I'm not trying to start an argument here and maybe i just don't get it. Ive been all over the web and all i see is how much better the 4.0 is compared to the 258. Now I'm not a hardcore offroader, more interested in the utility and just general love for the jeep. I recently decided to swap my 258 out of my cj5 into my 81 bler. Tore it apart to replace gaskets and found the big ugly, needs to be overhauled. Long story short. I'm searching web for performance mods or things i can do while rebuilding. Everything I read is 4.0 this and that, use 4.0 head or cam engine like the 4.0. My experience with the 4.0 (2 wranglers 91 and 01) was that hp was ok but they sucked when pulling utility trailer or just pulling a hill . Now i get it, fuel injection is great compared to carb. and i get the 4.7 stroker (no replacement for displacement). What i don't understand is an inline 6 cyl. that make max power at 4000 rpm. Fuel mileage is not that much better than the 258 1or2 mpg (w/o emissions). I'm just going off my personnel experience with these 2 engines and i understand that gearing and power/weight play a big role but just could not believe the torque that the (worn out) 258 had in a 78 cj5 w/3.54's vs. wranglers with 4.0L 4.10's and 3.07's. Am I way off base here, I think I'll be happy with the 258 in my bler for utility use and daily driver. Sorry for rambling but i am really interested to know what others think (real world experience). Does the 258(aftermarket carb.) exceed the 4.0(stock) in useable power and why did manufacurers go to this high rpm power configuration.
4.0 hype they don't make em like they used to
- Thread starter iron5jp
- Start date
LetchcoreCJ7
Legacy Registered User
- City
- Nashville
- State
- TN
Well the reason the 4.0L head works so well on the 4.2L is you still get the longer stroke of the 4.2L bottom end but the better flow of the 4.0l head. Whats even better is a 4.2L with a 4.0l head and MPI or stock 4.0L FI setup from a 91-95. THEN you get the longer more torquey stroke of the 4.2L, better flowing head, and FI. Will run circles around a stock 4.0L. Did all that make sense?
I did the 4.6L stroker and its nice but its not a V8. Very reliable and solid power but I was slightly dissapointed.
I did the 4.6L stroker and its nice but its not a V8. Very reliable and solid power but I was slightly dissapointed.
- City
- Cobourg, Ontario, Cana
- State
- da
I had a stock 258... it sucked.
I rebuilt the 258 block then slapped on a rebuilt 4.0L head with stock (ish) MPFI out of an XJ. It was great for power but sucked gas back bad. (13mpg)
Had a stock 4.0L with California emissions in the same Jeep... not as much power but not a huge difference either but got 17 mpg.
Now I'm finishing the final details of my 5.3L Vortec V8. Should have almost double the horsepower and will probably get 20mpg on the highway.
I rebuilt the 258 block then slapped on a rebuilt 4.0L head with stock (ish) MPFI out of an XJ. It was great for power but sucked gas back bad. (13mpg)
Had a stock 4.0L with California emissions in the same Jeep... not as much power but not a huge difference either but got 17 mpg.
Now I'm finishing the final details of my 5.3L Vortec V8. Should have almost double the horsepower and will probably get 20mpg on the highway.
- City
- Cincinnati
- State
- Oh
The early '87-90 Renix 4.0s made its torque at a lower RPM. When they went to the H.O. in '91, they bumped the H.P. from 173 to 190, but the torque curve moved higher.
Some try to get a lot more HP and torque from the AMC Inline six and you can be successful to a point. The beauty of these engines is their lower RPM torque (258 especially)... It's what they were made for.
I rebuilt a 258 with the 4.0 HO Head conversion and I am very happy with the results (more than doubled the HP)..... My expectations were inline with my results....If I want a lot more power and want to run a higher RPM engine then I'll go with a V8.
I rebuilt a 258 with the 4.0 HO Head conversion and I am very happy with the results (more than doubled the HP)..... My expectations were inline with my results....If I want a lot more power and want to run a higher RPM engine then I'll go with a V8.
- City
- Yorktown
- State
- Va
Biggest issues with Torque and where it comes in the power band is totally related to the cam.
The 4.0l HO heads just flow better, and MPFI can adjust fuel air mix much better at part throttle and off camber. But it is the Valve train and its timing that will put the power in that engine where you want it. The 258 crank and proper pistons will get you more displacement and better stroke for more power down low. But without the right cam it is wasted.
Biggest issue for raising the torque curve in the RPM range was to get engine and exhaust hotter and more able to burn on oxides from combustion to meet stricter emission requirements. It was not done for fuel mileage. Also folks are getting used to higher reving smaller engines to 4K RPM is nothing to them.
If you can get a good RV cam in a 4.6l stroker you will have a nice crawler engine that loves to lug along at 180 RPM all day.
If you want more and less expensive power with higher MPG, Then go get a late model Chevy 5.3l V-8 and do the swap. They can be found pretty cheep and in the end you will probably spend less than the Stroker.
Carl
The 4.0l HO heads just flow better, and MPFI can adjust fuel air mix much better at part throttle and off camber. But it is the Valve train and its timing that will put the power in that engine where you want it. The 258 crank and proper pistons will get you more displacement and better stroke for more power down low. But without the right cam it is wasted.
Biggest issue for raising the torque curve in the RPM range was to get engine and exhaust hotter and more able to burn on oxides from combustion to meet stricter emission requirements. It was not done for fuel mileage. Also folks are getting used to higher reving smaller engines to 4K RPM is nothing to them.
If you can get a good RV cam in a 4.6l stroker you will have a nice crawler engine that loves to lug along at 180 RPM all day.
If you want more and less expensive power with higher MPG, Then go get a late model Chevy 5.3l V-8 and do the swap. They can be found pretty cheep and in the end you will probably spend less than the Stroker.
Carl
- City
- Biloxi
- State
- MS
I have 3 Jeeps with in-line 6 engines currently, all slightly different, here is my opinion on each
(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
I would NOT swap one of these motors into a CJ over a 4.2 Jeep "cuts off" at the 93 MPH factory installed set point
.
(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
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
So, IMO, 258 + stock 258 head + MOPAR MPI for the win
I often times wonder, would the slight power gain from swapping a 4.0 head on the 258 be worth it $$$ wise I do not see how this head swap would "double" the HP i have on the stock 258 with MPI. I seriously doubt it. Maybe a 20 HP gain MAX, and then I would be worrying about JB welded up coolant passages, or spend the big $$ on a "custom" head, don't see the $$$/HP gain logic in this swap
As far as the money spent on building a stroker 4.0, I think a V8 swap would be much better money spent
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
(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
I would NOT swap one of these motors into a CJ over a 4.2 Jeep "cuts off" at the 93 MPH factory installed set point.
(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
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 stripSo, IMO, 258 + stock 258 head + MOPAR MPI for the win
I often times wonder, would the slight power gain from swapping a 4.0 head on the 258 be worth it $$$ wise
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 swapAs far as the money spent on building a stroker 4.0, I think a V8 swap would be much better money spent
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
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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.
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.
- City
- Biloxi
- State
- MS
I would be interested to know how much power my current stock 258/Mopar MPI set up is making. I wouldn't mind just a little bit more power in the 2,000-2,700 RPM range. A mild RV cam, headers, and minor head work to my 258 head might be all I would want, famous last words
For instance, when I drove from Biloxi to Michigan, I could maintain 75 MPH on 85% of the hills with no drop in speed, staying in 5th gear, spinning 2,500 RPM. Of the hills were I left it in 5th and dropped speed, I would lose at the most 8 MPH. A downshift to fourth would let me maintain speed, but at 3,000 RPM.
I think all I need/want is a little more airflow, either through a slightly longer duration cam, less restrictive exhaust (stock manifold with Magnaflow muffler, seems to flow good), larger valves, or a combination of all of the above. Basically, it seems like if it would flow/suck a little more air and fuel, it would hold 5th/maintain speed on all but the steepest/longest grades
But, a super/turbo charger would be sweet, too
- City
- Dillsboro
- State
- IN
As soon as I get on the stick, I can let you know how the "Built" 258 will do. The "New" red Scrambler in my shop has the block bored .030, decked .010, head shaved .020, 1.94/1.50 valves, ported and "Semi-polished". I used Compititionn Cams "RV" low end tourque Hyd/Roller cam and MoPar Performance MPI. Pistons are fly-cut for valve relief and this combo is at 9.25/1 compression. Exaustis still up in the air, have a ported stock manifold on it, but do have an equal length tube coated split 3 into 1 header. It's got an automatic , 4.10s and 33X12.50 MTs on 15X12 wheels. May have to do an overdrive down the road to make it as cross country friendly as Raymonds. 
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mysunnshine
Legacy Registered User
- City
- Phoenix
- State
- AZ
I too would like to see how it would compare. Tower210, I'll have to see if I have any other dyno runs to compare a "stock" 258 to on my dyno...
- City
- Port Allen
- State
- LA
I dropped the head, intake, exhaust, and fuel injection from a 1994 Grand Cherokee on my scrambler. Very noticeable difference. So it's still a 4.2 L engine, but with the multi point fuel injection and improved intake and head. The other two advantages are not pumping the accelarator to get it to go in the morning, and not dieing out on steep inclines. I had a MC2100 carb on it before, so the HP gains weren't absolutely huge like some people report, but it's still better. I'm looking to do the same to the '84 I just purchased for my kids. I also ordered a set (should get them today) of the Bosch fuel injectors. These are supposed to make a better spray pattern than the original Siemens injectors. I saw some tests on youtube, and decided it was worth a try as my injectors were dirty anyway. We'll see how that works out.
Guy here in Baton Rouge want $100 to dyno. I might do it just for fun and blow the $$$$.
Guy here in Baton Rouge want $100 to dyno. I might do it just for fun and blow the $$$$.
Initially I compared my 258 build on paper to a list of build options that is from a website based on 4.0 liter and Stroker builds. www.jeep4.0performance.4mg.com Use the "stroker" tab in website and go towards the bottom of the page. There is a lot of info in the website, great FI resource.
I agree with CBRogers above. It is the proper valvetrain, timing and engine machine work that makes the difference.
I stayed with the 258 block for it's long stroke and bored +.060 for a few more inches. Now at 266 Cubic Inches or 4.37 Liters. Only 18 cubic inches less than a stroked 4.0 to 4.7. So why the extra expense just to say you have a 4.0 stroker when you will be using the 258 crank anyway???
Here is what my build entails:
4.0 HO head - 2.02/1.62 valves, Comp Cam Springs, Harland Sharp Ajustable Roller Rockers
Block - "0" Decked, Oil Passages Chamfered and bored +.060 - 266 Cubic Inches
Comp Cam - Extreme 4x4 - 68-235-4 - Changed Lobe center to 113' if changed to Fuel Injection (Ya never know)
Clifford 4.0 HO Intake
HEI Distributor
Weber DGES 38/38 - 400cfm
JBA Header - 2 1/2" single collector
2 1/2" Pipe from header back - Dynomax Super Turbo Muffler
From this build and compared to builds on stated website, 200 HP+ and about 300 fp Torque should not be a stretch at all. Actually by comparison, my numbers are very conservative to website's numbers. A good running, properly tuned carb can put up very similar numbers to Fuel injection.
I agree with CBRogers above. It is the proper valvetrain, timing and engine machine work that makes the difference.
I stayed with the 258 block for it's long stroke and bored +.060 for a few more inches. Now at 266 Cubic Inches or 4.37 Liters. Only 18 cubic inches less than a stroked 4.0 to 4.7. So why the extra expense just to say you have a 4.0 stroker when you will be using the 258 crank anyway???
Here is what my build entails:
4.0 HO head - 2.02/1.62 valves, Comp Cam Springs, Harland Sharp Ajustable Roller Rockers
Block - "0" Decked, Oil Passages Chamfered and bored +.060 - 266 Cubic Inches
Comp Cam - Extreme 4x4 - 68-235-4 - Changed Lobe center to 113' if changed to Fuel Injection (Ya never know)
Clifford 4.0 HO Intake
HEI Distributor
Weber DGES 38/38 - 400cfm
JBA Header - 2 1/2" single collector
2 1/2" Pipe from header back - Dynomax Super Turbo Muffler
From this build and compared to builds on stated website, 200 HP+ and about 300 fp Torque should not be a stretch at all. Actually by comparison, my numbers are very conservative to website's numbers. A good running, properly tuned carb can put up very similar numbers to Fuel injection.
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- City
- Biloxi
- State
- MS
I too would like to see how it would compare. Tower210, I'll have to see if I have any other dyno runs to compare a "stock" 258 to on my dyno...
I will look and see if there is a Dyno around here, I would be interested to know the true rear wheel HP, I would guess around 140
Next time I am in Baton Rouge, if I can't find a Dyno around home, I will see if I can find/utilize the place you are talking about
mysunnshine
Legacy Registered User
- City
- Phoenix
- State
- AZ
I will look and see if there is a Dyno around here, I would be interested to know the true rear wheel HP, I would guess around 140
The dyno will only do good if you can log the A/F and knock(If it's fuel injected). That way you have an idea how close the tune actually is...
I had a 84 cj7 Laredo that I put a 4.0L engine into and I absolutely loved it! It had 4:10 gears t-4 tranny stock axles rockin 34x9.50 super swamper tsl specail service tires on factory chrome 15x7 rims. That jeep was so much fun to drive, always started, it ran perfect hot or cold and it would clime most anything I put in front of it with no hesitation. Also my dad who was a mopar mechanic for 30 years figured out how to make the factory oem cj tachometer work with a 4.0l engine. I am definitely going to put a 4.6 stoker engine in my 86 Cj7 Laredo.
MomoJeep
Basic User
- City
- Seattle
- State
- WA
REVIVING this old thread - I don't know a lot about engines/valves. How does installing those chevy valves make a difference?
FLCJ8
Legacy Registered User
- City
- Palm Bay
- State
- FL
The larger diameter valves will allow for increased flow into and out of the cylinders.