rear gears - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 20 (permalink) Old 02-22-2010, 04:46 AM Thread Starter
 
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rear gears

Hi guys my names Neil i'm new to the forum i have a 94 f350 7.3 ps 5speed with 3:55s. I just recently have taken a job hauling camper trailers from the factory to the dealers. I am trying to figure out how i can get better fuel mileage I have the 3 inch down pipe and 5 inch exhaust a superchips tuner and a cold air intake, when i'm cruising down the highway between 65 and 70 i'm running 2000 rpm i'd like to know if they'res somthing i can do to drop my rpm down to like 1800 like change the gears would that help in fuel milage. currently i get get 300 miles to a tank unloaded. the company i work for most of they're drivers have dodges with the 5.9 and they're getting far better fuel mileage what can i do to improove mine? Thanks in advance sorry for such a long thread.
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post #2 of 20 (permalink) Old 02-22-2010, 04:55 AM
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Re: rear gears

welcome to the nation.

If I were you I would look into a gear vendors over drive unit or on from us gear.US gear

02 f250
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post #3 of 20 (permalink) Old 02-22-2010, 05:03 AM Thread Starter
 
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Re: rear gears

Thanks was just on gear vendors website they're pretty pricey $2500 for the unit plus another $200 for the processor thatsa alot of money to shell out. has anyone tried different gears like 3.36 alot of the dodge guys i run with have 3.36 i know the olf f150 i had was 3.o8 and it got awesome milage but that was gas.
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post #4 of 20 (permalink) Old 02-23-2010, 01:08 AM
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Re: rear gears

Its getting tough to find R&P sets under 3.55:1.

If you have a 4x4 you need 2 R&P sets.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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post #5 of 20 (permalink) Old 02-23-2010, 06:04 AM Thread Starter
 
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Re: rear gears

mines 2wd standard cab. with the 3.08 gears what are your Rpms? any i dea where i can pick up a gear set?
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post #6 of 20 (permalink) Old 02-23-2010, 06:21 AM
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Re: rear gears

Sorry, I don't think that your going to the fuel mileage that you want with a set of gears even if your able to find them in a 3.08. I have a gear vendor and with my trailer I find my self spending mor time in 3 over then in 4 over, It pull much better and use less fuel on the hills. One other thing in 4 over with the trailer it causes my o/d light to flash becouse the trans wants to slip. Try taking out the superchip and Have "bryans truck shop" build you a tow chip for fuel mileage .
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post #7 of 20 (permalink) Old 02-23-2010, 05:25 PM Thread Starter
 
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Re: rear gears

how much did you pay for the gear vender? on they're web site the 1 i was looking at was over 2 grand can change a set of gears alot cheaper than that. As for tranny slip I have a zf 5speed so that won't be an issue. I want to get rid of of the superchips though.
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post #8 of 20 (permalink) Old 02-23-2010, 05:30 PM
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Re: rear gears

concerns I have is if you swap to 3.08s how will that effect the power band? How will it effect you being able to tow up and down hills?
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post #9 of 20 (permalink) Old 02-24-2010, 12:35 AM
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Re: rear gears

When I put 3.08s on my truck, I got a 3 MPG improvement. I tow just fine thank you, up and down hills with a more trailer than my brakes are good for, but remember: I have the 6 speed.

If you have the "Tool of OPEC" (automatic), forget gearing. If you slow the engine down, it will trash an automatic, including the over-rated Allison. A stick? No problem.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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post #10 of 20 (permalink) Old 02-24-2010, 01:34 AM
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Re: rear gears

I suppose I doomed to spend my life enlightening noobs.

Us fat guys go through life thinking there will be a magic pill we can take and we'll be as cut as Olympic athletes without starving and working out 26 hours a day for decades. Alas, I haven't found one yet.

The great belief that a chip or exhaust pipe will get you 30 MPG is exactly the same - a version of the great cosmic search for a free Lunch. I can see why there is a lot of blind faith in chips. They greatly improve acceleration and speed with minimal work and outlay. If that's all you are after, they deliver.

But they don't help MPG. I run a chip burned by one of the more knowledgeable dudes in the Nation and it gains me maybe 0.6 MPG over stock.

Over the last nine years I've tried everything. Big exhaust, high-flow air filters, synthetic oil, etc. A 203 degree stat helps a little (about 0.5 MPG) but beyond that what works is limited to better aerodynamics and numerically lower gearing.

Those two things are why I get 24-27 MPG and you don't.

Aero is obvious to anybody who has ever stuck his hand out the window.

Gearing works because it reduces engine speed at a given road speed. Less engine speed means less engine frictional HP. Engine frictional HP is why you never, ever want to exceed 2000 RPM. Above that, engine frictional HP goes up exponentially with RPM. Below that, engine frictional HP goes down proportional to RPM. Below 2000 HP frictional torque is fairly constant but above 2000 RPM gas flow through the engine is congested by turbulent flow.

I go down the highway at 70 MPH turning 1700 RPM. If I put a GV on, I'll reduce RPM to maybe 1300 RPM, so my engine frictional HP will be 65% of.that of a guy turning 2000 RPM.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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