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Surfhockey 01-07-2014 09:56 PM

Want more horsepower
I have a '79 cj5 with an inline 258. I want some more horsepower so I can get up some of the sand dunes I frequent easier and quicker. I've heard of a supercharger, but I don't know if that would be best. Any ideas or suggestions would be greatly appreciated.

jeepdaddy2000 01-08-2014 05:08 AM

Jeep info?
Tire size?
All of theses factors should be looked at prior to "fixing" the engine.

As for the 258, there are many upgrades. 4BBL carb, header, cam (best combo of all three) which will garner you a nice power increase without breaking the bank.

Surfhockey 01-08-2014 08:33 PM

I have a 3 speed manual transmission and I'm riding on 31" Pro Comp mud terrains. I'm not sure of my gear ratio. How would I find that out? Also,I live in southern California, if that changes any type of things I can do to my engine or exhaust. Thank you for the help!

jnicewan 01-09-2014 12:09 AM

Depending on your budget there's not much you can do to gain significant power out of the 258 without rebuilding and spending a chunk of money, that's why a lot of people swap in V8's. Even though your engine might run good but if its old then its probably a little tired. Not trying to be a downer here but on its best day a brand new stock 258 was rated at approx 110 HP, I would say you would at least need another 100 HP to run up the dunes at any respectable pace. Even with a healthy V8 when running in deep sand or climbing dunes you can run out of power quick especially if you can't build momentum before the climb.

jeepdaddy2000 01-09-2014 07:20 AM


Originally Posted by Surfhockey (Post 19243538)
I have a 3 speed manual transmission and I'm riding on 31" Pro Comp mud terrains. I'm not sure of my gear ratio. How would I find that out? Also,I live in southern California, if that changes any type of things I can do to my engine or exhaust. Thank you for the help!

First, it always helps if you fill out your profile.

A lot of what were talking about here hinges on what your expectations are. A stock Jeep with wide (not tall) tires running 10 PSI of pressure can conquer most sand obstacles. Understand, there is a huge difference between a toy that can "tool around" in the sand and a focused sand runner. If your looking for a rig that will blast 500' dunes, then your looking at dropping some serious time and money into a build that goes well beyond a powerful engine.

Gear ratio can be found on the tag affixed to the cover, however, it is always best to drop the lid and do a tooth count, as Jeeps have a tendency to be modified over the years. This has the added benefit of giving you the chance to inspect the innards for any issues and refill the diff with some fresh oil. gearing becomes important due to the tall gears being installed in later models. This and taller than stock tires can seriously open up the shift points to where you simply can't get to the next gear due to low RPM's.

As for power. While you will never get the "bang for the buck" power that you would find in an 8, the six can squeeze out some worthwhile HP with the "big three" mods (intake/carb, cam, open exhaust). Just the carb and exhaust alone will garner a noticeable increase, especially in the upper RPM band, which is where you want to be in sand. Being in California poses some unique issues with emissions and registration. That is something you will have to take some time and research to insure you remain in compliance.

In the sand, tires are a huge issue. You will reap large rewards with low profile, wide tires that are able to spin effectively. Tall and narrow tires do not work comparatively well in the same situation. A 30-12.50 will go much farther than a 33-10.50, even if the taller tire has better tread. Couple this with gearing that allows you to get to the next gear without bogging, and you have a good chance of dealing with most everything you encounter.

One of the greatest upgrades for the sand is an automatic transmission. Between the torque converter taking up some slack and instantaneous shifts, auto's will outperform manuals in the sand almost every time.

Remember, sand saps power. Systems you don't normally think about become important. Insure your cooling system is up the the task. Long, continuous loading of the engine will create excessive heat. Boiling over at the far end of the beach will require a "beer break" to allow cool down.

Sand gets into everything and the salt will draw moisture. Try to pressure wash your rig prior to going out to keep as much sticky fluids off surfaces as possible. You HAVE TO wash at the end of the day. The salt will cause every exposed spot of metal to begin to rust.

Sand breaks things. Remember to insure the front end isn't bouncing, your not carrying excessive speed over dune tops, and you're not "bang shifting" the transmission getting to the next gear.

If your going to get serious, do yourself a favor and install a full rollcage and have at least a three point (stock) belt system. It is stupid simple to get sideways on a dune face and wind up rolling to the bottom.

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