david85
Full Access Member
I don't know enough about the DNE2 (I have the GVOD), but I'd be worried about sourcing a tailshaft housing adapter for the E4OD. They are usually the thing that junkyards don't include when they sell the OD. I know that I'd never switch to the E4OD, because with my 3.55's and GVOD, I'm pretty comfortable with the RPM's and highway speed. Also, we haul a lot on our trips, and never had any issues with the tranny and gearing.
Another thing I'd be worried about is EGT's with double OD's, and also, I'd be worried about high-end speeds in these vans. Running double OD's with a low gear ratio could easily get you over 75mph at under 2100 rpms. While that kind of sounds interesting and efficient, you gotta wonder how appropriate it is to take a van designed to top out at around 3000rpms/60mph on a 3-speed C6, and push that steering and suspension up to 80mph. I have replaced my tie rod ends, steering links, put in bilstein HD shocks, installed a steering stabilizer, and some of the best coils I could buy, so that my steering could be the least sloppy that I could make it, but even with all that, whenever I get up to 80mph, it's like driving one of those bumper cars from a crappy carnival. I'd hate to get my 8'6" tall van sloppy at 83mph with a cross wind. As I get older, I find myself cruising a bit slower on road trips, not just for fuel efficiency but also I'm thinking the Ford engineers never really wanted these vans to go over 70mph.
Ultimately, the E4OD is up to you. I wouldn't, but that's just me.
As for the ecomods, I've detailed all my stuff on my site. I think running a double OD won't give you better fuel economy. Just because you're running lower RPM's doesn't mean that you are using less fuel. Depending on the grade, headwind, and other factors, the extra gearing might force you to use more throttle to keep the vehicle up to the higher speed. Also, your Banks upgrade is probably going to cost you a few MPG as well. Once you go turbo, you won't go back to the days of creeping up to speed on the on-ramp, stoplight, and passing lane. You'll hammer down and love every second of it.
I can't say my truck has any problem cruising well above its original designed "top speed". The basic E-series and F-series platforms in question here were in production before and after the national speed limit of 55 MPH, so I don't quite understand the 60 MPH comfortable limit. Gasser Econolines don't suffer the same 3000 RPM limit, after all. And that's before considering the AOD option for the E-150s.
As for running low RPM at high speed, I agree to a point. If you are towing, hill climbing or pushing into a headwind, it might be more than the engine can handle. However what I found with my 3.08/E4OD setup is that my truck has two top gears. It is more than capable of burbling along at 65-80 MPH and tackling up to a 5% grade in overdrive. Anything more then that, and I have to gear down. But the point is, I can gear down. If I'm towing a trailer, I lock out overdrive and have the ideal 2200-2400 RPM range to keep turbo boost available at all times. And best of all, if I REALLY want to get serious, I can still gear all the way down to 2nd gear, let the converter lockup, and run all the way up to 3000 RPM for those steeper grades. It's a rough equivalent of 4.56 gears and a C6, minus the slip.
There were many skeptics when I first put together my tall gearing, but I maintain then, and now, that the only time you ever regret having tall gears is when you're first getting out of the hole. Anything above 20 MPH works just fine, while still giving you the ability to get better fuel economy on days that don't involve heavy loads.
Just for fun, I even tried cruising in overdrive at 55 MPH a few years back. A 3 consecutive tank hand calculated average returned 24MPG! Towing a flatbed on the same route netted 19MPG. Booooring drive, but made for some sticker shock at the pump.
I totally agree about fuel economy going down after a turbo though. Even today, I can't help myself.