[funkhoss]

[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.

Originally Posted by racprops

What is P&G With EOC please??

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.

Originally Posted by racprops

Well your info is what I am running into with my wanted changes.

Case in point: The problems with going to the super tall gears.

There just is too much cost and problems with them.

[...]

For the Chevy, nearly same deal, I cannot just bolt the tall gears in, again I have to replace the carrier, and as it seems GM is no longer supplying clutches for their posi I am stuck with used or hope to find some NOS parts. And again the cost just to buy the parts to do all of this is also around $500.to $600.00 And I should do a complete rebuild so add another $300.00+.

I was working from the idea of around $200.00 for just the gears, all this extra costs make it less a good deal.

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.

Originally Posted by racprops

Your information may be an answer. The Chevy rear ends are prone to howling, so far every van I have had howled so it seems to be a design flaw, so I am considering swapping it a different rear end, but need one better made and able or even comes with those gears… and another concern will be finding one that is wide enough to fit the van. Perhaps finding one that the axle tubes can be swapped?? Or Dodge or Ford...like the Ford 9inch...?

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.

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.)

Originally Posted by racprops

Adding the old B&W Overdrive looks so very good now.

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.

Originally Posted by racprops

The best thing of all worlds would be a rear end stronger with less prone to howling with the super gears and perhaps convertible from drum to disk brakes.

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.

Originally Posted by racprops

Reading between the lines I figure your apox. 50MPG was done by a lot of engine off coasting....as you made a bunch of changes to allow that.

My clams of 35MPG in a 2000 Mercury Grand Marques was made with the engine fully engaged at all times. Driving on cruse control at 65MPH.

I plan on doing that with my Van. It just is too much bother and even technically illegal within most states as have lost of control of your car.

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.

Originally Posted by racprops

I have read in a number of books that for best highway performance and mileage you want everything geared to be running at as near the torque peek and your cruising speed, + or – 10 to 20%. So if my engine’s peek is 2000 RPMS I want my cruse speed to be within 200 to 400 of that RPM which on the low end would be from 1600 to 1800 and on the high end be 2200 to 2400. Every V8 I have tested gets it best MPG running under 2000 RPMs.

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.

Originally Posted by racprops

Lastly as the Van has 3:43 rear end gears which helps move it off the line, but also runs in higher RPMs as highway speeds, I am thinking that a second overdrive added to a stock 4 speed auto with a OD gear can work and in fact greatly increase a stock car/van’s MPG, just by lowing the cruse RPMS from around 2600 RPMs to 1700 RPMs.

This seems to be the best of all worlds, stock gearing until the added Over Drive is engaged and the advantage of super highway gearing.

Plus under some conditions like upgrades I might find the act of being able to “Gear Spiting” as in using say the vans third gear and switching in the second over drive to get a good RPM about ½ of third and fourth.

As I have a couple of 50s B7W overdrives these will most likely only cost from a couple of hundreds to $500.00 low enough that there is a chance I will be able to pay off the cost in a couple of years thanks to the savings in fuel costs.

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.

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.

Originally Posted by racprops

The only thing I found that worked on my 2000 Mercury GM was leaning the A/F ratio to 16:1, on that car on the highway I was able to get 35MPG @ 65MPH, this was fully engaged motor running on cruse control full time.

But as I could not make the switch to a lean burn and back to normal it had a major loss of power. It was not a thing I could use daily.

The 80s Camaros TPI cars had such a set up. It was called at that time a Lean Burn Cruse setting, now it is called Highway Mode, what is did/does, was/is under light load, light throttle it automatically leaned the A/F mix, and with nearly any change in load and/or throttle smoothly switch out of Highway Mode to normal A/F mixes giving back full power.

This mode took a 20/25 MPG car to 30/35 MPG, just that little switch hidden inside the PCM.

And I did NOT make this up, I first learned about this on a site called Third Gen.org decades ago, here is a fast search showing some data about tuning highway mode as proof: https://www.thirdgen.org/forums/diy-...servation.html

And a cure for NOX with this mode is to increase the EGR. This cools the chamber, lowing the NOX, allows for burning left over fuel normally take care by the Cats, displaces some of the incoming charge, and can help cut pumping loses by forcing the throttle to be opened more lowing the drag of engine vacuum.

There is also recover of engine oil vapors and gas tank gas vapors.

Now we come to the big questions. Will all of this work??

I will find out this spring.

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.

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