Tall Rear End Gears

[racprops]

Originally Posted by Ecky

Corvette 7th gen. There are 8 generations, typically referred to as C1-C8. The C7 has incredible gearing. I believe the rear end for the auto is a 2.56 with a 0.67 6th gear, while the manual has a 3.42 rear end with a 0.42 7th gear. Tires are P285/35R19.

EDIT: I believe I recall seeing the C7 as being able to break 40mpg from the factory (at the right speed) with a 6.2L pushrod V8.

OK that is a 378 CI motor, very close to my 383 build.

I saw that about the C7 Corvette and it was more validation of my nearly 20 year old ideas.

Now to find a gear set in the ranges I am looking for.

Rich

[hayden55]

Originally Posted by Ecky

Corvette 7th gen. There are 8 generations, typically referred to as C1-C8. The C7 has incredible gearing. I believe the rear end for the auto is a 2.56 with a 0.67 6th gear, while the manual has a 3.42 rear end with a 0.42 7th gear. Tires are P285/35R19.

EDIT: I believe I recall seeing the C7 as being able to break 40mpg from the factory (at the right speed) with a 6.2L pushrod V8.

Yup.
Corvette 7th gen 14-17?
Triple over drive.
Version 1 7th: 0.50
Version 2 7th: 0.42

Interestingly they have pretty much used the same chassis and drivetrain since 1997. vvt and some changes, but besides the 0.42 ratio change a lot of it is extremely similar. In my mind the C7 is the C5 version 3.

[funkhoss]

I did some pretty extensive research on high-geared GM rear ends when I was working on my wagon. At one point, my wagon had a 2.14 rear, .73 overdrive (NV3500 transmission) and the factory 350 motor. It would do 55 MPH at just under 1000 RPM. At the time, I was using a heavy, 4.3 V6 flywheel, which helped with low RPM torque, but yes--the engine pulled that speed/RPM just fine. In fact, I would often cruise at 45 MPH and ~800 RPM.

The highest ratio that is available for the 8.5" 10-bolt in your G20 is 2.41. The 7.5" 10-bolt (which is what I put into my wagon) was available with 2.29 and 2.14 ratios, but that might not be heavy duty enough for your van, depending on how much you haul. (Astro vans had that rear, though, so they're tougher than you think. I don't know if an Astro van would swap into your G20 or not. They have the same wheel bolt pattern, but the differential is off-center and it may be a bit narrower.)

The only other option is a fairly rare 8.75" GM rear, with 12 bolts on the ring gear and 10 bolts on the cover, that came in some cars in the late 70's and early 80's. There was a 2.28 gearset for it, but that gearset only came in Cadillacs from 1977-1979. You could weld spring mounts onto one of those Cadillac rears and bolt it into your van, as it has the same wheel bolt pattern (5x5"), but it would be narrower than your factory rear and the axle shafts and outer bearings would be smaller/lighter duty. If you wanted a rear that was roughly the same width and the same strength (same shafts and outer bearings) as the factory rear in your van, you would need to find one of these 8.75" rears from a late 70's/early 80's B-body station wagon and swap in the 2.28" gearset from a 77-79 Cadillac. I seriously considered doing just that with my wagon, before I fully embraced P&G with EOC and gave up on extremely high gearing.

I hope this helps! Let me know if you have other questions about high-geared GM rears. Unfortunately I know very little about Ford rear ends.

-Funkhoss

[racprops]

Originally Posted by funkhoss

I did some pretty extensive research on high-geared GM rear ends when I was working on my wagon. At one point, my wagon had a 2.14 rear, .73 overdrive (NV3500 transmission) and the factory 350 motor. It would do 55 MPH at just under 1000 RPM. At the time, I was using a heavy, 4.3 V6 flywheel, which helped with low RPM torque, but yes--the engine pulled that speed/RPM just fine. In fact, I would often cruse at 45 MPH and ~800 PRM.

The highest ratio that is available for the 8.5" 10-bolt in your G20 is 2.41. The 7.5" 10-bolt (which is what I put into my wagon) was available with 2.29 and 2.14 ratios, but that might not be heavy duty enough for your van, depending on how much you haul. (Astro vans had that rear, though, so they're tougher than you think. I don't know if an Astro van would swap into your G20 or not. They have the same wheel bolt pattern, but the differential is off-center and it may be a bit narrower.)

The only other option is a fairly rare 8.75" GM rear, with 12 bolts on the ring gear and 10 bolts on the cover, that came in some cars in the late 70's and early 80's. There was a 2.28 gearset for it, but that gearset only came in Cadillacs from 1977-1979. You could weld spring mounts onto one of those Cadillac rears and bolt it into your van, as it has the same wheel bolt pattern (5x5"), but it would be narrower than your factory rear and the axle shafts and outer bearings would be smaller/lighter duty. If you wanted a rear that was roughly the same width and the same strength (same shafts and outer bearings) as the factory rear in your van, you would need to find one of these 8.75" rears from a late 70's/early 80's B-body station wagon and swap in the 2.28" gearset from a 77-79 Cadillac. I serious considered doing just that with my wagon, before I fulled embraced P&G with EOC and gave up on extremely high gearing.

What is P&G With EOC please??

I hope this helps! Let me know if you have other questions about high-geared GM rears. Unfortunately I know very little about Ford rear ends.

-Funkhoss

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.

I was told by IWE read ends only, that for the Ford, my rear end is a 8.8 carrier with 28 Splines axles. To get to a 2.41 gear set I have to convert the rear end to an 8.5. Of which they never made a posi carrier for. So I have to do some major mods to perhaps get it to fit and then worry if I got it right. AND this set will cost around $500.00+ just for the parts and I still have to make it work. That some machining or slims might be needed etc.

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.

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...?

So I am going back to my old plan. I am fairly happy with both cars as they are, the Ford is a real jackrabbit jumper off the line and the normal shift points work great under light to moderate power.

The only lack is in a power down shift, which can be a little off, either too low or too tall, lugging a little or over revving, but the main thing I need is a second over drive 5th gear. Adding the old B&W Overdrive looks so very good now.

And the same can be said for the Van.

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.

Otherwise the Borg Warner OD gives me the deep drop in RPMs at cruse I think I need and if it does not work out I am only out a few hundred of dollars not thousands.

But considering the wright and large front end I truly think a 6 or 8 speed auto would work best in it.

I would very much like to talk with you more.

Thanks for your input and help.

Rich

[racprops]

I have read your efforts with a large GM car.

I gather a lot from what you have done. I found it very interesting about how you ended up keeping the 4.10 rear end gears...

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.

Other than that I find the lack of engine changes interesting, this is where I am putting major design changes first:

I have searched a dozen times for what I plan on building.

I cannot find any one is doing what I am going for:

A low rpm 383. My plan is for this motor to spend most of its life running at 1700 to 2200 RPMs ranges and operate from 500 to 4000. Everyone builds a Hot Rod version. i find it interesting that the Chevy 400 and the Olds 403 both had such torque curves, peeking at 2000RPMs.

I am trying to build as much torque as possible using a mild the 90 Caddy Cam, and plan on advancing it 4 degrees. I am much more interested in LOW RPM Torque than house power, Torque is better at low RPMs than HP which is made at higher gas using RPMs.

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.

The combo I want is: a 400 crank machined for a 350. Stock 400 rods so I can keep my KB “D” shaped pistons. I am aware of the side loading on the bore, but as I do not plan on running over 5000 max, this is not a major problem. (This WAS custom 350, doing the 383 was too costly at the time.)

Cam will be a 1990 Caaddy Chevy stock cam which stock torque peek is 2000 to 2200. Lifters are stock 350 roller lifter set up.

Heads are 1970 early swirl port 192s, and other that major cleanup and 3 angled seats, springs tested and Perfect Circle Street Running (Oiling) valve seals, all rest left stock. I only plan of light grinding to ports to gasket match.

I will also run stock ratio roller tip rocker arms to lower the scuffing of the valves in the guilds.

I plan on feeding this with a 85 to 90s Camaro/Corvette TPI running MAF controls. I plan on having the stock Highway Mode turned on until I can get a special add on board to the PCM which allow greater tuning of both stock type tuning and fine tuning of the lean burn cruse settings, I will be able to super tune all operating systems.

Everything is built counter wise to common Hot Rodding standards. Stock heads, no opening the ports, no polishing them, (Everything I have read says the textured surfaces of stock ports HELP low RPM power, polished and opened (larger) ports are for HIGH RPM air flow and HARM lower RPM power) same for the heads. Low RPM cam that will not shift to higher RPM power curves, (the way most cams make more power, move the power curve up the RPM range)

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.


I did a lot of research and testing into MPG.

I tried HHO, special tuners called interrupt between the PCM and its sensors trying to fool the car to use less fuel. And a few other odd MPG devices.

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.

Rich

Originally Posted by funkhoss

I did some pretty extensive research on high-geared GM rear ends when I was working on my wagon. At one point, my wagon had a 2.14 rear, .73 overdrive (NV3500 transmission) and the factory 350 motor. It would do 55 MPH at just under 1000 RPM. At the time, I was using a heavy, 4.3 V6 flywheel, which helped with low RPM torque, but yes--the engine pulled that speed/RPM just fine. In fact, I would often cruise at 45 MPH and ~800 RPM.

The highest ratio that is available for the 8.5" 10-bolt in your G20 is 2.41. The 7.5" 10-bolt (which is what I put into my wagon) was available with 2.29 and 2.14 ratios, but that might not be heavy duty enough for your van, depending on how much you haul. (Astro vans had that rear, though, so they're tougher than you think. I don't know if an Astro van would swap into your G20 or not. They have the same wheel bolt pattern, but the differential is off-center and it may be a bit narrower.)

The only other option is a fairly rare 8.75" GM rear, with 12 bolts on the ring gear and 10 bolts on the cover, that came in some cars in the late 70's and early 80's. There was a 2.28 gearset for it, but that gearset only came in Cadillacs from 1977-1979. You could weld spring mounts onto one of those Cadillac rears and bolt it into your van, as it has the same wheel bolt pattern (5x5"), but it would be narrower than your factory rear and the axle shafts and outer bearings would be smaller/lighter duty. If you wanted a rear that was roughly the same width and the same strength (same shafts and outer bearings) as the factory rear in your van, you would need to find one of these 8.75" rears from a late 70's/early 80's B-body station wagon and swap in the 2.28" gearset from a 77-79 Cadillac. I seriously considered doing just that with my wagon, before I fully embraced P&G with EOC and gave up on extremely high gearing.

I hope this helps! Let me know if you have other questions about high-geared GM rears. Unfortunately I know very little about Ford rear ends.

-Funkhoss

[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

[racprops]

Originally Posted by 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.



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

As a replies on your last thoughts, The stock 350 is normally geared for a torque curve at 2800 RPMs.

My van gets 14MPG at any speed and seemly up hill and down hill.

It is a TBI POS, a standard carb intake with a pair of injectors.

A tune port intake was created to make a 305 feel and drive like a 350, on a 350 it could make it feel like a 400, on a 383/400..well I am hoping for something like a 450/500. Really. I talking torque.

But now a days everyone want HP...at the standard cost in gas mileage.

I really think I have spotted a real answer that most everyone has missed, a low RPM Engine fed by an intake MADE to make low rpm torque controlled by a highly tuned PCM running though a 6 or 8 speed transmission with super low 1st and 2nd gear and double over drives so in top gear the engine is running low rpms and pulling my van though super tall rear end gears.

IF I can get 20/25 I will be very happy, above that I will dance a jig....

And I have a few other tricks to throw at it.

More EGR, and reclaiming and feeding gas vapor from the vapor recovery system and oil vapor from the engine.

Who know what I might get.

Rich

I really need a photo host to share pictures, wish the site hosed pictures like most.

My van is a special model, it is aerodynamic...it does NOT get pushed around at 75/85 MPG passing or being passed by big rigs...their bow wake does not hit the van like all the other vans...Wish I could post picture here.

[racprops]

Well it is sometime very frustrating how much we can find on the internet and what we cannot find.

Case in point; Rear axle widths.

I am looking into a swap for a 93 Chevy van. I can not find how wide the rear axle is.

I am looking into using a 1970 to 1990 Chevy Caprice rear end, and need to know how wide that one is too.

Thanks.

Rich

[racprops]

I have to say to funkhoss: 1000 Thanks for your fantastic help.

I have began the hunt for one of the suggested rear ends.

A good amount of choices….now to find a needle in a hay stack…I lean towards the 8.75 rear end for it being stronger than the 8.5 and in the hope to find a 2.41 with Possi. There are only about 100 of RPMs between the 2.21 and a 2.41, and the 2.41 is much easier to find.

This with a 6L80e will make my van a real great powered set up. More or less a complete updating of the whole drive line. A TPI 383 with a 6 speed automatic to a stronger 8.75 rear end with 2.41 gears.

At last this set up is within my grasp...

Rich

Question: I was told I would have to replace the carrier to get a 2.41 gear set into my 8.5 rear end. Is that correct?

Originally Posted by funkhoss

The highest ratio that is available for the 8.5" 10-bolt in your G20 is 2.41.

-Funkhoss

[funkhoss]

Originally Posted by racprops

I am looking into a swap for a 93 Chevy van. I can not find how wide the rear axle is.

I am looking into using a 1970 to 1990 Chevy Caprice rear end, and need to know how wide that one is too.

Here's info on B-body rear end widths. This says 91-96, but I know that sedan and wagon rear end dimensions are the same from 77-96:

https://www.impalassforum.com/thread...widths.237620/

Using that as a starting point, you can then use a parts website like rockauto.com to compare the length of axleshafts to determine the overall width of other assemblies, too.

It turns out that van rear ends (like yours) are wider than C10 pickup rear ends of the same generation. This was confirmed on the part interchange guides as well. I had assumed that they would be the same as pickup rear ends, but evidently they aren't.

Based on the information above, here are the approximate widths, from wheel mounting surface to wheel mounting surface, of the rear ends in question:

1977-1996 B/D body sedan: 61.7"
1977-1996 B body wagon: 64.7"
1981-1987 C10 truck: 63.7"
G10/20 van: 67.8"

So, you could run a B-body wagon rear end, but if you wanted to keep the same track width you'd need to use 1.5" spacers.

Originally Posted by racprops

Question: I was told I would have to replace the carrier to get a 2.41 gear set into my 8.5 rear end. Is that correct?

Yes. The carrier breaks for the 8.5" 10-bolt are 2.56 and down, and 2.73 and up.

-Funkhoss