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Old 04-09-2002, 04:49 AM
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Unhappy Gas guzzler

I've built and have been running a 64 Chev full size street machine. Car is totally debugged and runs great except... this thing drinks gas like it's going out of style. Some basic specs- 400 SB that is very well built but not running a lot of horsepower (Maybe 400-425), TH350 with 2800 converter, 3.55 gears, AC, etc. This is NOT a fire breathing dragon. Have a brand new Street Avenger carb on it as well.

I don't expect this thing to sip gas like a VW, but I've got friend running 700+ HP who get better mileage. I know 400SB's are not economy motors but 5-7 MPG is NUTS!

Open to any and all suggestions.


Let me add some more detailed specs as to the motor. 400SB 10:1 compression. Trick Flow heads with roller rockers. Edelbrock Performer cam and manifold. Holley Street Avenger 670CFM, headers. Moroso 9 quart pan and high volume pump. Accel ignition and distributor. This car is a total frame off and is literally a new automobile. Runs like Jack the Bear but drinks like WC Fields!

[ April 10, 2002: Message edited by: larry1210 ]</p>

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Old 04-09-2002, 06:38 PM
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If in reality you are putting out 400hp it should be a stout performer. I'm not sure where the problem is but I would check the basics first. Timing,more concerned with total than initial,also when it is all in. When you find the problem your mileage and performance will show a large increase.
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Old 04-09-2002, 07:27 PM
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Hi larry, any chance of getting some more specs go get an accurate idea of what you've got. Cam specs, carb cfm rating, intake, compression ? I also think the street avenger has adjustable vacuum secondaries. Any of this info might give someone ideas.
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Old 04-09-2002, 07:35 PM
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Larry, I had a 455 Trans Am that had the same problem. It was well built and ran great, but got 7-10mpg. It wasn't a show car but it was nice, what I found out was after I replaced the fuel tank and added a few in line filters before the initial fuel filter in the engine bay it got much better gas mialage, from 7-10 to 12-16mpg. By having cleaner fuel and airorating it more often it got way better gas mialage. That car was like a fish in a fish bowl, if you didn't keep the water clean enough and enough oxygen in the water the fish will die. Not a mechanic but its worth a try.
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Old 04-09-2002, 09:52 PM
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If you are running a Holley try going down to a lower number power valve (say from 8.5 to 6.5). Vacuum conditions could be causing it to open slightly when you don't need it, this will make a big difference in fuel economy. Other carbs have similar adjustments you can make to them to change the power valve opening, you didn't say what you had.
“She may not look like much, but she's got it where it counts, kid. I've made a lot of special modifications myself.”

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