4.2 head on a 4.0 block?
08-30-2009, 08:14 PM
#1
CF Veteran
Thread Starter
Join Date: May 2009
Location: Columbus, Ohio
Posts: 1,471
Likes: 0
Received 1 Like
on
1 Post
Year: 1996
Model: Cherokee
Engine: 4.0L
4.2 head on a 4.0 block?
So I have been thinking for a while now about converting my 4.0l to a 4.2 l.Now after some research i heard that the 4.2 head and the 4.0 head is simalar.So what should i know about this befor really thinking about attempting to get to it.
08-30-2009, 09:38 PM
#3
Senior Member
Join Date: Jun 2009
Location: Blakeslee, PA
Posts: 750
Likes: 0
Received 3 Likes
on
1 Post
Year: 97
Model: Cherokee
Engine: 4.7
What Frank said.
Ports are less efficient and are located slightly differently.
Different compression ratio as well.
Trying to increase displacment? That is done via crank mods/changes, not the head.
Joe
08-31-2009, 02:03 AM
#4
CF Veteran
Join Date: May 2008
Posts: 3,018
Likes: 0
Received 13 Likes
on
13 Posts
Year: 1988
Model: Cherokee
Engine: AMC242
The 258ci head is not only a step down from the 242ci, but the exhaust ports will not line up. The #3 and #4 ports on the 258ci head are "siamesed", while the 242ci head has those ports separated.
Throw in the fact that the 242ci head flows better at all valve lifts, and that the combustion chamber is smaller (yielding a somewhat higher CR,) and there's really no reason to drop the 258ci head on (but yes, the 1975-up 258 and all 242ci heads will bolt to the 1975-up 258ci and 1987-2007 242ci engine blocks.)
Sounds like what you'd be looking for would be more along the lines of a "stroker" engine - this is done by putting the crankshaft and connecting rods of the 258ci into the 242ci engine block, and leaving the 242ci cylinder head in place. This will yield at least a 30ci jump in piston displacement, and a suitable increase in compression ratio - even without any machine work done to the engine block or cylinder head!
Why? Because the 242ci stroke is 3.44", and the 258ci stroke is 3.895". That's a jump of .450" in stroke per cylinder - doesn't sound like much, but that half-inch is over an eighth of the total stroke you're starting with (13%, actually.)
The increase in displacement from that relatively simple parts swap is (3.875/2)^2 * 3.14159 * .450; 1.9375^2 * 3.14159 * .450; 3.754 * 3.14159 * .450; 5.307ci per cylinder, or 31.84ci overall. 241.5ci + 31.84ci = 273.34ci, or around 4.5 litres piston displacement. (Sorry, but I'm old enough to think in inches.) So, you're picking up about 12-13% in displacement, and simulations show a similar increase (or possibly a bit more - up to 15%) in the overall torque and horsepower output curves.
Have the cylinders bored oversize (+.030", +.060", or more if your block can take it) and have the block "zero decked" (piston tops are even with the top of the block at TDC,) and the CR will increase even more - which will increase torque output even more. Bear in mind you don't want your pistons "proud" - protruding above the deck at TDC - since that could end up with them smacking the cylinder head casting. Oops. Ouch.
Head swaps are usually good for an improvement (if you go in the right direction,) but the gains are typically nominal. Increasing the displacement of the engine is probably the most effective way to increase torque (which is what you want with a truck anyhow,) and that can then be further complemented by improving the breathing characteristics of the cylinder head (and intake, and exhaust,) and altering valve timing events (via the camshaft - either advance or retard it on installation, or get a new bumpstick altogether.)
Throw in the fact that the 242ci head flows better at all valve lifts, and that the combustion chamber is smaller (yielding a somewhat higher CR,) and there's really no reason to drop the 258ci head on (but yes, the 1975-up 258 and all 242ci heads will bolt to the 1975-up 258ci and 1987-2007 242ci engine blocks.)
Sounds like what you'd be looking for would be more along the lines of a "stroker" engine - this is done by putting the crankshaft and connecting rods of the 258ci into the 242ci engine block, and leaving the 242ci cylinder head in place. This will yield at least a 30ci jump in piston displacement, and a suitable increase in compression ratio - even without any machine work done to the engine block or cylinder head!
Why? Because the 242ci stroke is 3.44", and the 258ci stroke is 3.895". That's a jump of .450" in stroke per cylinder - doesn't sound like much, but that half-inch is over an eighth of the total stroke you're starting with (13%, actually.)
The increase in displacement from that relatively simple parts swap is (3.875/2)^2 * 3.14159 * .450; 1.9375^2 * 3.14159 * .450; 3.754 * 3.14159 * .450; 5.307ci per cylinder, or 31.84ci overall. 241.5ci + 31.84ci = 273.34ci, or around 4.5 litres piston displacement. (Sorry, but I'm old enough to think in inches.) So, you're picking up about 12-13% in displacement, and simulations show a similar increase (or possibly a bit more - up to 15%) in the overall torque and horsepower output curves.
Have the cylinders bored oversize (+.030", +.060", or more if your block can take it) and have the block "zero decked" (piston tops are even with the top of the block at TDC,) and the CR will increase even more - which will increase torque output even more. Bear in mind you don't want your pistons "proud" - protruding above the deck at TDC - since that could end up with them smacking the cylinder head casting. Oops. Ouch.
Head swaps are usually good for an improvement (if you go in the right direction,) but the gains are typically nominal. Increasing the displacement of the engine is probably the most effective way to increase torque (which is what you want with a truck anyhow,) and that can then be further complemented by improving the breathing characteristics of the cylinder head (and intake, and exhaust,) and altering valve timing events (via the camshaft - either advance or retard it on installation, or get a new bumpstick altogether.)
11-02-2011, 05:33 PM
#5
MJ>XJ
Join Date: Mar 2009
Location: Griffin, G.A.
Posts: 17,836
Likes: 0
Received 4 Likes
on
3 Posts
Year: 1990
Model: Comanche
Engine: 4.0 I6
The 258ci head is not only a step down from the 242ci, but the exhaust ports will not line up. The #3 and #4 ports on the 258ci head are "siamesed", while the 242ci head has those ports separated.
Throw in the fact that the 242ci head flows better at all valve lifts, and that the combustion chamber is smaller (yielding a somewhat higher CR,) and there's really no reason to drop the 258ci head on (but yes, the 1975-up 258 and all 242ci heads will bolt to the 1975-up 258ci and 1987-2007 242ci engine blocks.)
Sounds like what you'd be looking for would be more along the lines of a "stroker" engine - this is done by putting the crankshaft and connecting rods of the 258ci into the 242ci engine block, and leaving the 242ci cylinder head in place. This will yield at least a 30ci jump in piston displacement, and a suitable increase in compression ratio - even without any machine work done to the engine block or cylinder head!
Why? Because the 242ci stroke is 3.44", and the 258ci stroke is 3.895". That's a jump of .450" in stroke per cylinder - doesn't sound like much, but that half-inch is over an eighth of the total stroke you're starting with (13%, actually.)
The increase in displacement from that relatively simple parts swap is (3.875/2)^2 * 3.14159 * .450; 1.9375^2 * 3.14159 * .450; 3.754 * 3.14159 * .450; 5.307ci per cylinder, or 31.84ci overall. 241.5ci + 31.84ci = 273.34ci, or around 4.5 litres piston displacement. (Sorry, but I'm old enough to think in inches.) So, you're picking up about 12-13% in displacement, and simulations show a similar increase (or possibly a bit more - up to 15%) in the overall torque and horsepower output curves.
Have the cylinders bored oversize (+.030", +.060", or more if your block can take it) and have the block "zero decked" (piston tops are even with the top of the block at TDC,) and the CR will increase even more - which will increase torque output even more. Bear in mind you don't want your pistons "proud" - protruding above the deck at TDC - since that could end up with them smacking the cylinder head casting. Oops. Ouch.
Head swaps are usually good for an improvement (if you go in the right direction,) but the gains are typically nominal. Increasing the displacement of the engine is probably the most effective way to increase torque (which is what you want with a truck anyhow,) and that can then be further complemented by improving the breathing characteristics of the cylinder head (and intake, and exhaust,) and altering valve timing events (via the camshaft - either advance or retard it on installation, or get a new bumpstick altogether.)
Throw in the fact that the 242ci head flows better at all valve lifts, and that the combustion chamber is smaller (yielding a somewhat higher CR,) and there's really no reason to drop the 258ci head on (but yes, the 1975-up 258 and all 242ci heads will bolt to the 1975-up 258ci and 1987-2007 242ci engine blocks.)
Sounds like what you'd be looking for would be more along the lines of a "stroker" engine - this is done by putting the crankshaft and connecting rods of the 258ci into the 242ci engine block, and leaving the 242ci cylinder head in place. This will yield at least a 30ci jump in piston displacement, and a suitable increase in compression ratio - even without any machine work done to the engine block or cylinder head!
Why? Because the 242ci stroke is 3.44", and the 258ci stroke is 3.895". That's a jump of .450" in stroke per cylinder - doesn't sound like much, but that half-inch is over an eighth of the total stroke you're starting with (13%, actually.)
The increase in displacement from that relatively simple parts swap is (3.875/2)^2 * 3.14159 * .450; 1.9375^2 * 3.14159 * .450; 3.754 * 3.14159 * .450; 5.307ci per cylinder, or 31.84ci overall. 241.5ci + 31.84ci = 273.34ci, or around 4.5 litres piston displacement. (Sorry, but I'm old enough to think in inches.) So, you're picking up about 12-13% in displacement, and simulations show a similar increase (or possibly a bit more - up to 15%) in the overall torque and horsepower output curves.
Have the cylinders bored oversize (+.030", +.060", or more if your block can take it) and have the block "zero decked" (piston tops are even with the top of the block at TDC,) and the CR will increase even more - which will increase torque output even more. Bear in mind you don't want your pistons "proud" - protruding above the deck at TDC - since that could end up with them smacking the cylinder head casting. Oops. Ouch.
Head swaps are usually good for an improvement (if you go in the right direction,) but the gains are typically nominal. Increasing the displacement of the engine is probably the most effective way to increase torque (which is what you want with a truck anyhow,) and that can then be further complemented by improving the breathing characteristics of the cylinder head (and intake, and exhaust,) and altering valve timing events (via the camshaft - either advance or retard it on installation, or get a new bumpstick altogether.)
11-02-2011, 06:54 PM
#6
CF Veteran
Join Date: May 2008
Posts: 3,018
Likes: 0
Received 13 Likes
on
13 Posts
Year: 1988
Model: Cherokee
Engine: AMC242
Why do you think I'm writing books? I've been able to verify most of what I don't know from personal experience, and I'm working on the rest.
Of course, it's funny when I walk into a "Ford v. GM" debate and tell them they're both silly. "Oh yeah - I suppose you're a Dodge guy?" "Hardly - AMC and International..." "What?"
11-02-2011, 07:06 PM
#7
MJ>XJ
Join Date: Mar 2009
Location: Griffin, G.A.
Posts: 17,836
Likes: 0
Received 4 Likes
on
3 Posts
Year: 1990
Model: Comanche
Engine: 4.0 I6
lol... i suppose you talk to blue (mike) a lot then? hes a Renix guru... got a link to your books on the AMC's? ive bought a couple XJ books but chances of you being involves are slim i know... lol... dont mean that in a bad way... just a lot of books out there... lol
Trending Topics
03-09-2012, 09:21 AM
#8
Newbie
Join Date: Mar 2012
Posts: 1
Likes: 0
Received 0 Likes
on
0 Posts
Model: Cherokee
Hey guys,
I was reading your posts and recommendations against placing a 4.2L head on a 4.0L block and it makes perfect sense as to why you do not recommend doing this, however, I'm in a position where I have no option but to do so.
I purchased a 88 YJ with a 4.2L which had a blown piston and severely damaged cylinder. I decided to use a 4.0L block to build a running engine because I have plenty of those blocks in my inventory.
I followed a post online that described the necessary procedure to mate a 4.0L head to a 4.2L block. The procedure depicted specific water ports on the 4.0L head that needed to be blocked. Since I was performing the opposite conversion I used these instructions to determine what water ports that would need to be blocked on the 4.0L block.
The procedure that I followed can be found at this URL: http://offroad-review.com/new/index.php?page=68
This is the second time that I mated a 4.2L head to a 4.0L block and the first time seemed to work just fine, but this time I'm getting water in the oil.
After noticing water in the oil I pulled the engine and checked the integrity of the water ports that I blocked and they looked fine. I blocked them with JB Weld and there does not seem to be any signs of the weld separating. I than changed the head gasket and used a 4.0L gasket instead of a 4.2L because it seems to provide better coverage
I'm getting ready to pull this engine out of the vehicle again and give it another in-depth inspection. I was wondering if you would be able to provide any advice as to what to look for that could be causing water to seep into the oil?
Thanks.
I was reading your posts and recommendations against placing a 4.2L head on a 4.0L block and it makes perfect sense as to why you do not recommend doing this, however, I'm in a position where I have no option but to do so.
I purchased a 88 YJ with a 4.2L which had a blown piston and severely damaged cylinder. I decided to use a 4.0L block to build a running engine because I have plenty of those blocks in my inventory.
I followed a post online that described the necessary procedure to mate a 4.0L head to a 4.2L block. The procedure depicted specific water ports on the 4.0L head that needed to be blocked. Since I was performing the opposite conversion I used these instructions to determine what water ports that would need to be blocked on the 4.0L block.
The procedure that I followed can be found at this URL: http://offroad-review.com/new/index.php?page=68
This is the second time that I mated a 4.2L head to a 4.0L block and the first time seemed to work just fine, but this time I'm getting water in the oil.
After noticing water in the oil I pulled the engine and checked the integrity of the water ports that I blocked and they looked fine. I blocked them with JB Weld and there does not seem to be any signs of the weld separating. I than changed the head gasket and used a 4.0L gasket instead of a 4.2L because it seems to provide better coverage
I'm getting ready to pull this engine out of the vehicle again and give it another in-depth inspection. I was wondering if you would be able to provide any advice as to what to look for that could be causing water to seep into the oil?
Thanks.
03-09-2012, 05:35 PM
#10
CF Veteran
Join Date: May 2008
Posts: 3,018
Likes: 0
Received 13 Likes
on
13 Posts
Year: 1988
Model: Cherokee
Engine: AMC242
lol... i suppose you talk to blue (mike) a lot then? hes a Renix guru... got a link to your books on the AMC's? ive bought a couple XJ books but chances of you being involves are slim i know... lol... dont mean that in a bad way... just a lot of books out there... lol
Information on my book(s) is on my site - I'm working primarily on Swappology at the moment.
03-09-2012, 06:45 PM
#12
MJ>XJ
Join Date: Mar 2009
Location: Griffin, G.A.
Posts: 17,836
Likes: 0
Received 4 Likes
on
3 Posts
Year: 1990
Model: Comanche
Engine: 4.0 I6
Originally Posted by 5-90
Who? I've had to figure most of this out the hard way (and I've lost track of who I talk to anymore - either them giving me information, me giving them information, or both of us hammering away at it...)
Information on my book(s) is on my site - I'm working primarily on Swappology at the moment.
Thread
Thread Starter
Forum
Replies
Last Post
jeefersjeepers
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
3
09-20-2023 12:51 PM
cdf43
Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go here
18
09-09-2015 02:47 AM
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)