73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Ds2014 on October 14, 2014, 08:16:16 pm
-
I have the stock rear in my 81 step side. I have a 10.5:1 small block 408. How deep should I go with the turbo 350? I was thinking 3.42?
-
What tire are you running?
-
http://www.competitiondiesel.com/Phil/bg/
This chart will show rpm's vs mph
Sent from my iPhone using Tapatalk
-
Stall speed or stock converter, cam rpm range and type of driving are all considerations for your choice.
-
Street driven 2800 stall 292/292 cam
-
Right now I have 31 10.50
-
Around town or highway? What gears do you currently have? How does the truck perform now?
-
I wouldn't go to 3.42 with 31" tires. That 3.73 on there is like a 3.49:1 with those tires. A 3.42 would be like a 3.2:1.
-
Right now I can do a burn out at 45 mph
-
I am getting 17" rims and a 28 inch tire
-
I have 2.73
-
If it were me I'd leave well enough alone then
-
No posi tho. I thought about just putting a posi and leaving stock or going with 3.08
-
I mis-read, with 2.73 I would jump up to a 3.42. When I replied earlier I thought it said 3.73. A bump to 3.08 would barely be noticeable.
-
Limited slip of some sort is always a good thing, just make sure you know what it will do and get use to it. I've had more than my share my back end passing me, luckily it was on the track and nothing happened except a little embarrassment.
-
So 3.42 it is! What carrier do I need? A 3 series?
-
For that question I would consult whoever is going to supply it. You should have a 10 bolt differential but you need to verify that for sure so when you chose what posi unit to go with. Each carrier differs with gear ratios offered.
-
I just went from a 2.7 to a 3.73 posi. Right now I'm running a TH350 and a 26" tire. It's a bit gear bound now. Future plans include taller tires and a 700R4 so I'll be fine. Otherwise, I'd have stuck with a 3.42. That's a pretty good all around ratio.
-
Thanks for all the info. What carrier,3series?
-
maybe neither. gm started using a weird carrier in either 81 or 82, I cant remember. neither 3 or 4 series gears will fit. if you have this carrier, you will need to switch carriers to use any aftermarket gears. I ended up sending back alot of gear sets before i figured this out. I finally went with a detroit true-trac differential that comes in a 4-series style carrier and all was well.Turns out the PO had installed an early 80's rear in my 74. wish I would have known this to begin with as it would have saved me, summit racing, and my mechanic alot of wasted time. Also, as a comparison, I went from 2.73 to 3.73. I run 31-10.5 tires on back as well and with a th400 trans I'm turning about 3200rpm at 65mph. it sucks on the interstate. I'm going to be going to a set of nitto 325/50 drag radials in the future(28") but I think all be switching to an overdrive transmission first. If this was my daily driver I would have went to a 3.08 at the most with no overdrive! Of course my engine only spins to about 4800 rpms so with that cam you got you can probably tolerate those kinds of rpms.
EDIT: its the 82-up that uses the carrier that doesnt fit anything so you should be good if yours is an 81. If your truck came with 2.73 gears then it should be a 3 series carrier. 3.40 down is 3 series, 3.42-up is a 4 series. If you're planning on a good posi unit though, go ahead and get them at the same time as most of the aftermarket differentials come with a new 4 series style carrier.
-
I'm looking for a POSI rear end for my 81 c10 2wd. Any ideas
-
3 series case fits 3.42 down.Pretty sure they make a thick 3.73 set to fit 3 series.Higher gears will work with a spacer.Gm's posi was a goc lock,a good unit but not for a lot of abuse.Go with an eaton or auburn.I used a true track once on a truck with big tires and lasted about a year.It made a horrific sound in tight turns,but since then I believe they have made some improvements to them