I'm not sure 86.. I know as far as I was told when I got the car ..the rear and the transmission (200 r4) then were supposed to be stock. The transmission blew and I ran across the Th350 for $75 so I used it.
Gas Mileage
- Thread starter Billys88SS
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If you're turning 3200 at 70 mph, and have a 26 inch tall tire that comes out to be about a 3.55 rear gear ratio. If you had highway gears say 2.41's, with that same 26 inch tire you would be around 2200 at 70.
http://www.richmondgear.com/101032.html
Still shouldn't cause that bad of mpg... A buddy of mine has a 71 C20 with a 402 big block, th400, and 3.54's out back and he knocks down 14-15 on the highway. Definitely look into the carb and other components.
http://www.richmondgear.com/101032.html
Still shouldn't cause that bad of mpg... A buddy of mine has a 71 C20 with a 402 big block, th400, and 3.54's out back and he knocks down 14-15 on the highway. Definitely look into the carb and other components.
Yeah.. that's how I plan to spend the weekend.. Carb and fuel lines then go from there. Thanks Man
Certainly a square bore (WOT carb) and the old non overdrive 3 speed are costing you a ton but you need to start with accurate fuel mileage instead of a couple estimates linked together. Fill the tank run the route record the actual mileage then refill the same way and record the actual gallons and tenths then calculate your actual mileage. Sounds like you have a gas leak also. And find the actual gear ratio. If your odometer is off as it very well may be find the actual mileage via google route navigation.
With a 509 I got 17.0 on the highway. But it had 3.42 gears with a 200-4R for a final drive ratio of 2.29. It also had a working lock up converter good for a solid 1 mpg and a vacuum advance Q-jet that normally run on the 390cfm primaries. It also had a mild cam for its displacement. But it would still run 12.5 at 110 in the quarter all day.
Without the overdrive and lock up converter I think I would have been lucky to get 12.0 and with the average in need of adjustment fuel slobbering square bore carb probably 10.
With a 509 I got 17.0 on the highway. But it had 3.42 gears with a 200-4R for a final drive ratio of 2.29. It also had a working lock up converter good for a solid 1 mpg and a vacuum advance Q-jet that normally run on the 390cfm primaries. It also had a mild cam for its displacement. But it would still run 12.5 at 110 in the quarter all day.
Without the overdrive and lock up converter I think I would have been lucky to get 12.0 and with the average in need of adjustment fuel slobbering square bore carb probably 10.
Thanks Dog... That's my plan as far as getting a more accurate reading. I'm looking for an overdrive transmission and My father in law is rebuilding a quadrajet for it. I guess I will start at the carb and work my way to the tank looking for a leak. I haven't seen anything when it's parked though.
I'm also getting bigger tires .. hopefully that will help a little. Right now they are 215-65-15..What should I go with?
Thats the factory size for a GN/442/MCSS. A lot of people keep that up front and add a 27" tall 255/60/15 in the rear. If you want a little wider up front you can run a 235/60/15 its the generally the same height as the 215/65 but a little wider yet still fits up front without rubbing. If you have 15x8s on the rear you can a run a 28" 275/60/15. I ran 235s & 275s on both my GN & 442.
Ok guys.. I looked for leaks ...found none.. I did however discover that the secondaries on the Weber carb are not closing all the way..probably almost a quarter inch. Advance got me a complete rebuild kit for the quadrajet for 21.99. That is being done now. Sooo..I'm going to tune it up again, change the carb and we will see..
I appreciate everyones input and advice since this post started. The main thing I've learned is to figure out exactly what the drivetrain consist of. As of the last post I've figured this much of it out... please correct me if I did it wrong.. 3:73 rear ,Open rear so I did 2 tire rotations and got 3 & 3/4 turns of the driveshaft turbo 350 trans, 14101148 casting # which is a 1987-90 350 4 bolt main with a One-piece rear seal and it also has a one piece oil pan gasket but it does not have center bolt valve cover heads? Being it was used starting in 87 shouldn't it? And could this be playing a major part in the bad fuel milage? Thanks again in advance. You guys and this site are great.
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