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  #1  
Old 07-27-2011, 08:22 PM
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nothercrash nothercrash is offline
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How many mpg will a 435 save over a C6?

Still might be switching. I'm getting right around 10 now, driving nice and soft, how many do I stand to gain by switching to a Np435 (a clutch).

I'm losing about 500 RPM to my converter on the highway.

I'm thinking maybe up to 13 mpg? Even more?!

What do you guys get? Thanks, AleX
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79 F150 4X4. 408. Np435, the clunk. Np205. 9" + HPD44, 3.50's. 31" BFG A/T's. True duals, flowmaster 44's. Full custom interior. 5 color primer and weld on patches!

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Old 07-27-2011, 09:45 PM
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Quit driving in 4x4 on the road and you will pick up a few mpg couldnt help myself!
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Old 07-27-2011, 09:48 PM
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I wish my truck was a 4 speed
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Old 07-27-2011, 10:03 PM
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Haaaahaaaahaaaa bamaf.... but ha, ya I know, thanks.

I've actually always wondered what driving in only front wheel drive would do to performance and mileage. You can do it if you twin stick the T case. With our knobby tires, and the crazy resistance these trucks put up to moving, I've always wondered how efficient the rear wheels are at transmitting power to the road with the bed empty, as opposed to the heavy front end.
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79 F150 4X4. 408. Np435, the clunk. Np205. 9" + HPD44, 3.50's. 31" BFG A/T's. True duals, flowmaster 44's. Full custom interior. 5 color primer and weld on patches!

Henry Ford, puting bow ties out of style since 1903!
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Old 07-27-2011, 10:10 PM
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If you are losing 500 to the converter then its bad!!! The more realistic number is about 230-320 rpms ( That is from Dave at Hughes ) consider one of their Fuel Miser conveters!! I really enjoy mine over the sloppy stock converter!! really brought the truck to life with the 1200 rpm stall and dropped the rpms at 55 mph about 200 !! Well worth the 220.00 cost of the unit and my trans temp is down over 20 degrees on the highway which is a huge help!!
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Old 07-27-2011, 10:33 PM
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joshjones.thewelder
Unless you have a 4000 stall convertor it should not be slipping that much.

When I switched from a C6 with 3000 stall convertor to a 5:1 1st gear T19 I *might* have gained 1/2 mpg, maybe 1 mpg.

Josh
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Old 07-28-2011, 12:41 AM
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That close ratio T19 (or even better, the ZF 5 speed) would be the one you want for mileage, but the ration gaps in the 435 will probably cancel out any mileage increase you would get, just because you have to revv it harder to maintain speed. I've never driven a 5speed in one of these trucks, but I've ridden in a few, and they are nice! The ratios in them don't leave any big gaps, and it's got the overdrive 5th gear.

I still love my 435 the best though, it's built the way truck trannies were meant to be, it's a big, heavy, and you can't kill it to save your life! Combine it with a gear vendor (or a similar overdrive unit) and it would be the perfect setup.

Sam
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Old 07-28-2011, 12:55 AM
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Hmmm, that zf5 sounds interesting, with the OD. How much would a used one run me? How tough is it to fit into these trucks? Can it take a beating?
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79 F150 4X4. 408. Np435, the clunk. Np205. 9" + HPD44, 3.50's. 31" BFG A/T's. True duals, flowmaster 44's. Full custom interior. 5 color primer and weld on patches!

Henry Ford, puting bow ties out of style since 1903!
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Old 07-28-2011, 08:48 AM
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I've been wondering myself would it takes to put a zf 5 speed in one of these trucks...
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Old 07-28-2011, 12:54 PM
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I've read about the ZF swap, and since both your motors have the 351m/400 you could get a ZF for a 460, since they both use the ford big block pattern. You would have to swap in a a hydralic clutch setup, and modify the 73-79 clutch petal to work (not difficult, a lot of guys have done it) and also figure out drivelines and transfer case. It's pretty involved, but not bad.

From what I've heard the 4x4 versions will run $500 to $1000 used, and they can take a beating. They aren't bomb proof like the old 4 speeds though, but are tough.

Sam
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Old 08-01-2011, 02:28 AM
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Quote:
Originally Posted by Rusty_Old_F250 View Post
but the ration gaps in the 435 will probably cancel out any mileage increase you would get, just because you have to revv it harder to maintain speed.
So did you get no change in mileage with your swap, Sam?
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Old 08-01-2011, 02:45 PM
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To be honest, I don't know. The rig always got a solid 10 mpg with the c6, but I haven't been able to drive it far enough to calculate the current mileage.

Sam
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Old 08-01-2011, 04:41 PM
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both trannys have a 1:1 final gear so you wont be gaining much of anything. if you went to a 5 speed like a zf then there would be something to gain since you have over drive
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Old 12-29-2012, 04:01 PM
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And the answer, from my corner at least, is after a year of driving on the 435, I save, on average, .5-1 mpg over a C6. The 435 can approach 12 mpg in the summer (mid 11's, these are per tank averages), but in the winter it can easily be 8-9, which is lower than what my C6 got in the winter, 9-10. On average, I'd say the manual edges the auto out just enough to be measurable, over a long period of time, a full year. My favorite part about the swap is the granny first gear on the 435, I use it all the time and combined with an Np205 Tcase it literally turns your truck into a tractor. My least favorite part about it (other than the cost, time, and disappointment over lack of mpg gains) is the clunkiness with which it shifts. It's just such a long stroke to shift it, and the ratios are so wide, you can't help but drive like a tractor trailer, gooooooooooo- coast (clutch, shift, clutch)- goooooooooooo- coast (clutch, shift clutch). It's a truck transmission though, what can I say.

Hope this helps someone in the future, Alex.
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79 F150 4X4. 408. Np435, the clunk. Np205. 9" + HPD44, 3.50's. 31" BFG A/T's. True duals, flowmaster 44's. Full custom interior. 5 color primer and weld on patches!

Henry Ford, puting bow ties out of style since 1903!
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Old 12-29-2012, 04:18 PM
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Great knowledge gained through your experience so thank you!
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Old 12-29-2012, 04:18 PM
 
 
 
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