6.4 W/ 3.55's?

Powerstroke Man 6.4 · Feb 27, 2014

Does anybody have a 6.4 with 3.55 LS how you guys like it? The 6.4 i'm buying has 3.55LS. The 6.7 I have has 3.55 but that's the 6R. So will it mostly likely be the same other than one less gear?

Whats you guys input on this

Power

Fuel Economy

I hope is better F E then my 6.4 f-350 DRW it has 4.30's and that bugger sucks some diesel LOL even with 19.5's man oh man.

Thanks in advance.

bigrpowr · Feb 27, 2014

love it. i switched from 3:73 , but the truck is lowered so i really noticed it.

Dzchey21 · Feb 27, 2014

3.55s for anything under 35s is only the way to go on a 5r or 6r

my reg cab has 3.73s and i hate it

MrMike2010 · Feb 27, 2014

My 6.4 has 3.55s with 35s and I have no complaints. Turns just about 2k rpms at 78 mph. Mpg seem to average around 14.8. That's with a lot of stop and go traffic. Like 70 mph, stop back to 70mph. Over and over again. The Long Island expressway is relentless. All highway I've pulled off 17-18. Might be able to get better with easier driving habits.

Dzchey21 · Feb 27, 2014

I will say only thing bad about 3.55s and 6.4s is if you have to tow allot at about 65mph, its right between gears then, 3.73s shine more

Morgan@Midwest Diesel & Auto · Feb 27, 2014

Had two basically identical setup 6.4 at the shop. Both lifted with 35's. One had 3.55 and one had 3.73's. Definitely would have to have 3.73's. But 3.55's with 33's or less rock.

3.55's in a 6r works great. Lock out 6th when towing and puts it in a really nice range about 70-80 mph. When not towing its nice to run unloaded and get decent mileage on 6th.

Powerstroke Man 6.4 · Feb 27, 2014

bigrpowr said:
love it. i switched from 3:73 , but the truck is lowered so i really noticed it.

Mike i'm Booking my tickets tonight for texas its official LOL finally have another 6.4 to screw around with.

How much was the parts if I ever want to switch to 3.73 etc?

TY'S08FX4 · Feb 27, 2014

What brand do most guys go with when changing gear sets? Looking to switch to 3.55's before the pulling season.

Morgan@Midwest Diesel & Auto · Feb 27, 2014

Either stock(ford-spicer gears) or Yukon.

bigrpowr · Feb 27, 2014

Powerstroke Man 6.4 said:
Mike i'm Booking my tickets tonight for texas its official LOL finally have another 6.4 to screw around with.

How much was the parts if I ever want to switch to 3.73 etc?

about $14-1500 with bearings, seals, fluid etc ..

morgan - the 3:31 in my 13' with 35's is a goddamn dog. im putting in 3:73 next week.

Morgan@Midwest Diesel & Auto · Feb 28, 2014

bigrpowr said:
about $14-1500 with bearings, seals, fluid etc ..

morgan - the 3:31 in my 13' with 35's is a goddamn dog. im putting in 3:73 next week.

I look forward to a text with a burnout video.....

sootie · Feb 28, 2014

3.55's are great for hwy mileage, other than that i would prefer 3:73s.

On 3:55s with a true 35" tire it is a bit slower off the line (harder on the transit feels like) as Morgan said above.

RedRice589 · Feb 28, 2014

If you tow at all heavy with 3.55's they suck. Personally I loved th 4.10's but that was because I could leave the cruise on all the way to Va line. And again when I got through WVA. But for driving arounfpd I don't think you can beat them. Get good mileage if you retain stock tire size.

RSK · Feb 28, 2014

i've only had my truck since december, and haven't driven it on the highway much more then 10-15 mins, its nice to see the rpm down on the highway, but i think it hurts my around town a lot. my right foot could have a lot to do with it too, but at 80 its dead on 2000rpm with the stock size tires. I generally get from 11-13mpg pretty much all stop and go, very little highway driving involved. my 7.3 has 4.10's and its also my work truck, so it tows 5-6 days a week, and plows snow, so its a perfect match up. but even in the 6.4 i think i might regear it with 3.73's not sure yet.

JrStroker · Feb 28, 2014

My truck has 3.73s runs pretty good if you ask me. Its on '37s' but I can cruise at 70 and turn less than 2000 rpm.

Had a buddy that had a huge lifted 6.4 on 40s and 3.55s. Said he got great milage!

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WoodBoy · Feb 28, 2014

JrStroker said:
My truck has 3.73s runs pretty good if you ask me. Its on '37s' but I can cruise at 70 and turn less than 2000 rpm.

Had a buddy that had a huge lifted 6.4 on 40s and 3.55s. Said he got great milage!

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Since his tires circumference was about 15 percent bigger than stock then he should have gotten about 15 percent better right?

JrStroker · Feb 28, 2014

WoodBoy said:
Since his tires circumference was about 15 percent bigger than stock then he should have gotten about 15 percent better right?

Beats me. Ha! And by good I mean 15-16 mpg.

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ncollins64 · Feb 28, 2014

So far I'm liking my 3.73s. I tow some so that's why I like them mostly. I'm on 35s and still under 2000 rpm at about 75 mpg

JDub · Feb 28, 2014

Dzchey21 said:
I will say only thing bad about 3.55s and 6.4s is if you have to tow allot at about 65mph, its right between gears then, 3.73s shine more

I would agree with this. My 08 was 3.73's, the 2010 was 3.55's. In the 2010 I had to run 80 if was towing heavy, anything lower and the rpms were too low and it didn't like the weight behind it. I preferred the 3.73's

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fordman2121 · Mar 1, 2014

Ive got the 3:73 in my 2wd and would love to switch to 3:55s. But if I had 35s I think I'd stick with the 3:73s if towing much at all. Ive been looking for a whole rear end to just swap it in.