Odd fuel econ issue
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CF Beginner
Joined: Mar 2014
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Odd fuel econ issue
Good morning, all.
This may be a bit long-winded, but I've exhausted most of my options.
Original setup straight 6 (250) w/ a monojet carb that I rebuilt was giving me 5.6MPG, which completely sucks for an inline 250.
I swapped for a rebuilt 350 (specced, checked, and all stock minus a double-roller timing chain, flat pistons, and a high flow oil pump), rebuilt an early-model qjet which I also jetted 8% lean and was getting 4.3MPG.
Thinking it may be the qjet, possibly the fuel line since my econ sucked with two totally different engines, carbs, fuel pumps, etc., I swapped the qjet for an Edlebrock 1406 that was purchased new last fall and running on a different application flawlessly - also jetted 8% lean... and I'm getting 3.9MPG.
Engine holds good vacuum and compression readings when I tested. Initial timing it set at 10 degrees BTDC.
At the moment, I haven't cracked the pumpkin to check the gears, but my assumption is that they should be stock (around 3.73, 4.10 at the highest) considering the fact that this truck hasn't been lifted and was owned by a guy in his 70s. Either way, a near-stock gear ratio on 31s with a stock ride height with damn near everything under the hood having been rebuilt shouldn't be giving me a third of this truck's capabilities.
I'm at a loss - and would GREATLY appreciate any word on it (or question if I missed something).
This may be a bit long-winded, but I've exhausted most of my options.
Original setup straight 6 (250) w/ a monojet carb that I rebuilt was giving me 5.6MPG, which completely sucks for an inline 250.
I swapped for a rebuilt 350 (specced, checked, and all stock minus a double-roller timing chain, flat pistons, and a high flow oil pump), rebuilt an early-model qjet which I also jetted 8% lean and was getting 4.3MPG.
Thinking it may be the qjet, possibly the fuel line since my econ sucked with two totally different engines, carbs, fuel pumps, etc., I swapped the qjet for an Edlebrock 1406 that was purchased new last fall and running on a different application flawlessly - also jetted 8% lean... and I'm getting 3.9MPG.
Engine holds good vacuum and compression readings when I tested. Initial timing it set at 10 degrees BTDC.
At the moment, I haven't cracked the pumpkin to check the gears, but my assumption is that they should be stock (around 3.73, 4.10 at the highest) considering the fact that this truck hasn't been lifted and was owned by a guy in his 70s. Either way, a near-stock gear ratio on 31s with a stock ride height with damn near everything under the hood having been rebuilt shouldn't be giving me a third of this truck's capabilities.
I'm at a loss - and would GREATLY appreciate any word on it (or question if I missed something).
Last edited by Nalanthi; Jun 20, 2014 at 9:23 AM.
Thread Starter
CF Beginner
Joined: Mar 2014
Posts: 8
Likes: 0
86 (or 87).
The flat pistons I used in the engine build should put me at around 9 or 9.5:1 w/ stock heads.
I was under the impression that this wasn't too high of a compression for a low grade setup - am I wrong? Would i really make that much of a difference i.e. 1/3 of what I should expect from MPG?
The flat pistons I used in the engine build should put me at around 9 or 9.5:1 w/ stock heads.
I was under the impression that this wasn't too high of a compression for a low grade setup - am I wrong? Would i really make that much of a difference i.e. 1/3 of what I should expect from MPG?
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CHEVYCRZY007
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Jan 15, 2013 8:50 AM