Aviator857

For a street cruiser with a stock LS1/T56 what would be a good gear ratio to install? The car is original 2.77 (73?) which with the 6 speed will likely be way too slow off the line and geared for top speeds I don't ever plan on hitting. If I ever race the car it will be mild auto cross for fun. I'll probably baby the stock rear until next year and then probably order a custom ford 9"

LsxMatt

iTrader: (4)

Aviator857

Thanks btw trolled your you tube channel as background noise while programming...
I do have the stock 4th gen rear and thought about pulling the gears out of it and putting in the right spline axles in the stock housing. What were your RPM's at say 70mph in 6th gear with the different ratio's you have ran? With the stock LO3/700R4 I use to cruise at like 12-1300 rpms on the interstate... no wounder that engine was still running at 215k miles it spent its entire life idling along.

QwkTrip

iTrader: (22)

Don't fear the gear. 4.10 is a good marriage with a T56 and makes up for the weak low end of an LS1. But you really shouldn't go over 3.90 with a 10 bolt because the 4.10 breaks like a pretzel.

STREETDEMON

When I built my 8.8, I used the 4.10 gears that were in it. When I switched over to the new Dana 44, it has 3.92s. I didn't think it would be that noticeable, but I love the 3.92's. First gear is almost usable now when I wood the pedal. I'm still on stock size 245/50R16 rubber.

redmaroz

iTrader: (4)

I had 2.77's in mine for a little bit after i did the swap, it wasnt very much fun to say the least lol. I ended up going to 4.10's in my old 10 bolt and was much happier. The 4.10's are a good match for the ls/t56 combo. I want to say at 70mph in 6th i was just below 2000rpm, but its been almost a year since i drove it last so i might be off a bit on that number.

Aviator857

Yeah I don't plan on spending money on new gears for either 10 bolt I have but when I drop the money on a new rearend I want to get the ratio right. If you could post rpms for speeds/gear that would be helpful... I guess I could calculate it.

I'll either be keeping stock size tires or the 17x9 GTA wheels hawks sells. Nothing too crazy.

Aviator857

OK if I did this right

the stock t56 is
1st 2nd 3rd 4th 5th 6th Rev
2.66:1 1.78:1 1.30:1 1.00:1 0.74:1 0.50:1 2.90:1

so with 3.90 gears you end up with final drive of
1st 10.374
2nd 6.942
3ed 5.07
4th 3.9
5th 2.886
6th 1.95

So if you shifted at say 4k RPM
thats
28 MPH
42 MPH
59 MPH
79 MPH
105 MPH
160 MPH

And I know there isn't enough HP to red line the engine but 220MPH would be 5620 RPMs in 6th with 3.90 gears

Cruising at 70mph looks like 1788 RPM's with the 3.90's

This is with stock tires at 25.65 inches tall.

QwkTrip

iTrader: (22)

3.90 or 4.10 is a good gear but there is a downside. You may not like the gear if you're one of those maniacs that just can't turn down a highway challenge. 2nd will be too close to redline so you'll have to drop to 3rd at 55 mph and that's not exactly a peppy gear choice to start a race with someone.

V6canvas

iTrader: (1)

I have 3.70:1 in my 9 bolt and it works very well, coming from 3.27 stock. At 70, it's right around 1700-1800 rpm. The engine is pretty close to stock, and 1st is usable, I guess that adds to consensus that high 3.xx - low 4.xx seem to be the sweet spot.

Jaysz28

iTrader: (30)

I have a dana60 with 3.73's in my car and really wish I had gone with 4.10's

I was convinced that anything more than 3.73's was going to be too much. Then I drove a car with 4.56's and thought it was awesome! So I can see 4.10/11's being about perfect.

When I get enough money to regear my dana 60 I will be going to 4.10's

86White_T/A305

When i had my cammed only lq4/t56 and stock 3.27 9 bolt wasnt too bad.From a dig the car would bog for sure but the mid-topend felt good.It was the best fuel mileage on the hwy. In 6th doing 60-65mph was about 1300rpms..idling along but no passing power.had to drop to 5th or 4th for sure! Once my 9bolt gave up the ghost I swapped in a stock 4thgen 10 bolt with 3.42gear. this was a noticeable difference. Keep in mind that at this point I had already going turbocharged,boost heavily changes the need for a numerically higher gear outback.Its plenty fun still..and freight trains uptop.Still get good mileage..roast tires off the line..dont need to shift as quickly since I use every bit of each gear at wot.

Stock 3.42's arent exactly bad,if you want to make it a fun weekend warrior with light mods like exhaust intake tune..go 4.10,if you want a mix of grunt and hwy then 3.73

Aviator857

So-- ended up taking the 4th gen rear I had from the donor car I got the engine out of and using the gears and posi out of it (3.42s). I bought new 28 spline axles and new bearings for pretty cheap so I now have 3.42s with a posi. I also finally got around to modifying the thirdgen housing to use the 4th gen rear brakes so I now have 4th gen brakes (master, front, rear) and all braided soft lines. Its about as good as it can be without sinking more money into the car. Eventually I will build an 8.8 I think, but figured since I had never set up a rear before I would try the 10 bolt with mostly "already have, no additional cost" parts. I've always been skittish on setting up a rear, but after doing it once I no longer fear it, sure shimming and re shimming several times is annoying but nothing too hard. Though for the 8.8 if I do build it I think I may use a crush sleeve elimination kit, as wow getting that to crush without using the impact is tough. And now I have all the tools to do it, though the bearing puller I bought to pull the bearings off the posi and pinion wasn't up to the task, I will probably return those and buy better since they are all bent. I'll keep the 4th gen housing around so if I build an 8.8 I can either use those tubes or brackets off it.

rearview

I am building a LS1 third gen and I'll be using the 4th gen 3.42 rear axle. It's pretty good in the 4th gen and should only be better in a 3rd if I ever buy a REAL rear end I was thinking 3.73s...

Rodolfo76

I read that the 4th gen axle is narrower than 3rd gen, and won't work? Tires will hit the body!

pg29

No, it's the opposite. 4th gen rear ends are about 1-1.5" wider on each side, and the tires will stick out past the rear fender if you don't use wheels with 4th gen backspacing.

rearview

Yeah. I REALLY wish I could find some 17x9 IROC wheels with the proper backspace for the 4th gen rear end. :\