The official 6bt conversion thread

[Ranchero50]

The hydraulic clutch option isn't impossible. I just did it in my 2wd F250 during the 6.9l diesel swap. With power brakes I had to locate the master cylinder nearly above the gas pedal. I took the factory clutch rod off the lever and welded an extension on the lever so it would line up with the master cylinder and welded another block on that dropped to the new rod. The biggest problem is taking the flex out of the firewall. I had to fab a 8" x 8" x 1/8" steel backing plate for the firewall and then fabbed a 14ga sheetmetal rib that mimicked the factory ribs by the brake master cylinder. That took 98% of the flex out. Then to get enough throw to actuate the clutch I had to redrill the mount for the pedal stopper so the clutch pedal sticks a little abovde the brake pedal (1/2" or so). The pics are in the 'project updates' section.

Jamie

[68Mercury250Ranger]

Ford had an upgrade for the firewall at clutch master. All the diesel were eligable .

Hey what did you do for an oil pan on the 6.9 with your 2wd bump. Custom pan or steering in front of axles?

I've seen 6.9/7.3s in 78/79 Ford 4x4s but not 2wd.

[Ranchero50]

http://www.fordification.com/forum/view ... hp?t=24239

Is the link with the pics of the install so far. For the pan I had to section out an inch for clearance to the drag links. Hard part is the power steering box vs the drivers exhaust manifold, gets tight.

Jamie

[68Mercury250Ranger]

Take a look at the Left manifold and oil cooler from a 6.9/7.3 that is in the E250/350 Econoline. The manifold sits significantly higher and the cooler sits closer to the block. That may help you out with the steering box problem.
Good luck.

[briney]

i ended up getting my starter modified to clear. worked a treat. hopefully i'll get some smoke out of it this weekend.

[LincTex]

i ended up getting my starter modified to clear.

Glad to hear you got it figured out!

[briney]

ended up fitting the starter today. the people who did the machining f-ed it up, and now the drive pinion hits the ring gear instead of meshing and starting the engine. oh well. i will try a 12 tooth starter pinion. it is so close i can almost taste it.

[briney]

well, it finally goes. moved into the shed under its own power today.

[mljjones67]

[averagef250]

Congrats!

[Zeke71250]

So, the ZF 5-speed is good - Is a T-18/19 with a Ranger or Gear Vendors overdrive better?

Would a ZF 5-speed with a Ranger or GV unit be massive overkill? (10 forward speeds)

Either would give an obvious advantage in towing - I just wonder if the (unloaded) truck with 4BT and a ZF-5 is capable of high speed cruising (75mph+) without one.

[Zeke71250]

.... and ANOTHER dumb question.

I did some eyeballing - a 5" lift with 33" tires (while looking cool and giving me ground clearance, Clarence) will make the truck too tall to fit through my garage door!

So, I guess I'll be sticking with pretty much stock height and tires.

Anyhoo - it was said that the 4BT engine, ZF5 tranny, 3.73 gears, and 33" tires make a good combo... so if the tires were only 30", would the gears need to drop to 3.08?

[averagef250]

High speed cruising in a brick old truck kinda negates the whole point of going with the 4BT. Why put an engine in for fuel economy and then drive 75+? Mileage goes down the crapper past 65. If mileage is a concern, you should learn to drive <65 and gear the truck appropriately. Your RPMs should be under 2000 @ 65 for best results.

What do you plan to tow? If you really plan to tow a lot and are contemplating spending big money on a tranny setup for 10 forward gears, forget the 4BT and get yourself a 12 valve.

[Zeke71250]

Sorry - my armchair drivetrain theories will sometimes outpace reality by several steps.

I'm not a speed demon by any means.. I'm just trying to lay out the truck to handle a wide variety of situations. As far as what I'll be towing, it's an uknown - the kids will be out of school in a couple years and I'd like to get a boat... total load weight (boat plus camping gear in the bed) will probably be under 6,000lbs.

The 75mph number is for those times when cruising the interstate without the trailer - and would be the exception rather than the norm... 75 to 80 would be in the instance of passing a slower vehicle... 65 to 70 would be regular speed. And surely, even if the 4BT isn't running at peak efficiency pushing the aerodynamic equivalent of sideways UPS truck down the road, it should still get better mileage than an FE - no?

With a 4BT, the truck will be my daily driver - 45 minute drive at 50 to 55 mph - 60 miles a day.

Moneywise - even if I sink 8 grand into the old Ford over the course of the next three or four years, I'm still coming in under the price of a new truck.

I guess what I'm afraid of (with a ZF5 alone) is not being able to go faster than 60mph down the interstate - so I thought maybe adding an auxilliary transmission might give the extra gearing for higher speed without losing the lower gears to pull with.

Sorry if I misunderstood the 4BT code of ethics - I ain't the brightest star sometimes .

[71PA_Highboy]

OK,

Having looked at fuel and torque curves for the 4BT, ~1800 is the most efficient place to run a 4BT.

That said, the below numbers are based on 2000RPM, .75 final ratio (guestimate of an OD tranny) and 33" tires.

RPM = Speed
2.59 = 101.08
2.73 = 95.89
3.08 = 84.99
3.36 = 77.91
3.55 = 73.74
3.70 = 70.75
4.11 = 63.69
4.56 = 57.41


Looks like 3.70 is right about where you want to be as far as gear ratios with an OD tranny. (With 35" tires it would be 3.89).

That said, 1:1 ratio (NP435/C4/C6/T19 final) you would want 2.73 gears.

Now... if you were to get a ZF6 with a final of .49:1 then you want something in excess of 5:13 if you want to be able to use 6th effectively.


Should you want to run more calcs or change the other variables, look here:

http://www.angelfire.com/fl/procrastination/rear.html

hth,

eric