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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.

Thanks

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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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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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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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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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.
 
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