9 inch Gearing question.

[spap]

Hey everyone i know this has been beaten to death but im ob the fence
77 bronco linc towncar 5.0 (it was a great deal and had 35k miles) with a 4r70w and 35 inch tires and i need to re gear its stock 3.50 now. Low rev motor makes 280 lbs torque at 2,200rpm do. Run 4.56 gears or 4.88. I am just thinking wth the 4.88 will the motor in a rev range where it desnt make any power. It actually can pull the overdrive gears now on the fwy 80 at about 1400 rpm.
What do you think

 

[Sun_and_Steel77]

Go 5.13 or at the very least 4.88

I originally was 4.56 but changed to 5.13 and am much happier with the all-around performance.
I was on the fence just like you and I'll tell you I could have saved alot of cash by listening to the guys on here from the start but was to apprehensive to go deep and it cost me a gear change as 4.56 was not near enough.

I have a mild explorer 5.0 with a 4r70w and 35" tires for reference.

These little 302's need some RPM to run happy regardless if they are in explorer trim or mustang,there is only so much low-rpm torque you can get out of these engines regardless of cam profile.

IIRC I'm at around 2300-2400RPM at 110kmh (65'ish MPH?) in OD. Where I live is mountainous but I do long distances frequently on the highway and do a good amount of moderate wheeling as well.

 

[Sun_and_Steel77]

Forgot to mention I found no noticeable difference in fuel mileage dropping from 4.56 to 5.13
With the doors and top on and the tires aired-up I can still manage 14 MPG at 60MPH on the highway.

 

[70_Steve]

www.grimmjeeper.com/gears.html

 

[Apogee]

Moving from 3.50's to 4.88's would be a 39% change. Moving from 3.50's to 5.13's is about a 44% change. Either would be a huge step in the right direction IMHO. I've never run a 302/5.0 that was happy to lug along at 1400 RPM, especially in a aerodynamic brick like an EB. At least the 4.88's and 5.13's would get you up into the peak of your torque curve.

Even a "low rev" 5.0 should still easily spin up to 4500-5000 RPM, so how fast do you need or want to ever go? Assuming it's under 100 MPH, I would say don't fear the gear and go deep while you're doing it.

 

[spap]

Thats what had me surprized the town car motor which i will probanly change so day. Just pulled it i was surprized. But it was built to lug around a big fat lincoln town car. But this motor runs out of breath very quickly like nothing over 3500 rpm. But i think the 4.88 are the choice. Ya i ahve been over that jeeper creeper all the time trying to figure this out. Over 80mph gets a little sketchy no matter what anyone says
Thanks. For the comments

 

[sykanr0ng]

35 inch tires, 5.0L engine and 4R70W transmission?

5.13 gears.

Even the 4.88's will have you too low RPM to get use of the overdrive.

 

[galen1970b]

I just swapped from 3.50s to 4.56s. Its a totally different truck. I'm running 35s as well and trun around 2700rpms at 60 mph on the highway....I don't go faster than that...with an over drive im sure it be alot lower. Just make sure when you do that swap...especially if you are runnin the stock trac-loc....to either upgrade the LS or rebuild it with premium parts...I just added some torque....and gearing....and shattered the rear spiders gears....just got done installing a yukon dura grip LSD..I got lucky that I didnt do anydamage to my bearings or ring and pinion..

 

[ren71]

You're in SoCal and your last sentence said your engine was fine at pulling OD at 80 mph. Your current 3.5 to 4.56 would be fine then. And you won't be revving to the moon just to keep up with most SoCal freeway speeds.

 

[ren71]

And just curious how are you smogging the 77 with FI in SoCal? PM me if it's a secret =)

 

[spap]

Ha I just don't want the revs out of the power band.
The motor has all the smog equipment and cats I bought the whole town car for 800 bucks and it had 35 k miles on it. So I had everything all of the smog equip etc exhaust etc

 

[Broncobowsher]

4.88 in OD will come out to something like 3.42 gears. If you are driving it now with 3.50 gears take it down the highway with the OD off. That is almost the same (a touch higher but not really enough to notice).

Now if you are driving the town car and cruising at 1400 RPM comfortably, yes that is understandable. You are only punching about a quarter of the aero and rolling load of the Bronco.

My 4R70w experience is 4.88 gears with 33s and a 351. My thought was it would be perfect with 35s OR only a 5.0/302 engine. But not both. You are considering both, that would push more for the 5.13 gear. I have not driven the crown vic 5.0, but it can't be that incredible on the low end. Torque is based on displacement and cylinder pressure and the displacement is known and the cylinder pressure still has the limits of the octane of the fuel used.

 

[Digger556]

4.56s


No need to over rev the engine on the freeway. I use to spin 35's with 4.0 V6 that had 160hp using 4.56 gears.

Now with a V8 I could drop to 4.10s if I wanted, but 4.56s are a great mix of economy and power.

 

[Bluebolt]

I have to agree with either 4.88's or 5.13's.