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Unread 07-18-2010, 08:37 PM   #1
Newfie_Jeeper
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V8 unexpected fuel Mileage... Woo Hoo!

Just did some mileage testing on my YJ. Its an 87 that I built from the chassis up. I put in a stock 305 Chevy V8 and a SM465(granny low)4 speed tranny, NP231, 4.10 gears, 35's, about 6 inches of lift.

The engine had been sitting for 8 years, maybe started once a year. When I put it on the road a month ago, I burned $60.00 for a couple runs around town.
So, I started picking at the engine. I ran some Seafoam through it, rebuilt the carb, new Distributor cap and rotor, NGK wires, and regular plugs gapped to .045, Quaker State high Mileage 10w30 and half a bottle of Lucas oil stabilizer.

I ran the engine like that for about 1000 kms, and it starts and runs, dare I say, Perfect!

Took it on the highway today, and clocked the mileage twice, and boy was I pleased. On both fill ups, I averaged over 22 MPG, which I think is good for a V8 and 35's! That was at about 90KM/Hr or 50 Miles/hr, with the engine at 3100 rpms, which is buzzing for a V8. So overall, Im very pleased. Now if I can just get the oil pressure a little higher.....Hmm

How often do you hear someone say their 4X4 is great on gas!!!???

Newfie

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Unread 07-18-2010, 08:42 PM   #2
jeepinmichguy_
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about as often as someone from your province wins the stanley cup
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Unread 07-18-2010, 08:45 PM   #3
Newfie_Jeeper
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And I forgot to mention it has the stock Quadrajet carb with Electric Choke

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Unread 07-18-2010, 10:21 PM   #4
MoparFreak69
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I am getting around 20 on my 5.2 swap but I cant keep my foot out of the loud pedal! As long as you drive nicely its easy to get good fuel mileage because a V8 isnt working very hard at all to push our bricks around.
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Unread 07-19-2010, 09:45 AM   #5
squibload
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Sweet numbers!! Is that GPS verified? (I was getting strange mileage numbers until realized that I hadn't changed out the original speedo gear!)
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Unread 07-19-2010, 04:28 PM   #6
Newfie_Jeeper
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actually, I broke my speedo cable, so all I have is the GPS!

I was wondering, a few weeks ago, i noticed my temp staying lower then normal. I assume I have a sticky Thermostat. So it seems like the engine runs 20-30 degrees less then it used to. Could this improve or diminish fuel mileage?

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Unread 07-22-2010, 11:50 AM   #7
87TPIYJ
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man i get 8 mpg in mine! your lucky!
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Unread 07-22-2010, 12:09 PM   #8
remmons
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Those are some awesome numbers! I have to agree with MoparFreak69 though. Our Jeeps don't weigh that much so that V8 isn't working that hard. Still good mileage with what you have on your Jeep though!
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Unread 05-29-2013, 05:42 AM   #9
Newfie_Jeeper
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To Resurect this from years ago.... As the original poster with the great mileage... Here is some interesting info.

I have since replaced the carbed 305 with a brand new GM 350 crate engine, and Affordable Fuel Injection TPI kit, aluminum conversion radiator, all else the same.

I also recently swapped in an 8.8 and changed from 35" AT's to 35" MTZ's.

I havent clocked it off, but I am positive my gas mileage has been cut in half for sure. Over the next couple of weeks I will clock it off and see what kind of numbers Im getting with the EFI.

For the record , the engine runs awesome at any temp, smooth all the time, dont miss the carb that way. And certainly didnt do the swap for better mileage. But it is really suprising that the fuel mileage is so much worse then the carb. I'm thinking 10 MPG. Its just a pain in the A** for longer trips!

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Unread 05-29-2013, 07:42 AM   #10
87TPIYJ
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Well I have fixed a few issues with vacuum and wiring this winter so I'm doing a lot better than the 8mpg that I used to get. I am now getting 13mpg on 33" tires and 410 gearing. I "may" get a little bit better when I replace my egr valve or solenoid. One of them is throwing my check engine light. I'm running a TPI set up out of an IROC, with a mild cam, and true dual 2-1/4" exhaust.
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Unread 05-29-2013, 10:11 AM   #11
superj
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damn, put the carb back on then, ha ha ha.

i know my 350 with a quadrajet got about 14 with the ac on doing 65mph on the highway when i had a 79 chevy step side. same aerodynamic qualities, ha ha ha
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Unread 05-29-2013, 06:22 PM   #12
USMCBuckWild
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I am getting around 22-24 consistently in mine. I upgraded the intake/carb to an edelbrock performer set. Much better torque and better mileage, but seems like less HP than the Holley.

All in all, pretty happy. Contemplating swapping to a 6.5 diesel with a hack job turbo.
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Unread 05-29-2013, 09:37 PM   #13
czjeeper
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I get 14. My problem is the 4.88 w/only 33" tires.
Good thing is, it's the same mileage as the old 2.5!
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Unread 05-30-2013, 02:09 AM   #14
SunDevilJeeper
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This thread gives me the lulz... I'm STILL trying to move forward with my V8 swap. Too bad I bought an AR15 on Saturday, can barely afford to eat for the next week and a half but it was worth it!
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Unread 05-30-2013, 08:07 AM   #15
vadslram
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You have enough power now to be able to run the engine at the sweet spot at highway speeds instead of having to beat it to death.
My truck gets 26 on the highway for the same reason.
You probably have enough power to reduce the rear gearing or go even bigger on tires and get even better milage. I know it sounds wrong but it's true.
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