Mission Possible: A Boxy 1984 Caprice Classic

[101Volts]

OK, I'm looking at these:

http://www.tirerack.com/tires/tires....omCompare1=yes

P225/70R15s. LRRs. The sidewalls say they go up to 44 PSI.

[spacemanspif]

I'm just now seeing this thread and commend you for doing work to eco-mod that beast. I have a big American car too but I use it for performance and don't really worry about MPG with it. That being said, I also have pretty good experience with older V8 cars of the era and have some insights for you.

Please clarify when you drive the car. If only in the warm months, there is no need for engine/trans heaters, your money will be better invested elsewhere.

Advice:

1. Don't use Lucas oil stabilizers or other products. They are very thick and will turn your 5-20oil into 20-50 oil. Better to run 10-40 on that car if it is only run in the warm weather.

2. Depending on what emissions equipment you have, there is a small gain in MPG to be had. Please take a few pics of the engine compartment for us to see what you are working with...bonus points if you remove the air cleaner to take the pics so we can see carb stuff.

3. A cheap set of headers will last a long time if you don't drive in the salt and will allow the engine to breathe easier making a little more power AND getting better MPG.

4. Look for marks on the carb to identify it. Then go to the library or internet and get a book on carb tuning. Vacuum gauges are cheap and help, but once past the basic tune, wideband O2 sensors will help you with tuning but can be expensive.

5. Buy a cheap tachometer at your local parts store so you at lease have info of what RPM you are cruising at and if a gear change would be beneficial.

My Monte has 3.73 rear in it and for a short time I ran a 2.29 out of a Malibu. 65mph was around 1600rpm and got terrible mileage. Brought the engine (and car) speed up to 2000rpm (~80mph) and was getting 25mpg. RPM "sweet spot" is important and can be overshot. You having an OD trans means you are better off on the high side of the 2.xx gears. So if you do actually have a 2.73, you should probably leave it alone.

[101Volts]

Wow, Thanks. I'm primarily using the car in the summer because hey, We have other cars to drive in the winter. I'm off to get the camera.

[101Volts]

OK. I've had the new General Grabber HTS 225/70R15s on for a week now and they've been re-torqued at Wal-Mart. I haven't gone on whole tank with them yet, I have another 330 miles or more before the next fill-up if I continue filling up after 400 miles. So far, I'm pleased with the tires. They're set at 35 at the moment but I won't be keeping them there, That's just for a short time. The tires have much more grip than the last ones and the car rides quieter with the new ones, but what do I have to compare with? The old ones were dry-rotted and two of them were at least 19 years old, they even said to not set them higher than 35 PSI.

I got 19.96 MPG on the last tank which was mostly with the old tires set to 35. Fewer than 10 miles of that tank were with the new tires. Something like 200 miles of that tank were on one trip, though.

These new tires are also .3 inches larger in diameter than the old ones. Should I be checking for a discrepancy between the odometer and the actual miles put on now? The old ones were P205/75R15s.

I shot some photos including some of what spacemanspif asked for:

First, one of the car with the new tires and close to the same spot of the first photo in the thread of the car:



A closer-up image of one of the tires:



The QuadraJet Carbureter:



A farther-out photo of the Carburetor, and some of the engine:



Some of the Air-Cleaning equipment on the car. This one is behind the driver's-side headlight:



(One of the tubes was taken off for the photo and was put back on.)

(That blue part is a paper towel - or a few of them - from Sheetz to rub fluids from dip-sticks off with.)

So, What kind of a higher MPG figure can be seen from going from 35 to 45 PSI?

[101Volts]

Also, The Stickman on the Station Wagon Forums went and made his Oldsmobile Custom Cruiser Wagon more aerodynamic on the under-side. I'm not posting the photos here as I didn't ask him about it but here's a link, I'm sure some folks here will be interested:

Station Wagon Forums - View Single Post - 16 or 17 inch rims for 1984 Caprice?

(I was asking about other rim sizes on there too before I settled on staying with R15s.)

[mechman600]

Headers aren't gonna do squat for mileage. They only benefit in the torquey RPM range. And if you are hypermiling, you will be well below those revs.
I would be disabling half of the V8. Remove the pan, unhook the rods on one bank and secure them all at TDC, put clamps (nut & spring kind instead of gear) on the empty rod journal oil holes to stop the oil spray. Disable the valve train on the same bank. Voila, a 2.5 four banger.
And aeromod the living crap out of it.

[101Volts]

Originally Posted by mechman600

Headers aren't gonna do squat for mileage. They only benefit in the torquey RPM range. And if you are hypermiling, you will be well below those revs.
I would be disabling half of the V8. Remove the pan, unhook the rods on one bank and secure them all at TDC, put clamps (nut & spring kind instead of gear) on the empty rod journal oil holes to stop the oil spray. Disable the valve train on the same bank. Voila, a 2.5 four banger.
And aeromod the living crap out of it.

Thanks but is that a good thing to do here? I have a lot of hills around here in Pennsylvania at this time. I'll keep the cylinder-delete in mind, going to a six cylinder engine may help (and some of these cars did come equipped with 6-cylinder engines but, I'm thinking of a Diesel swap too - so, I have to decide.) And yes, I am thinking of aero-mods. I read the wheel skirts for Pontiacs won't fit, but there's a great place to mod between the gas tank and rear bumper.

[spacemanspif]

I'm going to stand by my statement that headers MAY help MPG due to the fact that those old exhaust manifolds don't flow well at all and are definitely a choke point in the system. The Y-pipe before the CAT isn't the best either, nor the CAT itself.

You're running an electronic QuadraJet which has a love/hate relationship with car people as some swear by them and other swear they are only good for paper weights. Either way, they are basically the half step between carburetors and TBI because they are still carbs but can adjust fuel mixture like EFI. The carb isn't tunable quite like an old mechanical one but are still tune-able, just a little more complicated. A good book on Rochester carbs will show you where to tweak. One of the first steps is to make sure the giant secondaries aren't opening too soon and adjust your driving style to stay in the zone where only the small primaries are in use. Also turn the key to the run position and listen for the clicking of the mixture control solenoid it should click for about 5 seconds (Kinda like the fuel pump on new cars).

FWIW the carb on my Monte was never tweaked when I bought it with 140K and I didn't touch it either before I pulled the engine at 195k. But I also only got about 15mpg the entire time I drove it except for 1 summer where I ran it with a 2.29 rear on the highway getting 25mpg.

If you are set up like my 305 was there is a secondary air pump that pumps air down to the CAT. Located low on the passenger side if the engine. It should have it's own belt. If you want to fiddle with taking off ALL the other belts to remove that one, go for it, but I just cut mine out and never had any issues, removed all the equipment eventually but ran with no belt for quite a while. Those cars have a ton of vacuum lines too, a good check to make sure they are all in good shape and not leaking is one of those preventative things that keep the engine running well and might net a gain in MPG. The vinyl tubing that controls the HVAC ducts can get brittle and crack if you look at it wrong. Also check that the EGR valve is holding vacuum. If you don't have a vacuum pump, unhook the hose, reach under and push the diaphragm up, while holding it up put a finger over the vacuum port and let go of the diaphragm, hold for a minute or 2 and release; if you hear air hiss chances are the EGR is good. You can also keep a finger under the EGR to feel if the diaphragm is moving while keeping the finger over the port.

Sorry for the novel but basic maintenance is the key to a good running, efficient engine.

[mechman600]

Originally Posted by spacemanspif

I'm going to stand by my statement that headers MAY help MPG due to the fact that those old exhaust manifolds don't flow well at all and are definitely a choke point in the system.

They don't need to flow well if you keep it below 1500 RPM.

[spacemanspif]

Originally Posted by mechman600

They don't need to flow well if you keep it below 1500 RPM.

I'll agree with that statement and it's all the more reason to add a cheap/small tachometer to keep an eye on RPMs. Will keep him out of the secondaries too...