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Old 06-16-2016, 11:40 PM   #1 (permalink)
EcoModding Lurker
Join Date: Jun 2010
Location: Edinburg, VA
Posts: 95

The Little Car - '00 Chevrolet Metro
90 day: 91.08 mpg (US)

The Big Car - '94 Chevrolet Caprice Wagon
90 day: 44.9 mpg (US)
Thanks: 11
Thanked 165 Times in 52 Posts
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:

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

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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

-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)

-"UTCOMP" trip/MPG computer

-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. 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!


Last edited by funkhoss; 01-08-2020 at 10:47 AM..
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