94 Caprice Wagon project--now 50.55 MPG with "3/4 ton" drivetrain/suspension
 

UPDATE 1/8/20: To read about this car as it is currently configured, please jump to this post: https://ecomodder.com/forum/showthre...tml#post614665

The original post below, from 3+ years ago, remains unchanged.

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https://ecomodder.com/forum/attachme...1&d=1546880701

This project started when we wanted a second car in addition to our 2000 Chevy Metro (which has also been ecomodded and currently averages about 77 MPG, with tanks as high as 90 MPG). We were looking for a vehicle with 7+ seats for carpooling that could also tow/haul moderate to heavy loads if necessary.

So in August 2013 we bought a 1994 Chevy Caprice station wagon with 83,000 miles (it currently has about 99,000 miles). This vehicle has a 5.7 liter (350 c.i.) V8 engine, eight seat belts, and can tow 5000+ pounds. Since purchasing it, we have slowly but surely been modifying it, with the most recent mods (about three weeks ago) being a complete drivetrain swap (a manual transmission replacing the stock automatic, a higher geared rear end, and a kill switch). It probably would have been more interesting to start a running build thread, but I just didn't have the time to devote to keeping it updated.

I have also tried to be as frugal as possible with this project. I have less than $4000 total in the car, including the purchase price and all modifications.

Since the drivetrain swap, we've had two fill ups. The first was a very mixed tank, with some highway, some in-town driving, and some short trips and idling for tuning and test runs. It calculated out to 39.2 MPG. The second fill up was basically a highway trip from one side of Virginia to another and then back again, which ended up being 46.3 MPG.

I have a feeling, based on these fill-ups and what my MPG gauge tells me, that we'll end up averaging 38-40 MPG with highs approaching 50 MPG from here on. Before the drivetrain swap and kill switch, we were averaging 25 MPG overall with highway trips around 31-32 MPG (which really wasn't bad at all for an automatic).

Now for the most important part...the mods. :) I've included both a "Cliffs Notes" summary, as well as a more detailed description, below. More pics are available here: Caprice Wagon - Album on Imgur


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Mods Summary

Aero mods
-Roof rack delete
-Rear wiper delete
-Moon disc wheel covers
-Side skirts
-Rear fender skirts
-Front air dam that is wider and lower than stock
-Rear kammback extension
-Full grill block and front gap sealing
-Shorter and narrower front tires for less frontal area and lower ride height
-Slightly lower rear springs to match lowered front
-Power antenna override switch, to allow CD listening with antenna down

Drivetrain
-Manual steering conversion, using manual steering box from an S10 pickup
-Lightweight, 23% underdrive crank pulley (made by "ASP")
-A/C compressor override switch, to allow use of any HVAC setting without running the compressor
-Engine tuning, using "Tuner CAT" program (mainly moderate tweaks to AFR and ignition timing)
-Before the manual swap, I created an optional "manumatic" mode that allowed complete manual control of the automatic transmission (see below)
-Manual transmission swap--NV3500 transmission from 1996 Chevy 1/2 ton truck
-"GM 7.625 inch 10-bolt" rear axle from a Caprice sedan, with 2.14 gears installed
-Lightweight 9.5" aluminum brake drums from an early 80's GM car (weighing 8 lbs. each vs. 25 lbs. stock)
-Kill switch (interrupting the distributor sensor feed)
-Auxiliary brake vacuum reservoir and electric vacuum pump, to allow for indefinite engine off coasting
-16" aluminum wheels from a Jeep Grand Cherokee, installed using spacers/adapters
-Bridgestone "Ecopia" low rolling resistance tires; 215/65R16 front (27") and 235/70R16 rear (29")
-Compact spare tire from Jeep Grand Cherokee (in place of stock full size spare)

Instrumentation
-"UTCOMP" trip/MPG computer

Fluids
-Amsoil full synthetic in engine, transmission, and axle
-Ethanol free premium gas

Other (non-eco) mods
-Installed a child seat tether
-Installed locking seat belts from a Chevy Trailblazer in the middle row, in order to make child seats easier to install
-Monroe "Severe Service" heavy duty shock absorbers

Planned future mods
-smaller and/or skinnier front tires, when they need replacing; I'm thinking either 215/55R16 or 205/65R15 (both are about 25.5")
-lower rear springs to go with the shorter front tires
-A/C delete(?); the A/C doesn't do much with a lot of engine off coasting anyway
-"Clear" window tint, to reduce summer interior heat
-Power vent windows; I've got motors (form a Nissan minivan) that I think will work, but I just haven't had the time to do it yet
-Set up the car for interchangeable rear axles, using quick disconnects on the brake lines and cables; one axle will be an "economy" axle (the one that's in the car now) and one will be a "towing axle"
-The towing axle will be a "GM 9.5 inch 14-bolt" rear with 3.73 gears and heavy duty 11x2.75 "truck" drum brakes, from a commercial chassis Cadillac Fleetwood; I already have this axle in my shop
-The "towing" setup will also include heavy-duty rear springs, a rear sway bar (from a Ford Crown Victoria), 235/70R16 tires on all four corners, and a full size spare
-Heavy duty "J55" front suspension/brakes, also from the commercial chassis Fleetwood; this will stay in the car all the time, since it won't really affect fuel economy

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Mods Details

When we first bought the car, it was in good mechanical condition with hardly any rust (having spent most of its life in Georgia), but the engine did have some oil leaks. They ended up being fairly easy to fix--just a waterpump shaft seal and an oil filter adapter seal. The best part is that the previous owner's mechanic told her that the leaks would cost $1700 to fix, so she adjusted the sale price accordingly (cheap!).

The first thing I did, after fixing the leaks and doing a tune up (fluids, oil filter, fuel filter, spark plugs, wire, O2 sensors, etc.) was to install a gauge. Being a 1994 model, an OBDII unit like a Scangauge wasn't an option. I ended up buying a "UTCOMP" on eBay, and I have been very pleased with it. It works a lot like an MPGuino, in that you have to tap into the VSS and FI signals, but it has a much friendlier interface, more features, and the capability to wire in a lot more sensors (I also wired in a temp sensor for the automatic transmission, for example). The gauge has been very accurate for as long as we have owned the car.

The car did need a new crank pulley/harmonic balancer, and since it needed to be replaced anyway, I spent a few extra dollars and bought an underdrive pulley. I never did A/B testing with it, but it probably made a slight difference, particularly with the A/C running.

The next step was to start the aero mods. Most of this was pretty straightforward. I got a good deal on 15" wheel covers on eBay; the grill block is black "Gorilla tape," with home insulation strips for gap sealing; the front air dam was made using lawn edging material; the side skirts are made from plastic guttering; and the wheel skirts are coroplast pieces that are held on with screws going into homemade brackets. The most complicated part was the kammback. The kammback on our Metro was pretty simple--I just attached it solidly to the rear door, since the door is one piece with a metal frame around the rear window. On the Caprice, though, the window and tailgate operate separately, and the window does not have a metal frame. What I did was to make a lightweight metal frame with hinges that attach to the roof above the rear glass and arms that come down and attach to the car near the bottom of the rear glass using wingnuts. The kammback itself is made from coroplast and is attached to the metal frame. The sides of the kammback that meet the sides of the car have rare earth magnets in them to keep them in contact with the car. This allows the entire kammback to be detached at the wingnuts and swing upwards on the hinges, allowing the rear glass to open. It works very well and has proven to be durable after several years.

Buying the "Tuner CAT" tuning program was also an excellent investment. I have used it for everything from adjusting the speedometer after tire and gear changes, to tweaking ignition timing and AFR, to making the cooling fans turn on sooner, to modifying shift points and TCC engagement, to giving the car a "manumatic mode." This car uses the same "LT1" engine that was also used in the Corvette, Camaro, and Firebird. The Firebird had a "performance mode" button that, when selected, caused the transmission to shift differently (later, mostly, for a more "sporty" feel). Even though the other cars with the LT1 did not have that feature, the programming still exists in the PCM. So I put one of the Firebird "Transmission Perform" buttons in the wagon, wired it to the engine computer, and then reprogrammed the "performance mode" tables so that the transmission would go to and stay in whichever gear the shift lever was moved to. I then wired up another button, and placed it on the end of the shifter, which would ground the TCC solenoid and lock the torque converter clutch. Between the two, I could shift into any gear I wanted, and lock the TCC whenever I wanted to, giving me complete control over the transmission. Once I got the hang of it, this "manumatic mode" gained me several MPG, particularly in city driving. The best part is that the "manumatic mode" was completely optional--if one got into the car, started it up, and drove, it would work like any other automatic. It would only go into "manumatic mode" if the "Transmission Perform" button was selected. My wife really liked that feature.

Another thing I did fairly early on was to convert it to manual steering. I did some research and discovered that a manual steering gearbox from an S10 pickup bolts right into a Caprice. So I found a box, swapped it in, and replaced the PS pump with an idler pulley (just like the tensioner pulley). I simply bolted it into one of the bolt holes from the pump, and it worked great with the stock serpentine belt.

I knew that when the tires needed to be replaced I would be looking for LRR replacements. However, there are very few LRR 15" options, especially in the taller sizes. So I figured out that 1999 to mid 2000's Jeep Grand Cherokees have the same bolt pattern as the Caprice, just with a different offset and hub center bore, and come in 16" and 17" sizes. So I got a set of aluminum 16" wheels for really cheap from a local U-pull yard, and got a set of adapters/spacers for the wheels. I then settled on the tires and sizes I listed above, and bought them used on eBay. We put so few miles on this car that we really don't need new tires for it, and used tires have lower rolling resistance anyway. Switching to the LRR tires was another mod that made a big difference--about 2 MPG across the board. Running different sizes front and back gives the best of both worlds--taller tires in the rear for lower rpms, and shorter, narrower tires in the front for less weight and better aerodynamics. I plan to go with even shorter front tires the next time they need to be replaced.

Once all of the mods I have described so far were completed, I didn't do anything more for a while. I began collecting parts for the drivetrain swap, but even once I had collected everything I needed, I didn't do anything for about a year and a half. Life kind of got in the way--we had another baby, bought a house, and I had other projects to work on. I had figured that a manual transmission with a kill switch would make a pretty substantial difference. I just didn't have the time to do it. :(

But I finally did it this Memorial Day weekend. :D I had gotten the transmission, clutch, flywheel, hydraulics, pedal, etc. from a 1996 Chevy 1/2 ton pickup. I went to our local U-pull's "all you can carry sale" and got everything for $65. I also was fortunate in that the particular truck I pulled everything from had just had a new clutch and hydraulics put in before it was wrecked. I got inspiration and guidance to do the swap from this thread, which has a lot of details: 1992 Olds Custom Cruiser project - Chevy Impala SS Forum. The only things I'll add to it is that the crossmember was a lot easier for me because I was starting with a 1994 model; all I had to do was elongate one of the holes in the center of the crossmember. I also used the clutch pedal from the truck. I had to modify it a little bit, but it went in fairly easily. It doesn't look as nice, since it sits closer to the driver than the brake pedal, but it works very well.

I knew that I wanted the highest rear gearing that I could get, particularly since the overdrive of the NV3500 manual is slightly lower than the overdrive of the 4l60E automatic. However, the highest gears that are available for the 8.5" 10 bolt rear that came in the car are 2.41 ratio (stock ratio was 2.56). With the 7.5/7.625" 10 bolt, the highest is 2.14. So I found a 7.625" axle from a Caprice sedan (with less than 100,000 miles), found a set of 2.14 gears (which, surprisingly, were not too difficult to find or too expensive, given their rarity), and had a local shop install them for me. The axle was $150, the gears were $85, the bearing/install kit was $60, and the labor was $150--so $445 total. It was the single most expensive part of the project, but still not too bad and, after I saw the difference it made, definitely worth it. The car now turns slightly less than 1000 RPM at 55 MPH.

To go with the 2.14 axle, I thought I might as well go all the way and put a set of aluminum brake drums on it. I found a set from an 80's GM car, and had a local machine shop enlarge the center bore and bolt pattern to fit the Caprice sedan axle (all of the other dimensions were perfect). These drums saved 17 pounds per wheel, for a total of 34 pounds of rotational mass deleted.

The only problem with running a "lightweight" axle like this with really high gearing is that you practically eliminate your ability to tow a trailer. My solution to this problem will be to set up the car for easily interchangeable rear axles. Once I install the brake quick disconnects, it should only take me about an hour and a half to swap axles. The "heavy duty" 14 bolt 3.73 Cadillac axle (which has only 50,000 miles and only cost me $175) is basically like what you would find in a 3/4 ton pickup--so I'll have the best of both worlds. In fact, when the 14 bolt rear axle is combined with the "J55" heavy duty front suspension, which I also plan to swap in, the car should be able safely to tow significantly more weight than stock. In towing mode, I'll have higher capacity brakes (front and rear), axles, bearings (front and rear), ball joints, springs, and sway control than stock, and (in my opinion) a more reliable transmission.

Last but not least, the single most significant MPG mod I've done to this car is the kill switch--which of course was only possible after the manual transmission swap. This car, being pretty heavy and fairly aerodynamic, will coast for a long, long time. It also uses a fairly large amount of fuel at idle (approximately .45 GPH, compared with .12 GPH in the Metro). These two characteristics together mean that a kill switch will have a BIG impact. I put a switch in the manual shifter, ran the wires to a relay, and initially used the switch to interrupt the fuel injector power supply. This is what I did in our Metro, and it works very well. However, in the Caprice, interrupting the FI power supply did cut the engine off, but if I held the button for more than a second or two, it would create an error in the PCM that would not allow the injectors to fire again unless the key was turned to "off" and then back to "run." I had originally thought that it might be setting a "silent" check engine code, but when I ran a scan no codes were set. So I wired the switch instead to interrupt the power supply for the sensors in the distributor, which serve as an engine RPM signal for the PCM (among other things). When those sensors are tuned off, the PCM thinks the engine is turning 0 RPM and cuts both spark and fuel, killing the engine. It works very well, without causing any other errors or issues.

To allow for long coasts with the engine off, I wanted to still be able to have brake vacuum. In the Metro, an auxiliary vacuum canister doubled my vacuum capacity, but that was not nearly enough for this Caprice. So I decided to go with an auxiliary vacuum pump as well. You can buy vacuum pump kits online, but they're very expensive. Instead, I got an electric pump from a late-model VW diesel in a junkyard, and purchased only the relay and vacuum switch from one of the kits online. The pump is the most expensive part of the kits, so doing it that way made it pretty economical. I've included a picture of the vacuum pump setup under the hood. It sits where the cruise control module used to be before I deleted it. ;)

There are a lot more details that I could share, but I've already probably written too much. I hope y'all have found it interesting. Please let me know if you have any questions or feedback!

Fascinating! My folks had a Buick Roadmaster (1996 model I think) back in the day and I always loved that car. Great, thanks to you I'm about to go cruise craigslist looking for one! LOL

welcome!!
nice work!
Those things are the battle ship of cars!!!!

btw, have you bumped the psi up to 40+?

another question, w the highway rearend, what is the rpm on the V8? at say 60mph?

Thanks! :D

The tires are at about 46 psi. Sidewall max is 44.

It does slightly less than 1000 RPM at 55 MPH. So slightly less than 1090 at 60 and slightly less than 1273 at 70.

With a ring and pinion of 2.14:1 and the NV3500 OD of 0.73:1 and 29" tires, engine rpm at 60 mph should be 1,086.

EDIT: ha we posted at the same time. Guess my math was right tho ;)

man that is a serious low rpm!!!.. :eek::eek:....explains the mpg:thumbup::thumbup::thumbup:

Do you have to downshift to get some acceleration at that point?


When I had my Infiniti Q45 (4.5 liter V8), I was at about 1700rpm at 60.
I had only increased the tire diameter about 6%.
but it helped get me to 30+ mpg.

The LT1 has 330 lb/ft of torque, which, because of the B-body cam, comes in at a very low RPM. It's like an RV cam.

I try to keep the engine between 700 and 1000 RPM as much as possible.

On the trip where I got 46.3 MPG, I was mostly on rural, state highways with speed limits of 55 or 60 MPH.

I would P&G in 5th gear, pulsing from 45-55, 45-60, or 50-60 MPH, depending on conditions. The car could even pull or maintain most hills in 5th gear at 45 MPH or more. So yes, it will accelerate at those speeds in top gear. I'd say that it accelerates slowly, but it's still faster than our Metro. :turtle:

I even let it get down to 40 in fifth gear, in some instances. The engine turns about 725 RPM at that speed.

This car is a textbook example that the higher the gearing, and the lower the RPM, the better.

I just really wanna see a picture. Sounds awesome! I'm content on eventually ecomodding a v8 as well. Aiming for a scca autocross car that is competitive and gets 30mpg on the interstate. Well a mustang not just any.

There's a link to pics in the initial post. Here it is again: Caprice Wagon - Album on Imgur

I've added a picture and moved the link in the initial post to the opening section, rather than the end.

I am in awe. You've one something amazing with that car.

Thanks for writing that up. All that (and that result) for $4000? How much for the shop space and tools to make it happen? :)

This is my favorite generation of station wagons (esp. the Vista Cruisers), after the 4-door hardtops in the 60s

http://ecomodder.com/forum/member-fr...zzzvcnbvnb.jpg

I may have missed anything you said about the hitch. Did it come stock? Receiver or not? I ask because there are a lot of ecomodders who are interested in hitches and hitch accessories.

Like receiver mounted boat tail boxes. Is the lower gate side-hinged? Have you considered a collapsible boat tail hung on that?

I run 50-series front tires myself; but the trend seems to be taller and narrower with the same contact patch (BMW i3).

Very impressive! Gotta love tall gearing.

Shop?! What "shop"? I did the trans and axle swaps on our uncovered concrete patio. :p

Okay--so there were some implied costs. ;) The point I'm trying to make, though, is that I did this build on a very limited budget. In many cases, parts that I was able to sell from the car helped the overall cost. For example, I sold the stock "wire" wheel covers on eBay--for $239! :eek: (Two guys got into a bidding war). I also won't be surprised if I sell the 4L60E automatic for more than I spent on the entire manual swap.

These cars did not come from the factory with a hitch, and the aftermarket wagon hitches have been out of production for several years (sedan hitches are still available). My hitch is a Reese class III/IV receiver hitch that I picked up used (3,500 WC/10,000 WD).

I've thought about a boat tail, but that would interfere with the two main jobs for which we bought it: carpooling and towing. If we're just driving around as a family, we'll take the Metro.

General towing ability, or a specific rig?

http://ecomodder.com/forum/showthrea...tml#post466804

How much of your trailering needs could be met with a single-wheel foamie teardrop? Because that's where the next 0.10 reduction in Cd is.

A teardrop trailer would be really cool. Maybe when I get around to making a woodgas generator for it I'll put it in one of those... :thumbup:

Right now, we have a pretty heavy 6x12 tilt-bed trailer that we use to haul our garden tractor, firewood, hay/straw bales, sand/lime, etc.

In the future, we'd like to do some small farming, and have the ability to tow a livestock trailer, dump trailer, flatbed equipment trailer, or the like.

One of my goals in undertaking this project is to prove that you can have a very sturdy tow vehicle that is also very efficient.

Excellent work! You've pretty much thrown the kitchen sink at it and are getting better than double the stock MPG.

This vehicle shows that to get the really big numbers you have to do both aero and mechanical mods.

How much trailer towing do you do? Most people do a lot less than they think. Changing axles is going to get to be a pain going forward. I'd just run in the lower gears when towing than to change axles.

Short of changing to a diesel engine (a 6.5 NA fits a B-Body) or converting the CNG and jacking up your compression sky-high, I really don't see much in the way of big improvements to MPG left.

Excellent work! You've pretty much thrown the kitchen sink at it and are getting better than double the stock MPG.

This vehicle shows that to get the really big numbers you have to do both aero and mechanical mods.

How much trailer towing do you do? Most people do a lot less than they think. Changing axles is going to get to be a pain going forward. I'd just run in the lower gears when towing than to change axles.

Short of changing to a diesel engine (a 6.5 NA fits a B-Body) or converting the CNG and jacking up your compression sky-high, I really don't see much in the way of big improvements to MPG left.

Yes. Though that's dependent somewhat on the car in question. Our Metro, for example, has only had a final drive gearing swap and a camshaft swap. Everything else was aero (besides the kill switch). But the Metro was more efficient to begin with.

I think it's also important to note that, though we've done a lot to the wagon, nothing we have done is groundbreaking, or radical, or cutting edge. Every mod is pretty much a standard, accepted economy improver. No single one of these mods by itself will get you to 100% over EPA--but taken together, they do.


I've thought about that. I think that I will plan in advance to do several projects involving the trailer at once--so that I can swap the towing axle in, leave it in for a week or two while I do a bunch of projects, and then swap it back out. That way I won't have to go back and forth as much.

I have two concerns with trying to tow with the 2.14's. First, I'm concerned that I won't have enough gear to get going in some situations (regardless of how much I slip/burn the clutch). We live in a part of Virginia where there are a lot of hills, and I really don't want to get stopped at a light on a hill somewhere and not be able to get going again. Second, I'm concerned about how much stress/wear the NV3500 will get if I try to tow any significant amount of weight with the 2.14's. It's already in a heavier vehicle, with a stronger engine than it had from the factory. I don't want to have to take it out again any time soon. :(


I think you're right--the biggest thing from here on will be getting used to how the car works with the manual transmission and making improvements through technique. I'd like to get a tank over 50 at least once. :thumbup:

I saw your initial posts on here when you first started and was wondering how you were doing. Holy amazing, this is what I wanted to do but never really did with a Wagon since I saw your posts. I knew the 1991-1996 G.M whales were already pretty aerodynamic for Wagons but here you've up and done all of this. Speaking for a Diesel conversion, putting a 6.2 in one of these isn't unheard of. I'm not sure what's in this car though:

https://www.youtube.com/watch?v=_omGg8hZto0

If you switch to Diesel and put in a smaller fuel tank though, really... MPGs will be going into the stratosphere...

Mass is great for glides.

Back in the day I used to see how far I could shut down from 55 mph and coast and still make it home. I pretty much came to know the exact spot where I would just make it in my '74 Nova. Tried the same spot in my '78 Corolla- no way, fell way short. Same today with the Metro. I should try it with the '59 Bel Air- that Baby has ball bearings throughout! And four-wheel drums. Give the front wheels a spin when the car is jacked up and they go forever.

Love the project :)

I've always thought a big V8 can still hit great number with EOC, and I just picked up my own V8 project truck.

Regarding hypermiling and towing, I have the same issue, I do a lot of towing and towing in city traffic, so the ratio choice is always a big compromise. So, I've been thinking about sourcing a two speed (external overdrive) diff like was popular with British cars in the 60's-70's. Most often these could only be engaged in 3rd and 4th, but I don't see why that couldn't be modded out. Two speed diffs these days are still around in some smaller trucks like the Iveco Daily, which might be too big for your use, and the ratios might not suit, but it would be a lot easier than swapping diffs every time you want to tow something.

The other thing I'm going to to is build a much lighter trailer :)

This is a great project!

It's on the front page now.

It's like seeing an elephant in a hang glider and watching it sail away. 40+ in a Caprice is just so far outside what anyone would believe possible.

How about 50 MPG in a full-sized truck?

The only thing I can think of adding is a L99 with AFM.

Don't get me wrong, I find the results believable and awesome, but I'm just thinking: if all the V8 is ever- or mostly- called upon to do is putter around at sub-1000 rpm speeds, it is generating very little hp and torque down there and those hp and torque requirements could easily be handled by a smaller, lighter engine that doesn't have to be shut off and coddled as much. Could a six or even a four move that wagon around with the same acceleration rates and cruising speeds? A Suzuki G10 probably could!

Also I believe there's an optimum operating speed range for engines as witnessed by BSFC charts and if operating below optimum rpms some efficiency is being compromised by relatively more heat loss to the cooling system. But I suppose that mainly counts at steady and/or prolonged operations at certain rpms, not simply pulsing up to speed.

Yeah, I've thought long and hard about other options, too--such as a Gear Vendors overdrive, a 4WD transfer case with the "transfer" part cut off, or a "Quick Change" rear end out of a race car or hot rod. All three of those options would allow for an easily accessible wider range of gearing. But any one of them would increase the time and expense of the project considerably, and also add a significant amount of extra weight and parasitic drag.

I don't tow that often, so to me the interchangeable axle idea seemed like the best compromise--minimum cost, with maximum efficiency and/or maximum grunt/durability depending on what's needed. But who knows...maybe I'll change my mind in a year or two.

I actually have a 4.3L L99 V8 (with only 40,000 miles) sitting in my shed right now. It would bolt/plug in without any modifications.

I don't think I'm going to swap it, though. If I didn't use the kill switch, it might make a difference, since it uses less fuel at idle. But I never idle, and I can keep the LT1 in roughly the same BSFC range as the L99 by just shifting sooner and keeping the RPM lower.

Most certainly, a smaller, more modern engine would do the job (of passenger transport, at least), and probably be somewhat more efficient, too. But I would lose the ability to tow 7,000 lbs if I needed to, and it would make the project much more complicated and expensive. And I doubt there are very many other engines that could go 500,000 miles before needing a rebuild (as LT1's often do).

If I do any major engine mods, it will probably be one of two things. Either I'll convert it to run on wood gas using the LT1, or do a (bio) diesel swap. A 6.2 would be the easiest, but one of the new 2.8L Duramax engines would be both more powerful and more efficient. I'll have to wait a while until they're available cheaply in junkyards, though.

I have a 95 Astro and after reading your story I was looking at specs on your car (stock) and we have, or had, the same wieght, transmission (4L60E), engine, almost, I have 4.3 v6 yours had a 4.3 v8 option, and same towing rating. I wanted to just be able to get 30 mpg highway. I think with our vehicles being fairly similar and you getting 43-46 mpg I should be able to hit 30 with mine, despite it being less aerodynamic. Im planning on doing aeromods though. I would like to do a manual swap but that'd be a long ways away.
Matt

The inline overdrive you only have to do once. The quick change rear end requires occasional 'adjustment' but I doubt it adds weight or parasitic drag. It's swap meet season right now.

If you swap the whole axle (twice!), bleeding the brakes would get to be a drag.

Thanks, hadn't see the Gear Vendors unit -reading their site and it seems pretty convincing. It's pricey but could be taken to your next car or sold after you're done with it. If you did a 4wd transfer case mod it would whine when in low, I think a lot of them are speed limited too (?).

You're right--mechanically, our vehicles are very similar.

The best highway mileage I got before the manual swap and kill switch was about 32 MPG. That's with the stock (fairly high) 2.56 ratio, a more aerodynamic body from the factory, and aero mods.

If you want 30 MPG highway in your Astro without a manual swap, you'll almost certainly need to change your gearing and do as many aero mods as you can. That might get you there...

But a manual swap and kill switch will definitely put you over 30 MPG.

Quick change rearends are cool, but even if I got one for $500 it would be at least $1500-2000 total by the time I figured out brakes, mounting, axles/hubs, modifying the gas tank under the car to fit, etc.

Then I would be worried about long-term durability (especially towing), and the high parasitic losses of a QC rear end are well documented in the racing community. They eat more HP than a 9" Ford rear, which is already less efficient than the GM diffs.

I'm planning to put quick disconnects on the brake lines, so I won't have to bleed them each time. I will also make an easily removable bracket for the parking brake cables, so they won't have to be readjusted either.

I'm figuring that with both of those things in place, the axle swap will only take me about an hour or an hour and a half. That doesn't sound like a lot of time to me, and if I schedule all my towing projects together so that I don't have to change it very often, it shouldn't be too bothersome. But I may change my mind after doing it a few times...

How much ratio change do you think is needed? Perhaps swapping on a set of smaller diameter wheels and tires will do the trick. It might look funny but then again the skirts might hide it. Put air shocks or air bags on the rear to level it out again- helps with the load, aero, and looks.

When I first got my '59 running after it sat for more than 30 years, I borrowed the far smaller than stock wheels and tires from my Corvair for the drive home and until another set was bought. IIRC they were 13% smaller than stock, or than what I run now which is quite a bit oversize. The difference in available starting torque and responsiveness from just that alone was astonishing!

P.S. I quickly played with a tire size calculator; 15" tires are available that would make the effective rear axle ratio 2.74 vs 2.14; 14" are too if they clear your brakes.

A 5.3L running on 4 cylinder (~2.6+L?) might be a bigger jump. I'm guessing your car maybe requires ~25hp at 55mph, and your LT1 makes ~80hp at 1k rpm, which puts you at ~30% load.

Corvette C7 LT1 vs Our LS3 dyno graphs - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums - Camaro5.com

Going to ~60% load might make low speed cruising a lot more efficient if you can tolerate how the engine runs with AFM on.

http://www.tulatech.com/uploads/7/5/...13-01-0359.pdf

Your getting close to the mpg range that I got with my Honda Civic VX (on the freeway)! This is amazing.

What about a two-speed rearend?

Weren't those available O.E. from GM in the '60's?

An old hot rodder told me about street racing waaaaaay back when with his '62 or '63 Impala and it had a two-speed rear axle.

Could have been pulling my leg... :)

Absolutely amazing work, by the way, OP. :)