Im thinking of swapping out my 10 bolt 3.42 for a 3.27 9 bolt posi disk. Will i lose any low end or very much low end doing this. I just hate my highway cruising RPM with these gears. Thanks for any help.

 

You're only changing about 200 RPM on the highway with this swap. Is it really worth the effort for that?

 

Only that little huh? I was hoping for 500rpms. idk now. The upgrade to disks would be worth it as well as the fact its a stronger rear than the 10 bolt but the main reason i wanted to do it was because of the reduction in engine rpms.

 

my car has 3.42's and does 60 at like 1850 rpms or so. its not bad on highway at all with OD. how much lower do you want to go?

i had 3.27's and it was only marginally better on cruising, seriously like 100-150 rpm, but you do lose alittle low end acceleration feel. Not a huge difference but you can feel alittle difference.
2.77's will get you down 350 rpms but performance stinks with those gears compared to 3.27's or 3.42s

you could try a taller tire as well

 

Actually it's 116 rpm's difference.

Go here to calculate rpm's with different tire sizes/rear ratios/overdrive ratios.

http://www.csgnetwork.com/multirpmcalc.html

I use the last calculator. Easy to use with just a few entries.

 

Hmmm so its so close that it might not be worth the effort. Another reason i wanted to do it was this car is putting out some decent power and this 3.42 is from a 6 cylinder car. Not sure how well it will hold up in the long haul.

 

if its posi its a good rear. 6 cyl cars i'm not sure if theygot a posi or not

disk brakes are nice upgrades tho but no worries... you can always upgrade your current rear

 

Yes it is a POSI drum 10 bolt. I wasnt sure if 6 cylinders came with posi's as well but we assumed it came from a 6 cylinder car because of the 16mm or thereabouts sway bar.

 

I'd debate the comment that the 9 bolt is stronger than the 10 bolt. Also, consider this... there is only a tiny after market available for the 9 bolt compared to the 10 bolt. Break something on the 3.27 and you are hatin' it.

The only good reasons for this swap is the increase in fuel economy, the disk brakes, and you are getting the 9 bolt for nothing.

 

I def wouldnt be getting the 9 bolt for nothing. It wouldnt be expensive though. And i agree that both rear ends are not all that strong but the 9 bolt is stronger. There is a big difference in weight and size between the two and why would they require the 9 bolt to be put behind the 350 if it wasnt strong?

 

3.42 - 3.27 = 0.15

0.15 / 3.42 = 0.04386

You will get a 4.4% reduction in cruising RPM.

 

also just for additional info. if u are wantin to lower ur rpm. u can always go with the tall 2.73's. my 70mph cruise in OD is about 1750rpm. and it'll still light the (tire) up. lol.

 

I just swapped out my 3.42 open drum rear for a 3.23 posi/LS1 disk rear. I have to say, I like the 3.23s better. The engine isn't screaming at 110, quieter at highway cruise, plus I got to upgrade to posi and disks. When the transmissions down shifts, it doesn't immediately have to up shift again like with the 3.42s. Ya I do miss the 3.42 off the line, but it's a good compromise. Especially when I swap a 350 in.

 

Thanks for all the replies guys. As of now i think ill stick with the 3.42s since they arnt broken and its in good shape. I just swapped in a WS6 rear sway with poly bushings instead and wow..what a difference over the wimpy 6 cylinder sway bar.

 

I would hold on the the smaller sway bar as you may need it to tune the "rear" with one day. IE: it helps with weight transfer if you need to tighten up the rear. On mine the 24 mm bar felt better but the added "plant" of the smaller bars just gets you off a corner better IMO.

 

lol smaller one is already gone to the scrap heap. Oh well. If i need one in the future i know where i can get one. Im more interested in the bigger bar for better cornering.

 

To answer the original question...whenever you switch to a numerically lower gear...you GAIN low end...you don't lose low end...by reality of the gears....

In your situation...keep the 3.42s...too close to 3.27 to make the swap.

 

Yep hind site is 20/20...as me how I know...

The thicker bar definitely feels better through the corner...

What year are the disc brakes? Old style or the newer ones?