258 4.0 Head Swap Results

[Rescue Diver]

Don't forget that the computer controlled years had distributers with very little mechanical advance. The computer was responsible for allot of the advance so the distributer didn't need it. Once the computer is gone now the total advance is hindered. I have seen this more than once on the old AMC 258 i6 / 4.2l motors. If you switch to a newer distributer its like majically gaining horsepower. The old distributer could be adjusted by filing the factory advance stops so it allows more timing and the same results would shine through.

Very good point! Not having enough advance will kill your hp, torque and mpg!

 

[IOPort51]

A very good point Kane. Unfortunately it not valid in my case. The vehicle in question was not my CJ but rather my J-10. I think we can agree that a AMC 258 i6 / 4.2l is a AMC 258 i6 / 4.2l ? The distributer was refitted with cap, adapter, rotor wires and a TFI coil but nothing else changed, not even the timing. The improvement was impressive. The parts I replaced were not "old".

 

[TheDirtyCJ]

pics from after the job. compare to previous pics in my gallery!

 

[Renegade]

Here are the pics of my swap also. I finally got it finished, I am looking to get my clutched fixed this week so I can feel the real power of the upgrade. It does purr like a kitten and has tons of extra power when you punch it. Thank You for all your help Rescue.

 

[Rescue Diver]

Here are the pics of my swap also. I finally got it finished, I am looking to get my clutched fixed this week so I can feel the real power of the upgrade. It does purr like a kitten and has tons of extra power when you punch it. Thank You for all your help Rescue.

Wow! That looks great! If it runs half as good as it looks, you should be really happy with it.

 

[TheDirtyCJ]

Here are the pics of my swap also. I finally got it finished, I am looking to get my clutched fixed this week so I can feel the real power of the upgrade. It does purr like a kitten and has tons of extra power when you punch it. Thank You for all your help Rescue.

Rock and roll, my Brother! Feel the punch yet? Best thing I ever did to her. The engine compartment looks comparable to mine, It's a big job though is'nt it?

 

[Renegade]

Hey DirtyCJ,

Got a question, if you look at my linkage you can see it uses a cable that looks like a bicycle brake cable. When I push the gas pedal it has free travel for about an half inch to an inch. Then when the cable is tight it is hard to push the cable down and runs fine but it just seems like a bad design on my mechanics part. (I have also just installed a new cable as well) As you can see he has a stiff spring to pull the throttle all the way back I know that adds to the extra tension as well. To make a long story short, what cable are you using with yours? It looks like it works well with not a lot of free play. Please send me the info on how to purchase it if you know where I can get it, and the mounting brackets you are using as well. More pics would be great also. Thank You Again

 

[Renegade]

Well I am going to answer my own question, I was running to the parts store and I had just crested a small incline and backed off the gas, and instantly the Jeep roared and it started to scream I instantly pushed in the clutch and shut it off, I was in the center lane of a 2 lane both directions with a suicide lane in the middle. I had to turn the key on again to get it to where I could at least coast to the suicide lane. Traffic cleared and I pushed it to an empty lot, opened it up and noticed the spring was missing and the carb was stuck wide open and the bicycle cable had loosened Ha Ha!! Luck was on my side the spring was lodged on the sidewall in my wiring harness. So I was able to just hook it up again and took it easy. I ran straight to the auto store. My new set up works much better, I wish I would have tried to do it myself instead of paying a shop. It is such a great feeling fixing the problem yourself! I will post some new pictures of it. I can't believe the difference, it feels like a new Jeep. It always seemed so sluggish at take off and I knew it should have been stronger than that with all the mods. I took it for a test drive and it lit up my new BFG Mud terrains from a stop, and runs like a scalded DOG!!! So YES I have felt the NEW POWER and I am pumped!!!!! Thank You to all you guys.
Now after loading the pics it looks like I need to go back out and see why I see brake fluid!!! O'well looks like another opportunity to fix something!!! LOL!!!

 

[TheDirtyCJ]

Well I am going to answer my own question, I was running to the parts store and I had just crested a small incline and backed off the gas, and instantly the Jeep roared and it started to scream I instantly pushed in the clutch and shut it off, I was in the center lane of a 2 lane both directions with a suicide lane in the middle. I had to turn the key on again to get it to where I could at least coast to the suicide lane. Traffic cleared and I pushed it to an empty lot, opened it up and noticed the spring was missing and the carb was stuck wide open and the bicycle cable had loosened Ha Ha!! Luck was on my side the spring was lodged on the sidewall in my wiring harness. So I was able to just hook it up again and took it easy. I ran straight to the auto store. My new set up works much better, I wish I would have tried to do it myself instead of paying a shop. It is such a great feeling fixing the problem yourself! I will post some new pictures of it. I can't believe the difference, it feels like a new Jeep. It always seemed so sluggish at take off and I knew it should have been stronger than that with all the mods. I took it for a test drive and it lit up my new BFG Mud terrains from a stop, and runs like a scalded DOG!!! So YES I have felt the NEW POWER and I am pumped!!!!! Thank You to all you guys.
Now after loading the pics it looks like I need to go back out and see why I see brake fluid!!! O'well looks like another opportunity to fix something!!! LOL!!!

Hey, sorry it took so long to reply, I was in San Diego with the family, good times! I glad you got it figured out! That thottle cable and linkage look a little tight to me, but that might be the pic. I believe I have a slightly longer cable so the curve/bend is'nt as severe. It allows an easier motion so the cable inside slides without getting bound up. Great job my man!

 

[Rescue Diver]

I made my throttle cable a custom length by cutting the stock one shorter and putting a screw down cable end from the hardware store on the gas pedal end of it. With a little persuasion The cable housing will pull out of the plastic block that clips into the firewall. Then once cut to length, the cable housing can be pushed back into the block. The stock CJ throttle cables, both V8 and I6 are way too long for an I6 with a cable going straight to a regular bracket for an aftermarket carb.

 

[TheDirtyCJ]

5 month follow up- This has been the single best performance upgrade I've ever done. I've put about 600 miles on it since then, all off-road and in climbing areas. A couple of wrench turns to keep it properly torqued after it got seated in. I even got my CJ featured in powerblock tv! Gearhead of the week and in the magazine as well! So thanks for everyones input and comments, Thank you all.http://www.powerblocktv.com/magazine/?pub=40775/24

 

[Rescue Diver]

5 month follow up- This has been the single best performance upgrade I've ever done. I've put about 600 miles on it since then, all off-road and in climbing areas. A couple of wrench turns to keep it properly torqued after it got seated in. I even got my CJ featured in powerblock tv! Gearhead of the week and in the magazine as well! So thanks for everyones input and comments, Thank you all.PowerBlock Magazine | PowerBlockTV

That's great to hear. I've put about 15,000 miles on mine since the swap and no problems what so ever!

So much for that guy that didn't know anything but insisted on swearing the swap wouldn't work because the valve train was "different".

The 4.0 head swap was by far the best mod I've ever done to any engine in my life. The horse power percentage gained was unbelieveable for so little money, and the gas mileage increase is amazing!

 

[Petescj]

The horse power percentage gained was unbelieveable for so little money, and the gas mileage increase is amazing!

Been awhile since I visited this thread. Im really thinking about this swap. Can you throw out some ballpark numbers for the above.

 

[Rescue Diver]

Been awhile since I visited this thread. Im really thinking about this swap. Can you throw out some ballpark numbers for the above.

They say you gain 4r0 hp out of a stock 110hp AMC 258 i6 / 4.2l , so supposedly you end up with AMC 150 hp.

I believe that from the huge gain in power that I got out of mine. It wouldn't maintain 55 or 60 mph up highway hills with my foot on the floor before the swap. Now it holds 70 or 75 mph like nothing with only 1/4 throttle.

I use to be able to drive to work three days on a tank of gas. Now I can drive four days on a tank.

Others have doubted these claims, but I'm telling you from personal experience. I SWEAR BY THIS SWAP!

Like I said, I've built a whole lot of different engines in my life, and this was the easiest gains in hp and mpg that I've ever seen.....

 

[CJim7]

I gained a huge amount of power...but I also did a few other "upgrades" at the time.
My mileage stayed about the same but I was also turning 300hp out of this engine when all was said and done

 

[Petescj]

They say you gain 4r0 hp out of a stock 110hp AMC 258 i6 / 4.2l , so supposedly you end up with AMC 150 hp.

I believe that from the huge gain in power that I got out of mine. It wouldn't maintain 55 or 60 mph up highway hills with my foot on the floor before the swap. Now it holds 70 or 75 mph like nothing with only 1/4 throttle.

I use to be able to drive to work three days on a tank of gas. Now I can drive four days on a tank.

Others have doubted these claims, but I'm telling you from personal experience. I SWEAR BY THIS SWAP!

Like I said, I've built a whole lot of different engines in my life, and this was the easiest gains in hp and mpg that I've ever seen.....

No need to defend yourself. My hopes are to use this on a fresh rebuilt AMC 258 i6 / 4.2l . Im still unsure what manifold and carb combo I will use. Im still in the planning phase.

 

[CJim7]

No need to defend yourself. My hopes are to use this on a fresh rebuilt AMC 258 i6 / 4.2l . Im still unsure what manifold and carb combo I will use. Im still in the planning phase.

I went with a 500cfm Edelbrock and a Clifford aluminum intake with an XJ header.
Internal mods included flat pistons, 272 duration Competition cam, p&p on the head, 30 over on the cylinders. Desmogged with a TFI ignition.
Power and torque were tremendous, acceleration was scary crisp

 

[Petescj]

This will be my first rebuild and I'll be asking some questions when the time comes. Probably wont go as far as a p&p on the head but I like what you say about that combo.

 

[Sasquach]

I can give this mod 2 thumbs up myself. I did the head and the Mopar system at the same time so can't break it down but my milage is vastly better although I have to attribute that to the fuel injection? It runs sooo much better than the original set up it's hard to beleive they are just bolt on parts.

 

[73CJ]

Powerblock! Nice.