm @70mph. Got to love it.

 

[Jack_K]

I have 2.29 gears in my 80 with a 700R4. It's OK, but not great. I also have a posi with 3.42 gears I'll put in some day.

Jack

 

[Wayne Parrish]

I didn't even know they ever made a 2.29 ! A little more and it would be direct drive ! I think when and if I have to change gears I'll also go to the 3:23 also.