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Discussion Starter · #1 ·
I have an 87 YJ I-6. Ok, I plan on going to 33" tires and I am in the process of rebuilding my engine. I want power and gas milage. What should I do to the engine to increase performance and milage? Also with this engine and this tire size what is the optimum gear ratio for milage and power. I am a weekend off-roader, but nothing to hardcore. I need my jeep to be reliable and get me to college everyday without problems. I have 3.07 gears now. Thank you for your help everyone.


1987 YJ Laredo
Rylan D.
 
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Discussion Starter · #3 ·
WELL DEPENDS ON HOW MUCH YOU WANT TO SPEND IN THE LONG RUN.
I HAVE A 88 WITH A 258 I6. IF YOU WANT TO GO CHEEPO LIKE I
DID IN THE BEGINNING .. I TOOK OUT
THAT BIG AIR CLEANER ASSEMBLEY . I BY PASSED ALL THE EMISSION STUFF SO
THEY WORK ALL THE TIME NOT ON CALL WITH THE AIR CLEANER AND
I PUT ON A MR GASKET 4" AIR CLEANER RIGHT ON THE CARB. IT GAVE SOME POWER
AND I STILL PASSED EMMISSION SO NOTHING BAD HAPPENED. I COULD GO
ON AND ON BUT IT ALWAYS GOES DOWN TO HOW MUCH YOU WANT TO SPEND.
GET A WEBER .........INSTANT POWER
4X4 JOE

 
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Discussion Starter · #4 ·
the 258 respond really well to new ignition like Jacobs Omni Pack or milage master set up, these motors are one of the few I've seen that actually make the $300 price tag is worth it just make sure you get the timing right. you would probably be better off putting your money into some 4.10 gears

Jeff
'83 Toyota long bed
"look Ma no doors!"
 

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Official Curmudgeon
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4,707 Posts
Performance and mileage are usually mutually exclusive, however I did replace my 258 with a 305 TPI
and went from 16-17 MPH to 19-20 MPG. Now that's 90% interstate driving, I live about a mile from the
highway and work about a mile from the highway and it's a little more than a 20 mile trip. The way I've
got it figured, the savings on gas will have the engine swap paid for in about 19 years. Only thing is, that
means I have to keep working at the same place until I'm 71. Maybe I could find a job further away, that
would pay for it quicker.


 
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Discussion Starter · #6 ·
You could also hope for the oil price to go even higer, that will improve the payback time /wwwthreads_images/icons/crazy.gif!

but seriously, not only improve your air intake, improve the exhausts as well, that will improve the power as it is easier for the engine to get rid of exhausts, well that is the theory anyway. I don't think any upgrades will pay them selves back in any short time. You could do all kinds of calculation on NPV/discount factors/infaltion rates/fuel prices. Just go for the power and forget about pay back!

BlueJay
93 YJ with upgrades (and it is Blue!)
 
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Discussion Starter · #7 ·
I have an 89 YJ. 4.11 gears worked great for me with 33" tires. I had the straight 6 and 5 speed tranny. The 258 is not known for lots of power but it is known for lots of torque. keep that in mind. I replaced mine with a chevy 350, unbelievable difference. However, it is costly.

 
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Discussion Starter · #9 ·
Ok, in the line of spending, maybe Under $400. I was considering a header, cam, and 4bbl with intake. Any opinions on that?

1987 YJ Laredo
Rylan D.
 

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1,748 Posts
I have an 88YJ, rebuilt 258, pacesetter header, weber 32/36, HEI, 33s and 4.10 gears (4 cyl. YJ axles) and the automatic tranny 999. It is a reasonable all-around Jeep. I don't pay attention to MPG, though, as with the weight of a winch up front, a swing-away tire carrier out back, hardtop and hard doors in the winter, hi-lift jack, etc., etc., MPG is the first thing to go. For performance and MPG, fuel injection is really a gain. A friend of mine has a 95 YJ with the injected 4.0, and man that motor is nice. Rather than rebuild the 258, perhaps you could swap in a 4.0, or go to the Mopar MPI with the 4.0 head on a new 258....

Good luck
Pete

88YJ, 4"susp, 33"BFGMT, 9k#winch, rear homemade swingout, reb.258, 999, 4.10, weber32/36, GMHEI.
 
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