More power out of a 258 - JeepForum.com

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post #1 of 35 Old 09-25-2011, 10:10 PM Thread Starter
dylan0708
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More power out of a 258

Ok I feel as though my cj is lacking in power it's got a 258 in it with a weber no emissions sh** and a tuned duel output header. It has to work hard to get to 65 and god forbid I have to slow for traffic because getting back to that speed takes forever... I think maybe the issue is gearing I have 32 inch tires and plan to go to 33's but I have 2.73 gears would rehearing to say a 3.54 or 4.10 be even slower?

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post #2 of 35 Old 09-25-2011, 10:16 PM
ol78cj
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i was having the same trouble w/ my 78 cj w/ 258(brand new to) and i switched from 3.55's to 4.10's and man what a difference!! i couldnt believe it instead of losing speed on a slight incline i for once gain speed and hang with typical traffic haha! im running a 31 inch tire to...33's and 4.10's would be a good combo in my opinion and would be a big change for you also.
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post #3 of 35 Old 09-25-2011, 10:53 PM
VACJ7
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Definitely need to do a gear swap! I went to 3.73 with my 31s and my tired 258 has new found pep.

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post #4 of 35 Old 09-26-2011, 06:05 AM
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Your 2.73's are closer to 2.56's with 32" tires.

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post #5 of 35 Old 09-26-2011, 06:54 AM
bkeese
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Dylan, I think there are several issues here.
1st - you should have problems getting to 65 mph with 2.73s and 32" tires with a good running 258, My was tired and would do that all day long with 2.73s and 32" tires.
2nd - Bigger gears (numerically higher) will give you more accelleration but less top end (your speed at red line, which you shouldn't ever see in a CJ). You didn't say wether it was a 4 spd or a 5 spd. If you got over drive then bigger gears are possible. I just had a thought, you weren't tring to hit 65 in 5th gears were you? If so that's the problem. Don't use 5th gear, ever. 4.10s are kinda steep for 32/33" tires without a 5th gear.
Provide more info and you will get better recommendations.

1985 CJ7 - total customization underway, Sublime green and Plum crazy purple, Ford 9", 258 w/ Holley 475
1985,93 CJ7,YJ - L98 TPI Vette motor, Atlas twin stick, Dana 60s front and rear, Arbs, 39.5 Swampers
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post #6 of 35 Old 09-26-2011, 09:15 AM
swatson454
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I have God awful 2.73s and 33 inch swampers but I can nab 65 mph pretty darn quick. I think you need to look into your advance curve. If you still have the stock distributor, check this thread out. Matt did a great job of getting his stock distributor right. http://www.jeepforum.com/forum/f8/he...-curve-1238634

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post #7 of 35 Old 09-26-2011, 09:48 AM Thread Starter
dylan0708
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I have a t176 4 speed I mean it will get to 65 but getting there will take like a half mile... It's a newer engine out of an 86 with 55000 miles
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post #8 of 35 Old 09-26-2011, 09:51 AM Thread Starter
dylan0708
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Also how would I go about changing my gears what do I need to buy specifically I have never done that before I haven't even opened my diff
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post #9 of 35 Old 09-26-2011, 12:52 PM
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I feel your pain with 2.73 gears and 32" tires. I did that for years in my 82. I switched to 3.73's about 14 years ago and am very happy with it. My wife had an 84 with 3.54's and a 258 5 speed running 33's and it was fine. Great on gas, but again it was a 5 speed. I think the 3.73's are a good compromise for 33's used on and off road.

You'll need to buy a new carrier for the rear amc20 for sure and the front Dana30 will need one only if you go numerically higher than the 3.54's, otherwise your current one will work. And then of course gears and bearings for both. Plus now's the time to do a locker if you want, it'll save the cost of a carrier in the rear.
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post #10 of 35 Old 09-26-2011, 02:16 PM
bkeese
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Quote:
Originally Posted by swatson454 View Post
I have God awful 2.73s and 33 inch swampers but I can nab 65 mph pretty darn quick. I think you need to look into your advance curve. If you still have the stock distributor, check this thread out. Matt did a great job of getting his stock distributor right. http://www.jeepforum.com/forum/f8/he...-curve-1238634
I agree with Swatson. You need to get the 258 running correctly first. When you do the gears and tires will be tough on your clutch. Then move to 3.50s - 3.70s. I don't know about the different carrier, usually the break is 4.10 and down. Remember the cost is times 2. The AMC 20 is a decent rear if you get 1 piece axles, another $300, R&P $200 each, Master re-build kit $150 each, Aussi-locker $400 and lots of beer for your friends $100.

A much easier way would be to find complete front and rear axles with the correct ratio, hard to do but not impossible.

1985 CJ7 - total customization underway, Sublime green and Plum crazy purple, Ford 9", 258 w/ Holley 475
1985,93 CJ7,YJ - L98 TPI Vette motor, Atlas twin stick, Dana 60s front and rear, Arbs, 39.5 Swampers
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post #11 of 35 Old 09-26-2011, 02:17 PM Thread Starter
dylan0708
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Can anyone give me a list of what I need to regear to a higher gear?
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post #12 of 35 Old 09-26-2011, 02:21 PM Thread Starter
dylan0708
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How will I know when the 258 is running correctly? It feels as though it is running fine... I just have no acceleration I can nearly keep speed uphill never mind accelerate
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post #13 of 35 Old 09-26-2011, 02:28 PM
Renegade82
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Quote:
Originally Posted by dylan0708 View Post
Can anyone give me a list of what I need to regear to a higher gear?
You first need to decide on the ratio you want, and then if your going to put in any kind of locker.
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post #14 of 35 Old 09-26-2011, 03:15 PM Thread Starter
dylan0708
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Ok I'd like a locker in the front and maybe 3.54. Now what's better mechanical locker or air how do both work? And do you need on board air for the air locker? And where does it sit in the diff?
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post #15 of 35 Old 09-26-2011, 04:00 PM
swatson454
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Quote:
Originally Posted by dylan0708 View Post
How will I know when the 258 is running correctly? It feels as though it is running fine... I just have no acceleration I can nearly keep speed uphill never mind accelerate
This ^^^ is how you know that it isn't running correctly .

If you currently have the distributor from the feedback BBD era installed on an aftermarket carb or nutter bypassed BBD engine, your ignition timing is way off of optimal and will definitely keep you from making the power that it is able to.

I'm a little surprised at how many people overlook this important fact and buy new carbs, big distributor caps, fancy ignition parts, etc. to try to get more power when the ignition curve itself is often times the main culprit.

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