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post #1 of 13 Old 02-24-2014, 04:28 PM Thread Starter
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Question 3.55 gears on 37's question

New to the diesel world and this forum.

I have an '09 FX4 with
* Fab-Tech 6" basic system lift
* Bilstein 5160 on all four corners
* Dick Cepeck 37X12.5X20 Fun Counrty
* H&S Minni Maxx
* Gearhead 6.4 Tune by Matt
* S&B Si stage 2
* 5" Flow-Pro
* 3" Pipe from Intercooler
HP should be about 550 @ the rear wheels and about 1050 ft lb of torque.

I ordered the truck with 3.55 gears when I bought it new along with the 18" wheels.
I have just put on the 37's and Matt re-did my tune for the new tire size.
5TH gear TC will activate at 60 MPH.
@ 65 MPH, RPM's are just over 1500.

With all that said, my hand calculated mileage is 15.5. I thought I would get
a little better fuel mileage. 15.5 is what I was getting with my previous tires which were 35X12.5X20 MT ATZ's.
Before making the leap to a higher gear, I wanted ask for some knowledgeable opinions.
Do I need more HP/Trq to turn the 37's with 3.55's or is 4.10's the way to go.
I'm planning on going with a Jr. High-Power Compounds set turbos from Elite Diesel which is said to make about 700 RW HP with stock injectors and upwards of 800 RW HP with larger nozzles.
Although the 37' look real good with the 6" lift, I may go back down to 35's depending on the research.
What do you think.
Thanks
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post #2 of 13 Old 02-24-2014, 05:48 PM
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Ive been running the Icon 7" lift with 37's sine day 1 in 09. I put 4.10 gears and never looked back. I don't get very good milaege like 15 highway. I have SCT Offroad tuner w/ dpf delete. Hope that helps. Mine came w/ 17's and 3.23 gears
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post #3 of 13 Old 02-24-2014, 05:57 PM
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Quote:
Originally Posted by HotRodDiesel View Post
Ive been running the Icon 7" lift with 37's sine day 1 in 09. I put 4.10 gears and never looked back. I don't get very good milaege like 15 highway. I have SCT Offroad tuner w/ dpf delete. Hope that helps. Mine came w/ 17's and 3.23 gears
3.23????? First I have ever heard of a 6.4 with any lower than 3.55. Even the 6.7s only come down to a 3.31

2010 CC/SB FX4 Lariat.. Tuned By Eric@IDP and Matt@Gearhead

Thinking about getting rid of the stock 6.7 turbo?
Check this out... and research before buying



http://www.powerstroke.org/forum/6-7...ustration.html

http://www.powerstroke.org/forum/6-7...round-2-a.html
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post #4 of 13 Old 02-24-2014, 06:36 PM Thread Starter
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HRD
Thanks for your input.
For what it's worth, my lye-o-meter is kind of accurate. On a tank full of mix
driving, in and around Houston i average 15.5. If I'm on a Beltway trip with over passes
cross town it comes up to about 19.

Should I just be content with that or can it get better?

This is my DD and I keep a light foot 99% of the time.
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post #5 of 13 Old 02-24-2014, 07:59 PM
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I say you should be content with that. I wouldn't do nothing to my truck if it got that kind of fuel mileage. I drove around 300 miles or so the other day and I kept it at around 71mph 3.55s on 35s and averaged around 15.5mpg hand calculated IIRC. Doesn't matter what tune I run whether its from Gearhead or IDP.. I don't even see people on stock size wheels and tires getting the fuel mileage you are claiming much so I would go to sleep and wake up smiling like a jackass if I were you
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2010 CC/SB FX4 Lariat.. Tuned By Eric@IDP and Matt@Gearhead

Thinking about getting rid of the stock 6.7 turbo?
Check this out... and research before buying



http://www.powerstroke.org/forum/6-7...ustration.html

http://www.powerstroke.org/forum/6-7...round-2-a.html
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post #6 of 13 Old 02-24-2014, 09:01 PM Thread Starter
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"Thank you Sir...May I have another"...JK

That sound like I'll be saving me some money.
One more question. I was thinking of getting a Detroit Trutrak rear dif installed for stronger and better tracktion control as apposed to my stock Limited Slip.

Yes...No...
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post #7 of 13 Old 02-25-2014, 04:56 AM
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I don't have a Trutrak, but I have seen a lot of guys that are running it that seem happy with it. The factory limited slip sucks to say the least

2010 CC/SB FX4 Lariat.. Tuned By Eric@IDP and Matt@Gearhead

Thinking about getting rid of the stock 6.7 turbo?
Check this out... and research before buying



http://www.powerstroke.org/forum/6-7...ustration.html

http://www.powerstroke.org/forum/6-7...round-2-a.html
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post #8 of 13 Old 02-25-2014, 03:59 PM
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oops I was wrong 3.31 was my gear ratio. 2010 6.4 w/ 3.31
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post #9 of 13 Old 02-25-2014, 04:14 PM
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Quote:
Originally Posted by HotRodDiesel View Post
oops I was wrong 3.31 was my gear ratio. 2010 6.4 w/ 3.31
Ive never heard of 3.31 in a 6.4..... 3.73 was the lowest offered until 2009 and then the 3.55 became an option for 2009 and 2010

2010 CC/SB FX4 Lariat.. Tuned By Eric@IDP and Matt@Gearhead

Thinking about getting rid of the stock 6.7 turbo?
Check this out... and research before buying



http://www.powerstroke.org/forum/6-7...ustration.html

http://www.powerstroke.org/forum/6-7...round-2-a.html
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post #10 of 13 Old 02-25-2014, 05:34 PM
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3.55 was standard for 2010, with 3.31 optional. Factory was trying to improve fuel mileage.

2010 F350 KR CCLB, mini max, H&S pyro kit, ARP studs, II 71/59 billet turbos, Alradco, RCD ported intake, ceramic BD 6.0 exh manifolds, stainless uppipes, SDP 4" ceramic downpipe, 5" MBRP stainless, sinister egr delete with intake elbow, 3" CAC cold side pipe, BD boots, AFE custom air intake, AirdogII, Mann&Hummel CCV filter, 4.10 Yukon locker rear, Eaton TrueTrac front, Coolant filter
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