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ZenArcade 01-19-2010 03:02 AM

New user with a classic car
 
Now, I've trolled this forum for a bit and I'm fully aware of the V8 flames that are coming.

I've got a 1979 Buick LeSabre with a Pontiac 301 (4.9L) V8. This beast weighs in at around 5000 pounds (according to driver's door stickers.) Not sure on the transmission type, but it's either a TH200 or TH350 3 speed automatic.

By this point everybody must be thinking it's a gas guzzler and I should dump it for a much smaller car. Well, on the contrary, this car is actually quite fuel efficient for it's age and type. My best recorded trip was a 116 mile trip with a 25 mpg average. This was at a constant 60 mph for the first 80 miles, and through rush-hour traffic on a Saturday for the next 36 miles.

Since then I've taken half the exhaust off to offset the fuel required for warming it up in the winter. The original owner had the catalytic converter taken off, for whatever reason. So now I'm running with an open exhaust after the headers, with no muffler. The car is surprisingly quiet despite not having a muffler, and is still just as clean burning as it was before. (Due to the cat already being removed)

Around town I'm averaging from 17-20 mpg, and on the highway I'm getting around 21-23 mpg. Highway traffic now is slow going due to the winter weather, so I'm not getting as much mileage as I should.

In the near future I'm going to be reassembling the exhaust, this time with full 2.5" piping, a cat, and a magnaflow straight-through muffler. This will be a huge improvement over the stock system which trimmed down from 2.5" piping at the headers, to 1.75" at the tailpipe. I'm also keeping the stock design, which has the piping wrap around the rear axle, in the interest of preserving torque over a straight-piped design.

As far as emissions, which I am still concerned about (HC's and NOx's. CO2 as the main drive for global warming has been proven to be a crackpot theory by the global science community), this V8 was the only GM-made V8 that conformed to ALL emission standards for 1977-1981. It went a bit under the standards, in fact. But due to GM corporate mandates, Pontiac was forced to stop making V8's.

I'll also look into my gearing in the future and let you guys know. My torque peak is at 2000 rpm, and that's usually where I'm at when cruising 55-60 mph. I've got 265/70/15 radial tires all around.

So, let the V8 flames ensue. But I'm proud of this little small block, and I'm sure this will provide hope for the rest of us with classic cars that are still concerned about fuel savings. :)

Laurentiu 01-19-2010 04:42 AM

Welcome...What matters is that you are concerned with your fuel consumption and your efforts to improve that . Someone can drive a 4 cyl. 1.6 liter and have a greater consumption if they drive inappropriately..

Hope you enjoy the forums and hope you improve your MPG...:turtle:

P.S. I also love high torque in cars, that's why I plan to acquire a Diesel-engine car in the future...


http://i48.tinypic.com/20qnr0o.jpg

tim3058 01-19-2010 08:51 AM

Welcome to the site ZenArcade, and congrats on the "lead sled". I'm slowly working on a few old cars myself ('74 Corvette and a couple 79 Camaros), I'm with you on trying to up their mpg. Cheaper it is to drive em the farther we can cruise em.
Always liked the look of the real big cars like yours. And getting 25mpg @ 80mph in a 5000lb land yacht is pretty impressive. I bet it rides nice too.

Ryland 01-19-2010 11:58 AM

If you read up on exhaust design you will quickly learn that bigger is not always better, exhaust fallows the same rules as a musical instrument does because it's a pulsating flow, It's about the math not the "restriction" unless of course you don't believe in math.
With a vehicle of your size and I imagine you would like to keep the look of the vehicle as much as possible, then I would start with synthetic fluids all around, an aluminum belly pan is going to help smooth air flow on the rough underside is going to help alot at highway speeds, also going with the next step narrower in tire sizes at max side wall pressure is another proven way to help.

Frank Lee 01-19-2010 03:54 PM

Quote:

also going with the next step narrower in tire sizes at max side wall pressure is another proven way to help.
It is?

gone-ot 01-19-2010 04:04 PM

...with "headers" there are two movements going on: (a) an acoustic 'wavefront' that moves through the gas at about 1700 fps (speed of sound in hot air) and (b) the mass movement of the gas slug itself as it moves down the pipe at about 300 fps.

...pipe diameter affects speed of mass movement down the pipes, while piple length affects acoustic "reflection" (Helmholtz tuning) time and strength (camshaft valve timing comes into play here too).

...too large diameter pipe and the mass movement slows down below the optimum value of about 300 fps; too small diameter pipe and the mass movement increases above the optimum value and 'back pressure' builds. 300 fps seems to produce the best "scavanging" action between the exhaust gas flow and the cylinders.

Clev 01-19-2010 04:15 PM

That's excellent mileage from such a beast. You might benefit also from a newer 4-speed with lockup torque converter (especially if you do a lot of freeway driving.)

BTW, I don't want to start a flamewar, but the global science community is not known to pursue "crackpot theories."

gasstingy 01-20-2010 08:54 AM

Welcome to the forum. I wouldn't dare attack a vehicle because it's a V-8. My daughter has a '99 Trans-Am with a 350 / 6-speed. We drove it to the National Corvette Museum in November and challenged each other to maximize fuel economy. I drove up and we got 29.8 mpg @ ~60 / 65 mph. She drove back and got 29.4 @ about the same speeds. How did I beat her in her car? When we came back, she had heavy traffic in Nashville and before we got to the Alabama line, she had to turn on the (popup) headlights. Either way, a properly driven V-8 in the right vehicle can get reasonable economy. There are some great tips here. Enjoy the ride :)

rgathright 01-20-2010 09:01 AM

Welcome to the forums!

If you only you had a 700R4 tranny!

Clev 01-20-2010 10:18 AM

Quote:

Originally Posted by gasstingy (Post 155477)
Welcome to the forum. I wouldn't dare attack a vehicle because it's a V-8. My daughter has a '99 Trans-Am with a 350 / 6-speed. We drove it to the National Corvette Museum in November and challenged each other to maximize fuel economy. I drove up and we got 29.8 mpg @ ~60 / 65 mph. She drove back and got 29.4 @ about the same speeds. How did I beat her in her car? When we came back, she had heavy traffic in Nashville and before we got to the Alabama line, she had to turn on the (popup) headlights. Either way, a properly driven V-8 in the right vehicle can get reasonable economy. There are some great tips here. Enjoy the ride :)

Back in the mid-90's, Car and Driver claimed an average 26 mpg while driving 100 mph across Montana in a Z-28.


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