Default 258 4.0 Head Swap Results 

Old 03-14-2011, 10:22 PM   3 links from elsewhere to this Post. Click to view. #1
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Can we try this one again?

Post your thoughts about your 258 4.0 Head Swap Results .

 

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Default Re: 258 4.0 Head Swap Results 

Old 03-15-2011, 06:46 AM   #2
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Quote:
Originally Posted by 73CJ View Post
Can we try this one again?

Post your thoughts about your 258 4.0 Head Swap Results .
Thank you for starting this valuable thread again!

My Swap

1978 258 Block that takes 1/2" Head Bolts(No spacers required)

1995 Cherokee #7120 4.0 Head Casting with all stock parts(Rebuilt)

1978 Stock Push Rods(Correct Length for my swap)

1995 Tubular Exhaust Manifold(New)

1980's Aluminum Intake Manifold

1960's or early 1970's Motorcraft 2100 Carburetor(Rebuilt)

1995 Cherokee 4.0 Valve Cover(Baffle restrictor plates removed!)

I had to seriously remove a lot of metal, Steel and Aluminum from my power steering bracket to get it to clear the front exhaust manifold tube. I filled the extra water jacket ports using bio degradable packing peanuts to hold JB Weld in place while it hardened. No leaks so far. Home made throttle cable bracket, and I shortened the cable quite a bit so it's not wrapped around. The rest was pretty much plug and play. It all bolted together like the parts were made for each other.

I gained a huge amoung of horse power. I don't need to down shift nearly as often as I use to. I no longer lose a lot of speed on long highway up hills, I almost never have to put my foot on the floor like was almost always the case on the highway before, and my gas mileage went up quite a bit as well! I now get roughly 4 days of driving to work on a tank of gas instead of three! It's the cheapest increase in horse power that I've ever had on any engine I ever built. I just wish I'd done this swap last year when I first built the engine.

 

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Default Re: 258 4.0 Head Swap Results 

Old 03-15-2011, 08:49 AM   #3
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2 thumbs up. I used a Clearwater ready to install 7120 head with welded jackets. As mentioned the PS pump bracket takes a little modification but nothing major.
My opinion is it's job #1 for the 258.
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Default Re: 258 4.0 Head Swap Results 

Old 03-15-2011, 09:04 AM   #4
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Vehicle(s): 1977 cj-5 4.2 W/MC2100 carb, 4.0 head W/3 angle valves,SS Header,TFI ignition with MSB-6 offroad module,CS144 140 amp RPS alternator with remote regulator T-150,d-20,Dana 44 with OX lock and disk brakes. D-30 with Spartin locker, skyjacker 2.5 lift?nitro shocks,31" BFG A/T off road.8000 lb Warn winch, original owner.=^) 2006 Toyota Tacoma
 
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Did either of you guys do any other changes at the same time as you did the head swap?
like a new carb?
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Default Re: 258 4.0 Head Swap Results 

Old 03-15-2011, 09:36 AM   #5
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Quote:
Originally Posted by IOPort51 View Post
Did either of you guys do any other changes at the same time as you did the head swap?
like a new carb?
I had to swap carbs because my original cast iron 1978-1979 intake was for a 1 barrel Carter YF carb. The 1980's intake I had to switch to to make the swap work was a two barrel. That shouldn't have affected HP or MPG much during normal operation as long as both were jetted correctly. My old Carter YF was rebuilt and working perfectly. After the head swap I'm barely giving any gas when maintaining 65mph or better on highway up hills, where before the swap I had my foot on the floor and watched my speed drop rapidly!

It's my opinion that anyone with a stock 258 that has the mechanical know how to pull this off should do it asap. They will be thrilled with the results.

 

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Default Re: 258 4.0 Head Swap Results 

Old 03-15-2011, 10:17 AM   #6
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I replaced the 1 BBL with a 2 BBL and got a major improvement, I replaced/updated the ignition system and got a major improvement, I replaced the 4.2 head with a 4.0 head and got some improvement but not major amounts of horsepower and torque.
I think the 4.0 head swap is a good idea and if you have a cracked 4.2 head it would be the best replacement. Without an upgrade in cam shaft, especially from a 1 BBL cam, I have my doubts as to the stellar claims made of this mod.
I read something in one of the "I'm not spam" threads about a dyno test on the head upgrade producing 3-5 HP above the 4.2. I would like to produce this for you but have been unable to find it again. So we can say my information is flawed or we can say the information is lacking to determine this one way or the other.
As "seat of the pants" testing goes, if you are happy with the results, I am happy for you. Until someone finds a power comparison done on a dyno my first priority will be to upgrade the ignition.
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Default Re: 258 4.0 Head Swap Results 

Old 03-15-2011, 11:09 AM   #7
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Quote:
Originally Posted by IOPort51 View Post
I replaced the 1 BBL with a 2 BBL and got a major improvement, I replaced/updated the ignition system and got a major improvement, I replaced the 4.2 head with a 4.0 head and got some improvement but not major amounts of horsepower and torque.
I think the 4.0 head swap is a good idea and if you have a cracked 4.2 head it would be the best replacement. Without an upgrade in cam shaft, especially from a 1 BBL cam, I have my doubts as to the stellar claims made of this mod.
I read something in one of the "I'm not spam" threads about a dyno test on the head upgrade producing 3-5 HP above the 4.2. I would like to produce this for you but have been unable to find it again. So we can say my information is flawed or we can say the information is lacking to determine this one way or the other.
As "seat of the pants" testing goes, if you are happy with the results, I am happy for you. Until someone finds a power comparison done on a dyno my first priority will be to upgrade the ignition.
I had already upgraded my ignition with the great choice of an HEI when I first built my engine last year, so that stayed the same. I also stuck with the stock 1 barrel cam, which I believe is the exact same cam they put in 2 barrel engines from the factory. Someone please correct me with the actual lift and duration numbers if I'm wrong about that. I do know that the HP rating between the 1979 1 and 2 barrel engines were about the same at 110 hp. One other reason I don't believe the carb made any real difference is that on long uphills at highway speed with the 1 barrel carb before the head swap, it didn't really make any difference if I was at 3/4 throttle or full throttel, which tells me the engine just didn't have enough in it to use all of the 1 barrel. I'm noticing that even more with the 2 barrel with which I never floor it.

With a 4.0 head you get bigger valves, bigger better flowing ports, much higher compression(9.2 to 1 instead of 8.0 to 1) and a much better flowing exhaust manifold. All of those things other than changing cams are exactly what you would do to build a race engine, so there's no way you shouldn't see a serious horse power gain. Even with the same small cam, the engine will flow a whole lot better with the larger ports, and the bigger valves opened at the same lift and duration.

My seat of the pants comparison is more than just a feeling that it has more power and better MPG. It's a simple fact that before, I could not maintain 65 mph on hills and now I can do it easily, and it's a fact that before, I could only drive to work for three days on a tank of gas and now I can make about four trips on the same exact roads. This is an apples to apples comparison. The only other change I made was the carb, and I wasn't even using the whole CFMs of the old one barrel Carter because the engine couldn't make use of it.

It's the head that did it. Plain and simple.

I'm with you that I would love to see a before and after Dyno comparison. Most sites claim a 40 hp gain from the head. I haven't found a site that backs that up with actual dyno charts, but based on my results, I totally believe I gained that much. It's like night and day.

****EDIT****

I've swapped a whole lot of carbs in my life on a lot of different engines and vehicles 2 barrel to 4 barrel, quadrajet to Holley etc...) and I've never come close to seeing this kind of HP gain unless the old carb was not functioning correctly, and my old Carter was freshly rebuilt and working fine.

Last edited by Rescue Diver; 03-15-2011 at 11:32 AM..

 

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Default Re: 258 4.0 Head Swap Results 

Old 03-15-2011, 07:33 PM   #8
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Quote:
Originally Posted by IOPort51 View Post
Did either of you guys do any other changes at the same time as you did the head swap?
like a new carb?
I did several things at one time so have little idea of what each on their own was responcable for but the improvement the head, new exhaust and Mopar MPI yeilded was very significant to say the least.
I still have the 1bbl cam and no plans to replace it, the Jeep runs great as is.
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Default Re: 258 4.0 Head Swap Results 

Old 03-16-2011, 06:22 PM   #9
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Well I wasn't sure if this post would survive or not, but it looks stable for now.

Quote:
Originally Posted by IOPort51 View Post
Did either of you guys do any other changes at the same time as you did the head swap?
like a new carb?
I did many changes at the same time:

Reman 7120 head w/ JB Weld
.030 OS pistons - stock
Comp fuel injection cam
Holley 1D fuel injection
Clifford Intake
Clifford exhaust
HEI




Not sure what each item contributed. . . .

It pulls much harder. Doesn't cough (bog) at the top of hills and almost though a long mud hole.

Would I do it again? H*ll Ya!

Last edited by Petescj; 03-24-2011 at 04:54 PM..

 

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Default Re: 258 4.0 Head Swap Results 

Old 03-16-2011, 06:47 PM   #10
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I would too, no question, but when we do multiple changes it is not possible to attribute the performance to any one thing.

I don't have fancy test equipment but I do have a hill. It's about 1/8 mile 20 degrees and paved. I start at the bottom in 2nd gear and time the distance with a stop watch. As long as I am doing one thing at a time I can get a pretty good idea how much bang I got for my buck. We need to establish a personal constant to measure against.

I am not saying the head swap is a bad idea, it is a good one. I had a cracked 4.2 head and this was the very best solution. I am saying there is a lot of mist and smoke blowing around this and a lot of other modifications because we can not document the results in measurable quantity.
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We remember the times, when the voice in our head was screaming like a little girl.

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