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What is the difference between a HO head and a non HO head

M

mfds91cherokee

NAXJA Forum User
Location
Tacoma, WA
I have a engine I bought and is claiming to be a 91 wrangler. I have a 93 cherokee and I want to do this swap cause my block is shot. I just want to know if the new engine has a HO head how can I tell?
 
HO stands for high out put, just the inside of the motor is different and stronger than the non HO head
 
Pretty sure the Wrangler 4.0s are all HO since they used the 4.2 before the 4.0.
 
There are three HO heads out there, so let's narrow things down a bit for you...

#2686 (1987-1990) A/K/A "RENIX" head. This was the first 242ci head, and was essentially a revision of the #2685 last-gen 258ci cylinder head (primary change was that #3 & #4 exhaust ports were separated.)

#7120 (1991-1995) This was the OBD-I 242ci HO head. The intake ports were raised ~5/8" on the side of the cylinder head to reduce the port angle, and to improve airflow through the port. The exhaust ports, I believe, were also changed slightly.

#0630 (1996-1999) OBD-II 242ci HO head #1. Intake ports were changed slightly internally, and the exhaust port volume was reduced slightly (in order to retain exhaust pulse heat and to shorten catalyst light-off times.)

#0331 (1999-2006) OBD-II 242 HO head #2. Distinguished readily by the presence of drilled/tapped bosses to retain the coil rail for the COP/DIS ignition setup. Exhaust ports were reduced significantly to further improve catalyst light-off times, and intake ports were slightly revised. NB: Avoid 1999-2002 #0331 heads - these are the heads that are prone to cracking! cf: "0331 club". Replace this head from a 2002-up TJ or WJ/WK for a direct swap, if you have a cracked #0331. The crack tends to form atop the casting between #3 and #4 cylinders (usually right under the oil filler cap,) and you'll get coolant in your oil as a first symptom. Note that you do not lose power or compression with this sort of crack!

The cylinder head casting number can be found on the top of the cylinder head, between the #3 and #4 exhaust ports, outside of the valve cover rail. You should not need to do much apart from push some wiring out of the way to see it. If you need a picture, I'll either have to take one or find one - I don't have it on the system right at this moment.
 
I just went out to the garage to measure the intake port dimensional differences on my HO long block with a 7120 head and Renix intake gasket on it as 5/8" seemed wrong. The floor of the intake port is raised only 1/4" higher than the Renix, not 5/8".
 
I know a former DC mechanic that put an HO head on his 89 and used the stock exhaust header. It did not leak and worked great for him. I 3D modeled the heads for a project but don't remember the difference. I don't believe it is 5/8" as the heads would not be interchangable with the exhaust.
 
Cylinder head

The stock cylinder head is cast iron and weighs 60lb. The valve head diameter is 1.91" intake/1.50" exhaust. Casting numbers are as follows:

Year............Casting No
1987-90......2686
1991-95......7120
1996-99......0630
2000-01......0331

Cylinder head flow figures (cfm) at 25inH2O pressure drop are:

Non-HO head #2686

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 122.0 168.0 186.0 189.0 192.0
Exhaust flow....88.0 114.0 130.0 134.0 138.0

Ported non-HO head #2686

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 124.0 183.0 197.0 207.0 216.0
Exhaust flow....87.0 113.0 138.0 153.0 159.0

HO head #7120 & #0630

Valve lift (in)... 0.1 ... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 66.0 128.0 179.0 206.0 209.0 209.0
Exhaust flow. 55.0 100.0 120.0 136.0 141.0 141.2

HO head #0331

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 114.0 165.0 194.0 199.0 205.0
Exhaust flow....94.0 117.0 126.0 130.0 133.0

Ported big valve 2.02/1.60 HO head

Valve lift (in)... 0.1 ... 0.2 ... 0.3 ... 0.4 ... 0.5
Intake flow.... 73.9 142.4 197.8 229.8 247.0
Exhaust flow. 65.3 114.0 135.9 146.3 157.1

The early '87-'90 non-HO heads have low intake ports that flow rather poorly. The later HO heads have higher intake ports that flow more air by allowing a straighter shot into the cylinders. The '91-'95 HO heads with casting no.7120 have the highest intake and exhaust port airflows, especially at lower valve lifts where it is most important, and are the best for performance. The '96-'99 0630 heads are almost identical except that they don't have a port for the coolant temp. gauge sending unit. The '00 and later HO heads with casting no.0331 have smaller exhaust ports to produce a faster warm-up of the catalytic converter and improve emissions, but performance also suffers because the ports don't flow as well as those of the 7120 and 0630 castings.
The exhaust ports flow relatively poorly compared to the intake ports on all the 4.0 heads so this engine would perform better with a dual pattern cam that has more exhaust valve opening duration and lift than the intake.
The intake ports of the HO head are rectangular and measure 1.625" x 1.375", while the exhaust ports are elliptical and measure only 1.375" x 1.250". The port cross-sectional areas are 2.234 and 1.350 sq. inches respectively. For good street performance, it is recommended that the port c/s area should be about 85% of the valve head area. Therefore it should be 2.435 sq. in. for the intake ports and 1.502 sq. in. for the exhaust ports. The stock port c/s areas therefore need to be enlarged by 9.0% for the intake and 11.3% for the exhaust. The ports should be matched to the intake and exhaust manifold runners to smoothen airflow and prevent power-robbing turbulence.
For those who would like to undertake a DIY head porting job, the Standard Abrasives DIY Head Porting Guide is a must read.

Head gaskets

The compressed thicknesses of the following gaskets for the 4.0 engine are:

Stock 4.0 (all years) 53020754AB----0.051"
Mopar Performance P4529242 / Victor Reinz Dana 5713----0.043"
Corteco 20667CS '87-'95, Corteco 20871 '96-'06 ----0.051"
Fel-Pro 9076PT----0.043"
Fel-Pro 9076PT1----0.051"
Fel-Pro 530SD----0.051"
 
revmeup said:
Cylinder head

The stock cylinder head is cast iron and weighs 60lb. The valve head diameter is 1.91" intake/1.50" exhaust. Casting numbers are as follows:

Year............Casting No
1987-90......2686
1991-95......7120
1996-99......0630
2000-01......0331

Cylinder head flow figures (cfm) at 25inH2O pressure drop are:

Non-HO head #2686

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 122.0 168.0 186.0 189.0 192.0
Exhaust flow....88.0 114.0 130.0 134.0 138.0

Ported non-HO head #2686

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 124.0 183.0 197.0 207.0 216.0
Exhaust flow....87.0 113.0 138.0 153.0 159.0

HO head #7120 & #0630

Valve lift (in)... 0.1 ... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 66.0 128.0 179.0 206.0 209.0 209.0
Exhaust flow. 55.0 100.0 120.0 136.0 141.0 141.2

HO head #0331

Valve lift (in)..... 0.2 ... 0.3 ... 0.4 ... 0.5 ... 0.6
Intake flow.... 114.0 165.0 194.0 199.0 205.0
Exhaust flow....94.0 117.0 126.0 130.0 133.0

Ported big valve 2.02/1.60 HO head

Valve lift (in)... 0.1 ... 0.2 ... 0.3 ... 0.4 ... 0.5
Intake flow.... 73.9 142.4 197.8 229.8 247.0
Exhaust flow. 65.3 114.0 135.9 146.3 157.1

The early '87-'90 non-HO heads have low intake ports that flow rather poorly. The later HO heads have higher intake ports that flow more air by allowing a straighter shot into the cylinders. The '91-'95 HO heads with casting no.7120 have the highest intake and exhaust port airflows, especially at lower valve lifts where it is most important, and are the best for performance. The '96-'99 0630 heads are almost identical except that they don't have a port for the coolant temp. gauge sending unit. The '00 and later HO heads with casting no.0331 have smaller exhaust ports to produce a faster warm-up of the catalytic converter and improve emissions, but performance also suffers because the ports don't flow as well as those of the 7120 and 0630 castings.
The exhaust ports flow relatively poorly compared to the intake ports on all the 4.0 heads so this engine would perform better with a dual pattern cam that has more exhaust valve opening duration and lift than the intake.
The intake ports of the HO head are rectangular and measure 1.625" x 1.375", while the exhaust ports are elliptical and measure only 1.375" x 1.250". The port cross-sectional areas are 2.234 and 1.350 sq. inches respectively. For good street performance, it is recommended that the port c/s area should be about 85% of the valve head area. Therefore it should be 2.435 sq. in. for the intake ports and 1.502 sq. in. for the exhaust ports. The stock port c/s areas therefore need to be enlarged by 9.0% for the intake and 11.3% for the exhaust. The ports should be matched to the intake and exhaust manifold runners to smoothen airflow and prevent power-robbing turbulence.
For those who would like to undertake a DIY head porting job, the Standard Abrasives DIY Head Porting Guide is a must read.

Head gaskets

The compressed thicknesses of the following gaskets for the 4.0 engine are:

Stock 4.0 (all years) 53020754AB----0.051"
Mopar Performance P4529242 / Victor Reinz Dana 5713----0.043"
Corteco 20667CS '87-'95, Corteco 20871 '96-'06 ----0.051"
Fel-Pro 9076PT----0.043"
Fel-Pro 9076PT1----0.051"
Fel-Pro 530SD----0.051"
Click to expand...

^Alot of great info for anyone planning on building a stroker and needing to know some of the specifics.
 
cruiser54 said:
I just went out to the garage to measure the intake port dimensional differences on my HO long block with a 7120 head and Renix intake gasket on it as 5/8" seemed wrong. The floor of the intake port is raised only 1/4" higher than the Renix, not 5/8".
Click to expand...

I haven't measured it myself - just going from what I was told (and 5/8" did make a lot of sense.)

However, it's easy to spot - the RENIX has all of the port "floors" more or less lined up, while the intakes are higher on all three of the HO heads.
 
I recently purchased a crate motor from Mopar 1 year ago. It is for a 2000 XJ and has the 0331 head. I was told there would not be a problem with this head cracking like the previos 0331 head. Do you know if they reinforced the new head on my crate motor at the factory or fixed the casting problems at some point?
 
The Renix also has a notch above the port ceiling for the injector where the HO is flat across the ceiling. Does that make sense? I'm port matching the HO head by lowering the floor of the ports to match the Renix gasket.
 
Also there was a new mopar crate motor next to mine that was for a 2002 TJ and it had the same 0331 head on it.
 
cruiser54 said:
The Renix also has a notch above the port ceiling for the injector where the HO is flat across the ceiling. Does that make sense? I'm port matching the HO head by lowering the floor of the ports to match the Renix gasket.
Click to expand...

Thanks - I'd forgotten about that as well.

I believe there is a slight "notch" (your word - as good as any...) in the HO ports, but it's not as pronounced due to the ports being raised in the first place.
 
chris420 said:
I recently purchased a crate motor from Mopar 1 year ago. It is for a 2000 XJ and has the 0331 head. I was told there would not be a problem with this head cracking like the previos 0331 head. Do you know if they reinforced the new head on my crate motor at the factory or fixed the casting problems at some point?
Click to expand...

The only way to tell is look for "TUPY" cast into the head. That is the good 0331 head. You have to remove the valve cover for this. It will be in between the #3 and #4 cylinders.
 
Last edited:
5-90, you are correct. Very slight notch in ceiling of HO port where Renix is very pronounced. All my intake ports are matched now and I continue to work on the exhaust ports to match the gasket. Those exhaust ports, while pretty much the same between the Renix and 92 HO, are a long ways from the gasket size. The intakes needed much less work.
 
The Hoe's head will have crack sore's..a crusty bloody nose, and her lips will be chaffing..

A non-hoe's head wont
 
Do not match the exhaust port to the gasket! It will be too larger, slow down the exhaust speed and possibly create reversion. An you shouldn't be gasket matching really.. you want to match the head ports to the manifold ports. Or leave the intake manifold port a little smaller than the head intake port and leave the exhaust manifold port a bit larger than the head exhaust port.
 
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