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4.0 hype they don't make em like they used to

I agree with Spanks post #7 option 3 but would like to add... 258 + 4.0 head + MOPAR MPI for the win
My 258 is a fun little motor, but where spanks said power drops off at 2800, I am good for about 3,000 (3,200 MAX).

I have everything Post #15 Rguest 3 has + MPFI and I bet I am just over 200 on HP.

If I pull the head, I am going to look into the larger valves-- this is a 4.0 head
 
YJ-8 said:
I agree with Spanks post #7 option 3 but would like to add... 258 + 4.0 head + MOPAR MPI for the win
My 258 is a fun little motor, but where spanks said power drops off at 2800, I am good for about 3,000 (3,200 MAX).

I have everything Post #15 Rguest 3 has + MPFI and I bet I am just over 200 on HP.

If I pull the head, I am going to look into the larger valves-- this is a 4.0 head
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I'm no expert on this, but I've been told by a few experts that you might not want larger valves ... because ... If this was a race car we're talking about you *would* want larger valves, but apparently the inhibition of airflow really isn't an issue until you get into higher RPM's which means just starting around 3000 and going up from there. However, at lower rpm where you will be most of the time in a Jeep, a larger valve actually slows down the airflow into the cylinder (the same volume of air has to flow faster to get through a smaller opening than a large opening). And when the air flows faster into a cylinder the air-fuel mixture become more thoroughly mixed and therefore it combusts more efficiently and more fully for MORE torque/power. Also, more torque multiplied through gearing does equate to more power and speed if/when needed.
 
MomoJeep said:
I've been told by a few experts that you might not want larger valves
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Good, its not often a Jeep forum saves me money. :LOL:

You may have a point, I will attest that down low it is a stump puller.
I will investigate because If its not broke, I don't need to fix it.

As far as the theory of larger valves/ports-- my other "toy" is a 1970 Boss 302 i.e. small displacement motor with intake ports the size of your fist. It is the polar opposite of a Jeep 258.

I will say, something is limiting our 258's to low-ish RPM's vs a 4.0. I would love to have another 1,000 rpm on the power band.
 
YJ-8 said:
I will say, something is limiting our 258's to low-ish RPM's vs a 4.0. I would love to have another 1,000 rpm on the power band.
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l
Look at your ignition system.
 
Being MOPAR MPFI My ignition system is off a 4.0 so I would like to think its a wash.

I have always chocked part of it up to being the characteristics of the motor-- under square vs over square.
 
YJ-8 said:
Being MOPAR MPFI My ignition system is off a 4.0 so I would like to think its a wash.

I have always chocked part of it up to being the characteristics of the motor-- under square vs over square.
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The way I look at it, it's an engine designed for torque, not high speeds. Drive the engine at it's most efficient rpm range, and then use gearing to multiply that torque into speed. Higher rpms does not necessarily mean more power. It's driving at the peak of the torque and/or horsepower curve that matters.

I think people get confused when comparing torque and horsepower. It's kindof an apples to oranges comparison. In terms of basic physics, Horsepower is a measure of "power", torque is a measure of "work". Power =Work / Time. In other words, power is the rate at which work can be done. A V8 and a 4-banger can both get the same Jeep over the mountain pass (work), the V8 can do it faster (power).
 
Air start....Take a cylinder out of service....pour walnut shells in the turbos every morning round....A Mechanical Marvel. Was extremely happy when low sulfer came to town. Fuel oil purifier cleaning turned into the best job ever.
 
rguest3 said:
spankrjs,

Correct with just the 4.0 HO head swap you would get an increase of 20-40 HP. But with a good combination of Cam, Heads, Intake, Headers and Carb with proper block machine work done the HP levels can be doubled. Remember the stock 258 with Carter carb is in the 110-120 HP range. 200HP is not a stretch at all for a 258 cubic inch motor. If done correctly the torque numbers will increase very nicely as well.

The other option is to machine the 258 Head and install 1.94, 1.50 chevy valves. Seems to wake up the stock head quite well.
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Interesting option with the valves, do you have experience with this mod? I was just wondering what kind of cam options would compliment that scenario.
 
MomoJeep said:
The way I look at it, it's an engine designed for torque, not high speeds. Drive the engine at it's most efficient rpm range, and then use gearing to multiply that torque into speed. Higher rpms does not necessarily mean more power. It's driving at the peak of the torque and/or horsepower curve that matters.

I think people get confused when comparing torque and horsepower. It's kindof an apples to oranges comparison. In terms of basic physics, Horsepower is a measure of "power", torque is a measure of "work". Power =Work / Time. In other words, power is the rate at which work can be done. A V8 and a 4-banger can both get the same Jeep over the mountain pass (work), the V8 can do it faster (power).
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I agree, but road/highway driving is high speed and highway driving negates the benefits of a 258. My power band drops off at 3,800 and by 4,000 RPM the party is over. On the street It would be nice to have another 1000 rpm like a 4.0, or even an additional 2,000 rpm on tap for a V8.

You see the 4.0 team gear to 4.88 to turn 35's, while the 258 team usually gears to 4.56 for the same size tire.-- this is accounting for the torque curves mentioned above.

IMO a 4.0 would beat a comparable 258 in a drag race, where as a 258 is more favorable chugging along over rocks.
 
YJ-8 said:
I agree, but road/highway driving is high speed and highway driving negates the benefits of a 258. My power band drops off at 3,800 and by 4,000 RPM the party is over. On the street It would be nice to have another 1000 rpm like a 4.0, or even an additional 2,000 rpm on tap for a V8.

You see the 4.0 team gear to 4.88 to turn 35's, while the 258 team usually gears to 4.56 for the same size tire.-- this is accounting for the torque curves mentioned above.

IMO a 4.0 would beat a comparable 258 in a drag race, where as a 258 is more favorable chugging along over rocks.
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I hear what you're saying. But (correct me if I wrong) but doesn't it all comes down to gearing!? Say you have a 258, and you hit 3000rpm, and shift up to the next gear, and rpms drops to say 2000 rpm (with plenty of torque), aren't you now ready to rock and roll up into much higher speeds.

It seems to me it doesn't matter where you're rpm's are, as long as you are in your power band and have the right gearing, you're going as fast!

Example - with my current set-up (3.31 gears, 31.5" tires), in 4th gear, at 2000rpm I'm doing 57mph. At 3000rpm I'm doing 85mph. I don't plan on going that fast, therefore no need for higher rpm's.
 
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MomoJeep said:
I hear what you're saying. But (correct me if I wrong) but doesn't it all comes down to gearing!? Say you have a 258, and you hit 3000rpm, and shift up to the next gear, and rpms drops to say 2000 rpm (with plenty of torque), aren't you now ready to rock and roll up into much higher speeds.

It seems to me it doesn't matter where you're rpm's are, as long as you are in your power band and have the right gearing, you're going as fast!

Example - with my current set-up (3.31 gears, 31.5" tires), in 4th gear, at 2000rpm I'm doing 57mph. At 3000rpm I'm doing 85mph. I don't plan on going that fast, therefore no need for higher rpm's.
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Yes and to support this diesel engines never really go past 3000rpm.
 
spankrjs said:
I have 3 Jeeps with in-line 6 engines currently, all slightly different, here is my opinion on each:twocents:

(1) 2005 TJ Rubicon - Bone stock engine and jeep. Bought brand new, now has 130,000+ miles on it, 6 speed manual transmission. This engine does not start to "pull hard" until over 2500 rpm. It works fine off road, mainly due to the fact it has 4:10 axle gears/4:1 t-case/31" tires. The higher RPM power is useful on the highway, but I miss the low RPM power of the older engines. IMO, this vehicle performs OK, but if I put 33" tires on it without a R+P change, it would be a gutless dog. But, I am used to having the "pull hard" right off idle motors, so maybe I am biased:shrug: I would NOT swap one of these motors into a CJ over a 4.2:twocents: Jeep "cuts off" at the 93 MPH factory installed set point
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(2) 1983 Scrambler STOCK -258, Carter computer controlled carb, 5 speed, 3.31 axle gears, 30" tires, 127,000 miles. This jeep is fun to drive, will blow the doors off my 05 TJ in a drag race. Pulls hard from the 650RPM idle all the way to around 2500 RPM, then power drops off significantly. Vehicle tops out at around 85 MPH, will not go much faster. This jeep is "quicker" then the TJ, and pulls much harder then the 4.0 below 2500 RPM.

(3) 1983 Scrambler MODIFIED - stock 258 with MOPAR MPI, 5 speed, 4.10 gears, 33" tires. This jeep is the best of all 3 to drive. Pulls hard from the 700RPM idle up to around 2800 RPM, then power drops off. This engine pulls even harder then the carb equipped 258, I guess due to the efficiency gains of MPI. It tops out close to 100MPH. At 75 MPH, I spin 2400 RPM, and average 17MPG. This, to me, is a perfect combo. I am running a stock exhaust manifold on this Jeep, so maybe a header would slightly improve the "engine breathing" at higher RPM, but I like this set up just as it is:thumbsup: Even with 33" tires versus the TJ's 31" tires, this jeep is faster/pulls harder. If I put 33's on the TJ, this Scrambler would humiliate the TJ on a drag strip:twocents:

So, IMO, 258 + stock 258 head + MOPAR MPI for the win:thumbsup:


I often times wonder, would the slight power gain from swapping a 4.0 head on the 258 be worth it $$$ wise:shrug: I do not see how this head swap would "double" the HP i have on the stock 258 with MPI. I seriously doubt it. Maybe a 20 HP gain MAX, and then I would be worrying about JB welded up coolant passages, or spend the big $$ on a "custom" head, don't see the $$$/HP gain logic in this swap:shrug:

As far as the money spent on building a stroker 4.0, I think a V8 swap would be much better money spent:twocents:

All in all, the stock 258 with MPI makes more then enough power for my close to stock red Scrambler. I drove it cross country and back with no problems. It seems to be a very reliable set up. I think that a V8 swap, especially with a more modern/big HP TPI/MPI set up, would be too much power for my red Scrambler, unless I swap out the entire drive train. For me, my sub 200 HP in-line 6 is more then enough for most driving situations, except on big sand hills/big mud holes, where another 100HP would be cool:thumbsup:
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It seems that every time I convince myself AGAIN that my 4.2 is inadequate and has not the potential to be good enough no matter what, I come across this thread and this post gets me all revved up that I'm wrong. All I want is a little more highway power. The ability to hold speed on hills. That's it. At this very moment in time I think I have a chance. I would much rather keep my 4.2 rather than swap for a 5.3 any day, but the 4.2 must be a well rounded driver. Currently 65 mph is just a wild idea.

Chris
 
BDCCLARK said:
It seems that every time I convince myself AGAIN that my 4.2 is inadequate and has not the potential to be good enough no matter what, I come across this thread and this post gets me all revved up that I'm wrong. All I want is a little more highway power. The ability to hold speed on hills. That's it. At this very moment in time I think I have a chance. I would much rather keep my 4.2 rather than swap for a 5.3 any day, but the 4.2 must be a well rounded driver. Currently 65 mph is just a wild idea.

Chris
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What size tires are you running? What axle gears? Which transmission?
 
MomoJeep said:
What size tires are you running? What axle gears? Which transmission?
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Currently I am running 33 12.50s, 3.54 gears, and a t4.

Engine is stock with a little weber and Dui distributor. Best money spent hands down was the Dui.

Chris
 
BDCCLARK said:
Currently I am running 33 12.50s, 3.54 gears, and a t4.

Engine is stock with a little weber and Dui distributor. Best money spent hands down was the Dui.

Chris
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I think it really depends on your expectations for your driving experience. IMO the 6 power output/acceleration doesn't feel like a modern vehicle. The 6 can be adequate as long as you aren't wanting modern passing power or hill climbing ability.

That said gearing isn't helping your issue. 4:10 gears would really help your engine perform better.

With enough work the 6 can be descent performers. I went to Dallas a couple weeks ago and rode in a friends 2004 4.0 TJ. In his case a turbo and 5 lbs of boost. Still needs more tuning but he is getting almost 240 to the tire with 33s and 3.73 gearing. His next move is 4.56 gears and 35s.

Another friend has a 99 TJ 4.0 with 4.88s and 35s. This one is pretty much stock and struggles in the wind and up hills. It drives pretty well up to 65. He normally wants to run 75-80 and the jeep really isn't capable even in 4th vs 5th gear. Unless you are downhill with a tailwind....
 
sdsupilot said:
I think it really depends on your expectations for your driving experience. IMO the 6 power output/acceleration doesn't feel like a modern vehicle. The 6 can be adequate as long as you aren't wanting modern passing power or hill climbing ability.

That said gearing isn't helping your issue. 4:10 gears would really help your engine perform better.

With enough work the 6 can be descent performers. I went to Dallas a couple weeks ago and rode in a friends 2004 4.0 TJ. In his case a turbo and 5 lbs of boost. Still needs more tuning but he is getting almost 240 to the tire with 33s and 3.73 gearing. His next move is 4.56 gears and 35s.

Another friend has a 99 TJ 4.0 with 4.88s and 35s. This one is pretty much stock and struggles in the wind and up hills. It drives pretty well up to 65. He normally wants to run 75-80 and the jeep really isn't capable even in 4th vs 5th gear. Unless you are downhill with a tailwind....
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Gearing would definitely help.

I am switching from 3.54s to 4.56s this winter. I am also switching to 35s at the same time. I am doing a full tear down rebuild of my entire platform starting with a new frame.

I never understand the whole modern engine theory. I drive a 1996 12 valve cummins truck and generally shift between 2000 and 2500 rpms. I also drive a 1989 and 1985 suburban. One is tbi and the other carbureted. They are both 700r4 trucks, but I feel like I drive them the same as my diesel. I feel like these are modern engines.

I have no interest in a shorter stroke 4.0 engines. I am a fan of torque based engine builds.

I would love to keep an inline 6 in my jeep if it will do the job, but I will kick it to the curb and throw a 5.3 nv4500 package in there if that's what it takes.

I am considering giving the 258 a chance in the new frame. If it doesn't do it, then I'm only looking at a drive train swap the next winter. No big deal.

Chris
 
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