I am putting my 67 belvedere back together finally after much trouble with oil pressure, rearends giving out and all sorts of other nonsense. I am in the market for a new 8-3/4 center section and I am wanting some recomendations for gearing? This is a midly built 440 mated to a 727 with a fairly high stall (dont know for sure) and a reverse fully manual valve body. I have my eye on a 4.56 geared posi truck chunk... is this waaaay to much for a street strip app? should i go more 3.55? any help would be appreciated.
Thanks,
Dave

 

What gearing do you have now?

For the street 4.56 may be a little steep for a big block. You need to consider rpm potential of the motor as well, if the motor only makes power to 5,500 then a 3.55 gear may be better.

But reall I have never herd any complaints with 3.90's. I went from a 3.21 to 3.90 in my 440 dodge ram with a 727, mpgs remained the same. I think 4.56 would have been to much for me.

Now if you were into drag racing and have a very strong head/cam combo then 4.10 would be the way to go.



If you are torn between 3.55's and 4.56's then go between with 3.90's. You will have the extra lowe end and gear advantage, but at the same time you will still be able to street drive it to higher cruising speeds.

 

whats your max rpm?

 

355's will be more user friendly aka driveable.

 

Much like 440truck said, what RPM range does your motor make its power in and what size tires are you going with? Also how often are you going to be on the street with it and how often are you going to be on the strip with it?

I would probably go with 3.90 - 4.10 though with a traction device of some kind.

 

I currently have 3:91 gears in my car, and at 70 miles per hour, I am turning close to 4000 rpm with an A833 4 speed behind a 440. I am swapping out for a 3:55 setup.

 

3.55 are probably the way to go

 

I must have stuttered...lol

 

appreciate all the suggestions guys. Honestly this car has been a money pit from day one. Its only run about 3 or 4 months out of the say... 3 yrs I have had it! I have no tach so I dont know for sure the power to rpm range... but if I had to guess I would say it runs out around 4500... it feels like it was built for all low end torque and horsepower no real high end stuff. With the way things are going she will spend most her time parked in the back yard!.. but really I intend for the car to cruise into town and occasionally hit the strip. I have my eye on two 3.55 geared posi units as well one recently rebuilt the other "guaranteed like new". Both of them are significantly more expensive than the 4.56 gear, but hearing about the High rpm running at 70 with lower gearing than what im looking at running... I think I better pop for the more expensive 3.55 units. thanks again!

 

forget what polaradude says and go with 3.55's ......hehe

 

I think you will be happier with 3.90's

 

I just completed the 3:91 to 3:55 swap yesterday, what a huge difference! Now I can comfortably run 70 on the freeway with plenty left over for passing. When you get your 3:55, make sure you get the 742 case. It has heavier duty components and is meant to be behind a big block. my 3:91 was a 741 case that was meant to be behind a small block. There is one even heavier duty case (489 I think), but it has a crish collar and is not as straight forward to work on. Also, I highly recommend switching to green bearings (ball bearings) as opposed to the tapered roller bearings which need adjustment. The green bearings just press on and no need to adjust which means the spring between the axels can also go away.

Keep in mind that I have an A833 4 speed, and you are using an automatic, so I am not completely sure how our gearing would match up transmission wise. I would really hate to see you go to 3:91 and find out you still rev too high on the freeway. No 4:56 for sure unless you are going to do 1/4 mile only. No 3:91 (at least with a 4 speed) unless you are going to drive mostly in town or you are comfortable with running high revs on the freeway. 3:55 really feels good, plenty of pep off the line and much more comfortable on the freeway. As people say, just my .02.

 

His last post he said he occasionally cruises to down a few times out of the year and likes to hit up the strip as well, 3.90's would suit him better for track results.

 

Got so busy with work today and all other things I completely spaced on my Ebay auctions! Oh well I think I will keep looking anyway still torn between 3.55 and/or going higher... I really want that off the line launch but I would like to be able to drive it places at more than 55 mph decisions decisions! Thanks again for all the input... or as it was very aptly put .02 any more suggestions would be welcome....particularly someone with a similar set up... running the 727 trans which third gear is about a thousand miles long it seems.

 

tire size will effect the rpm at highway speeds also. there is a calc online that you can check out.. i dont have any of the links handy but im sure someone else here will!

 

I say keep the 4.56's and get a 6 speed!!!! Problem solved!

 

unless i am mistaken the non overdrive 4sp has a 1:1 4th gear as do 727's i have a set of 3.91's for my 440 charger has a lot better response than the 3.23's in it now with 295/50/15 s its comfortable to drive on the freeway and is great for the occational trip to the track

 

http://www.wallaceracing.com/Calculators.htm


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