[Preliminary sidebar: I typed my response in a hurry last night, and didn't stop to proofread. I only noticed this morning how many typos there were in what I wrote.
They're fixed now. Quite embarrassing...]
Here are my answers to your questions, and some additional ideas.
Pulse and glide, with engine off coasting. If you're not familiar with this, I won't go into it here; there's plenty you can read up on about it elsewhere on this forum. However, P&G with EOC is only possible with a manual transmission, not an automatic (so it's not really relevant to your application, unless you're willing to do a manual transmission swap, as I did). For a vehicle with an automatic transmission, cruising on the highway, the lower the RPMs you can get, the better--so higher gearing will be the ticket for your goals/vehicles.
I am aware of it it just was not spelled out....no disrespect meant.
If you are patient and resourceful, a custom rear-end swap doesn't have to be expensive. The 2.14 rear that I had in the wagon for a while only cost about $500 total. The breakdown was approximately:
-$150--GM 7.5" Caprice rear with only 99,000 miles
-$100--2.14 gears and carrier, in good condition
-$100--Bearing/installation kit
-$150--Labor for setting up the gears
One excellent resource, if you haven't heard of it, is car-part.com. It's a search engine for basically every junkyard in the country. If you know what you're looking for, you can find very specific parts, often for pretty low prices. Complete rear ends with relatively low miles can be had for $150-$300, if you're willing to call around to find them.
Thanks I am aware of them it just is very costly to ship a whole rear end, BUT I will now start shopping around local junk yards.
The 8.75" rear is known for being considerably stronger than the 8.5" 10-bolt in your van. That's one of the reasons I suggested it. What's more, it came from the factory with some pretty high gearsets in it already--2.28, 2.41, and 2.56, depending on the application.
Loving it!!
Here's some screenshots of a search on car-part.com for one of these rears in late 70's/early 80's B-body wagons (I've included a shot of each step, and what you'll need to select). This rear should be about the same width as the one in your van, with the equivalent axle shafts and bearings, and equivalent brakes. In theory, all you would need to do if you bought one is cut off the wagon brackets, weld on spring mounts, and bolt it in your van. As you can see, there are several available with 2.56 gears, and at least one with 2.41 gears. Some also state that they have a posi. Some others don't specify either way, and for them you would need to call the yard to confirm. (None of these would have the 2.28 gearset, though, as those only came in Cadillacs. For that ratio, you'd need to buy those gears separately have have them installed in one of these rears.)
I looked into this option, too, several years ago. The BW Overdrive is tempting, but it probably wouldn't be strong enough for either of your applications. They aren't built to handle the torque of a more modern engine combined with the weight of a heavier vehicle, and would most likely fail very quickly.
There I am an old had at, there are two versions the R10 and the R11. I as a teenager drove a 56 Studebaker Golden Hawk which was a full 50s frame with body, and it came with a massive Packard 352 and a R11 over drive.
I broke a number of axles but never the transmission in the four years I raced Mustangs. I also played 6 speed on them, I took off in first, then dropped OD then kick it out of OD as I shifted to 2nd..then dropped OD so far 4 gears 3 shifts..then I shifted to 3rd off OD and then dropped OD that was 6 gears in 1964.
These are tough systems the were made from 1935 to 1965.
There is one more GM rear-end option that is not
quite as high of a ratio change from your stock 3:42 gears, but still an improvement--with SUBSTANTIALLY more strength. 1994-1996 Cadillac "commercial chassis" vehicles (limos, hearses, and armored cars) came with a 9.5" 14-bolt rear with a 2.93 ratio (and can be found in junkyards with low miles for $200-300). These also had the same wheel bolt pattern as your van. They were a bit narrower, but that could probably be corrected with a fairly inexpensive set of spacers. Again: weld on spring mounts, slap on spacers, and bolt it in--and you'd have
both a higher ratio AND a
significantly heavier-duty rear.
Well... there's really not anything "between the lines" about it. I use EOC constantly, and that's a large factor behind the results I get in both of my cars. I disagree that it is unsafe
or illegal, if done correctly (as would many others on here). If coasting with an ICE off were illegal, then hybrid vehicles would be categorically against the law...
I also disagree that it's a bother. It's become so habitual and instinctive for me that I don't even think about it anymore. I just drive. I'd also point out that the time and money that I put into configuring my cars for safe, effective EOC is only a small fraction of the time and money that your hypothetical engine build will require. But, to each his own...
If you would rather focus on lean, low RPM cruise, I can respect that. I'd just ask that the respect go both ways.
It does...I have a frozen engine, and the build when I started it was cheaper that a unknown crate engine...and darn near everyone is a hot rod engine.
So to get a low rpm engine I had to build it.
I'd say that the experience of many on here (including myself) is that for the most efficient, engine-on highway driving you want the lowest possible RPM you can get--NOT cruising at peak torque. Again, my wagon would do slightly less than 1000 RPM at 55 MPH, and thus about 1270 RPM at 70 MPH. With that setup, I could achieve 35 MPG highway cruising with the engine running, WITHOUT lean burn. Leaning out the mixture would have pushed that even higher. I was far below peak torque, but that's what you want. Higher RPM (closer to peak torque) would have made highway MPG
worse, not better.
From what I have read lugging an engine is as bad as over revving it....when an engine starts bumping it is lugging, my Studebaker a low RPM torque would lug at 40MPH in 3 Overdrive...I am aiming for 1600 RPMs at 80MPH with a big van...
Yes, having an extra overdrive would definitely help--but only if it's strong enough. Again, the BW overdrive probably wouldn't last long in either of your vehicles.
It is, I could not break mine as a teenager...
Another way to achieve the same effect is to have a high-geared rear end, and add additional
lower gears--like a granny-gear manual, or a range box from a transfer case mounted behind the transmission. If you are not planning to tow with your van, though, an automatic transmission with any of the highest ratio rear-end gearsets that GM offered (2.14 through 2.41) will still give you plenty of first gear, even fully loaded. You'd only need a lower first gear if you wanted to start on a hill with a trailer. I've learned this by experience.
IF I can get the rear end I plan on putting is a 6L80 or a 8L90...first gears are 6L80 4.02 and 4.56 for the 8L90 even with a 2.41 it will have more take off power that the stock transmission and rear end.
I agree--with steady state cruising, lean burn done properly can offer significant efficiency gains. Yes, as you say, the GM TBI vehicles had this capability built into the PCM, and with tuning it could probably be exploited to great effect. Setting up a reliable "lean cruise" mode will probably make a big step towards achieving your goals, and for a relatively small investment of money.
They are in the TPI Tuned Port Injection systems which are said to produce 30% more torque, HP and MPG just by them self's....These are why my little 03 Ford 281 4.6 Motor hauls ass...It HAS a TPI intake system.
I question, though, whether the mechanical engine modifications you propose are necessary, or will offer any significant gains over a stock motor in good condition. GM optimized their stock truck/van/large car engines for low RPM torque from the factory already. You might just end up throwing a lot of time and parts at this engine, only to find that the MPG results you get aren't really much better than stock. If you want more power than stock, that's different...but a stock small-block Chevy in good shape already has plenty of torque for the majority of the vehicles it came in (in my opinion).
Just some thoughts...
-Funkhoss