rear end gearing?

[whitey]

I just put a 454 BB. in my 71 chevelle and its a beast. having done that, it runs higher RPM. right now im running 3200 RPM at 55 MPH. i have 3:73 gears in my rear end and was wondering if anyone had suggestions for better gearing so i wasnt running at such a high RPM. Looking for some more top end but still would like it jumpy at the bottom end too.

[shadowgray396]

The factory had 3:31 gears in the SS unless you ordered 4:11. I'm running 3:31 in mine. A few years ago the only way you could get them was to buy a used set. I believe they make 3:42 gears if you want new. The 70 vets came with 3:07 with a 454 which is great for cruising at high speeds but won't get you off the line that fast.

[whitey]

thanks. i was thinking 3:55 or 3:42 gears. that way i should still have some jump from the start and a little more top end. i'll definitely be bying new though.

[Hank70SS]

I have 3.73 gears with a 454, 3.42 gears would be nice. I do have 275/60x15 tires on the rear right now, that helps a little.

[carpoor]

What transmission do you have? If you ever plan to do some upgrades to it... you could always swap in a higher numerical gear set (1st & 2nd) in the transmission. Then drop the rear gears down to something more highway friendly like a set of 3.08's. Taller tires will help too like Hank70SS mentioned.

[Ms Grumpy]

I went the changing the trans route. If anything I lost just a very small amount of power off the line. But dropped the RPM's while cruising at 55..

[whitey]

I have a TH 350 trans in it right now and i have 295/50/15 tires on the back.

[carpoor]

A swap to 3.55s and a 28" tall tire would drop the rpm by around 350. A 2.75 first gear swap with 3.55s out back would make it take off like a set of 3.90s - just food for thought.

[Bullcrappy]

I think your speedo is wrong because a th350 with 3.73's does not run 3200 rpm at 55mph

if the speed is righg that would be more like 4.60 rear with the 26.5" tiresen maybe th

if your your sure of the rear then maybe the wrong speedo gear is in there? because 3200 rpm with a 3.7 rear is 68mph

[Bullcrappy]

to elaborate on my above post something does not add up or i misunderstood?

there are many calculators on line but here are two i use:
http://www.sccoa.com/faq/tirecalc.html

http://www.corvetteactioncenter.com/tech/tools/rearend.html

those coupled with this chart and you see that your tire height with that trans and rear does not equal 3200rpm. maybe trans speedo gear is wrong one?

http://i877.photobucket.com/albums/ab336/RichStrapple/transratios.jpg

[Derek69SS]

Sounds more like a 4.10 gear, with about ~300rpm of converter slip.

If you have a high RPM stall converter though, it could be 3.73 with 550rpm of converter slip... hope you have a big trans cooler if that's the case.

[carpoor]

Don't forget to allow for converter slippage. However, what the OP has for RPM vs. MPH would = excessive slippage. I am with you, needs to take it somewhere and have the speedometer certified.

[whitey]

im not 100% sure about the gearing. and the speedo was used with a GPS. i just got the motor in and just need to work out a few bugs is all. I'll get er' right.

[BBChevelle]

im runnin 3.55's and a 215/75 rear tire and im around 70 at 3k, 2700 is about 60-65. And as far as getting off the line, the straight tracks are mine from nearly 2 weeks prior to the picture. 213 feet and I just stabbed it on green.http://img.tapatalk.com/d/12/09/17/a3ene3u4.jpghttp://img.tapatalk.com/d/12/09/17/4u9a3a7e.jpg