New Tranny or New Rearend?

[Tmwoodall]

I checked my gear ratio this weekend (its a roller, never been on the road since I owned it). It turns out I have a 4.10 rearend mated to a TH350 and a 350 SB.

From my research that thing is going to suck, and suck up the gas at anything other than city driving. My question is, should I pull my freshly rebuilt TH350, and find a 700R4 so that I have overdrive, or should I put in 3.73 (I have a used 3.73 ring an pinion in a box)/3.55 gears.

I know both will get me closer to highway cruising speeds, but I am not sure I am aware all of the pros and cons of the two alternatives. Keep in mind my engine should be hovering around 400HP and close to that in Ft/TQ.

I believe I already have a 700r4 drive shaft as the one that came with the truck was too short for my 350, and we had to move the cross member forward to install the 350, so that part of the cost equation has been handled.

[chopnchaneled]

I put a 700R4 behind my 350 and used a 3:73 rearend and 255x70x15
bfg tires and it worked out to 2100 rpms = 70 miles per hour.

I've read on here that a lot of folks are using a 3:08 rear end with a 350 eng.
which came in our automatic trucks, just not sure of the years.

[jborders]

I had a th350 with 373 gears and it was taching 2600 to 2700 at 65. I'm pretty sure your not going to want to stay with the 410. I would do the 700r4 and the 373 gears if it were me.

[todd99]

I had the exact same setup as you and I just switched to the 700R4, it was worth the $$. I am still thinking about switching to 3.73 just to maximize mileage. If you have the gears install them but they won't be enough by themselves.

700R4 will drop your rpm at highway speeds by about 1000
4.10 to 3.73 will only bring it down about 150.

What brand and size of gears do you have? I have been having a hard time figuring out what will swap for a 4.10 rear.

[todd99]

Gear ratio calculator
http://tri-5.chevyrides.com/rpm.php

[Tmwoodall]

Originally Posted by todd99

I had the exact same setup as you and I just switched to the 700R4, it was worth the $$. I am still thinking about switching to 3.73 just to maximize mileage. If you have the gears install them but they won't be enough by themselves.

700R4 will drop your rpm at highway speeds by about 1000
4.10 to 3.73 will only bring it down about 150.

What brand and size of gears do you have? I have been having a hard time figuring out what will swap for a 4.10 rear.

Currently I have 20x8.5 with 45 profile tires. I am going to switch to a 10.5" wide and will likely bump it up to a 50 profile this go around. (I bought wheels when I was sixteen, and think they look HORRIBLE now).

[Tmwoodall]

My other concern is I don't want to loose that low end grunt and off the line jump by going too low. I suppose 3.73 or a 3.55 is a nice compromise in terms of drivability and the low end?

My towing will be so infrequent, if ever I should probably ditch the 4.10's regardless.

[todd99]

The R4 with 4.10 at 1500rpm will be at 10mph, with 3.73 at 1500rpm it will be at 11mph. The 700R4 has a pretty good first gear. When I had the TH350 with 4.10 both 1st and 2nd gears were pretty much unusable.

[stich626]

700r4 first gear is way to low (3.00ish) with anything more than 3.42 reargears..
1st will be useless as will 2nd..
if you're gonna keep the 4.10's get a 200r4, first gears is about the same as a th350 and the gear splits are better..
it bolts in use'n your driveshaft and yoke..
if you run the 700r4 think of changine to mid 3 rear gears,

700r4 with 410's will go like a bat out of hell if you can get it to hook,,
otherwise your just gonna fry tires,

[Tmwoodall]

Sounds like I should drop the 3.73s in and start watching for a 200r4 in the meantime, and that the TH350 will be drivable as-is as long as I don't plan to take any long highway trips.

[Tmwoodall]

Originally Posted by todd99

I had the exact same setup as you and I just switched to the 700R4, it was worth the $$. I am still thinking about switching to 3.73 just to maximize mileage. If you have the gears install them but they won't be enough by themselves.

700R4 will drop your rpm at highway speeds by about 1000
4.10 to 3.73 will only bring it down about 150.

What brand and size of gears do you have? I have been having a hard time figuring out what will swap for a 4.10 rear.

I believe they are factory GM Ring and Pinions. They were pulled from a donor 12 bolt chevy axle.

[eastcoastcivil]

I have a 67 C20 with a 350 SBC bored to 355, 245/75/16 tires, 4:10 gears and a Saginaw 3 speed thats on the tree. I run close to 3000 RPM at 50 MPH. I am going to put 31x10.5x16.5 tires and rims I have and change the tranny out to a 200R4 that I picked up (Rebuilt with a shift kit). I think this should solve my problem... Just wondering if a stall convertor would be wise and what type. I believe the tranny is out of an early 80's Monte Carlo SS. Any thoughts on how this will work? Especially with a C20?

[Tmwoodall]

Im thinking I may pick this puppy up.

http://austin.craigslist.org/pts/2237803675.html

[mustardjimmy71]

1 thing at a time!!!! drive it the way it is. if u like it how it goes off the line and want the rps lower on the highway go for a 200r4. if u want more off the line with the bigger tires and lower rpms on the highway go with the 700r4. If u find u never take it on the highway and u like how it takes off u just saved a bunch of work and money.
bottom line is change it one thing at a time. my dad is an old hotrodder and has done this a million times. every car is different. is this going to be a daily driver, streetand strip, highway truck, weekend warrior? put a couple thousand miles on it. you might just like it the way it is

[Already Gone]

Originally Posted by stich626

700r4 first gear is way to low (3.00ish) with anything more than 3.42 reargears..
1st will be useless as will 2nd..
if you're gonna keep the 4.10's get a 200r4, first gears is about the same as a th350 and the gear splits are better..
it bolts in use'n your driveshaft and yoke..
if you run the 700r4 think of changine to mid 3 rear gears,

700r4 with 410's will go like a bat out of hell if you can get it to hook,,
otherwise your just gonna fry tires,

So from your experience a 700R4 with 3:42's out back would be a great all around setup. I have a 396/350Hp in my truck and was figuring this would be the way to go for all around performance and reasonable fuel economy.