same engines... different power? - JeepForum.com
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  • 2 Post By Fourtrail
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post #1 of 12 Old 07-09-2020, 09:25 PM Thread Starter
Davebrown777
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same engines... different power?

I have an 86 CJ-7 with 178k miles on it. Inline 6 258 4.2L. I just test drove an 84 with the same engine but only 110k miles on it... and it seemed to have way less power in 2nd and 3rd gear. Is that possible or is it just in my head?

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post #2 of 12 Old 07-09-2020, 09:33 PM
Fourtrail
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Gear ratios will make a big difference in the power you feel. The 84 likely has 2.73's which will make it feel like a dog.
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post #3 of 12 Old 07-09-2020, 11:17 PM
BagusJeep
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Quite possible, the ignition timing and/or carb setup could be way off. These engines, especially if the CEC computer is connected or partly Nuttered, require a level of understanding and work to get tuned properly.

Could just be the gearing of course. And big tyres etc take their toll.

My 1984 has headers and is much faster than my 1981, but they are both solid performers.
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post #4 of 12 Old 07-10-2020, 01:28 PM Thread Starter
Davebrown777
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Thanks for the feedback. Also forgot to mention that the 86 was a four speed and the 84 is a five speed. Would that play a factor? Just want to make sure there's nothing wrong internally in the 84 that makes it feel so sluggish in 2nd and 3rd gear. The 5 speed also doesn't sound as throaty...
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post #5 of 12 Old 07-10-2020, 01:48 PM
Fourtrail
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4 spd vs 5 spd if they are T-4/T-5 then no, 1st through 4th are all the same ratios. Throaty all depends on what muffler is installed normally. Both engines should perform the close to the same. As long is it has oil pressure and doesn't make any funny noises you should be ok. Might see if you can run a compression check just to double check for any underlying issues.

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post #6 of 12 Old 07-10-2020, 09:27 PM
REDnBLUES
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You did not say whether both Jeeps have the same size tires and wheels. Tires and Gears will change everything, it doesn't take much to make a 258 struggle.
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post #7 of 12 Old 07-12-2020, 06:16 AM Thread Starter
Davebrown777
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Different wheels and tires, but not massively different. The 86 has 15x7 wheels with traditional treads. The 84 has 15x8 wheels with a slightly nobbier tire. You think that could make a big difference?
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post #8 of 12 Old 07-12-2020, 06:11 PM
REDnBLUES
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There are still a few unanswered questions. What does each CJ have as far as gears? They were likely the same from the factory but...that's been a few years. Fourtrail made good points and you should follow that but you need to consider that it could be as simple as the '84 needs a tune up/plugs/wires/basic maintenance.

Either way, they are still both 35 year old carburated 6's. Most people don't daily drive them and they sit and bad things happen that cause you work and money to fix.

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post #9 of 12 Old 07-14-2020, 01:39 PM
ccoyle71
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In my recent experience with my own 258.....a new (correctly tuned) carburetor and an upgraded distributor completely changed the way my engine performed. Obviously.....same engine, tires, gears, etc - but it went from really sluggish to feeling like a new Jeep.
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post #10 of 12 Old 07-16-2020, 12:27 PM
0hcanada
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Quote:
Originally Posted by ccoyle71 View Post
.... and an upgraded distributor completely changed the way my engine performed...
what do you mean by "upgraded distributor"?

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post #11 of 12 Old 07-16-2020, 12:42 PM
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Quote:
Originally Posted by Davebrown777 View Post
Different wheels and tires, but not massively different. The 86 has 15x7 wheels with traditional treads. The 84 has 15x8 wheels with a slightly nobbier tire. You think that could make a big difference?
What size are the tires on each Jeep?

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post #12 of 12 Old 07-17-2020, 09:30 AM
ccoyle71
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Quote:
Originally Posted by 0hcanada View Post
what do you mean by "upgraded distributor"?

Previously I had the original duraspark ignition control / distributor and I had problems with mis-firing. I swapped it out for an HEI distributor, new plugs and wires......and it made a huge difference.
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